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due to unusually quiet solar activity conditions during the previous 2009 and 2020 solar minima, record high levels of galactic cosmic rays (gcrs) were reported. however, anomalous cosmic ray (acr) intensities did not show such extremely high levels. this discrepancy between gcr and acr intensities remains unresolved. using a 2d acceleration and transport model, we simulate the transport of gcr and acr oxygen during such atypically quiet solar minimum conditions. higher gcr intensities can be reproduced by assuming less efficient particle scattering during quiet solar minimum periods, while acr intensities are lower during very quiet solar minimum conditions. this is because of the interplay between acr acceleration, which is more efficient when more turbulence is present, and transport, which becomes increasingly inefficient when more turbulence is present. our results are in general agreement with both gcr and acr observations. | simulating gcr and acr oxygen intensities during very quiet solar minimum conditions |
the large area telescope (lat), on-board the fermi satellite, proved to be, after 8 years of data taking, an excellent instrument to detect and observe supernova remnants (snrs) in a range of energies running from few hundred mev up to few hundred gev. it provides essential information on physical processes that occur at the source, involving both accelerated leptons and hadrons, in order to understand the mechanisms responsible for the primary cosmic ray (cr) acceleration. we show the latest results in the observation of galactic snrs by fermi-lat. | supernova remnants with fermi large area telescope |
in the extreme environment of the galactic center, the magnetic fieldmay play a key role in regulating the ism. we propose a deep xmm-newtonobservation of g0.17-0.41 -- a distinct 2.6'-long x-ray thread embeddedwell within a locally broadened nonthermal radio filament. thisx-ray/radio association provides probably the best evidence so farfor magnetic reconnection to occur in the ism. we will criticallytest our proposition, chiefly by determining the thermal or nonthermalnature of the x-ray emission, as well as its spatially-resolved spectralproperties. the understanding of the reconnection, theoretically predictedby analogy to solar flares, can have strong implications for the studyof plasma heating and cosmic-ray acceleration in the ism. | exploring the nature of the x-ray thread g0.17-0.41 in the galactic center |
accretion of gas onto already virialized structures like galaxy clusters should give rise to accretion shocks which can potentially accelerate cosmic rays. here, we use the radio emission detected from coma cluster and models of evolution of cosmic accretion shocks, to constrain the possible contribution of unresolved galaxy clusters to the cosmic radio background. we assume that coma is a typical galaxy cluster and that its entire radio emission is produced by cosmic rays accelerated in accretion shocks, making our prediction an upper limit. our models predict that at lower frequencies accretion shocks can have a potentially large contribution to the cosmic radio background, while on larger frequencies, e.g. 5 ghz, their contribution must be lower than < 2-35%, depending on the models of evolution of accretion shocks that we use. | constraining the collective radio emission of large scale accretion shocks |
massive stars have a profound astrophysical influence throughout their tumultuous lives and deaths. stellar feedback - the injection of energy and momentum by stars to the interstellar medium (ism) - occurs through a variety of mechanisms: radiation, photoionization heating, winds, jets/outflows, supernovae, and cosmic-ray acceleration. despite its importance, stellar feedback is cited as one of the biggest uncertainties in astrophysics today, stemming from a dearth of observational constraints and the challenges of considering many feedback modes simultaneously. in this talk, i will discuss how a systematic approach to multiwavelength observations can be used to overcome these issues. i will summarize results from application of these methods to massive-star regions in the milky way and nearby galaxies, where feedback processes are best resolved. finally, i will highlight exciting prospects of using current and upcoming facilities to explore feedback in diverse conditions. | the tumultuous lives and deaths of stars |
the global records of infectious diseases, including western and eastern documents from 1825 to 2020, during which sunspot observations are considered reliable, show that 27 of the 34 pandemic outbreaks were coincident with sunspot number maxima or minima. there is evidence that the intensity of galactic cosmic rays is anti-correlated with solar activity and that cloud seed formation is accelerated by galactic cosmic rays. there are a substantial number of research papers showing the relationship between covid-19 and vitamin d deficiency. the data analysis of ozone thickness measured based on nasa satellite observations revealed that ozone thickness has 11-year and 28-month cycles. because the 11-year cycles of ozone thickness and cloud seed attenuation are anti-correlated, when either one becomes extremely thick, such as at the maximum or minimum point of solar activity, uv radiation is over-attenuated, and human vitamin d deficiency is globally increased. this finding explains the coincidence of pandemic outbreaks with the extrema of the sunspot numbers. vitamin d supplementation can be an effective countermeasure against the spread of infectious diseases, which is a paramount importance to global society. future pandemic forecasting should include the 11-year and 28-month cycles of uv radiation. this founding completes the relationship between solar activity and human health through the earth's environment. | relation of pandemics with solar cycles through ozone, cloud seeds, and vitamin d |
under nonuniform convection, the distribution of diffusive particles can exhibit dipole and quadrupole anisotropy induced by the fluid inertial and shear force, respectively. these convection-related anisotropies, unlike the compton-getting effect, typically increase with the cosmic-ray (cr) energy, and are thus candidate contributors for the cr anisotropy. in consideration of the inertial effect, cr observational data can be used to set an upper limit on the average acceleration of the local interstellar medium in the equatorial plane to be on the order of 100 μm s-2. using oort constants, the quadrupole anisotropy above 200 tev may be modeled with the shear effect arising from the galactic differential rotation. | cosmic-ray convection-diffusion anisotropy |
