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we analyze the high-energy neutrino events observed by icecube, aiming to probe the initial flavor of cosmic neutrinos. we study the track-to-shower ratio of the subset with energy above 60 tev, where the signal is expected to dominate, and show that different production mechanisms give rise to different predictions even accounting for the uncertainties due to neutrino oscillations. we include for the first time the passing muons observed by icecube in the analysis. they corroborate the hypotheses that cosmic neutrinos have been seen and their flavor matches expectations derived from the neutrino oscillations. | what is the flavor of the cosmic neutrinos seen by icecube? |
we know that magnetic fields are pervasive across all scales in the universe and over all of cosmic time and yet our understanding of many of the properties of magnetic fields is still limited. we do not yet know when, where or how the first magnetic fields in the universe were formed, nor do we fully understand their role in fundamental processes such as galaxy formation or cosmic ray acceleration or how they influence the evolution of astrophysical objects. the greatest challenge to addressing these issues has been a lack of deep, broad bandwidth polarimetric data over large areas of the sky. the square kilometre array will radically improve this situation via an all-sky polarisation survey that delivers both high quality polarisation imaging in combination with observations of 7-14 million extragalactic rotation measures. here we summarise how this survey will improve our understanding of a range of astrophysical phenomena on scales from individual galactic objects to the cosmic web. | using ska rotation measures to reveal the mysteries of the magnetised universe |
this paper considers turbulent damping of alfvén waves in magnetized plasmas. we identify two cases of damping, one related to damping of cosmic-ray streaming instability, the other related to damping of alfvén waves emitted by a macroscopic wave source, e.g., a stellar atmosphere. the physical difference between the two cases is that in the former case the generated waves are emitted with respect to the local direction of the magnetic field, and in the latter, waves are emitted with respect to the mean field. the scaling of damping is different in the two cases. we explore effects of turbulence in the regimes from sub-alfvénic to super-alfvénic to obtain analytical expressions for the damping rates and define the ranges of applicability of these expressions. in describing the damping of the streaming instability, we find that for sub-alfvénic turbulence, the range of cosmic-ray energies influenced by weak turbulence is unproportionally large compared to the range of scales where weak turbulence is present. on the contrary, the range of cosmic-ray energies affected by strong alfvénic turbulence is rather limited. a number of astrophysical applications of the process ranging from launching of stellar and galactic winds to propagation of cosmic rays in galaxies and clusters of galaxies is considered. in particular, we discuss how to reconcile the process of turbulent damping with the observed isotropy of the milky way cosmic rays. | damping of alfvén waves by turbulence and its consequences: from cosmic-ray streaming to launching winds |
we have imaged the sunyaev-zel'dovich (sz) effect signals at 140 and 270 ghz toward 10 galaxy clusters with bolocam and aztec/aste. we also used planck data to constrain the signal at large angular scales, herschel-spire images to subtract the brightest galaxies that comprise the cosmic infrared background (cib), chandra imaging to map the electron temperature te of the intra-cluster medium, and hubble space telescope imaging to derive models of each galaxy cluster's mass density. the galaxy clusters gravitationally lens the background cib, which produced an on-average reduction in brightness toward the galaxy clusters' centers after the brightest galaxies were subtracted. we corrected for this deficit, which was between 5% and 25% of the 270 ghz sz effect signal within r 2500. using the sz effect measurements, along with the x-ray constraint on te, we measured each galaxy cluster's average line of sight (los) velocity vz within r 2500, with a median per-cluster uncertainty of ±700 km s-1. we found an ensemble-mean < vz > of 430 ± 210 km s-1, and an intrinsic cluster-to-cluster scatter σint of 470 ± 340 km s-1. we also obtained maps of vz over each galaxy cluster's face with an angular resolution of 70". all four galaxy clusters previously identified as having a merger oriented along the los showed an excess variance in these maps at a significance of ≃2-4σ, indicating an internal vz rms of ≳1000 km s-1. none of the six galaxy clusters previously identified as relaxed or plane-of-sky mergers showed any such excess variance. | imaging the thermal and kinematic sunyaev-zel'dovich effect signals in a sample of 10 massive galaxy clusters: constraints on internal velocity structures and bulk velocities |
magnetars are the most highly magnetized neutron stars in the cosmos (with magnetic field 1013-1015 g). giant flares from magnetars are rare, short-duration (about 0.1 s) bursts of hard x-rays and soft γ rays1,2. owing to the limited sensitivity and energy coverage of previous telescopes, no magnetar giant flare has been detected at gigaelectronvolt (gev) energies. here, we report the discovery of gev emission from a magnetar giant flare on 15 april 2020 (refs. 3,4 and a. j. castro-tirado et al., manuscript in preparation). the large area telescope (lat) on board the fermi gamma-ray space telescope detected gev γ rays from 19 s until 284 s after the initial detection of a signal in the megaelectronvolt (mev) band. our analysis shows that these γ rays are spatially associated with the nearby (3.5 megaparsecs) sculptor galaxy and are unlikely to originate from a cosmological γ-ray burst. thus, we infer that the γ rays originated with the magnetar giant flare in sculptor. we suggest that the gev signal is generated by an ultra-relativistic outflow that first radiates the prompt mev-band photons, and then deposits its energy far from the stellar magnetosphere. after a propagation delay, the outflow interacts with environmental gas and produces shock waves that accelerate electrons to very high energies; these electrons then emit gev γ rays as optically thin synchrotron radiation. this observation implies that a relativistic outflow is associated with the magnetar giant flare, and suggests the possibility that magnetars can power some short γ-ray bursts. | high-energy emission from a magnetar giant flare in the sculptor galaxy |
we carried out new co(j = 2-1) observations toward the mixed-morphology supernova remnant (snr) w49b with the atacama large millimeter/submillimeter array. we found that co clouds at ~10 km s-1 show a good spatial correspondence to the synchrotron radio continuum as well as to an x-ray deformed shell. the bulk mass of molecular clouds accounts for the western part of the shell, not the eastern shell, where near-infrared h2 emission is detected. the molecular clouds at ~10 km s-1 show higher kinetic temperatures of ~20-60 k, suggesting that modest shock heating occurred. the expanding motion of the clouds with δv ~ 6 km s-1 was formed by strong winds from the progenitor system. we argue that the barrel-like structure of fe-rich ejecta was possibly formed not only by an asymmetric explosion, but also by interactions with dense molecular clouds. we also found a negative correlation between the co intensity and the electron temperature of recombining plasma, implying that the origin of the high-temperature recombining plasma in w49b can be understood to be the thermal conduction model. the total energy of accelerated cosmic-ray protons wp is estimated to be ~2 × 1049 erg by adopting an averaged gas density of ~650 ± 200 cm-3. the snr age-wp diagram indicates that w49b shows one of the highest in situ values of wp among gamma-ray-bright snrs. | alma co observations of the mixed-morphology supernova remnant w49b: efficient production of recombining plasma and hadronic gamma rays via shock-cloud interactions |
the origin of galactic cosmic rays (gcrs) remains a mystery after more than one century of their discovery. the diffusive propagation of charged particles in the turbulent galactic magnetic field makes us unable to trace back to their acceleration sites. nevertheless, nearby gcr source(s) may leave imprints on the locally measured energy spectra and the anisotropies of the arrival direction. in this work we propose a simple but natural description of the gcr production and propagation, within a two-zone disk-halo diffusion scenario together with a nearby source, to understand the up-to-date precise measurements of the energy spectra and anisotropies of gcrs. we find that a common energy scale of ~100 tev appears in both energy spectra of protons and helium nuclei measured recently by cream and large-scale anisotropies detected by various experiments. these results indicate that one or more local sources are very likely important contributors to gcrs below 100 tev . this study provides a probe to identify source(s) of gcrs by means of joint efforts of spectral and anisotropy measurements. | indication of nearby source signatures of cosmic rays from energy spectra and anisotropies |
context. observations of chemical species can provide insights into the physical conditions of the emitting gas however it is important to understand how their abundances and excitation vary within different heating environments. c2h is a molecule typically found in pdr regions of our own galaxy but there is evidence to suggest it also traces other regions undergoing energetic processing in extragalactic environments.aims: as part of the alchemi alma large program, we map the emission of c2h in the central molecular zone of the nearby starburst galaxy ngc 253 at 1.6″ (28 pc) resolution and characterize it to understand its chemical origins.methods: we used spectral modeling of the n = 1−0 through n = 4−3 rotational transitions of c2h to derive the c2h column densities towards the dense clouds in ngc 253. we then use chemical modeling, including photodissociation region (pdr), dense cloud, and shock models to investigate the chemical processes and physical conditions that are producing the molecular emission.results: we find high c2h column densities of ∼1015 cm−2 detected towards the dense regions of ngc 253. we further find that these column densities cannot be reproduced if it is assumed that the emission arises from the pdr regions at the edge of the clouds. instead, we find that the c2h abundance remains high even in the high visual extinction interior of these clouds and that this is most likely caused by a high cosmic-ray ionization rate. | the distribution and origin of c2h in ngc 253 from alchemi |
the global survey method (gsm) technique unites simultaneous ground-level observations of cosmic rays in different locations and allows us to obtain the main characteristics of cosmic-ray variations outside of the atmosphere and magnetosphere of earth. this technique has been developed and applied in numerous studies over many years by the institute of terrestrial magnetism, ionosphere and radiowave propagation (izmiran). we here describe the izmiran version of the gsm in detail. with this technique, the hourly data of the world-wide neutron-monitor network from july 1957 until december 2016 were processed, and further processing is enabled upon the receipt of new data. the result is a database of homogeneous and continuous hourly characteristics of the density variations (an isotropic part of the intensity) and the 3d vector of the cosmic-ray anisotropy. it includes all of the effects that could be identified in galactic cosmic-ray variations that were caused by large-scale disturbances of the interplanetary medium in more than 50 years. these results in turn became the basis for a database on forbush effects and interplanetary disturbances. this database allows correlating various space-environment parameters (the characteristics of the sun, the solar wind, et cetera) with cosmic-ray parameters and studying their interrelations. we also present features of the coupling coefficients for different neutron monitors that enable us to make a connection from ground-level measurements to primary cosmic-ray variations outside the atmosphere and the magnetosphere. we discuss the strengths and weaknesses of the current version of the gsm as well as further possible developments and improvements. the method developed allows us to minimize the problems of the neutron-monitor network, which are typical for experimental physics, and to considerably enhance its advantages. | the global survey method applied to ground-level cosmic ray measurements |
after the submission of the original paper, our co-author hang zhou, has changed his affiliation to "school of microelectronics and control engineering, changzhou university, changzhou, jiangsu, 213164, china", and his email address to "zhouhang_hep@126.com". we hereby clarify this situation and make the correction of the author information. | erratum to: cosmic ray boosted sub-gev gravitationally interacting dark matter in direct detection |
cosmic-ray neutron intensity is inversely correlated to all hydrogen present in the upper decimeters of the subsurface and the first few hectometers of the atmosphere above the ground surface. this correlation forms the base of the cosmic-ray neutron soil moisture estimation method. the method is, however, complicated by the fact that several hydrogen pools other than soil moisture affect the neutron intensity. in order to improve the cosmic-ray neutron soil moisture estimation method and explore the potential for additional applications, knowledge about the environmental effect on cosmic-ray neutron intensity is essential (e.g., the effect of vegetation, litter layer and soil type). in this study the environmental effect is examined by performing a sensitivity analysis using neutron transport modeling. we use a neutron transport model with various representations of the forest and different parameters describing the subsurface to match measured height profiles and time series of thermal and epithermal neutron intensities at a field site in denmark. overall, modeled thermal and epithermal neutron intensities are in satisfactory agreement with measurements; however, the choice of forest canopy conceptualization is found to be significant. modeling results show that the effect of canopy interception, soil chemistry and dry bulk density of litter and mineral soil on neutron intensity is small. on the other hand, the neutron intensity decreases significantly with added litter-layer thickness, especially for epithermal neutron energies. forest biomass also has a significant influence on the neutron intensity height profiles at the examined field site, altering both the shape of the profiles and the ground-level thermal-to-epithermal neutron ratio. this ratio increases with increasing amounts of biomass, and was confirmed by measurements from three sites representing agricultural, heathland and forest land cover. a much smaller effect of canopy interception on the ground-level thermal-to-epithermal neutron ratio was modeled. overall, the results suggest a potential to use ground-level thermal-to-epithermal neutron ratios to discriminate the effect of different hydrogen contributions on the neutron signal. | cosmic-ray neutron transport at a forest field site: the sensitivity to various environmental conditions with focus on biomass and canopy interception |
on or about 2012 august 25, the voyager 1 spacecraft crossed the heliopause into the nearby interstellar plasma. in the nearly three years that the spacecraft has been in interstellar space, three notable particle and field disturbances have been observed, each apparently associated with a shock wave propagating outward from the sun. here, we present a detailed analysis of the third and most impressive of these disturbances, with brief comparisons to the two previous events, both of which have been previously reported. the shock responsible for the third event was first detected on 2014 february 17 by the onset of narrowband radio emissions from the approaching shock, followed on 2014 may 13 by the abrupt appearance of intense electron plasma oscillations generated by electrons streaming outward ahead of the shock. finally, the shock arrived on 2014 august 25, as indicated by a jump in the magnetic field strength and the plasma density. various disturbances in the intensity and anisotropy of galactic cosmic rays were also observed ahead of the shock, some of which are believed to be caused by the reflection and acceleration of cosmic rays by the magnetic field jump at the shock, and/or by interactions with upstream plasma waves. comparisons to the two previous weaker events show somewhat similar precursor effects, although differing in certain details. many of these effects are very similar to those observed in the region called the “foreshock” that occurs upstream of planetary bow shocks, only on a vastly larger spatial scale. | precursors to interstellar shocks of solar origin |
the milky way halo is the brightest source of dark matter annihilation in the sky. indeed, the potential strength of the galactic dark matter signal can supersede that expected from dwarf galaxies and galaxy groups even in regions away from the inner galaxy. in this paper, we present the results of a search for dark matter annihilation in the smooth milky way halo for |b |>2 0 ° and r <5 0 ° using 413 weeks of fermi pass 8 data within the energy range of ∼0.8 - 50 gev . we exclude thermal dark matter with mass below ∼70 gev that annihilates to b b ¯ at the 95% confidence level using the p6v11 cosmic-ray foreground model, providing the strongest limits on the annihilation cross section in this mass range. these results exclude the region of dark matter parameter space that is consistent with the excess of ∼gev photons observed at the galactic center for the b b ¯ annihilation channel and, for the first time, start probing the τ+τ- explanation. we explore how these results depend on uncertainties in the foregrounds by varying over a set of reasonable models. | search for dark matter annihilation in the milky way halo |