the boltzmann-gibbs thermodynamic equilibrium state of charged particles pitch-angle scattered by weak plasma waves is discussed. degrees of freedom of these waves play a fundamental role in constructing the grand canonical ensemble. via the gyro-resonance condition, fast particles have an inverse break power-law spectrum for ɛ - μ ≪ t , where ɛ is the particle energy, μ is the chemical potential, t is the temperature. the break energies are the rest energy and - μ . for ɛ ≪ - μ ≪ t , the energy spectral index α is δ / 2 + 1 and δ + 1 for non- and ultra-relativistic particles, respectively, with δ an effective fractal dimension of background magnetic field lines. the spectral index for - μ ≪ ɛ ≪ t is α + 1 . this thermal equilibrium scenario, combined with the leaky-box model and cosmic-ray observations, seems to suggest that the galactic magnetic field is super-diffusive with δ ≈ 1 . 4 . | power-law spectrum of energetic particles in classical thermal equilibrium by pitch-angle scattering process |
the mechanism accelerating cosmic rays in the milky way galaxy and galaxy clusters is identified and described. the acceleration of cosmic rays is a purely electrostatic process which operates up to the maximum energies of $10^{23}$ ev in galaxy clusters. galactic cosmic rays are accelerated in a pervasive electrostatic field active in the whole galaxy except in restricted regions shielded by interstellar and stellar plasmas as, for instance, the region occupied by the solar system. it is proved that the energy spectrum of the cosmic radiation in the milky way galaxy, in the region where the solar system resides, has a constant spectral index comprised between 2.64-2.68 and the maximum energies of galactic protons are $3.0 \times 10^{19}$ ev. the agreement of these results with the experimental data is discussed in detail and underlined. the various physical processes that maintain the stability of the electrostatic structure in the milky way galaxy are the same that generate the galactic magnetic field. accordingly, the intensity, orientation and direction of the galactic magnetic field are evaluated. the results of the calculation are compared with the observational data, optical and mostly radio astronomy data. the accord of the intensity, orientation and direction of the observed magnetic field with calculation is excellent. | the ubiquitous mechanism accelerating cosmic rays at all the energies |
the supertiger (trans-iron galactic element recorder) experiment was launched on a long-duration balloon flight from williams field, antarctica, on december 8, 2012. supertiger flew for a total of 55 days at a mean atmospheric depth of 4.4 g/cm2. the instrument measured the abundances of galactic cosmic rays in the charge (z) range z = 10 to z = 40 with high statistical precision and excellent charge resolution, displaying well-resolved individual-element peaks at every charge up to and including z = 40. we will describe the instrument, data analysis techniques used, balloon flight, and payload recovery. the data that will be presented contain more than 600 events in the charge range from z = 30 to z = 40, with charge resolution at iron of <0.18 cu. our results confirm with improved statistics the earlier results from tiger supporting a model of cosmic-ray origin in ob associations, with preferential acceleration of refractory elements over volatile elements. this research was supported by nasa under grants nnx09ac17g, nnx14ab25g, the peggy and steve fossett foundation, and the mcdonnell center for the space sciences at washington university. | ultra-heavy galactic cosmic ray abundances from the supertiger instrument |
cosmic rays (crs) are highly energetic nuclei (plus a small fraction of electrons) which fill the galaxy and carry on average as much energy per unit volume as the energy density of starlight, the interstellar magnetic fields, or the kinetic energy density of interstellar gas. the cr spectrum extends as a featureless power-law up to ~2 pev (the 'knee') and it is believed to be the result of acceleration of those crs in galactic sources and later diffusion and convection in galactic magnetic fields. those energetic crs can interact with the surrounding medium via proton-proton collision resulting in secondary gamma-ray photons, observed from 100 mev to a few tens of tev. the results obtained by the current cherenkov telescopes and gamma-ray satellites with the support of x-ray observations have discovered and identified more than 50 galactic gamma-ray sources. among them, the number of supernova remnants (snrs) and very-high-energy hard-spectrum sources (natural candidates to originate crs) are steadily increasing. we expect to increase by a factor 10 at least this population of source with the future cta experiment. i will review our current knowledge of galactic gamma-ray sources and their connection with energetic crs and the scientific prospects for cta in this field. those observations, together with a strong multi-wavelenght support from radio to hard x-rays, will finally allow us to establish the origin of the galactic crs. | gamma rays and the origin of galactic cosmic rays |
magnetic fields are important ingredients in the interstellar medium of galaxies. they accelerate cosmic rays, affect star formation, and regulate the redistribution of matter and energy. despite their ubiquitous presence, the growth and coevolution of magnetic fields with galactic processes are not well understood. we examine the interplay of these galactic components in the spiral galaxy ngc 6946 using wide-band polarization observations. we map the turbulent and coherent line-of-sight magnetic fields across the disk of the galaxy by fitting models of the magnetic fields structure to 3-21cm polarization observations taken with the westerbork synthesis radio telescope. we spatially correlate the results of these fits with star formation tracers and hi line profiles to determine how magnetic field structure is related to different galactic processes. this work is just one example of how the advanced capabilities of modern radio telescopes have opened a new frontier for the study of cosmic magnetism. | magnetic fields in ngc 6946 using wide-band radio polarimetry |
cosmological constraints from x-ray and microwave observations of galaxy clusters are subjected to systematic uncertainties. non-thermal pressure support due to internal gas motions in galaxy clusters is one of the major sources of astrophysical uncertainties, which result in large bias and scatter in the hydrostatic mass estimate. in this work, we analyze a sample of massive galaxy clusters from the omega500 high-resolution hydrodynamic cosmological simulation to examine the effects of dynamical state on non-thermal pressure. we use the adaptive refinement tree (art) code, an eulerian grid-based adaptive refinement mesh code, which is well suited for modeling shock heating of gas and generation of bulk and turbulent motions from cosmic accretion. we examine the effects of cluster mergers on the hydrostatic mass bias and the evolution of non-thermal pressure. we find that during a major merger about a third of the total pressure support in the system is in non-thermal pressure from random gas motions, which leads to a ~30% bias in the hydrostatic mass estimate. even after the clusters relax, we find a residual 10% bias due to the residual non-thermal pressure sustained by continuous gas accretion and minor mergers in cluster outskirts. however, when the non-thermal pressure support is accounted for in the mass estimates of relaxed clusters, we are able to recover the true mass to within a few percent. moreover, by accounting for the additional pressure contribution from gas accelerations, we find that the bias in the hse can be reduced by about half for our whole cluster sample. we also characterize the non-thermal pressure fraction profile and study its dependence on redshift, mass, and mass accretion rate. we find a universal, redshift-independent fitting formula for describing the fractional pressure support due to bulk motions. within the relation, we find that the mass accretion rate has a systematic effect on the amount of non-thermal pressure in clusters, with more rapidly accreting systems containing a larger fraction of pressure due to gas motions. we will discuss implications of our results for the recent tension in the planck cmb and galaxy cluster cosmological constraints. | effects of mergers and dynamical state on galaxy clusters in cosmological simulations |
owing to their utility for measurements of cosmic acceleration, type ia supernovae (sne ia) are perhaps the best-studied class of sne, yet the progenitor systems of these explosions largely remain a mystery. a rare subclass of sne ia shows evidence of strong interaction with their circumstellar medium (csm), and in particular, a hydrogen-rich csm; these objects are referred to as sne ia-csm. ptf11kx began life as a sn ia, but after a month it began to show indications of significant interaction with its csm. this well-studied object was revolutionary in that in solidified the connection between sne ia-csm and more typical sne ia, despite their spectral similarity to type iin sne (which likely come from massive star progenitors, as opposed to the white dwarf progenitors for the sne ia-csm). there are currently nearly 20 sne ia-csm with published data. the spectra of all sne ia-csm are dominated by hα emission (with widths of ~2000 km s-1) and exhibit large hα/hβ intensity ratios (perhaps due to collisional excitation of hydrogen via the sn ejecta overtaking slower-moving csm shells); moreover, they have an almost complete lack of he i emission. they also show possible evidence of dust formation through a decrease in the red wing of hα 75-100 days past maximum brightness, and nearly all sne ia-csm exhibit strong na i d absorption from the host galaxy. the absolute magnitudes (uncorrected for host-galaxy extinction) of sne ia-csm are found to be -21.3 mag ≤ mr ≤ -19 mag, and they also seem to show ultraviolet emission at early times and strong infrared emission at late times (but no detected radio or x-ray emission). finally, the host galaxies of sne ia-csm are all late-type spirals similar to the milky way, or dwarf irregulars like the large magellanic cloud, which implies that these objects come from a relatively young stellar population. | type ia supernovae strongly interacting with their circumstellar medium |
it will be presents an original etching-based technique of search for and analysis of tracks of heavy cosmic ray nuclei (z > 26) in olivine crystals from meteorites, developed by the authors team. this enabled detecting and identifying 21,743 galactic cosmic ray tracks of nuclei heavier than iron in the olivine crystals from meteorites. the obtained data on the relative fraction of heavy and superheavy nuclei in galactic cosmic rays is discussed within the existing concepts of nuclei formations in astrophysical processes. data of the olympia project searching of heavy nucleus tracks in olivine from pallasites are applied for checking concepts of formation and acceleration of heavy nuclei in astrophysical processes. analysis of etched tracks in two meteorites allows reveals the difference between the spectra of nuclei abounding in these pallasites and those registered by satellites detectors of cosmic rays, as well as the difference between the meteorites themselves. this confirms the suggestion that these nuclei originate mainly from r-processes (rapid capture of neutrons, on a timescale shorter than r-decays) in neutron star mergers or else neutron star - black hole mergers. the detected three tracks of nuclei with the estimated charges of 119 (with accuracy plus 10, minus 6) and lifetimes of about a hundred years can be treated as direct experimental evidence of the existence of superheavy nuclei from the "island of stability". | investigations of the tracks of galactic cosmic ray nuclei in olivines from meteorites |
it is currently accepted that supernova remnants are the main sites where galactic cosmic rays undergo acceleration. though this picture is energetically sustentable, the models predict spectra that do not match observations. on the other hand, the contribution of other kind of sources to the galactic cosmic-ray population is still unclear, and deserves investigation. in this work we explore a novel mechanism through which microquasars might produce cosmic rays, based on the generation of relativistic neutrons in situ, which escape and decay outside. protons and electrons created in neutron decays escape to the interstellar medium as cosmic rays. the proposed mechanism produces more energetic cosmic rays from microquasars than those presented by previous works. the spectral index agrees well with that required to explain the spectral signatures of galactic cosmic rays. best scenarios arise in the most luminous, slow jets, which produce a cosmic-ray power, by source, comparable to that of supernova remnants. the mechanism explored in this work may provide stronger cosmic-ray sources in the early universe, and therefore contribute to the heating and reionization of the intergalactic medium. | microcuásares como fuentes de rayos cósmicos |
recently, a diffuse γ-rays emission in the energy range 1-100 gev has been detected around m31, that extends up to 120-200 kpc from its center. such extended emission is difficult to be explained in the typical scenario of cosmic rays produced in the galactic disk or in the galactic center (gc) and diffusing in the galactic halo. we show that a cosmic ray origin, either hadronic or leptonic, of the emission is viable if non-standard cosmic ray transport scenarios are considered, or if particles are accelerated directly in the galactic halo (in situ acceleration). the cosmic ray halo can be powered by the accretion of intergalactic gas or by the activity of galaxy's central black hole. if giant cosmic ray halos are common around galaxies, the interactions of cosmic ray protons and nuclei with the circumgalactic gas surrounding milky way could explain the isotropic diffuse flux of neutrinos observed by icecube. | giant cosmic ray halos around m31 and the milky way |