the alpha magnetic spectrometer (ams) is a high energy physics experiment operating aboard the international space station (iss) since may 2011. so far more than 100 billion of charged cosmic ray events have been collected by ams. the ams silicon tracker, together with the magnet, measures the rigidity (momentum/charge) of cosmic rays in the range from ∼ 0 . 5 gv to several tv. to accurately determine the trajectory of charged particles, a novel tracker position reconstruction method has been developed. in the paper, the details of the method and the obtained tracker spatial resolution for nuclei with charge 2 ≤ z ≤ 26 are presented. | the spatial resolution of the silicon tracker of the alpha magnetic spectrometer |
a multimessenger campaign has associated a high-energy cosmic neutrino with a distant gamma-ray blazar, txs 0506+056. icecube archival data subsequently revealed that the high-energy neutrino flux from the direction of this source, integrated over the last 10 yr, is dominated by a single bright neutrino flare in 2014, leaving the multimessenger flare as a subluminous second flare. the extraordinary brightness of the blazar despite its distance suggests that it may belong to a special class of sources that produce cosmic rays. we show that the diffuse icecube flux discovered in 2013 can be accommodated by a subclass of blazars, on the order of 5%, that episodically produce neutrinos with the luminosity of the 2014 neutrino flare. matching the cosmic-ray flux required to produce the neutrinos to the one observed implies highly efficient neutrino sources with large target photon densities that are not transparent to high-energy gamma-rays. the opacity of the source modifies the straightforward multimessenger connection in a way that is consistent with the gamma-ray observations coincident with the 2014 neutrino flare. | on the neutrino flares from the direction of txs 0506+056 |
papers on research & development towards icecube-gen2, the next generation neutrino observatory at south pole, submitted to the 35th international cosmic ray conference (icrc 2017, busan, south korea) by the icecube-gen2 collaboration. | the icecube neutrino observatory - contributions to icrc 2017 part vi: icecube-gen2, the next generation neutrino observatory |
this article reports on the first application of muon tomography (a novel method for imaging density contrasts underground using cosmic rays) for imaging dense uranium deposits within the athabasca basin in canada. we present a qualitative assessment of the radiographic imaging and 3-d density inversion of a uranium deposit using muon tomography. the muon tomography survey summarized in this article was performed at the mcarthur river mine. we demonstrate the validity of muon tomographic imaging with data acquired at a depth of about 600 m underground. the statistical significance of the uranium deposit signature in the muon data was larger than 5 standard deviations, and the corresponding 3-d density inversion compared well with drill assay data from the deposit. | muon tomography applied to a dense uranium deposit at the mcarthur river mine |
the very high energy galactic γ-ray sky is partially opaque in the (0.1-10) pev energy range. in the light of the recently detected high energy neutrino flux by icecube, a comparable very high energy γ-ray flux is expected in any scenario with a sizable galactic contribution to the neutrino flux. here we elaborate on the peculiar energy and anisotropy features imposed upon these very high energy γ-rays by the absorption on the cosmic microwave background photons and galactic interstellar light. as a notable application of our considerations, we study the prospects of probing the pev-scale decaying dm scenario, proposed as a possible source of icecube neutrinos, by extensive air shower (eas) cosmic ray experiments. in particular, we show that anisotropy measurements at eas experiments are already sensitive to τdm~ 𝒪(1027) s and future measurements, using better gamma/hadron separation, can improve the limit significantly. | gamma-ray bounds from eas detectors and heavy decaying dark matter constraints |
we report rest-frame submillimeter h2o emission line observations of 11 ultra- or hyper-luminous infrared galaxies (ulirgs or hylirgs) at z 2-4 selected among the brightest lensed galaxies discovered in the herschel-astrophysical terahertz large area survey (h-atlas). using the iram northern extended millimeter array (noema), we have detected 14 new h2o emission lines. these include five 321-312ortho-h2o lines (eup/k = 305 k) and nine j = 2 para-h2o lines, either 202-111(eup/k = 101 k) or 211-202(eup/k = 137 k). the apparent luminosities of the h2o emission lines are μlh2o 6-21 × 108 l⊙ (3 <μ< 15, where μ is the lens magnification factor), with velocity-integrated line fluxes ranging from 4-15 jy km s-1. we have also observed co emission lines using emir on the iram 30 m telescope in seven sources (most of those have not yet had their co emission lines observed). the velocity widths for co and h2o lines are found to be similar, generally within 1σ errors in the same source. with almost comparable integrated flux densities to those of the high-j co line (ratios range from 0.4 to 1.1), h2o is found to be among the strongest molecular emitters in high-redshift hy/ulirgs. we also confirm our previously found correlation between luminosity of h2o (lh2o) and infrared (lir) that lh2o lir1.1-1.2, with ournew detections. this correlation could be explained by a dominant role of far-infrared pumping in the h2o excitation. modelling reveals that the far-infrared radiation fields have warm dust temperature twarm 45-75 k, h2o column density per unit velocity interval nh2o /δv ≳ 0.3 × 1015 cm-2 km-1 s and 100 μm continuum opacity τ100> 1 (optically thick), indicating that h2o is likely to trace highly obscured warm dense gas. however, further observations of j ≥ 4 h2o lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. we have also detected h2o+ emission in three sources. a tight correlation between lh2o and lh2o+ has been found in galaxies from low to high redshift. the velocity-integrated flux density ratio between h2o+ and h2o suggests that cosmic rays generated by strong star formation are possibly driving the h2o+ formation. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa.the reduced spectra as fits files are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/595/a80 | submillimeter h2o and h2o+emission in lensed ultra- and hyper-luminous infrared galaxies at z 2-4 |
aims: we aim to explore the capabilities of dust emission and γ rays for probing the properties of the interstellar medium in the nearby anti-centre region, using γ-ray observations with the fermi large area telescope (lat), and the thermal dust optical depth inferred from planck and iras observations. we also aim to study massive star-forming clouds including the well known taurus, auriga, perseus, and california molecular clouds, as well as a more diffuse structure which we refer to as cetus. in particular, we aim at quantifying potential variations in cosmic-ray density and dust properties per gas nucleon across the different gas phases and different clouds, and at measuring the co-to-h2 conversion factor, xco, in different environments.methods: we have separated six nearby anti-centre clouds that are coherent in velocities and distances, from the galactic-disc background in h i 21-cm and 12co 2.6-mm line emission. we have jointly modelled the γ-ray intensity recorded between 0.4 and 100 gev, and the dust optical depth τ353 at 353 ghz as a combination of h i-bright, co-bright, and ionised gas components. the complementary information from dust emission and γ rays was used to reveal the gas not seen, or poorly traced, by h i, free-free, and 12co emissions, namely (i) the opaque h iand diffuse h2 present in the dark neutral medium at the atomic-molecular transition, and (ii) the dense h2 to be added where 12co lines saturate.results: the measured interstellar γ-ray spectra support a uniform penetration of the cosmic rays with energies above a few gev through the clouds, from the atomic envelopes to the 12co-bright cores, and with a small ± 9% cloud-to-cloud dispersion in particle flux. we detect the ionised gas from the h iiregion ngc 1499 in the dust and γ-ray emissions and measure its mean electron density and temperature. we find a gradual increase in grain opacity as the gas (atomic or molecular) becomes more dense. the increase reaches a factor of four to six in the cold molecular regions that are well shielded from stellar radiation. consequently, the xco factor derived from dust is systematically larger by 30% to 130% than the γ-ray estimate. we also evaluate the average γ-ray xco factor for each cloud, and find that xco tends to decrease from diffuse to more compact molecular clouds, as expected from theory. we find xco factors in the anti-centre clouds close to or below 1020 cm-2 k-1 km-1 s, in agreement with other estimates in the solar neighbourhood. together, they confirm the long-standing unexplained discrepancy, by a factor of two, between the mean xco values measured at parsec scales in nearby clouds and those obtained at kiloparsec scale in the galaxy. our results also highlight large quantitative discrepancies in 12co intensities between simulations and observations at low molecular gas densities. | cosmic rays, gas and dust in nearby anticentre clouds. i. co-to-h2 conversion factors and dust opacities |
radio emission in the form of giant radio relics is observed at the periphery of galaxy clusters. this non-thermal emission is an important tracer for cosmic ray electrons and intracluster magnetic fields. one striking observational feature of these objects is their high degree of polarization, which provides information on the magnetic fields at the relics' positions. in this contribution, we test if state-of-the-art high resolution cosmological simulations are able to reproduce the polarization features of radio relics. therefore, we present a new analysis of high-resolution cosmological simulations to study the polarization properties of radio relics in detail. in order to compare our results with current and future radio observations, we create mock radio observations of the diffuse polarized emission from a massive galaxy cluster using six different projections, for different observing frequencies and for different telescopes. our simulations suggest that, due to the effect of faraday rotation, it is extremely difficult to relate the morphology of the polarized emission for observing frequencies below 1.4 ghz to the real magnetic field structure in relics. we can reproduce the observed degree of polarization and also several small-scale structures observed in real radio relics, but further work would be needed to reproduce some large-scale spectacular features as observed in real radio relics, such as the `sausage' and `toothbrush' relics. | polarization of radio relics in galaxy clusters |
we investigate the axion-like particle (alp)-photon oscillation effect in the high-energy $\gamma$ -ray spectra of pg 1553+113 and pks 2155-304 measured by fermi-lat and h.e.s.s. the choice of extragalactic background light (ebl) model, which induces the attenuation effect in observed $\gamma$ -ray spectra, affects the alp implications. for the ordinary ebl model that prefers a null hypothesis, we set constraints on the alp-photon coupling constant at 95% c.l. as $g_{a\gamma}\lesssim 5\times 10^{-11} ~{\rm{gev}}^{-1}$ for the alp mass $\sim 10$ nev. we also consider the ciber observation of the cosmic infrared radiation, which shows an excess at wavelengths of $\sim 1~\mu$ m after the substraction of foregrounds. high-energy gamma-rays from extragalactic sources at high redshifts would suffer from a more significant attenuation effect caused by this excess. in this case, we find that the alp-photon oscillation would improve the fit to the observed spectra of pks 2155-304 and pg 1553+113 and find a favored parameter region at 95% c.l.. * supported by the national key r&d program of china (2016yfa0400200) and the national natural science foundation of china (u1738209, 11851303) | implications of axion-like particles from the fermi-lat and h.e.s.s. observations of pg 1553+113 and pks 2155-304 |
the ams-02 collaboration has released preliminary data on the antiproton fraction in cosmic rays. the surprisingly hard antiproton spectrum at high rigidity has triggered speculations about a possible primary antiproton component originating from dark matter annihilations. in this note, we employ newly available ams-02 boron to carbon data to update the secondary antiproton flux within the standard two-zone diffusion model. the new background permits a considerably better fit to the measured antiproton fraction compared to previous estimates. this is mainly a consequence of the smaller slope of the diffusion coefficient favored by the new ams-02 boron to carbon data. | ams-02 antiprotons reloaded |
we study the ${r}_{31}={l}_{\mathrm{co}(3\mbox{--}2)}^{{\prime} }/{l}_{\mathrm{co}(1\mbox{--}0)}^{{\prime} }$ luminosity line ratio in a sample of nearby (z < 0.05) galaxies: 25 star-forming galaxies (sfgs) from the xcold gass survey, 36 hard x-ray-selected active galactic nucleus (agn) host galaxies from the bat agn spectroscopic survey, and 37 infrared-luminous galaxies from the scuba local universe galaxy survey. we find a trend for r31 to increase with star formation efficiency (sfe). we model r31 using the ucl-pdr code and find that the gas density is the main parameter responsible for the variation of r31, while the interstellar radiation field and cosmic-ray ionization rate play only a minor role. we interpret these results to indicate a relation between sfe and gas density. we do not find a difference in the r31 value of sfgs and agn host galaxies, when the galaxies are matched in ssfr (<r31> = 0.52 ± 0.04 for sfgs and <r31> = 0.53 ± 0.06 for agn hosts). according to the results of the ucl-pdr models, the x-rays can contribute to the enhancement of the co line ratio, but only for strong x-ray fluxes and for high gas density (nh > 104 cm-3). we find a mild tightening of the kennicutt-schmidt relation when we use the molecular gas mass surface density traced by co(3-2) (pearson correlation coefficient r = 0.83), instead of the molecular gas mass surface density traced by co(1-0) (r = 0.78), but the increase in correlation is not statistically significant (p-value = 0.06). this suggests that the co(3-2) line can be reliably used to study the relation between sfr and molecular gas for normal sfgs at high redshift and to compare it with studies of low-redshift galaxies, as is common practice. | the co(3-2)/co(1-0) luminosity line ratio in nearby star-forming galaxies and active galactic nuclei from xcold gass, bass, and slugs |
context. star-forming galaxies emit non-thermal radiation from radio to γ rays. observations show that their radio and γ-ray luminosities scale with their star formation rates, supporting the hypothesis that non-thermal radiation is emitted by cosmic rays produced by their stellar populations. however, the nature of the main cosmic-ray transport processes that shape the emission in these galaxies is still poorly understood, especially at low star formation rates.aims: our aim is to investigate the main mechanisms of global cosmic-ray transport and cooling in star-forming galaxies. the way they contribute to shaping the relations between non-thermal luminosities and star formation rates could shed light onto their nature, and allow us to quantify their relative importance at different star formation rates.methods: we developed a model to compute the cosmic-ray populations of star-forming galaxies, taking into account their production, transport, and cooling. the model is parametrised only through global galaxy properties, and describes the non-thermal emission in radio (at 1.4 ghz and 150 mhz) and γ rays (in the 0.1−100 gev band). we focused on the role of diffusive and advective transport by galactic winds, either driven by turbulent or thermal instabilities. we compared model predictions to observations, for which we compiled a homogeneous set of luminosities in these radio bands, and updated those available in γ rays.results: our model reproduces reasonably well the observed relations between the γ-ray or 1.4 ghz radio luminosities and the star formation rate, assuming a single power-law scaling of the magnetic field (with index β = 0.3) and winds blowing either at alfvenic speeds (∼tens of km s−1, for ≲5 m⊙ yr−1) or typical starburst wind velocities (∼hundreds of km s−1, for ≳5 m⊙ yr−1). escape of cosmic rays is negligible for ≳30 m⊙ yr−1. a constant ionisation fraction of the interstellar medium fails to reproduce the 150 mhz radio luminosity throughout the whole star formation rate range.conclusions: our results reinforce the idea that galaxies with high star formation rates are cosmic-ray calorimeters, and that the main mechanism driving proton escape is diffusion, whereas electron escape also proceeds via wind advection. they also suggest that these winds should be cosmic-ray or thermally driven at low and intermediate star formation rates, respectively. our results globally support that magneto-hydrodynamic turbulence is responsible for the dependence of the magnetic field strength on the star formation rate and that the ionisation fraction is strongly disfavoured to be constant throughout the whole range of star formation rates. | exploring the physics behind the non-thermal emission from star-forming galaxies detected in γ rays |