outflows are ubiquitous phenomena in the universe. they have been widely observed in both galactic and extragalactic objects. in this thesis, we analyze three individual sources. firstly, we re-analyze the high energy gamma-ray data of fermi-lat on the giant lobes of centaurus a. we utilize for the first time the planck observations to derive the fluxes of the lobes. the multiwavelength seds reveal a possible leptonic+hadronic origin of the non-thermal emission. secondly, we re-analyze chandra observations of the m87 jet with a total exposure time of 1500 kiloseconds to explore the x-ray emission characteristics along the jet. the variabilities of the nucleus and hst-1, as well as the photon spectra for all knots are investigated. fitting the radio to xray seds assuming a synchrotron origin, we show that a broken power-law electron spectrum allows a satisfactory description of the seds for most knots except for b, c and d, for which an additional component is needed. we discuss the implications and suggest that a stratified jet model may account for the differences. finally, we derive the energy distribution of ultrarelativistic electron in g1.9+0.3, which is the youngest known snr in the galaxy, under the assumption that the detected x-ray with chandra and nustar are of entirely synchrotron origin. the electron acceleration is found to be an order of magnitude slower than the maximum rate provided by the shock acceleration in the nominal bohm diffusion regime. we discuss the resultant implications in the context of contribution of snrs to the galactic cosmic rays at pev energies. | nonthermal processes of fast outflows from astrophysical objects |
passive radiation shielding is one strategy to mitigate the problem of space radiation exposure. while space vehicles are constructed largely of aluminum, polyethylene has been demonstrated to have superior shielding characteristics for both galactic cosmic rays and solar particle events due to the high hydrogen content. a method to calculate the shielding effectiveness of a material relative to reference material from bragg peak measurements performed using energetic heavy charged particles is described. using accelerated alpha particles at the national aeronautics and space administration space radiation laboratory at brookhaven national laboratory, the method is applied to sample tiles from the heat melt compactor, which were created by melting material from a simulated astronaut waste stream, consisting of materials such as trash and unconsumed food. the shielding effectiveness calculated from measurements of the heat melt compactor sample tiles is about 10% less than the shielding effectiveness of polyethylene. shielding material produced from the astronaut waste stream in the form of heat melt compactor tiles is therefore found to be an attractive solution for protection against space radiation. | measuring space radiation shielding effectiveness |
while from the energetic point of view snrs are viable sources of galactic crs, the issue of whether they can accelerate protons up to pev remains unsolved. here we discuss particle acceleration at the forward shock of sn and discuss the possibility that the escaping particle current may excite a non-resonant instability that in turn leads to the formation of resonant modes confining particles close to the shock and increasing the maximum energy. this mechanism works throughout the expansion of the sn explosion, from the ejecta dominated (ed) to the sedov-taylor (st) phase. because of their higher explosion rate,we focus on type ii snae expanding in the slow, dense red supergiant wind. when the explosion occurs in such winds, the transition between the ed and the st phase is likely to take place within a few tens of years. as a result, the spectrum of accelerated particles shows a break in the slope, at the maximum energy (em) achieved at the beginning of the st phase. above this energy, the spectrum becomes steeper but remains a power law than developing an exponential cutoff. we show that for type ii snae typical parameters, proton em can easily reach pev energies, confirming that type ii snrs are the best candidate sources for crs at the knee. we have tried to fit kascade-grande, argo -ybj and yac1-tibet array data with our model but we could not find any parameter combination that could explain all data sets. indeed the recent measurement of the proton and helium spectra in the knee region, with the argo-ybj and yac1-tibet array, has made the situation very confused. these measurements suggest that the knee in the light component is at 650 tev, appreciably below the overall spectrum knee. this finding would resolve the problem of reaching very high energies in snae, but, on the other hand, it would open a critical issue in the transition region between galactic and extragalactic crs. | on the cosmic ray spectrum from type ii supernovae expanding in their red giant presupernova wind |
we present new karl g. jansky very large array (jvla) observations of the merging galaxy cluster zwcl2341.1+0000 located at z=0.27. this cluster is known to contain two diffuse radio sources, the largest being about 1 mpc in size, located on opposite sides of the cluster center. the sources are separated by about 2 mpc. in addition, the presence of fainter emission located between the two diffuse sources has been suggested. diffuse mpc-size radio sources in clusters are classified as radio halos and relics. their existence implies the presence of cosmic rays and magnetic fields in the intracluster medium. the question is by which mechanism these cosmic rays are accelerated. for relics, there is increasing evidence that they trace particles (re)accelerated at large-scale shocks. however, the physics of the acceleration mechanism is not yet fully understood. radio halos are centrally located in clusters. for halos, it has been suggested that the cosmic rays are re-accelerated by magneto-hydrodynamical turbulence. we use our jvla observations of zwcl2341.1+0000 to (1) search for the presence of additional large-scale emission in the cluster and (2) measure the spectral and polarization properties of the diffuse emission to determine its origin. | jvla observations of cosmic rays in the galaxy cluster zwcl2341.1+0000 |
there are only a few pevatron candidates known in our galaxy which might contribute particles up to the knee of the cosmic-ray spectrum. hess j1641.0-4619, a gamma-ray source located in the galactic plane and detected by h.e.s.s. above 4 tev, is one of them. characterized as a point source with a hard spectral index, hess j1641.0-4619 remains unidentified but is coincident with a radio snr g338.5+0.1 and the dense hii region g338.4+0.0. with an angular extent of only 0.25^circ, the high energy gamma-ray source hess j1640.6-4633, coincident with the composite snr 338.3-0.0 and the pulsar psr j1640-4631, was originally classified as an extremely powerful snr. in this context, the escape of cosmic-ray protons accelerated by g338.3-0.0 colliding with the ambient dense gas would be able to produce the emission of hess j1641.0-619, providing a self-consistent explanation for the gamma-ray emission of both sources. using 9 years of fermi lat pass 8 data, we analyzed these two sources from 100 mev to 800 gev. our extensive morphological and spectral analyses provide new constraints on the origin of the gamma-ray emission as well as the efficiency of these two h.e.s.s. sources to accelerate protons and contribute to the galactic cosmic-ray flux around the knee. | efficient particle acceleration from hess j1640.6-4633 and the pevatron candidate hess j1641.0-4619 |
supertiger (super trans-iron galactic element recorder) is a large-area instrument designed to make precision measurements of the elemental composition of ultra-heavy galactic cosmic rays (uhgcr) with atomic number z $\ge$ 30. the abundance measurements provide sensitive tests and clarification of the ob-association model of galactic cosmic-ray origins, and test models for atomic processes by which nuclei are selected for acceleration to cosmic-ray energies. after a record-breaking 55 day supertiger-1 long-duration flight in the 2012/2013 antarctic season, a second flight was planned for the 2017/2018 season, however, the flight was postponed for two seasons due to unfavorable weather conditions and a balloon malfunction. on december 16, 2019 at 2:55 ndzt, the instrument was launched from the long duration balloon (ldb) site near mcmurdo station, antarctica and reached float altitude after 4.5 hours. the flight completed its first revolution around the continent in 16 days and continued on the second revolution to observe cosmic-ray events until january 17, 2020 at 12:29 nzdt, about 40 minutes prior to the flight termination. the total flight duration was 32 days, 11 hours and 4 minutes, collecting about 1.3 million cosmic-ray fe events, which was about 1/3 of the fe events observed by the supertiger-1 flight. the payload landed on the east antarctic plateau (latitude 71$^\circ$7.53 s, longitude 158$^\circ$35.10 e, altitude 2020 m), about 800 km from mcmurdo station. a quick access to the payload was performed in the following week and the full recovery is planned for the 2020/2021 season. while waiting for the full recovery of the payload with the data stored on disk, an initial instrument response calibration is being performed for the data transmitted through the tracking and data relay satellite system (tdrss). about 94% of the observed cosmic-ray events with z $\ge$ 26 were transmitted through tdrss. the preliminary charge resolution derived from the data obtained after adjusting sensor gains was 0.16 c.u. for fe events, which is equivalent to the supertiger-1 instrument performance. we report on the supertiger-2 flight overview and its preliminary results. | overview and preliminary results of the supertiger-2 flight |
the high energy charged particle environment (i.e. >30 mev protons and ~2 mev electrons) in mars orbit is of interest both in terms of the science of the heliosphere and of the space radiation hazard to key orbital assets and astronaut health. these particles have two primary sources: a) galactic cosmic rays which form a relatively steady background, varying by factors of 2 or 3, and b) solar energetic particles (seps) accelerated either at the sun or at interplanetary shock fronts, which can vary by several orders of magnitude. several instruments in mars orbit have been sensitive to these particles which penetrate the instrumentation creating a background signal which is dependent on high energy particles. examination of background count rates from the mars global surveyor electron reflectometer (mgs-er, 1997-2006) and the mars express electron spectrometer (mex-els, 2004-present), which are both proxies for fluxes of these penetrating particles, are studied since both instruments are influenced by the high energy environment. here we have two primary goals. first, we wish to understand the variability in these data sets, both temporal (during quiet times and sep events) and in regards to factors such as altitude and the planetary zenith angles formed with respect to the sun and the sun's motion through the galaxy. second, using these two data sets, we wish to construct a consistent database of the penetrating particle radiation environment in mars orbit from 1997 until the present. we will present preliminary findings with respect to both of the above goals. | understanding high-energy particle radiation in mars orbit: combining data sets from mars global surveyor and mars express |
there are gaps in our current understanding of how massive galaxies undergo the transformation from actively forming stars to quiescence with negligible ongoing star formation. most massive galaxies in the local universe quenched their star formation billions of years ago, and there is theoretical and observational evidence that feedback and outflows played a crucial role in quenching star formation in the progenitors of these massive galaxies. we use spectroscopic data from the sloan digital sky survey and the keck telescope, along with photometric data from the ultraviolet through the infrared, to analyze a sample of a dozen massive, compact starburst galaxies that are known to be driving large-scale outflows with speeds in excess of 1000 km/s. by comparing emission-line properties with modeling of their spectral energy distributions, we find that these galaxies possessed incredibly high star formation rates in the recent past but have weak optical emission lines at present. we trace outflowing gas using interstellar absorption lines, and we find evidence for large covering fractions that vary as a function of velocity, consistent with models of swept-up interstellar gas in an outflowing shell. these characteristics suggest a close connection between the quenching of the recent starburst and the expulsion of interstellar gas supply in the observed outflows. our analysis of the absorption-line profiles also places important constraints on the physical processes (supernovae, stellar winds, radiation pressure, cosmic rays, black hole accretion) that could accelerate the outflows and induce the transformation from star forming to quiescent. | compact starburst galaxies with fast outflows: constraints on recent star formation and outflow properties from optical spectroscopy and multi-wavelength photometry |
active galactic nuclei (agn), powered by accretion onto a central supermassive black hole in their host galaxies, are the most luminous persistent sources of electromagnetic radiation in the universe. non-thermal emission from agn jets is observed across the electromagnetic spectrum, up to tens of tev in the gamma-ray range, evidencing particle acceleration processes at work in these extreme objects and making them ideal candidates as cosmic ray sources. the detection of an astrophysical flux of high-energy neutrinos by icecube provides a crucial element towards testing this hypothesis, as neutrinos originate in hadronic interactions of cosmic rays. icecube has also uncovered tantalizing evidence for high-energy neutrino emission from the agn txs 0506+056, which has triggered a wide-range effort into understanding the multi-messenger emission from this object and other agn. this talk will summarize recent results from multi-messenger studies of agn involving neutrinos and photons, outline their theoretical modeling, and discuss what we can learn from these and future observations. | high-energy neutrinos as a multi-messenger probe of supermassive black hole environments |