we report a significant detection of the hot intergalactic medium in the filamentary bridge connecting the galaxy clusters abell 399 and abell 401. this result is enabled by a low-noise, high-resolution map of the thermal sunyaev-zeldovich signal from the atacama cosmology telescope (act) and planck satellite. the act data provide the 1.65 arcmin resolution that allows us to clearly separate the profiles of the clusters, whose centres are separated by 37 arcmin, from the gas associated with the filament. a model that fits for only the two clusters is ruled out compared to one that includes a bridge component at >5σ. using a gas temperature determined from suzaku x-ray data, we infer a total mass of $(3.3\pm 0.7)\times 10^{14}\, \mathrm{m}_{\odot }$ associated with the filament, comprising about 8 per cent of the entire abell 399-abell 401 system. we fit two phenomenological models to the filamentary structure; the favoured model has a width transverse to the axis joining the clusters of ${\sim }1.9\, \mathrm{mpc}$. when combined with the suzaku data, we find a gas density of $(0.88\pm 0.24)\times 10^{-4}\, \mathrm{cm}^{-3}$, considerably lower than previously reported. we show that this can be fully explained by a geometry in which the axis joining abell 399 and abell 401 has a large component along the line of sight, such that the distance between the clusters is significantly greater than the $3.2\, \mathrm{mpc}$ projected separation on the plane of the sky. finally, we present initial results from higher resolution (12.7 arcsec effective) imaging of the bridge with the mustang-2 receiver on the green bank telescope. | a high-resolution view of the filament of gas between abell 399 and abell 401 from the atacama cosmology telescope and mustang-2 |
using recent measurements of the spectrum and chemical composition of the highest energy cosmic rays, we consider the sources of these particles. we find that these data strongly prefer models in which the sources of the ultra-high-energy cosmic rays inject predominantly intermediate mass nuclei, with comparatively few protons or heavy nuclei, such as iron or silicon. if the number density of sources per comoving volume does not evolve with redshift, the injected spectrum must be very hard (α ≃1 ) in order to fit the spectrum observed from earth. such a hard spectral index would be surprising and difficult to accommodate theoretically. in contrast, much softer spectral indices, consistent with the predictions of fermi acceleration (α ≃2 ), are favored in models with negative source evolution. with this theoretical bias, these observations thus favor models in which the sources of the highest energy cosmic rays are preferentially located within the low-redshift universe. | indications of negative evolution for the sources of the highest energy cosmic rays |
cosmic ray (cr) sources leave signatures in the isotopic abundances of crs. current models of galactic crs that consider supernovae (sne) shocks as the main sites of particle acceleration cannot satisfactorily explain the higher 22ne/20ne ratio in crs compared to the interstellar medium. although stellar winds from massive stars have been invoked, their contribution relative to sne ejecta has been taken as a free parameter. here, we present a theoretical calculation of the relative contributions of wind termination shocks (wtss) and sne shocks in superbubbles, based on the hydrodynamics of winds in clusters, the standard stellar mass function, and stellar evolution theory. we find that the contribution of wtss towards the total cr production is at least 25{{ per cent}}, which rises to ≳ 50{{ per cent}} for young (≲10 myr) clusters, and explains the observed 22ne/20ne ratio. we argue that since the progenitors of apparently isolated supernovae remnants (snrs) are born in massive star clusters, both wts and sne shocks can be integrated into a combined scenario of crs being accelerated in massive clusters. this scenario is consistent with the observed ratio of snrs to γ-ray bright (lγ ≳ 1035 erg s-1) star clusters, as predicted by star cluster mass function. moreover, wtss can accelerate crs to pev energies, and solve other long-standing problems of the standard sn paradigm of cr acceleration. | realistic modelling of wind and supernovae shocks in star clusters: addressing 22ne/20ne and other problems in galactic cosmic rays |
cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our galaxy. recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. particularly striking are the differences between the low energy results collected by the space-borne pamela and ams-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. the pamela experiment has been measuring the time variation of the positron and electron intensity at earth from july 2006 to december 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. the positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. these results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field. | time dependence of the electron and positron components of the cosmic radiation measured by the pamela experiment between july 2006 and december 2015 |
a unique multipurpose cherenkov water detector, the nevod facility, uses quasispherical measuring modules to explore all the basic components of cosmic rays on earth's surface, including neutrinos. currently, the experimental complex includes the cherenkov water detector, a calibration telescope system, and a coordinate detector. this paper traces the basic development stages of nevod, examines research directions, presents the results obtained, including the search for the solution to the 'muon puzzle', and discusses possible future development prospects. | cherenkov water detector nevod |
we report a unique combination of ∼10 ev to ∼344 mev in situ ion measurements from the plasma science (pls), low energy charged particle (lecp), and cosmic ray subsystem (crs) experiments on the voyager 2 (v2) spacecraft, and remotely sensed ∼110 ev to ∼55 kev energetic neutral atom (ena) measurements from the interstellar boundary explorer (ibex) mission and ion and neutral camera (inca) on the cassini mission. this combination is done over the time period from 2009 to the end of 2016, along the v2 trajectory, toward assessing the properties of the ion energy spectra inside the heliosheath. the combined energy spectra exhibit a series of softening and hardening breaks, providing important insights on the various ion acceleration processes inside the heliosheath. ions in the <6 kev energy range dominate the total pressure distribution inside the heliosheath but the ion distributions at higher energies (>5.2 kev) provide a significant contribution to the total pressure. with the assumption that all enas (∼110 ev to 55 kev) are created by charge-exchange interactions inside the heliosheath, we estimate that the magnetic field upstream at the heliopause required to balance the pressure from the heliosheath in the direction of v2 is ∼0.67 nt. this number is consistent with the measured magnetic field at v2 from 2018 november, when the spacecraft entered interstellar space. | combined ∼10 ev to ∼344 mev particle spectra and pressures in the heliosheath along the voyager 2 trajectory |
we consistently include the effect of massive neutrinos in the thermal sunyaev zeldovich (sz) power spectrum and cluster counts analyses, highlighting subtle dependencies on the total neutrino mass and data combination. in particular, we find that using the transfer functions for cold dark matter (cdm) + baryons in the computation of the halo mass function, instead of the transfer functions including neutrino perturbations, as prescribed in recent work, yields an ≈0.25 per cent downward shift of the σ8 constraint from tsz power spectrum data, with a fiducial neutrino mass σmν = 0.06 ev. in λcdm, with an x-ray mass bias corresponding to the expected hydrostatic mass bias, i.e. (1 - b) ≃ 0.8, our constraints from planck sz data are consistent with the latest results from spt, des-y1, and kids+viking-450. in νλcdm, our joint analyses of planck sz with planck 2015 primary cmb yield a small improvement on the total neutrino mass bound compared to the planck 2015 primary cmb constraint, as well as (1 - b) = 0.64 ± 0.04 (68 per cent cl). for forecasts, we find that competitive neutrino mass measurements using cosmic variance limited sz power spectrum require masking the heaviest clusters and probing the small-scale sz power spectrum up to ℓmax ≈ 104. although this is challenging, we find that sz power spectrum can realistically be used to tightly constrain intracluster medium properties: we forecast a 2 per cent determination of the x-ray mass bias by combining cmb-s4 and our mock sz power spectrum with ℓmax = 103. | including massive neutrinos in thermal sunyaev zeldovich power spectrum and cluster counts analyses |
giant radio relics in the outskirts of galaxy clusters are known to be lit up by the relativistic electrons produced via diffusive shock acceleration (dsa) in shocks with low sonic mach numbers, m s ≲ 3. the particle acceleration at these collisionless shocks critically depends on the kinetic plasma processes that govern the injection to dsa. here, we study the preacceleration of suprathermal electrons in weak, quasi-perpendicular (q ⊥) shocks in the hot, high-β (β = p gas/p b) intracluster medium (icm) through two-dimensional particle-in-cell simulations. guo et al. showed that, in high-β q ⊥-shocks, some of the incoming electrons could be reflected upstream and gain energy via shock drift acceleration (sda). the temperature anisotropy due to the sda-energized electrons then induces the electron firehose instability (efi), and oblique waves are generated, leading to a fermi-like process and multiple cycles of sda in the preshock region. we find that such electron preacceleration is effective only in shocks above a critical mach number {m}ef}* ≈ 2.3. this means that, in icm plasmas, q ⊥-shocks with m s ≲ 2.3 may not efficiently accelerate electrons. we also find that, even in q ⊥-shocks with m s ≳ 2.3, electrons may not reach high enough energies to be injected to the full fermi-i process of dsa, because long-wavelength waves are not developed via the efi alone. our results indicate that additional electron preaccelerations are required for dsa in icm shocks, and the presence of fossil relativistic electrons in the shock upstream region may be necessary to explain observed radio relics. | electron preacceleration in weak quasi-perpendicular shocks in high-beta intracluster medium |
the pierre auger collaboration (auger) recently reported a correlation between the arrival directions of cosmic rays with energies above 39 eev and the flux pattern of 23 nearby starburst galaxies (sbgs). in this letter, we tested the same hypothesis using cosmic rays detected by the telescope array experiment (ta) in the 9 yr period from 2008 may to 2017 may. unlike the auger analysis, we did not optimize the parameter values but kept them fixed to the best-fit values found by auger, namely 9.7% for the anisotropic fraction of cosmic rays assumed to originate from the sbgs in the list and 12.°9 for the angular scale of the correlations. the energy threshold that we adopted is 43 eev, corresponding to 39 eev in auger when taking into account the energy-scale difference between two experiments. we find that the ta data is compatible with isotropy to within 1.1σ and with the auger result to within 1.4σ, meaning that it is not capable to discriminate between these two hypotheses. | testing a reported correlation between arrival directions of ultra-high-energy cosmic rays and a flux pattern from nearby starburst galaxies using telescope array data |
the surface of pluto as it is understood on the eve of the encounter of the new horizons spacecraft (mid-2015) consists of a spatially heterogeneous mix of solid n2, ch4, co, c2h6, and an additional component that imparts color, and may not be an ice. the known molecular ices are detected by near-infrared spectroscopy. the n2 ice occurs in the hexagonal crystalline β-phase, stable at t > 35.6 k. spectroscopic evidence for wavelength shifts in the ch4 bands attests to the complex mixing of ch4 and n2 in the solid state, in accordance with the phase diagram for n2 + ch4. spectra obtained at several aspects of pluto's surface as the planet rotates over its 6.4-day period show variability in the distribution of ch4 and n2 ices, with stronger ch4 absorption bands associated with regions of higher albedo, in correlation with the visible rotational light curve. co and n2 ice absorptions are also strongly modulated by the rotation period; the bands are strongest on the anti-charon hemisphere of pluto. longer term changes in the strengths of pluto's absorption bands occur as the viewing geometry changes on seasonal time-scales, although a complete cycle has not been observed. the non-ice component of pluto's surface may be a relatively refractory material produced by the uv and cosmic-ray irradiation of the surface ices and gases in the atmosphere, although uv does not generally penetrate the atmospheric ch4 to interact with the surface. laboratory simulations indicate that a rich chemistry ensues by the irradiation of mixtures of the ices known to occur on pluto, but specific compounds have not yet been identified in spectra of the planet. charon's surface is characterized by spectral bands of crystalline h2o ice, and a band attributed to one or more hydrates of nh3. amorphous h2o ice may also be present; the balance between the amorphization and crystallization processes on charon remains to be clarified. the albedo of charon and its generally spatially uniform neutral color indicate that a component, not yet identified, is mixed in some way with the h2o and nh3·nh2o ices. among the many known small bodies in the transneptunian region, several share characteristics with pluto and charon, including the presence of ch4, n2, c2h6, h2o ices, as well as components that yield a wide variety of surface albedo and color. the new horizons investigation of the pluto-charon system will generate new insight into the physical properties of the broader transneptunian population, and eventually to the corresponding bodies expected in the numerous planetary systems currently being discovered elsewhere in the galaxy. | the surface compositions of pluto and charon |
accreting compact objects are crucial to understand several important astrophysical phenomena such as type ia supernovae, gravitational waves, or x-ray and $\gamma$-ray bursts. in addition, they are natural laboratories to infer fundamental properties of stars, to investigate high-energy phenomena and accretion processes, to test theories of stellar and binary evolution, to explore interactions between high-density plasma and very strong magnetic fields, to examine the interplay between binary evolution and dynamical interactions (in the case they belong to dense star clusters), and they can even be used as a probe for the assembling process of galaxies over cosmic time-scales. despite the fundamental importance of accreting compact objects for astrophysics and recent progress with the comprehension of these fascinating objects, we still do not fully understand how they form and evolve. in this chapter, we will review the current theoretical status of our knowledge on these objects, and will discuss standing problems and potential solutions to them. | formation and evolution of accreting compact objects |
lorentz invariance (li) has a central role in science and its violation (liv) at some high-energy scale has been related to possible solutions for several of the most intriguing puzzles in nature such as dark matter, dark energy, cosmic rays generation in extreme astrophysical objects and quantum gravity. we report on a search for liv signal based on the propagation of gamma rays from astrophysical sources to earth. an innovative data analysis is presented which allowed us to extract unprecedented information from the most updated data set composed of 111 energy spectra of 38 different sources measured by current gamma-ray observatories. no liv signal was found, and we show that the data are best described by li assumption. we derived limits for the liv energy scale at least 3 times better than the ones currently available in the literature for subluminal signatures of liv in high-energy gamma rays. | improved limits on lorentz invariance violation from astrophysical gamma-ray sources |
the field of gamma-ray astronomy has experienced impressive progress over the last decade. thanks to the advent of a new generation of imaging air cherenkov telescopes (h.e.s.s., magic, veritas) and thanks to the launch of the fermi-lat satellite, several thousand gamma-ray sources are known today, revealing an unexpected ubiquity of particle acceleration processes in the universe. major scientific challenges are still ahead, such as the identification of the nature of dark matter, the discovery and understanding of the sources of cosmic rays, or the comprehension of the particle acceleration processes that are at work in the various objects. this paper presents some of the instruments and mission concepts that will address these challenges over the next decades. | the future of gamma-ray astronomy |
radio relics detected in the outskirts of galaxy clusters are thought to trace radio-emitting relativistic electrons accelerated at cosmological shocks. in this study, using the cosmological hydrodynamic simulation data for the large-scale structure formation and adopting a diffusive shock acceleration (dsa) model for the production of cosmic-ray (cr) electrons, we construct mock radio and x-ray maps of simulated galaxy clusters that are projected in the sky plane. various properties of shocks and radio relics, including the shock mach number, radio spectral index, and luminosity, are extracted from the synthetic maps and compared with observations. a substantial fraction of radio and x-ray shocks identified in these maps involve multiple shock surfaces along lines of sight (loss), and the morphology of shock distributions in the maps depends on the projection direction. among multiple shocks in a given los, radio observations tend to pick up stronger shocks with flatter radio spectra, while x-ray observations preferentially select weaker shocks with larger kinetic energy flux. as a result, in some cases the shock mach numbers and locations derived from radio and x-ray observations could differ from each other. we also find that the distributions of the spectral index and radio power of the synthetic radio relics are somewhat inconsistent with those of observed real relics; a bit more radio relics have been observed closer to the cluster core and with steeper spectral indices. we suggest that the inconsistency could be explained if very weak shocks with ms ≲ 2 accelerate cr electrons more efficiently, compared with the dsa model adopted here. | radio and x-ray shocks in clusters of galaxies |
the residence time of cosmic rays (crs) in the galaxy is usually inferred from the measurement of the ratio of secondary-to-primary nuclei, for instance the boron (b)/carbon (c) ratio, which provides an estimate of the amount of matter traversed by crs during their propagation, the so-called cr grammage. however, after being released by their parent sources, for instance, supernova remnants, crs must cross the disc of the galaxy, before entering the much lower density halo, in which they are believed to spend most of their time before eventually escaping the galaxy. in the near-source region, the cr propagation is shown to be dominated by the nonlinear self-generation of waves. here we show that due to this effect, the time that crs with energies up to ∼10 tev spend within a distance lc∼100 pc from the sources is much larger than naive estimates would suggest. depending on the level of ionization of the medium surrounding the source, the grammage accumulated in the source vicinity may be a non-negligible fraction of the total grammage traversed throughout the whole galaxy. moreover, there is an irreducible grammage that crs traverse while trapped downstream of the shock that accelerated them, though this contribution is rather uncertain. we conclude that some caution should be used in inferring parameters of galactic cr propagation from measurements of the b/c ratio. | grammage of cosmic rays around galactic supernova remnants |
heating of virialized gas by streaming cosmic rays (crs) may be energetically important in galaxy haloes, groups, and clusters. we present a linear thermal stability analysis of plasmas heated by streaming crs. we separately treat equilibria with and without background gradients, and with and without gravity. we include both cr streaming and diffusion along the magnetic-field direction. thermal stability depends strongly on the ratio of cr pressure to gas pressure, which determines whether modes are isobaric or isochoric. modes with $\boldsymbol {k \cdot b }\ne 0$ are strongly affected by cr diffusion. when the streaming time is shorter than the cr diffusion time, thermally unstable modes (with $\boldsymbol {k \cdot b }\ne 0$ ) are waves propagating at a speed ∝ the alfvén speed. halo gas in photoionization equilibrium is thermally stable independent of cr pressure, while gas in collisional ionization equilibrium is unstable for physically realistic parameters. in gravitationally stratified plasmas, the oscillation frequency of thermally overstable modes can be higher in the presence of cr streaming than the buoyancy/free-fall frequency. this may modify the critical tcool/tff at which multiphase gas is present. the criterion for convective instability of a stratified, cr-heated medium can be written in the familiar schwarzschild form dseff/dz < 0, where seff is an effective entropy involving the gas and cr pressures. we discuss the implications of our results for the thermal evolution and multiphase structure of galaxy haloes, groups, and clusters. | thermal instability of halo gas heated by streaming cosmic rays |
the supernova explosion which deposited <mml:mmultiscripts>fe 60 </mml:mmultiscripts> isotopes on earth 2-3 million years ago should have also produced cosmic rays which contribute to the locally observed cosmic ray flux. we show that the contribution of this "local source" causes the "anomalies" observed in the positron and antiproton fluxes and explains why their spectral shapes agree with that of the proton flux. at the same time, this local source component accounts for the difference in the slopes of the spectra of cosmic ray nuclei as the result of the slightly varying relative importance of the "local" and the average component for distinct cr nuclei. such a "local supernova" model for the spectra of nuclei can be tested via a combined measurement of the energy dependence of the boron-to-carbon (primary-to-secondary cosmic rays) ratio and of the antiproton spectrum: while the antiproton spectrum is predicted to extend approximately as a power law into the tev range without any softening break, the b/c ratio is expected to show a "plateau" at a level fixed by the observed positron excess in the 30-300 gev range. we discuss the observability of such a plateau with dedicated experiments for the measurement of the cosmic ray composition in the 10 tev energy range (nucleon, iss-cream). | cosmic ray signatures of a 2-3 myr old local supernova |
we report on a measurement of the cosmic-ray composition by the telescope array low-energy extension (tale) air fluorescence detector (fd). by making use of the cherenkov light signal in addition to air fluorescence light from cosmic-ray (cr)-induced extensive air showers, the tale fd can measure the properties of the cosmic rays with energies as low as ∼2 pev and exceeding 1 eev. in this paper, we present results on the measurement of ${x}_{\max }$ <!-- --> distributions of showers observed over this energy range. data collected over a period of ∼4 yr were analyzed for this study. the resulting ${x}_{\max }$ <!-- --> distributions are compared to the monte carlo (mc) simulated data distributions for primary cosmic rays with varying composition and a four-component fit is performed. the comparison and fit are performed for energy bins, of width 0.1 or 0.2 in ${\mathrm{log}}_{10}(e/\mathrm{ev})$ <!-- --> ,spanning the full range of the measured energies. we also examine the mean ${x}_{\max }$ <!-- --> value as a function of energy for cosmic rays with energies greater than 1015.8 ev. below 1017.3 ev, the slope of the mean ${x}_{\max }$ <!-- --> as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the models, indicating that the composition is becoming heavier with energy in this energy range. this is consistent with a rigidity-dependent cutoff of events from galactic sources. finally, an increase in the ${x}_{\max }$ <!-- --> elongation rate is observed at energies just above 1017 ev, indicating another change in the cosmic-ray composition. | the cosmic-ray composition between 2 pev and 2 eev observed with the tale detector in monocular mode |
the 21-cm signal from the cosmic dawn (cd) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. it is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the cd from one of these processes, namely the redshift-space distortions (rsds). when rsds are added, the resulting boost to the power spectra makes the signal more or equally detectable for our models for all redshifts, further strengthening hopes that a power spectra measurement of the cd will be possible. rsds lead to anisotropy in the signal at the beginning and end of the cd, but not while x-ray heating is underway. the inclusion of rsds, however, decreases detectability of the non-gaussianity of fluctuations from inhomogeneous x-ray heating as measured by the skewness and kurtosis. on the other hand, mock observations created from all our simulations that include telescope noise corresponding to 1000 h of observation with the square kilometre array telescope show that we may be able to image the cd for all heating models considered and suggest rsds dramatically boost fluctuations coming from the inhomogeneous ly α background. | redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn |
some catastrophic stellar explosions, such as supernovae (sne), compact binary coalescences, and microtidal disruption events, are believed to be embedded in the accretion disks of active galactic nuclei (agns). we show high-energy neutrinos can be produced efficiently through pp interactions between shock-accelerated cosmic rays and agn disk materials shortly after the explosion ejecta shock breaks out of the disk. agn stellar explosions are ideal targets for joint neutrino and electromagnetic (em) multimessenger observations. future em follow-up observations of neutrino bursts can help us search for yet-discovered agn stellar explosions. we suggest that agn stellar explosions could potentially be important astrophysical neutrino sources. the contribution from agn stellar explosions to the observed diffuse neutrino background depends on the uncertain local event rate densities of these events in agn disks. by considering thermonuclear sne, core-collapse sne, gamma-ray burst associated sne, kilonovae, and choked grbs in agn disks with known theoretical local event rate densities, we show that these events may contribute to ≲10% of the observed diffuse neutrino background. | high-energy neutrinos from stellar explosions in active galactic nuclei accretion disks |
the tibet-as γ collaboration has recently reported a measurement of diffuse γ -ray flux from the outer galactic disk in the energy range reaching pev. we complement this measurement with the fermi/lat measurement of the diffuse flux from the same sky region and study the pion decay model of the combined fermi /la t + tibet -as γ spectrum. we find that within such a model the average cosmic-ray spectrum in the outer galactic disk has the same characteristic features as the local cosmic-ray spectrum. in particular, it experiences a hardening at several hundred gv rigidity and a knee feature in the pv rigidity range. the slope of the average cosmic-ray spectrum above the break is close to the locally observed slope of the helium spectrum γ ≃2.5 , but is harder than the slope of the local proton spectrum in the same rigidity range. although the combination of fermi/lat and tibet-as γ data points to the presence of the knee in the average cosmic-ray spectrum, the quality of the data is not yet sufficient for the study of knee shape and cosmic-ray composition. | pion decay model of the tibet-as γ pev gamma-ray signal |
we present high-pass-filtered continuum images of the inner 3.°5 × 2.°5 of the galactic center at 20 cm with 6.″4 resolution. these mosaic images are taken with meerkat and reveal a large number of narrow filaments, roughly an order of magnitude increase in their numbers compared to past measurements. for the first time, we carry out population studies of the spectral index and magnetic field of the entire region. the mean spectral indices of the filaments are steeper than supernova remnants (snrs) (-0.62) with a value of α ~ -0.83. the variation in α is much larger than for the snrs, suggesting that these characteristics have a different origin. a large-scale cosmic-ray-driven wind has recently been proposed to explain the origin of filaments and the large-scale 430 pc bipolar radio and x-ray structure. this favors the possibility that the large-scale bipolar radio/x-ray structure is produced by past activity of sgr a* rather than a coordinated burst of supernovae. a trend of steeper indices is also noted with increasing distance from the galactic plane. this could be explained either by synchrotron cooling or weak shocks accelerating cosmic-ray particles in the context of the cosmic-ray-driven wind. the mean magnetic field strengths along the filaments range from ~100 to 400 μg depending on the assumed ratio of cosmic-ray protons to electrons. given that there is a high cosmic-ray pressure in the galactic center, the large equipartition magnetic field implies that the magnetic filed is weak in most of the interstellar volume of the galactic center. | statistical properties of the population of the galactic center filaments: the spectral index and equipartition magnetic field |
context. nearly a dozen star-forming galaxies have been detected in γ-rays by the fermi observatory in the last decade. a remarkable property of this sample is the quasi-linear relation between the γ-ray luminosity and the star formation rate, which was obtained assuming that the latter is well traced by the infrared luminosity of the galaxies. the non-linearity of this relation has not been fully explained yet.aims: we aim to determine the biases derived from the use of the infrared luminosity as a proxy for the star formation rate and to shed light on the more fundamental relation between the latter and the γ-ray luminosity. we expect to quantify and explain some trends observed in this relation.methods: we compiled a near-homogeneous set of distances, ultraviolet, optical, infrared, and γ-ray fluxes from the literature for all known γ-ray emitting, star-forming galaxies. from these data, we computed the infrared and γ-ray luminosities, and star formation rates. we determined the best-fitting relation between the latter two, and we describe the trend using simple, population-orientated models for cosmic-ray transport and cooling.results: we find that the γ-ray luminosity-star formation rate relation obtained from infrared luminosities is biased to shallower slopes. the actual relation is steeper than previous estimates, having a power-law index of 1.35 ± 0.05, in contrast to 1.23 ± 0.06.conclusions: the unbiased γ-ray luminosity-star formation rate relation can be explained at high star formation rates by assuming that the cosmic-ray cooling region is kiloparsec-sized and pervaded by mild to fast winds. combined with previous results about the scaling of wind velocity with star formation rate, our work provides support to advection as the dominant cosmic-ray escape mechanism in galaxies with low star formation rates. | γ-ray/infrared luminosity correlation of star-forming galaxies |
the hygal stratospheric observatory for infrared astronomy legacy program surveys six hydride molecules-arh+, oh+, h2o+, sh, oh, and ch-and two atomic constituents-c+ and o-within the diffuse interstellar medium (ism) by means of absorption-line spectroscopy toward 25 bright galactic background continuum sources. this detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ism, as demonstrated by recent studies with the herschel space observatory. the observations performed under the hygal program will allow us to address several questions related to the life cycle of molecular material in the ism and the physical processes that impact the phase transition from atomic to molecular gas, such as: (1) what is the distribution function of the h2 fraction in the ism? (2) how does the ionization rate due to low-energy cosmic rays vary within the galaxy? (3) what is the nature of interstellar turbulence (e.g., typical shear or shock velocities), and what mechanisms lead to its dissipation? in this overview, we discuss the observing strategy, the synergies with ancillary and archival observations of other small molecules, and the data reduction and analysis schemes we adopted; and we present the first results obtained toward three of the survey targets, w3(oh), w3 irs5, and ngc 7538 irs1. robust measurements of the column densities of these hydrides-obtained through widespread observations of absorption lines-help address the questions raised, and there is a very timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of h2 within the turbulent ism. the provision of enhanced hygal data products will therefore serve as a legacy for future ism studies. | hygal: characterizing the galactic interstellar medium with observations of hydrides and other small molecules. i. survey description and a first look toward w3(oh), w3 irs5, and ngc 7538 irs1 |
the emergence of the first, so-called population iii (pop iii), stars shaped early cosmic history in ways that crucially depends on their initial mass function (imf). however, because of the absence of direct observational constraints, the detailed imf remains elusive. nevertheless, numerical simulations agree in broad terms that the first stars were typically massive and should often end their lives in violent, explosive deaths. these fates include extremely luminous pair-instability supernovae (pisne) and bright gamma-ray bursts (grbs), the latter arising from the collapse of rapidly rotating progenitor stars into black holes. these high-redshift transients are expected to be within the detection limits of upcoming space telescope missions, allowing to place effective constraints on the shape of the primordial imf that is not easily accessible with other probes. this paper presents a framework to probe the pop iii imf, utilizing the cosmological source densities of high-redshift pisne and grbs. considering these transients separately could provide useful constraints on the pop iii imf, but tighter bounds are obtainable by combining pisn and grb counts. this combined diagnostic is more robust as it is independent of the underlying pop iii star formation rate density, an unknown prior. future surveys promise to capture most high-redshift grbs across the entire sky, but high-redshift pisn searches with future telescopes, e.g. roman space telescope, will likely be substantially incomplete. nevertheless, we demonstrate that even such lower bounds on the pisn count will be able to provide key constraints on the primordial imf, in particular, if it is top-heavy or not. | probing the initial mass function of the first stars with transients |