through observations in very-high-energy (vhe) $\gamma$-rays, the high energy stereoscopic system (hess) allowed studying the properties of the vhe $\gamma$-ray emission from the galactic center (gc) between 0.1~tev and 100~tev. hess observed a $\gamma$-ray diffuse emission strongly correlated with the central molecular zone (cmz) morphology, showing energies above 30~tev. the best scenario to generate the $\gamma$-ray diffuse emission is hadronic interaction between cosmic rays (cr) and the ambient gas. the observed $\gamma$-ray spectrum implies that the intrinsic cr spectrum could extend to energies $\sim 1\,\mathrm{pev}$. the cr density profile in the cmz shows an increased density towards the gc that is consistent with a source within the central 10 pc, with a continuous injection of cr over at least $10^4$ years. protons could be accelerated close to the supermassive black hole sagittarius a* or inside the clusters of young massive stars of arches, quintuplet and nuclear. the problem is that current diffusion models are spherical and isotropic, but the cr diffusion in the cg is anisotropic. we plan to model the vhe $\gamma$-ray emission from the cmz between 0.1 tev and 100 tev, generated by cr, considering different geometries, time dependence, and spectra of cr injection. we will include different diffusion coefficients, polar advection, and compute the interaction of cr with observed ambient gas. from the model, we will get the $\gamma$-ray morphology and spectrum observed by hess in the cmz, and predict $\gamma$-rays observation by the cherenkov telescope array in the cmz and other molecular clouds. finally, we will identify multi-wavelength and multi-messenger contributions. | vhe \\gamma-rays from the galactic center generated by cosmic rays |
supernova remnant is an important source of the interstellar medium, and important mediation to understand the mechanisms of supernova explosions, the acceleration of galactic cosmic-rays, and the abundance of chemical elements in the interstellar medium. an accurate measurement of the distance to an snr can better constrain other physical parameters of the snr. however, reliable distance measurement of snrs is very challenging. up to now, in the confirmed snrs and newly discovered snr candidates, about one-third of them have reliable distance measurements. generally, there are three main methods to measure snrs' distance: kinematic method, radio-surface-brightness-to-diameter relation and extinction-distance map. in recent years, based on the principle of extinction-distance relation, the method of measuring snr's distances using red clump (rc) as probe has been well developed and applied. rcs are a kind of low-mass stars in the burning stage of the helium nuclei. their absolute luminosity and dispersion are small, so they can be easily identified. therefore, they are often used as standard candles to measure the distance of other celestial bodies. this paper will first introduce the current progress in snr distance measurement, then will summarize the achievement using the rcs method. | measure distances of supernova remnants using red clump stars |
galaxy cluster mergers generate shocks and turbulence in the intracluster medium. diffuse cluster radio sources are proposed to trace cosmic rays accelerated by these shocks and turbulence. we propose to observe three nearby galaxy clusters that host extended radio emission at 150 mhz which were missed by previous surveys carried out at ghz frequencies. the nature of these extended radio sources, which all have very complex morphologies, is unclear. the goals of this proposal are to determine the global luminosity, temperature and dynamical state (i.e., merger vs relaxed) of these clusters. | a first characterization of galaxy clusters hosting diffuse low-frequency radio emission |
magic is a ground-based imaging atmospheric cherenkov telescope (iact) for gamma-ray astrophysics in the very high energy domain, which pioneered high-sensitivity measurements down to a few tens of gev. it includes two 17m diameter telescopes, operating in a coincidence (stereo) mode. the telescopes are located at 2200m a.s.l. in the el roque de los muchachos european northern observatory on the canary island of la palma. in recent years, the magic collaboration has been developing innovative techniques that increased the dynamic range and the sensitivity of the telescopes down to about 20 gev and up to 100's of tev. these expanded the capabilities and opened new scientific prospects for the instrument. in this report we plan to focus on some selected observational results of cosmic rays as well as of gamma-rays of galactic and extra-galactic origin. | selected studies of cosmic rays and acceleration sites with the magic telescopes |
solar wind turbulence is responsible for many physical phenomena in the heliosphere including energetic cosmic particle transport and acceleration. turbulence is generated in the solar wind by three major sources, these being shocks and stream-stream interactions in the inner heliosphere and by the generation of pick-up ions in the more distant outer heliosphere. corotating interaction regions are significant generators of turbulence due to the discontinuity between the slow and fast streams within them. numerical mhd simulation of the solar wind plasma is conducted to study this shear layer in order to illuminate the transport of the cosmic rays within corotating interaction regions. legendre harmonics generated by the pfss method provided by the wso interface for the two most recent solar minima are used for the inner boundary of the simulation. after simulating the solar wind plasma and turbulence during these two periods, a superposed epoch analysis was performed over the turbulent properties of the solar wind and diffusion properties of galactic cosmic rays. our results were compared to observations. the results of the superposed epoch analysis illustrate that the average properties of the solar wind turbulence and parallel and perpendicular diffusion coefficients are well reproduced near corotating interaction regions in our simulation. | turbulent properties of the solar wind within corotating interaction regions: superposed epoch analysis of simulations and observations |