we use hydrodynamical simulations of two milky way-mass galaxies to demonstrate the impact of cosmic-ray pressure on the kinematics of cool and warm circumgalactic gas. consistent with previous studies, we find that cosmic-ray pressure can dominate over thermal pressure in the inner 50 kpc of the circumgalactic medium (cgm), creating an overall cooler cgm than that of similar galaxy simulations run without cosmic rays. we generate synthetic sight lines of the simulated galaxies' cgm and use voigt profile-fitting methods to extract ion column densities, doppler-b parameters, and velocity centroids of individual absorbers. we directly compare these synthetic spectral line fits with hst/cos cgm absorption-line data analyses, which tend to show that metallic species with a wide range of ionization potential energies are often kinematically aligned. compared to the milky way simulation run without cosmic rays, the presence of cosmic-ray pressure in the inner cgm creates narrower o vi absorption features and broader si iii absorption features, a quality that is more consistent with observational data. additionally, because the cool gas is buoyant due to nonthermal cosmic-ray pressure support, the velocity centroids of both cool and warm gas tend to align in the simulated milky way with feedback from cosmic rays. our study demonstrates that detailed, direct comparisons between simulations and observations, focused on gas kinematics, have the potential to reveal the dominant physical mechanisms that shape the cgm. | the impact of cosmic rays on the kinematics of the circumgalactic medium |
context. diffusive shock acceleration (dsa) is the most promising mechanism that accelerates galactic cosmic rays (crs) in the shocks of supernova remnants (snrs). it is based on particles scattering caused by turbulence ahead and behind the shock. the turbulence upstream is supposedly generated by the crs, but this process is not well understood. the dominant mechanism may depend on the evolutionary state of the shock and can be studied via the crs escaping upstream into the interstellar medium (ism).aims: previous observations of the γ cygni snr showed a difference in morphology between gev and tev energies. since this snr has the right age and is at the evolutionary stage for a significant fraction of crs to escape, our aim is to understand γ-ray emission in the vicinity of the γ cygni snr.methods: we observed the region of the γ cygni snr with the magic imaging atmospheric cherenkov telescopes between 2015 may and 2017 september recording 87 h of good-quality data. additionally, we analysed fermi-lat data to study the energy dependence of the morphology as well as the energy spectrum in the gev to tev range. the energy spectra and morphology were compared against theoretical predictions, which include a detailed derivation of the cr escape process and their γ-ray generation.results: the magic and fermi-lat data allowed us to identify three emission regions that can be associated with the snr and that dominate at different energies. our hadronic emission model accounts well for the morphology and energy spectrum of all source components. it constrains the time-dependence of the maximum energy of the crs at the shock, the time-dependence of the level of turbulence, and the diffusion coefficient immediately outside the snr shock. while in agreement with the standard picture of dsa, the time-dependence of the maximum energy was found to be steeper than predicted, and the level of turbulence was found to change over the lifetime of the snr. | study of the gev to tev morphology of the γ cygni snr (g 78.2+2.1) with magic and fermi-lat. evidence for cosmic ray escape |
the association of grb170817a with a binary neutron star (bns) merger has revealed that bnss produce at least a fraction of short gamma-ray bursts (sgrbs). as gravitational wave (gw) detectors push their horizons, it is important to assess coupled electromagnetic (em)/gw probabilities and maximize observational prospects. here, we perform bns population synthesis calculations with the code mobse, seeding the binaries in galaxies at three representative redshifts, $z$ = 0.01, 0.1, and 1 of the illustris tng50 simulation. the binaries are evolved and their locations numerically tracked in the host galactic potentials until merger. adopting the microphysics parameters of grb170817a, we numerically compute the broad-band light curves of jets from bns mergers, with the afterglow brightness dependent on the local medium density at the merger site. we perform monte carlo simulations of the resulting em population assuming either a random viewing angle with respect to the jet, or a jet aligned with the orbital angular momentum of the binary, which biases the viewing angle probability for gw-triggered events. we find a gamma-ray detection probability of $\sim\!2{{\rm per\ cent}},10{{\rm per\ cent}},\mathrm{and}\ 40{{\rm per\ cent}}$ for bnss at $z$ = 1, 0.1, and 0.01, respectively, for the random case, rising to $\sim\!75{{\rm per\ cent}}$ for the $z$ = 0.01, gw-triggered aligned case. afterglow detection probabilities of gw-triggered bns mergers vary in the range of $\sim \! 0.3 \!-\! 0.5{{\rm per\ cent}}$, with higher values for aligned jets, and are comparable across the high- and low-energy bands, unlike gamma-ray-triggered events (cosmological sgrbs) which are significantly brighter at higher energies. we further quantify observational biases with respect to host galaxy masses. | host galaxies and electromagnetic counterparts to binary neutron star mergers across the cosmic time: detectability of gw170817-like events |
we investigate the observed muon deficit in air shower simulations when compared to ultrahigh-energy cosmic ray (uhecr) data. based upon the observed enhancement of strangeness production in high-energy hadronic collisions reported by the alice collaboration, the concomitant π ↔ k swap is considered as the keystone to resolve the muon anomaly through its corresponding impact on the shower development. we construct a toy model in terms of the π ↔ k swapping probability fs. we present a parametrization of fs in terms of the pseudorapidity that can accommodate the uhecr data. looking to the future, we explore potential strategies for model improvement using the massive amounts of data to be collected by lhc neutrino detectors, such as faserν and experiments at the forward physics facility. we calculate the corresponding sensitivity to fs and show that these experiments will be able to probe the model phase space. | an explanation of the muon puzzle of ultrahigh-energy cosmic rays and the role of the forward physics facility for model improvement |
it is expected that as the sun travels through the interstellar medium (ism), there will be different filtration of galactic cosmic rays (gcr) that affect earth. the effect of gcr on earth's atmosphere and climate is still uncertain. although the interaction with molecular clouds was previously considered, the terrestrial impact of compact cold clouds was neglected. there is overwhelming geological evidence from 60fe and 244pu isotopes that earth was in direct contact with the ism 2 million years ago, and the local ism is home to several nearby cold clouds. here we show, with a state-of the art simulation that incorporate all the current knowledge about the heliosphere that if the solar system passed through a cloud such as local leo cold cloud, then the heliosphere which protects the solar system from interstellar particles, must have shrunk to a scale smaller than the earth's orbit around the sun (0.22). using a magnetohydrodynamic simulation that includes charge exchange between neutral atoms and ions, we show that during the heliosphere shrinkage, earth was exposed to a neutral hydrogen density of up to 3000cm-3. this could have had drastic effects on earth's climate and potentially on human evolution at that time, as suggested by existing data. | terrestrial impact from the passage of the solar system through a cold cloud a few million years ago |
air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. these pulses have been measured successfully in the past few years at the low-frequency array (lofar) and are used to study the properties of cosmic rays. for a complete understanding of this phenomenon and the underlying physical processes, an absolute calibration of the detecting antenna system is needed. we present three approaches that were used to check and improve the antenna model of lofar and to provide an absolute calibration of the whole system for air shower measurements. two methods are based on calibrated reference sources and one on a calibration approach using the diffuse radio emission of the galaxy, optimized for short data-sets. an accuracy of 19% in amplitude is reached. the absolute calibration is also compared to predictions from air shower simulations. these results are used to set an absolute energy scale for air shower measurements and can be used as a basis for an absolute scale for the measurement of astronomical transients with lofar. | calibrating the absolute amplitude scale for air showers measured at lofar |
the deuterium fraction, [n2d+]/[n2h+], may provide information about the ages of dense, cold gas structures, which are important for comparing dynamical models of cloud core formation and evolution. here we introduce a complete chemical network with species containing up to three atoms, with the exception of the oxygen chemistry, where reactions involving h3o+ and its deuterated forms have been added, significantly improving the consistency with comprehensive chemical networks. deuterium chemistry and spin states of h2 and h3+ isotopologues are included in this primarily gas-phase chemical model. we investigate the dependence of deuterium chemistry on these model parameters: density ({{n}h}), temperature, cosmic ray ionization rate, and gas-phase depletion factor of heavy elements ({{f}d}). we also explore the effects of time-dependent freeze-out of gas-phase species and the dynamical evolution of density at various rates relative to free-fall collapse. for a broad range of model parameters, the timescales to reach large values of dfrac{{n2}{{h}+}}≳ 0.1, observed in some low- and high-mass starless cores, are relatively long compared to the local free-fall timescale. these conclusions are unaffected by introducing time-dependent freeze-out and considering models with evolving density, unless the initial {{f}d} ≳ 10. for fiducial model parameters, achieving dfrac{{n2}{{h}+}}≳ 0.1 requires collapse to be proceeding at rates at least several times slower than that of free-fall collapse, perhaps indicating a dynamically important role for magnetic fields in supporting starless cores and thus the regulation of star formation. | the deuterium fractionation timescale in dense cloud cores: a parameter space exploration |
we simulate an isolated, magnetized milky way-like disc galaxy using a self-consistent model of unresolved star formation and feedback, evolving the system until it reaches statistical steady state. we show that the quasi-steady-state structure is distinctly layered in galactocentric height z, with a broken power-law structure in alfven mach number and plasma beta. magnetic pressure exceeds turbulent and thermal pressures after the gas is depleted to levels below that of the present-day galaxy, but is subdominant at higher gas fractions and star formation rates. we find field strengths, gas surface densities, and star formation rates that agree well with those observed in the solar neighbourhood. the most significant dynamical effect of magnetic fields on the global properties of the disc is a reduction of the star formation rate by a factor of 1.5-2 with respect to an unmagnetized control simulation. at a fixed star formation rate of approximately $2 \, {\rm m}_{\odot }$ yr-1, there is no significant difference in the mass outflow rates or profiles between the magnetized and non-magnetized simulations. our results for the global structure of the magnetic field have significant implications for models of cosmic ray-driven winds and cosmic ray propagation in the galaxy, and can be tested against observations with the forthcoming square kilometre array and other facilities. finally, we report the discovery of a physical error in the implementation of neutral gas heating and cooling in the popular gizmo code, which may lead to qualitatively incorrect phase structures if not corrected. | the global structure of magnetic fields and gas in simulated milky way-analogue galaxies |
with continuous measurements from space-borne cosmic-ray detectors such as ams-02 and pamela, precise spectra of galactic cosmic rays over the 11 yr solar cycle have become available. for this study, we utilize proton and helium spectra below 10 gv from these missions from 2006 to 2017 to construct a cosmic-ray transport model for a quantitative study of the processes of solar modulation. this numerical model is based on parker's transport equation, which includes four major transport processes. the markov chain monte carlo method is utilized to search the relevant parameter space related to the drift and the diffusion coefficients by reproducing and fitting the mentioned observed spectra. the resulting best-fit normalized χ 2 is mainly less than 1. it is found that (1) when reproducing these observations the parameters required for the drift and diffusion coefficients exhibit a clear time dependence, with the magnitude of the diffusion coefficients anticorrelated with solar activity; (2) the rigidity dependence of the resulting mean free paths varies with time, and their rigidity dependence at lower rigidity can even have a larger slope than at higher rigidity; (3) using a single set of modulation parameters for each pair of observed proton and helium spectra, most spectra are reproduced within observational uncertainty; and (4) the simulated proton-to-helium flux ratio agrees with the observed values in terms of its long-term time dependence, although some discrepancy exists, and the difference is mostly coming from the underestimation of proton flux. | a numerical study of the solar modulation of galactic protons and helium from 2006 to 2017 |
radiation transport codes have been an increasingly important tool for studying the space radiation environment, which includes high-energy and high-nuclear-charge particles. the unique advantage of transport models lies in covering a wider range of particles, energies, and angles than would be attainable in a laboratory or measurable by an instrument. however, since there are several transport codes developed by different teams that have contributed heavily to the literature, differences are expected between such codes. in this work, we use five such radiation transport codes (fluctuating kascade, geometry and tracking, high-energy transport code-human exploration and development in space, monte carlo n-particle, and particle and heavy ion transport code system) to study the radiation environment near the moon, specifically the lunar "albedo" radiation, which is the radiation emitted by the lunar surface through interactions with incident galactic cosmic rays and solar energetic particles. the primary goal of this paper is to provide a general characterization of the lunar albedo radiation and to find the areas where the modeled transport codes agree and disagree by using almost identical input parameters. the results of this work show overall good agreement between the codes. however, some areas of discrepancies exist that are reported herein. thus, this paper equips the space weather and radiation biology communities with a comparison between popular radiation transport models applied to lunar albedo radiation. the overall agreement and, in some cases, discrepancies between these transport codes provide fundamental insight necessary for assessing code reliability and identifying where further study and improvements are needed to advance our understanding of lunar albedo radiation. | modeling the lunar radiation environment: a comparison among fluka, geant4, hetc-heds, mcnp6, and phits |
context. cosmic rays (crs), which are energetic particles mainly composed of protons and electrons, play an important role in the chemistry and dynamics of the interstellar medium. in dense environments, they represent the main ionising agent, hence driving the rich chemistry of molecular ions. furthermore, they determine the ionisation fraction, which regulates the degree of coupling between the gas and the interstellar magnetic fields, and the heating of the gas. estimates of the cr ionisation rate of molecular hydrogen (ζ2) span several orders of magnitude, depending on the targeted sources and on the method used.aims: recent theoretical models have characterised the cr attenuation with increasing density. we aim to test these models for the attenuation of crs in the low-mass pre-stellar core l1544.methods: we used a state-of-the-art gas-grain chemical model, which accepts the cr ionisation rate profile as input, to predict the abundance profiles of four ions: n2h+, n2d+, hc18o+, and dco+. non-local thermodynamic equilibrium radiative transfer simulations were run to produce synthetic spectra based on the derived abundances. these were compared with observations obtained with the institut de radioastronomie millimétrique 30 m telescope.results: our results indicate that a model with high ζ2 (>10−16 s−1) is excluded by the observations. also the model with the standard ζ2 = 1.3 × 10−17 s−1 produces a worse agreement with respect to the attenuation model based on voyager observations, which is characterised by an average ⟨ ζ2 ⟩ = 3 × 10−17 s−1 at the column densities typical of l1544. the single-dish data, however, are not sensitive to the attenuation of the cr profile, which changes only by a factor of two in the range of column densities spanned by the core model (n = 2−50 × 1021 cm−2). interferometric observations at higher spatial resolution, combined with observations of transitions with lower critical density - hence tracing the low-density envelope - are needed to observe a decrease in the cr ionisation rate with density. this work is based on observations carried out with the iram 30 m telescope. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain). | the cosmic-ray ionisation rate in the pre-stellar core l1544 |
adequate characterization of catchment storage dynamics is crucial in hydrological models, yet scale-representative storage measurements are rare. recent developments in cosmic ray neutron sensor (crns) technology and monitoring networks provide a powerful source of more scale-appropriate soil moisture data for many modelling applications. however, the potential in rainfall-runoff modelling is undeveloped. here we present the first application of crns data in conceptual rainfall-runoff modelling and explore this potential in the context of a mixed-agricultural landscape in scotland. we deployed and calibrated a crns in a heterogeneous soil-land use footprint over a ∼3-year period. in this generally wet environment, the crns shallow sensing depth and relatively high neutron count uncertainty were identified as major challenges. however, given the better spatial coverage (up to 14 ha) and ease for maintenance, crns was thought to represent the simplest approach for long-term monitoring of managed mixed-agricultural sites. we used crns-derived, as well as single point-scale estimates, of near-surface soil storage (sns) to explore their characterisation of storage dynamics at the catchment-scale. inter-comparison using linear regression showed that sns related well to catchment-scale storage dynamics, however this relationship was stronger for crns (r2 = 0.91) compared to point-scale derived estimates (r2 = 0.76). based on this, we evaluated the effect of using the crns and point scale derived sns data to constrain storage estimates controlling runoff generation in a common rainfall-runoff model (hbv-light). including crns or point-scale field sns data alone in model calibration was especially useful for intermediate and wet periods. a combined model calibration using discharge and either sns storage estimates provided a better representation of catchment internal dynamics, additionally reducing uncertainty during low flows. in the context of mixed-agricultural landscapes in humid environments, this study showed the potential of using crns over point scale data (in terms of representativeness for single point data and practicality for point sensor networks) to characterise the catchment storage-discharge relationship and inform hydrological modelling. | opportunities and challenges in using catchment-scale storage estimates from cosmic ray neutron sensors for rainfall-runoff modelling |
with the measurement of positron flux published recently by ams-02 collaboration, we show how the leptophilic dark matter fits the observation. we obtain the percentages of different products of dark matter annihilation that can best describe the flux of high energy positrons observed by ams. we show that dark matter annihilates predominantly into $\tau\tau$ pair, while both $ee$ and $\mu\mu$ final states should be less than $20\%$. when gauge boson final states are included, the best branching ratio of needed $\tau\tau$ mode reduces. | leptophilic dark matter confronts ams-02 cosmic-ray positron flux |
cosmogenic isotopes are produced by cosmic rays mostly in the middle-low atmosphere and then take part in the complicated processes of atmospheric transport and deposition that are different for the stratosphere and troposphere. cosmogenic isotopes are continuously produced by galactic cosmic rays (gcrs) with a hard energy spectrum and sporadically by solar energetic particles (seps) with much softer energy spectra. the partition of the isotope production between the stratosphere and troposphere in different latitudinal zones depends on the spectrum of cosmic rays, geomagnetic shielding, and the tropopause shape. the exact zonal distribution of the isotope production is not accurately known and needs to be precisely modeled as well as the isotopes' transport and deposition in climatic reconstruction. here, we present the results of the computations of 14c, 36cl, 10be, and 7be cosmogenic isotope production in the earth's atmosphere using the crac model. we provide zonal mean production rates separately for the stratosphere and troposphere in three latitudinal zones: tropical (0°-30°), midlatitude (30°-60°), and polar (60°-90°). the computations were performed for four scenarios: (a) production by gcr during a solar-cycle minimum; (b) production by gcr during a solar-cycle maximum; (c) sep event with the hardest known spectrum (gle#5); and (d) the strongest known soft-spectrum sep event (gle#24). the results confirm that, while all the latitudinal zones are relatively important for the isotopes produced by gcr, isotope production by seps in the tropical zone is small and can be neglected. the results are coupled to the socol-aer2-be chemistry-climate model and can be used for a simplified parametric modeling of the isotopes' atmospheric transport, for the conditions typical for the holocene. | zonal mean distribution of cosmogenic isotope (7be, 10be, 14c, and 36cl) production in stratosphere and troposphere |
the solar modulation effect of cosmic rays in the heliosphere is an energy-, time-, and particle-dependent phenomenon that arises from a combination of basic particle transport processes such as diffusion, convection, adiabatic cooling, and drift motion. making use of a large collection of time-resolved cosmic-ray data from recent space missions, we construct a simple predictive model of solar modulation that depends on direct solar-physics inputs: the number of solar sunspots and the tilt angle of the heliospheric current sheet. under this framework, we present calculations of cosmic-ray proton spectra, positron/electron and antiproton/proton ratios, and their time dependence in connection with the evolving solar activity. we report evidence for a time lag {{δ }}t=8.1+/- 1.2 months, between solar-activity data and cosmic-ray flux measurements in space, which reflects the dynamics of the formation of the modulation region. this result enables us to forecast the cosmic-ray flux near earth well in advance by monitoring solar activity. | evidence for a time lag in solar modulation of galactic cosmic rays |
we use a multimessenger approach to constrain realistic mixed composition models of ultrahigh energy cosmic ray sources using the latest cosmic ray, neutrino, and gamma-ray data. we build on the successful unger-farrar-anchordoqui 2015 (ufa15) model which explains the shape of the spectrum and its complex composition evolution via photodisintegration of accelerated nuclei in the photon field surrounding the source. we explore the constraints which can currently be placed on the redshift evolution of sources and the temperature of the photon field surrounding the sources. we show that a good fit is obtained to all data either with a source which accelerates a narrow range of nuclear masses or a milky way-like mix of nuclear compositions, but in the latter case the nearest source should be 30-50 mpc away from the milky way in order to fit observations from the pierre auger observatory. we also ask whether the data allow for a subdominant purely protonic component at uhe in addition to the primary ufa15 mixed composition component. we find that such a two-component model can significantly improve the fit to cosmic ray data while being compatible with current multimessenger data. | progress towards characterizing ultrahigh energy cosmic ray sources |
it is shown that high-energy astrophysical neutrinos observed in the icecube experiment can be produced by protons accelerated in extragalactic type iin supernova remnants by shocks propagating in the dense circumstellar medium. the nonlinear diffusive shock acceleration model is used for description of particle acceleration. we calculate the neutrino spectrum produced by an individual type iin supernova and the spectrum of neutrino background produced by iin supernovae in the expanding universe. we also found that the arrival direction of one icecube neutrino candidate (track event 47) is at 1.35° from type iin supernova 2005bx. | type iin supernovae as sources of high energy astrophysical neutrinos |
the local interstellar spectrum (lis) of cosmic-ray (cr) electrons for the energy range 1 mev to 1 tev is derived using the most recent experimental results combined with the state-of-the-art models for cr propagation in the galaxy and in the heliosphere. two propagation packages, galprop and helmod, are combined to provide a single framework that is run to reproduce direct measurements of cr species at different modulation levels, and at both polarities of the solar magnetic field. an iterative maximum-likelihood method is developed that uses galprop-predicted lis as input to helmod, which provides the modulated spectra for specific time periods of the selected experiments for model-data comparison. the optimized helmod parameters are then used to adjust galprop parameters to predict a refined lis with the procedure repeated subject to a convergence criterion. the parameter optimization uses an extensive data set of proton spectra from 1997 to 2015. the proposed cr electron lis accommodates both the low-energy interstellar spectra measured by voyager 1 as well as the high-energy observations by pamela and ams-02 that are made deep in the heliosphere; it also accounts for ulysses counting rate features measured out of the ecliptic plane. the interstellar and heliospheric propagation parameters derived in this study agree well with our earlier results for cr protons, helium nuclei, and anti-protons propagation and lis obtained in the same framework. | helmod in the works: from direct observations to the local interstellar spectrum of cosmic-ray electrons |
recently the ams-02 collaboration published detections of light cosmic-ray nuclei, including lithium, beryllium, boron, carbon, and oxygen. combined with the released energy spectra of proton and helium, both primary and secondary spectra have a prominent hardening above ∼200 gv. in particular, the spectral variation of secondary cosmic rays is greater than the primary ones. one of the plausible interpretations for the above anomalies is the spatial-dependent diffusion model. it has successfully described various observational phenomena, e.g., hardening of primary nuclei, diffuse gamma-ray distribution and cosmic-ray anisotropy, etc. in this work, we apply the spatial-dependent propagation model to the latest observations, including both primary and secondary nuclei. apart from the primary components, the spectra of secondary nuclei can be properly reproduced as well, especially the upturn above 200 gv. we also calculate the ratios of both secondary-to-primary and secondary-to-secondary. we find that except for the be/b ratio, the computations of the spatial-dependent propagation model are in good agreement with the current data. | revisiting the spatially dependent propagation model with the latest observations of cosmic-ray nuclei |
long-lived particles are predicted in extensions of the standard model that involve relatively light but very weakly interacting sectors. in this paper we consider the possibility that some of these particles are produced in atmospheric cosmic ray showers, and their decay intercepted by neutrino detectors such as icecube or super-kamiokande. we present the methodology and evaluate the sensitivity of these searches in various scenarios, including extensions with heavy neutral leptons in models of massive neutrinos, models with an extra u(1) gauge symmetry, and a combination of both in a u(1)b-l model. our results are shown as a function of the production rate and the lifetime of the corresponding long-lived particles. | searches for atmospheric long-lived particles |
much focus was on the possible slowing down of cosmic acceleration under the dark energy parametrization. in the present paper, we investigate this subject using the gaussian processes (gp), without resorting to a particular template of dark energy. the reconstruction is carried out by abundant data including luminosity distance from union2, union2.1 compilation and gamma-ray burst, and dynamical hubble parameter. it suggests that slowing down of cosmic acceleration cannot be presented within 95% c.l., in considering the influence of spatial curvature and hubble constant. in order to reveal the reason of tension between our reconstruction and previous parametrization constraint for union2 data, we compare them and find that slowing down of acceleration in some parametrization is only a ``mirage". although these parameterizations fits well with the observational data, their tension can be revealed by high order derivative of distance d. instead, gp method is able to faithfully model the cosmic expansion history. | test of the cosmic evolution using gaussian processes |
we extend a two-component model for the evolution of fluctuations in the solar wind plasma so that it is fully three-dimensional (3d) and also coupled self-consistently to the large-scale magnetohydrodynamic equations describing the background solar wind. the two classes of fluctuations considered are a high-frequency parallel-propagating wave-like piece and a low-frequency quasi-two-dimensional component. for both components, the nonlinear dynamics is dominanted by quasi-perpendicular spectral cascades of energy. driving of the fluctuations by, for example, velocity shear and pickup ions is included. numerical solutions to the new model are obtained using the cronos framework, and validated against previous simpler models. comparing results from the new model with spacecraft measurements, we find improved agreement relative to earlier models that employ prescribed background solar wind fields. finally, the new results for the wave-like and quasi-two-dimensional fluctuations are used to calculate ab initio diffusion mean-free paths and drift lengthscales for the transport of cosmic rays in the turbulent solar wind. | a generalized two-component model of solar wind turbulence and ab initio diffusion mean-free paths and drift lengthscales of cosmic rays |
the recent spatial and temporal coincidence of the blazar txs 0506+056 with the icecube-detected neutrino event ic-170922a has opened up a realm of multimessenger astronomy with blazar jets as a plausible site of cosmic-ray acceleration. after txs 0506+056, a second blazar, bzb j0955+3551, was recently found to be spatially coincident with the icecube-detected neutrino event ic-200107a and undergoing its brightest x-ray flare measured so far. here we present the results of our multifrequency campaign to study this peculiar event that includes observations with the nustar, swift, neutron star interior composition explorer (nicer), and 10.4 m gran telescopio canarias (gtc). the optical spectroscopic observation from gtc secured its redshift as $z={0.55703}_{-0.00021}^{+0.00033}$ and the central black hole mass as ${10}^{8.90\pm 0.16}$ ${m}_{\odot }$ . both nustar and nicer data reveal a rapid flux variability, albeit at low significance ( $\lesssim 3.5\sigma $ ). we explore the origin of the target photon field needed for the photopion production using analytical calculations and considering the observed optical-to-x-ray flux level. we conclude that seed photons may originate from outside the jet, similar to that reported for txs 0506+056, although a scenario invoking a comoving target photon field (e.g., electron synchrotron) cannot be ruled out. the electromagnetic output from the neutrino-producing photohadronic processes are likely to make only a subdominant contribution to the observed spectral energy distribution, suggesting that the x-ray flaring event may not be directly connected with ic-200107a. | multifrequency observations of the candidate neutrino-emitting blazar bzb j0955+3551 |
cosmic-ray neutron sensing (crns) is a novel technique for determining environmental water content by measuring albedo neutrons in the epithermal to fast energy range with moderated neutron detectors. we have investigated the response function of stationary and mobile neutron detectors typically used for environmental research in order to improve the model accuracy for neutron transport studies. monte carlo simulations have been performed in order to analyze the detection probability in terms of energy-dependent response and angular sensitivity for different variants of crns detectors and converter gases. our results reveal the sensor's response to neutron energies from 0.1 ev to 106 ev and highest sensitivity to vertical fluxes. the detector efficiency shows good agreement with reference data from the structurally similar bonner spheres. the relative probability of neutrons contributing to the overall integrated signal is especially important in regions with non-uniform albedo fluxes, such as complex terrain or heterogeneous distribution of hydrogen pools. | response functions for detectors in cosmic ray neutron sensing |
radio continuum observations of external galaxies provide us with an excellent outside view on the distribution of cosmic-ray electrons in the disc and halo. in this review, we summarise the current state of what we have learned from modelling such observations with cosmic-ray transport, paying particular attention to the question to what extent we can exploit radio haloes when studying galactic winds. we have developed the user-friendly framework spinnaker to model radio haloes with either pure advection or diffusion, allowing us to study both diffusion coefficients and advection speeds in nearby galaxies. using these models, we show that we can identify galaxies with winds using both morphology and radio spectral indices of radio haloes. advective radio haloes are ubiquitous, indicating that already fairly low values of the star formation rate (sfr) surface density (σsfr) can trigger galactic winds. the advection speeds scale with sfr, σsfr, and rotation speed as expected for stellar feedback-driven winds. accelerating winds are in agreement with our radio spectral index data, but this is sensitive to the magnetic field parametrisation, so that constant wind speeds cannot be ruled out either. the question to what extent cosmic rays can be a driving force behind winds is still an open issue and we discuss only in passing how a simple iso-thermal wind model could fit our data. nevertheless, the comparison with inferences from observations and theory looks promising with radio continuum offering a complementary view on galactic winds. we finish with a perspective on future observations and challenges lying ahead. | the radio continuum perspective on cosmic-ray transport in external galaxies |