the central few hundred parsecs of the galaxy harbors 5-10% of the molecular gas mass of the entire milky way. this central molecular zone exhibits 6.4 kev fe kα line and continuum x-ray emission with time-variability. the time-variable x-ray emission from the gas clouds is best explained by light echoes of past x-ray outbursts from the central supermassive black hole sgr a*. however,mev-gev cosmic-ray particles may also contribute to a constant x-ray emission component from the clouds, through collisional ionization and bremsstrahlung. sgr b2 is the densest and most massive cloud in the central molecular zone. it is the only known gas cloud whose x-ray emission has kept fading over the past decade and will soon reach a constant x-ray level in 2017/2018, and thus serves as the best probe for mev-gev particles in the central 100 pc of the galaxy. at the same time, the fe kα emission has also been discovered from molecular structures beyond the central molecular zone, extening to ~1 kpc from the galactic center. the x-ray reflection scenario meets challenges this far from the galactic center, while the mev-gev cosmic-ray electrons serve as a more natural explanation. our studies on sgr b2 and the large-scale moleuclar structures will for the first time constrain the mev-gev particles in the galactic center, and point to their origin: whether they rise from particle acceleration or dark matter annihilation. | probing galactic center cosmic-rays in the x-ray regime |
the heliopause (hp) separates the tenuous hot heliosheath plasma from the relatively dense cool magnetized plasma of the local interstellar medium (lism). fluid acceleration in the hp region can therefore drive rayleigh-taylor-like and kelvin-helmholtz- like instabilities. charge exchange coupling of plasma ions and primary interstellar neutral atoms provides an effective gravity, suggesting the possibility of rayleigh taylor-like (rt-like) instabilities. shear flow due to the velocity difference between the heliosheath and the interstellar flows drives kelvin helmholtz-like (kh-like) modes on the heliopause. magnetic fields damp the classical kh instability. however, we show that energetic neutral atoms (enas) destabilize kh-modes,even in the presence of interplanetary and interstellar magnetic fields. we consider a model that includes a number of effects that are important in the heliosphere such as resonant change exchange between the primary neutrals and the solar wind plasma, enas from the inner heliosheath, plasma flows along the heliopause and magnetic fields in the inner and outer heliosheath. we find that the nose region is unstable to rt-like modes for hp parameters, while the shoulder region is unstable to a new instability that has the characteristics of a mixed rt-kh-like mode. these instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath close to the nose and shoulder regions. whereas enas have a stabilizing influence on the rt instability in the vicinity of the nose region (due to counter streaming), they have a destabilizing influence on the kh instability in the vicinity of the flanks. we find that even in the presence of interplanetary and interstellar magnetic fields, enas can drive a new form of kh-like instability on the flanks. an analysis of the collisional and anomalous magnetic field diffusion time scales shows that ideal mhd is an appropriate model at the hp. the interstellar magnetic field therefore drapes over the hp and does not diffuse into the inner heliosheath (ihs). however, rt-like, rt-kh-like, and kh-like instabilities serve to drag outer heliosheath (ohs)/interstellar magnetic field into the ihs, allowing for local reconnection of interplanetary and interstellar magnetic field. such reconnection may 1) enhance the mixing of plasmas across the heliopause, and 2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and easy loss of anomalous cosmic rays. | instability of the heliopause |
most modeling attempts of blazars use a small emission zone located close to the central black hole in order to explain the broad-band spectral energy distribution. here we present a case where additionally to the small region a >kpc-scale jet is required to successfully reproduce the spectrum and especially the tev emission, namely the low-frequeny peaked bl lac object ap librae detected in the tev domain by the h.e.s.s. experiment. given that other parts of the spectral energy distribution follow the characteristics implied by the source classification, the inverse compton component spans 10 orders of magnitude, which cannot be reproduced by the one-zone model. additionally, observational constraints in both the synchrotron and inverse compton compoenent strongly constrain the parameters of a self-consistent model ruling out the possibility of tev photon production in the vicinity of the galactic center. we discuss the possibility that the tev radiation is emitted by highly energetic particles in the extended, arcsec-scale jet, which has been detected at radio and x-ray energies. the slope of the jet x-ray spectrum indicates an inverse compton origin, and an extrapolation to higher energies coincides with a break feature in the γ-ray band. modeling the jet emission with inverse compton scattering of the cosmic microwave background results in an excellent fit of the radio, x-ray and tev emission. implications will be discussed, such as properties of the jet, acceleration scenarios, and observations to test the model. if confirmed, large scale jets are able to efficiently accelerate particles and to keep relativistic speeds up to distances of several 100kpc. | the extended jet in ap librae as the source of the vhe γ-ray emission |
the effect of particle radiation on materials-of-construction used in inflatable habitat, composite habitat, and space suits was investigated. the materials irradiated are lightweight candidates having a variety of applications such as permeation barriers, micrometeoroid and orbital debris (mmod) protective layers, and restraint layers. the types of particle radiation used were chosen to be representative of the species and energies present in galactic cosmic ray (gcr) and solar particle event (spe) space radiation. for example, low-z (proton) and high-z (iron) 1-gev particle beams were used to bracket gcr ionization and displacement effects. intermediate energy (ca. 20 to 40-mev) protons were used to simulate ionization effects due to exposure to spe radiation. the amount of damage caused by either form of radiation was quantified by determining changes in relevant mechanical and physical properties. although lower and higher dose effects were ascertained in the study, materials were generally irradiated to doses representing up to a 50-hear exposure to deep space radiation (approximately 700 and 10,000 cgy for gcr and spe dosese, respectively). the test logic was, therefore, to qualify materials out to 50-years, rather than to determine terminal doses leading to catastrophic property loss.in most cases, little or no significant property change was observed after exposing materials to particle radiation representing a 50-year gcr or spe dose. however, in certain cases, moderate property changes were observed. for example, a 325-denier spectra space suit restraint layer exhibited a 20.6 percent drop in the