aims: we present observations of the first coronal mass ejection (cme) observed by the solar orbiter spacecraft on april 19, 2020 and the associated forbush decrease (fd) measured by the high energy telescope (het). this cme is a multi-spacecraft event that was also seen near earth the following day.methods: we highlight the capabilities of the het for observing small short-term variations of the galactic cosmic ray count rate using its single detector counters. we applied the analytical forbmod model to the fd measurements to reproduce the forbush decrease at both locations. input parameters for the model were derived from both in situ and remote-sensing observations of the cme.results: the very slow (∼350 km s−1) stealth cme caused an fd with an amplitude of 3% in the low-energy cosmic ray measurements at het and 2% in a comparable channel of the cosmic ray telescope for the effects of radiation (crater) on board the lunar reconnaissance orbiter, as well as a 1% decrease in neutron monitor measurements. significant differences are observed in the expansion behavior of the cme at different locations, which may be related to influence of the following high speed solar wind stream. under certain assumptions, forbmod is able to reproduce the observed fds in low-energy cosmic ray measurements from het as well as crater, however, with the same input parameters, the results do not agree with the fd amplitudes at higher energies measured by neutron monitors on earth. we study these discrepancies and provide possible explanations.conclusions: this study highlights the notion that the novel measurements of solar orbiter can be coordinated with observations from other spacecraft to improve our understanding of space weather in the inner heliosphere. multi-spacecraft observations combined with data-based modeling are also essential for understanding the propagation and evolution of cmes, in addition to their space weather impacts. movies are available at https://www.aanda.org | radial evolution of the april 2020 stealth coronal mass ejection between 0.8 and 1 au. comparison of forbush decreases at solar orbiter and near the earth |
in this paper, we study the galactic cosmic-ray (gcr) variations over the solar cycles 23 and 24, with measurements from nasa's advanced composition explorer/cosmic ray isotope spectrometer instrument and the ground-based neutron monitors (nms). the results show that the maximum gcr intensities of heavy nuclei (5 ≤ z ≤ 28, 50∼500 mev nuc-1) at 1 au during the solar minimum in 2019-2020 break their previous records, exceeding those recorded in 1997 and 2009 by ∼25% and ∼6%, respectively, and are at the highest levels since the space age. however, the peak nm count rates are lower than those in late 2009. the difference between gcr intensities and nm count rates still remains to be explained. furthermore, we find that the gcr modulation environment during the solar minimum p24/25 are significantly different from previous solar minima in several aspects, including remarkably low sunspot numbers, extremely low inclination of the heliospheric current sheet, rare coronal mass ejections, weak interplanetary magnetic field and turbulence. these changes are conducive to reduce the level of solar modulation, providing a plausible explanation for the record-breaking gcr intensities in interplanetary space. | variations of the galactic cosmic rays in the recent solar cycles |
we give an overview and describe the rationale, methods, and testing of the hubble space telescope (hst) archival legacy project "skysurf." skysurf uses hst's unique capability as an absolute photometer to measure the ~0.2-1.7 μm sky-surface brightness (sky-sb) from 249,861 wfpc2, acs, and wfc3 exposures in ~1400 independent hst fields. skysurf's panchromatic data set is designed to constrain the discrete and diffuse uv to near-ir sky components: zodiacal light (zl), kuiper belt objects (kbos), diffuse galactic light (dgl), and the discrete plus diffuse extragalactic background light (ebl). we outline skysurf's methods to: (1) measure sky-sb levels between detected objects; (2) measure the discrete ebl, most of which comes from ab≃17-22 mag galaxies; and (3) estimate how much truly diffuse light may exist. simulations of hst wfc3/ir images with known sky values and gradients, realistic cosmic ray (cr) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the "lowest estimated sky-sb" (les) in each image between the discrete objects. the best algorithms recover the les values within 0.2% when there are no image gradients, and within 0.2%-0.4% when there are 5%-10% gradients. we provide a proof of concept of our methods from the wfc3/ir f125w images, where any residual diffuse light that hst sees in excess of zodiacal model predictions does not depend on the total object flux that each image contains. this enables us to present our first skysurf results on diffuse light in carleton et al. | skysurf: constraints on zodiacal light and extragalactic background light through panchromatic hst all-sky surface-brightness measurements. i. survey overview and methods |
propagation of cosmic rays (crs) in turbulent and magnetized astrophysical media is a long-standing problem that requires both understanding of the properties of turbulent magnetic fields and their interaction with energetic particles. this review focuses on selected recent theoretical findings made based on the progress in understanding and simulating magnetohydrodynamic (mhd) turbulence. in particular, we address the problem of perpendicular and parallel propagation of crs and identify the conditions when the perpendicular propagation is superdiffusive and diffusive. for the parallel diffusion, we discuss the problems of the traditionally used diffusion mechanism arising from pitch angle scattering and the possible solutions provided by the recently identified "mirror diffusion" in the presence of turbulent magnetic mirrors. | cosmic ray propagation in turbulent magnetic fields |
the self-regulation of cosmic-ray (cr) transport in the interstellar and intracluster media has long been viewed through the lenses of linear and quasi-linear kinetic plasma physics. such theories are believed to capture the essence of cr behavior in the presence of self-generated turbulence but cannot describe potentially critical details arising from the nonlinearities of the problem. we utilize the particle-in-cell numerical method to study the time-dependent nonlinear behavior of the gyroresonant streaming instabilities, self-consistently following the combined evolution of particle distributions and self-generated wave spectra in one-dimensional periodic simulations. we demonstrate that the early growth of instability conforms to the predictions from linear physics, but that the late-time behavior can vary depending on the properties of the initial cr distribution. we emphasize that the nonlinear stages of instability depend strongly on the initial anisotropy of crs—highly anisotropic cr distributions do not efficiently reduce to alfvénic drift velocities, owing to reduced production of left-handed resonant modes. we derive estimates for the wave amplitudes at saturation and the timescales for nonlinear relaxation of the cr distribution and then demonstrate the applicability of these estimates to our simulations. bulk flows of the background plasma due to the presence of resonant waves are observed in our simulations, confirming the microphysical basis of cr-driven winds. | on the growth and saturation of the gyroresonant streaming instabilities |
in the interstellar medium of galaxies and the intracluster gas of galaxy clusters, the charged particles making up cosmic rays are moving almost exclusively along (but not across) magnetic field lines. the resulting anisotropic transport of cosmic rays in the form of diffusion or streaming not only affects the gas dynamics but also rearranges the magnetic fields themselves. the coupled dynamics of magnetic fields and cosmic rays can thus impact the formation and evolution of galaxies and the thermal evolution of galaxy clusters in critical ways. numerically studying these effects requires solvers for anisotropic diffusion that are accurate, efficient, and robust, requirements that have proved difficult to be satisfied in practice. here, we present an anisotropic diffusion solver on an unstructured moving mesh that is conservative, does not violate the entropy condition, allows for semi-implicit time integration with individual timesteps, and only requires solving a single linear system of equations per timestep. we apply our new scheme to a large number of test problems and show that it works as well or better than previous implementations. finally, we demonstrate for a numerically demanding simulation of the formation of an isolated disc galaxy that our local time-stepping scheme reproduces the results obtained with global time-stepping at a fraction of the computational cost. | semi-implicit anisotropic cosmic ray transport on an unstructured moving mesh |
morphological and geological observations reveal that most apenninic faults are highly segmented and that the majority of the fault segments are less than 10 km long. although these faults have undergone numerous paleoseismological investigations, quantitative data remain crucially lacking for a large number of fault segments. because such data are essential to understanding how these faults have ruptured and interacted in the past and how they might behave in the future, we investigated the holocene seismic history of the pizzalto normal fault, a 13 km long fault segment belonging to the pizzalto-rotella-aremogna fault system in the apennines. we collected 44 samples from the pizzalto fault plane exhumed during the holocene and analyzed the 36cl and rare earth element (ree) contents. together, the 36cl and ree concentrations show that at least six events have exhumed 4.4 m of the fault scarp between 3 and 1 ka, with slip per event values ranging from 0.3 to 1.2 m. no major events have been detected over the last 1 kyr. the rotella-aremogna-pizzalto fault system has a clustered earthquake behavior with a mean recurrence time of 1.2 kyr and a low to moderate probability (ranging from 4% to 26%) of earthquake occurrence over the next 50 years. | seismic slip history of the pizzalto fault (central apennines, italy) using in situ-produced 36cl cosmic ray exposure dating and rare earth element concentrations |
in the weak-field limit of general relativity, gravitational waves obey linear equations and propagate at the speed of light. these properties of general relativity are supported by the observation of ultrahigh-energy cosmic rays as well as by ligo's recent detection of gravitation waves. we argue that two existing relativistic generalizations of modified newtonian dynamics, namely, the generalized einstein-aether theory and bimetric modified newtonian dynamics, display fatal inconsistencies with these observations. | constraining relativistic generalizations of modified newtonian dynamics with gravitational waves |
the fundamental idea of laser wakefield acceleration (lwfa) is reviewed. an ultrafast intense laser pulse drives coherent wakefield with a relativistic amplitude robustly supported by the plasma. while the large amplitude of wake-fields involves collective resonant oscillations of the eigenmode of the entire plasma electrons, the wake phase velocity ∼ c and ultrafastness of the laser pulse introduce the wake stability and rigidity. a large number of worldwide experiments show a rapid progress of this concept realization toward both the high-energy accelerator prospect and broad applications. the strong interest in this has been spurring and stimulating novel laser technologies, including the chirped pulse amplification, the thin film compression, the coherent amplification network, and the relativistic mirror compression. these in turn have created a conglomerate of novel science and technology with lwfa to form a new genre of high field science with many parameters of merit in this field increasing exponentially lately. this science has triggered a number of worldwide research centers and initiatives. associated physics of ion acceleration, x-ray generation, and astrophysical processes of ultrahigh energy cosmic rays are reviewed. applications such as x-ray free electron laser, cancer therapy, and radioisotope production etc. are considered. a new avenue of lwfa using nanomaterials is also emerging. | laser acceleration |
an accurate review of the literature on surface exposure dating methods shows evidence of the difficulty in applying cosmogenic dating methods to old moraines because of the intensity of late quaternary erosion processes. moreover, as in some previous cases, we also found special difficulties in applying these methods to <!-[?thyc=10?]->lia<!-[?thyc=5?]-> moraines, caused by the intensity of current paraglacial processes. the objective of this study is to apply cosmogenic dating methods to very old and very young moraines, which in both cases have been or are being affected intensively by erosion. with this purpose, we collected samples of boulders from moraines corresponding to (i)<!-[?a3b2 show 146#?]-><!-[?}skip?]-><!-[?:skip?]->the penultimate glaciation and (ii) the little ice age (lia), both from sierra nevada in the south of the iberian peninsula. the sampling strategy was based on a preliminary accurate analysis of the geomorphological settings of two valley sites that resulted in the collection of only four boulder samples from an old moraine and three more from a very recent moraine. using in <!-[?thyc=10?]->situ-produced<!-[?thyc=5?]-> cosmogenic 10be to date these boulders, the old samples yielded an age of ca. 130-135 ka for moraine stabilization. the younger samples indicate that the <!-[?thyc=10?]->lia<!-[?thyc=5?]-> moraine accretion probably occurred between the fourteenth and seventeenth centuries, with a subsequent stage of accumulation during the nineteenth century as suggested by historical documents. dating a glaciation that occurred prior to the last pleistocene glacial cycle and dating <!-[?thyc=10?]->lia<!-[?thyc=5?]-> glacial stages are novel in the context of iberian glaciations and agree with other palaeoenvironmental studies in iberian and in other <!-[?thyc=10?]->europe<!-[?thyc=5?]->an mountains. the limited number of boulders adequate for <!-[?thyc=10?]->cosmic-ray<!-[?thyc=5?]-> exposure dating prevents statistical methods to be applied, and therefore highlights the need to improve geomorphological criteria in sample selection. | the challenging application of cosmogenic dating methods in residual glacial landforms: the case of sierra nevada (spain) |
the interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. cyanopolyynes are carbon chains delimited at their two extremities by an atom ofhydrogen and a cyano group, meaning that they could be excellent reservoirs of carbon. the simplest member, hc3n, is ubiquitous in the galactic interstellar medium and found also in external galaxies. thus, understanding the growth of cyanopolyynes in regions forming stars similar to our sun, and what affects them, is particularly relevant. in the framework of the iram/noema large program solis (seeds of life in space), we have obtained a map of two cyanopolyynes, hc3n and hc5n, in the protocluster omc-2 fir4. because our sun is thought to be born in a rich cluster, omc-2 fir4 is one of the closest and best known representatives of the environment in which the sun may have been born. we find a hc3n/hc5n abundance ratio across the source in the range 1-30, with the smallest values (≤10) in fir5 and in the eastern region of fir4. the ratios ≤10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate ζ is 4 × 10-14 s-1; (2) the gaseous elemental ratio c/o is close to unity; and (3) oxygen and carbon are largely depleted. the large ζ is comparable to that measured in fir4 by previous works and was interpreted as due to a flux of energetic (≥10 mev) particles from embedded sources. we suggest that these sources could lie east of fir4 and fir5. a temperature gradient across fir4, with t decreasing from east to west by about 10 k, could also explain the observed change in the hc3n/hc5n line ratio, without the need of a cosmic ray ionisation rate gradient. however, even in this case, a high constant cosmic-ray ionisation rate (of the order of 10-14 s-1) is necessary to reproduce the observations. based on observations carried out under project number l15aa with the iram noema interferometer. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain).the final iram data used in the paper (fits format) are available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/605/a57 | seeds of life in space (solis). i. carbon-chain growth in the solar-type protocluster omc2-fir4 |
multiple partonic interactions are often crucial for interpreting results obtained at the large hadron collider (lhc). the quest for a sound understanding of the dynamics behind mpi - particularly at this time when the lhc is due to start its "run ii" operations - has focused the aim of this workshop. mpi@lhc2014 concentrated mainly on the phenomenology of lhc measurements whilst keeping in perspective those results obtained at previous hadron colliders. the workshop has also debated some of the state-of-the-art theoretical considerations and the modeling of mpi in monte carlo event generators. the topics debated in the workshop included: phenomenology of mpi processes and multiparton distributions; considerations for the description of mpi in quantum chromodynamics (qcd); measuring multiple partonic interactions; experimental results on inelastic hadronic collisions: underlying event, minimum bias, forward energy flow; monte carlo generator development and tuning; connections with low-x phenomena, diffraction, heavy-ion physics and cosmic rays. in a total of 57 plenary talks the workshop covered a wide range of experimental results, monte carlo development and tuning, phenomenology and dedicated measurements of mpi which were produced with data from the lhc's run i. recent progress of theoretical understanding of mpi in pp, pa and aa collisions as well as the role of mpi in diffraction and small-x physics were also covered. the workshop forstered close contact between the experimental and theoretical communities. it provided a setting to discuss many of the different aspects of mpi, eventually identifying them as a unifying concept between apparently different lines of research and evaluating their impact on the lhc physics programme. | proceedings of the sixth international workshop on multiple partonic interactions at the large hadron collider |
the consistent determination of soil moisture across scales is a persistent challenge in hydrology. several measurement methods exist at distinct scales, each of which is challenging in terms of data processing, removal of vegetation and surface effects, and calibration. while in situ measurements are trusted at the point scale, distributed sensor networks extend the areal representation to the field scale. at this scale, also cosmic ray neutron sensing (crns) has become an established method to derive volume-averaged, root zone soil moisture over several tens of hectometers, but the signal is often biased due to biomass water. with airborne synthetic aperture radar (sar)remote sensing, it is possible to cover regional scales, but the method is limited to the topmost soil layer and sensitive to vegetation parameters. in this study, the performance and synergistic potential of these complementary methods is investigated for the determination of soil moisture within a 55-km2 alpine foothill river catchment in southern germany. the individual approaches are evaluated and brought into synergy for a 9-ha grassland and several other locations within the catchment. the results indicate that the sensor network data provide valuable information to calibrate the mobile crns rover, and to optimize the vegetation removal within the polarimetric sar retrieval algorithm. the root-mean-square errors for polarimetric synthetic aperture radar soil permittivity are 9.32 with the standard agriculture approach, 4.29 with the semi-stand-alone approach, and 0.31 with the sensor network optimized approach. furthermore, the crns soil moisture product was improved by considering the remotely sensed cross-polarized backscatter product as a biomass water proxy. | synergies for soil moisture retrieval across scales from airborne polarimetric sar, cosmic ray neutron roving, and an in situ sensor network |
since the century discovery of cosmic ray, the origin of cosmic ray is always a mystery. the study on the origin of high-energy cosmic ray is in an interdiscipline between the very high-energy (vhe) gamma-ray astronomy and the cosmic ray physics. the large high altitude air shower observatory (lhaaso) is a unique and new generation cosmic-ray station with the advantages of high altitude, all-weather, and large-scale. it takes the function of hybrid technology to detect cosmic rays and to upgrade greatly the resolving power between gamma rays and cosmic rays. the lhaaso is expected to make the full-sky survey to find new gamma-ray sources, to obtain the highest sensitivity of gamma-ray detection at the high energy band of > 30 tev, and to make the very high precision measurement on the component energy spectra of cosmic rays in a broad energy range of 5 orders of magnitude, in order to provide the evidence for revealing the mystery of the origin of cosmic ray. this paper describes the detector structure, performance superiority and scientific motivation of the lhaaso. | introduction to large high altitude air shower observatory (lhaaso) |
a 10 kilo-tonne dual-phase liquid argon tpc is one of the detector options considered for the deep underground neutrino experiment (dune). the detector technology relies on amplification of the ionisation charge in ultra-pure argon vapour and offers several advantages compared to the traditional single-phase liquid argon tpcs. a 4.2 tonne dual-phase liquid argon tpc prototype, the largest of its kind, with an active volume of \three has been constructed and operated at cern. in this paper we describe in detail the experimental setup and detector components as well as report on the operation experience. we also present the first results on the achieved charge amplification, prompt scintillation and electroluminescence detection, and purity of the liquid argon from analyses of a collected sample of cosmic ray muons. | a 4 tonne demonstrator for large-scale dual-phase liquid argon time projection chambers |
we describe an implementation of a particle physics module available for the pluto code appropriate for the dynamical evolution of a plasma consisting of a thermal fluid and a nonthermal component represented by relativistic charged particles or cosmic rays (crs). while the fluid is approached using standard numerical schemes for magnetohydrodynamics, cr particles are treated kinetically using conventional particle-in-cell (pic) techniques. the module can be used either to describe test-particle motion in the fluid electromagnetic field or to solve the fully coupled magnetohydrodynamics (mhd)-pic system of equations with particle backreaction on the fluid as originally introduced by bai et al. particle backreaction on the fluid is included in the form of momentum-energy feedback and by introducing the cr-induced hall term in ohm’s law. the hybrid mhd-pic module can be employed to study cr kinetic effects on scales larger than the (ion) skin depth provided that the larmor gyration scale is properly resolved. when applicable, this formulation avoids resolving microscopic scales, offering substantial computational savings with respect to pic simulations. we present a fully conservative formulation that is second-order accurate in time and space, and extends to either the runge-kutta (rk) or the corner transport upwind time-stepping schemes (for the fluid), while a standard boris integrator is employed for the particles. for highly energetic relativistic crs and in order to overcome the time-step restriction, a novel subcycling strategy that retains second-order accuracy in time is presented. numerical benchmarks and applications including bell instability, diffusive shock acceleration, and test-particle acceleration in reconnecting layers are discussed. | a particle module for the pluto code. i. an implementation of the mhd-pic equations |
recent gamma-ray and cosmic-ray observations have put strong constraints on the amount of primordial black holes (pbhs) in our universe. in this paper, we use the archival radio data of the inner galactic centre to constrain the pbh to dark matter ratio for three different pbh mass distributions including monochromatic, lognormal, and power law. we show that the amount of pbhs only constitutes a very minor component of dark matter at the galactic centre for a large parameter space. | constraining primordial black hole fraction at the galactic centre using radio observational data |
the anita experiment has observed two unusual upgoing air shower events, which are consistent with the τ -lepton decay origin. however, these events are in contradiction with the standard neutrino-matter interaction models as well as the eev diffuse neutrino flux limits set by icecube and the cosmic ray facilities like auger. in this paper, we have reinvestigated the possibility of using the sterile neutrino hypothesis to explain the anita anomalous events. the diffuse flux of the sterile neutrinos is less constrained by the icecube and auger experiments due to the small active-sterile mixing angle suppression. the quantum decoherence effect should be included for describing the neutrino flux propagating in the earth matter, because the interactions between neutrinos and the earth matter are very strong at the eev energy scale. after several experimental approximations, we show that the anita anomaly itself is able to be explained by the sterile neutrino origin, but we also predict that the icecube observatory should have more events than anita. it makes the sterile neutrino origin very unlikely to account for both of them simultaneously. a more solid conclusion can be drawn by the dedicated anita signal simulation. | sterile neutrinos as a possible explanation for the upward air shower events at anita |
cosmological shock waves play an important role in hierarchical structure formation by dissipating and thermalizing kinetic energy of gas flows, thereby heating the universe. furthermore, identifying shocks in hydrodynamical simulations and measuring their mach number accurately are critical for calculating the production of non-thermal particle components through diffusive shock acceleration. however, shocks are often significantly broadened in numerical simulations, making it challenging to implement an accurate shock finder. we here introduce a refined methodology for detecting shocks in the moving-mesh code arepo, and show that results for shock statistics can be sensitive to implementation details. we put special emphasis on filtering against spurious shock detections due to tangential discontinuities and contacts. both of them are omnipresent in cosmological simulations, for example in the form of shear-induced kelvin-helmholtz instabilities and cold fronts. as an initial application of our new implementation, we analyse shock statistics in non-radiative cosmological simulations of dark matter and baryons. we find that the bulk of energy dissipation at redshift zero occurs in shocks with mach numbers around m≈ 2.7. furthermore, almost 40 per cent of the thermalization is contributed by shocks in the warm hot intergalactic medium, whereas ≈60 per cent occurs in clusters, groups, and smaller haloes. compared to previous studies, these findings revise the characterization of the most important shocks towards higher mach numbers and lower density structures. our results also suggest that regions with densities above and below δb = 100 should be roughly equally important for the energetics of cosmic ray acceleration through large-scale structure shocks. | shock finding on a moving mesh - i. shock statistics in non-radiative cosmological simulations |
unified theories of strong, weak and electromagnetic interactions which have electric charge quantization predict the existence of topologically stable magnetic monopoles. intermediate scale monopoles are comparable with detection energies of cosmic ray monopoles at icecube and other cosmic ray experiments. magnetic monopoles in some models can be significantly lighter and carry two, three or possibly even higher quanta of the dirac magnetic charge. they could be light enough for their effects to be detected at the lhc either directly or indirectly. an example based on a d-brane inspired su(3) c× su(3) l× su(3) r(trinification) model with the monopole carrying three quanta of dirac magnetic charge is presented. these theories also predict the existence of color singlet states with fractional electric charge which may be accessible at the lhc. | magnetic monopoles and free fractionally charged states at accelerators and in cosmic rays |
cosmic rays are usually assumed to be the main ionization agent for the interior of molecular clouds, where uv and x-ray photons cannot penetrate. here, we test this hypothesis by limiting ourselves to the case of diffuse clouds and assuming that the average cosmic ray spectrum inside the galaxy is equal to the one at the position of the sun as measured by voyager 1 and ams-02. to calculate the cosmic ray spectrum inside the clouds, we solve the 1d transport equation taking into account advection, diffusion, and energy losses. while outside the cloud particles diffuse, in its interior they are assumed to gyrate along magnetic field lines because ion-neutral friction is effective in damping all the magnetic turbulence. we show that ionization losses effectively reduce the cr flux in the cloud interior for energies below ≈100 mev, especially for electrons, in such a way that the ionization rate decreases by roughly two order of magnitude with respect to the case where losses are neglected. as a consequence, the predicted ionization rate is more than 10 times smaller than the one inferred from the detection of molecular lines. we discuss the implication of our finding in terms of spatial fluctuation of the galactic cosmic ray spectra and possible additional sources of low-energy cosmic rays. | what causes the ionization rates observed in diffuse molecular clouds? the role of cosmic ray protons and electrons |
we present a study of the 21-cm signal bispectrum (which quantifies the non-gaussianity in the signal) from the cosmic dawn (cd). for our analysis, we have simulated the 21-cm signal using radiative transfer code grizzly, while considering two types of sources (mini-qsos and hmxbs) for ly α coupling and the x-ray heating of the igm. using this simulated signal, we have, for the first time, estimated the cd 21-cm bispectra for all unique k-triangles and for a range of k modes. we observe that the redshift evolution of the bispectrum magnitude and sign follow a generic trend for both source models. however, the redshifts at which the bispectrum magnitude reaches their maximum and minimum values and show their sign reversal depends on the source model. when the ly α coupling and the x-ray heating of the igm occur simultaneously, we observe two consecutive sign reversals in the bispectra for small k-triangles (irrespective of the source models). one arising at the beginning of the igm heating and the other at the end of ly α-coupling saturation. this feature can be used in principle to constrain the cd history and/or to identify the specific cd scenarios. we also quantify the impact of the spin temperature (ts) fluctuations on the bispectra. we find that ts fluctuations have maximum impact on the bispectrum magnitude for small k-triangles and at the stage when ly α coupling reaches saturation. furthermore, we are also the first to quantify the impact of redshift space distortions (rsd), on the cd bispectra. we find that the impact of rsd on the cd 21-cm bispectra is significant ($\gt 20{{\ \rm per\ cent}}$) and the level depends on the stages of the cd and the k-triangles for which the bispectra are being estimated. | redshifted 21-cm bispectrum - ii. impact of the spin temperature fluctuations and redshift space distortions on the signal from the cosmic dawn |
photo-nuclear reactions of light nuclei below a mass of $a=60$ are studied experimentally and theoretically by the pandora (photo-absorption of nuclei and decay observation for reactions in astrophysics) project. two experimental methods, virtual-photon excitation by proton scattering and real-photo absorption by a high-brilliance gamma-ray beam produced by laser compton scattering, will be applied to measure the photo-absorption cross sections and the decay branching ratio of each decay channel as a function of the photon energy. several nuclear models, e.g. anti-symmetrized molecular dynamics, mean-field type models, a large-scale shell model, and ab initio models, will be employed to predict the photo-nuclear reactions. the uncertainty in the model predictions will be evaluated from the discrepancies between the model predictions and the experimental data. the data and the predictions will be implemented in a general reaction calculation code talys . the results will be applied to the simulation of the photo-disintegration process of ultra-high-energy cosmic rays in inter-galactic propagation. | pandora project: photo-nuclear reactions below $a=60$ |
this is a review of the status of efforts to model the large-scale galactic magnetic field (gmf). though important for a variety of astrophysical processes, the gmf remains poorly understood despite some interesting new tracers being used in the field. though we still have too many models that might fit the data, this is not to say that the field has not developed in the last few years. in particular, surveys of polarized dust have given us a new observable that is complementary to the more traditional radio tracers, and a variety of other new tracers and related measurements are becoming available to improve current modeling. this paper reviews: the tracers available; the models that have been studied; what has been learned so far; what the caveats and outstanding issues are; and one opinion of where the most promising future avenues of exploration lie. | practical modeling of large-scale galactic magnetic fields: status and prospects |
galaxy clusters grow by gas accretion, mostly from mergers of substructures, which release powerful shock waves into cosmic plasmas and convert a fraction of kinetic energy into thermal energy, amplification of magnetic fields and into the acceleration of energetic particles. the modeling of the radio signature of cosmic shocks, combined with the lack of detected γ -rays from cosmic ray (cr) protons, poses challenges to our understanding of how cosmic rays get accelerated and stored in the intracluster medium. here we review the injection of crs by cosmic shocks of different strengths, combining the detailed "microscopic" view of collisionless processes governing the creation of non-thermal distributions of electrons and protons in cluster shocks (based on analytic theory and particle-in-cell simulations), with the "macroscopic" view of the large-scale distribution of cosmic rays, suggested by modern cosmological simulations. time dependent non-linear kinetic models of particle acceleration by multiple internal shocks with large scale compressible motions of plasma with soft cr spectra containing a noticeable energy density in the super-thermal protons of energies below a few gev which is difficult to constrain by fermi observations are discussed. we consider the effect of plasma composition on cr injection and super-thermal particle population in the hot intracluster matter which can be constrained by fine high resolution x-ray spectroscopy of fe ions. | shocks and non-thermal particles in clusters of galaxies |
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