initial puncture extension after receiving a 10,300-cgy proton dose simulating a worst case 50-year exposure to spe radiation. similarly, significant drops in the initial puncture extension were also noted for 325-denier spectra after receiving a 400 to 709 cgy 1-gev 26fe dose emulating an exposure to high-z gcr radiation. the largest mechanical property changes noted in this study were 133 to 205 percent increases in the room temperature ultimate tensile strength (uts) for a bladder materials reinforced with 210-denier spectra receiving 709 and 10,300 cgy doses emulating 50 year gcr and spe exposures, respectively. other commercially available bladder materials (cadpak hd200 and armorflex st10) exhibited small but reproducible increases in the uts, consistent with predominant cross-linking. thermogravimetric analysis (tga) of selected bladder materials suggested the occurrence of some cross-linking of high molecular weight polymeric species, with some increase in liberation of low molecular weight (non-polymeric) species; however, the changes noted were small. permeation results for an armorflex st10 bladder material revealed an initial drop in the permeation resistance after irradiation, which recovered to acceptable levels after repeated pressure cycling. deterioration in ballistic performance was noted after exposure of inflatable habitat mmod protective layers receiving doses equivalent to a 50-year high-z gcr exposure. results on filled and unfilled sandwich core constructions showed that panels with filled honeycomb core are significantly strengthened after iron & proton 1-gev particle exposures. last, the combined effects of radiation exposure and thermal aging on high density polyethylene (hdpe, similar make-up to spectra) were demonstrated, suggesting that physical aging may exacerbate radiation degradation processes occurring in spacecraft and space suit materials used in long term applications in space radiation environments.while catastrophic end-of-life material failure indicative of a terminal dose was not observed for any material investigated, the potentially antagonistic (accelerative) degradation by simultaneous radiation exposure and physical aging was. the relevance of the current findings to nasa's missions is discussed and recommendations for future testing are made. corroboration of current data with available scientific literature is also discussed. | particle radiation effects representing gcr and spe space radiation on spacecraft and spacesuit materials-of-construction |
galactic-scale superbubbles, such as the fermi bubble in the milky way, could be produced either by an agn or starburst. until now, the best studied superbubble in an external galaxy is in ngc3079, which hosts both an agn and nuclear starburst, leading to some uncertainties in explaining the result. we propose chandra observation of a star formation inactive galaxy ngc4438 to study the non-thermal hard x-ray emission from its lopsided 10kpc-scale superbubble. we will discriminate if cosmic rays are accelerated by individual snrs or by the bubble as a whole. we can also determine the primary energy loss channel for cosmic rays - inverse compton or synchrotron emission. finally, we will measure the pressures of the thermal and nonthermal components, which dictate the expansion of the system. | non-thermal hard x-ray emission from a superbubble in a non-starburst galaxy |
ic 443 is a middle-aged supernova remnant (snr) in our galaxy. a gamma-ray spectrum of ic 443 shows a pion-decay signature, which means that cosmic-ray protons are accelerated in the snr (ackermann et al. 2013, sci, 339, 807). since pion production requires cosmic-ray protons with > 280 mev, gamma-ray observations cannot constrain low-energy cosmic rays (lecrs). observations of h_3^+ absorption lines revealed that the ionization rate of h_2 is large in ic 443 (indriolo et al. 2010, apj, 724, 1357). this suggests that a large amount of lecrs are produced. however, h_3^+ observations cannot provide the information on energy density of lecrs. when lecrs collide with the surrounding interstellar material, they ionize the neutral iron in it and emit a fluorescent x-ray at 6.4 kev (tatischeff et al. 2012, a&a, 546, 24). since ic 443 interacts with molecular clouds, accelerated particles can collide with them to produce the 6.4 kev line. analyzing the suzaku archive data of ic 443, we discovered the 6.4 kev line with a significance level of ≥ 3 σ. we measured the spatial intensity distribution of the 6.4 kev line and found that the high-intensity region contains the site where the large ionization rate was observed. the 6.4 kev line would be produced by lecrs with the energy density of 10 - 100 ev/cc for protons and 0.01 - 0.1 ev/cc for electrons. | discovery of a 6.4 kev emission line in the supernova remnant ic 443: fluorescence induced by low-energy cosmic rays? |
the cosmological concordance model (λcdm) well accounts for a wealth of observations, from the existence of cosmic microwave background (cmb) to the discovery of the accelerated expansion of the universe from type ia supernovae. yet, it assumes a still unknown form of dark energy and matter and some tensions arose recently as, for instance, the discovery of a 3.4σ discrepancy between the local (riess et al. 2016) and planck (aghanim et al. 2016) measurement of h0. in addition, the λcdm model is poorly tested in the redshift interval between the farthest observed type ia supernovae (z 1.4) and that of the cmb (z 1100). we present new measurements of the expansion rate of the universe in the redshift range z=0.5-5.5 based on a hubble diagram of quasars. the distance of quasars have been estimated from the observed non-linear relation between the x-ray and ultraviolet emission, following a method developed by our group. the distance-redshift relation of quasars at z<1.4 is in agreement with that of supernovae and with the concordance model. nonetheless, a deviation from the λcdm model emerges at higher redshift, with a statistical significance of 4σ. we found that, if an evolution of the dark energy equation of state is allowed, our data suggest a dark energy density increasing with time. | discovery of a 4σ deviation from λcdm using the hubble diagram of quasars |
the powerful winds of highly-evolved wolf-rayet (wr) stars enrich the ism with metal-rich material to be recycled into future generations of stars. their supersonic winds create shocks that are potential sites of galactic cosmic ray acceleration and diffuse x-ray emission. the wr 38 complex harbors a rich collection of five wr stars, an x-ray pulsar, and a fermi gamma-ray source. the region has high discovery potential but has so far been understudied in x-rays. we propose to obtain a sensitive acis-i observation of the wr 38 complex. we will characterize the x-ray properties of the wr population to test wind shock model predictions, search for diffuse x-rays from wr winds interacting with the ism, and characterize the pulsar's x-ray emission. | a panoramic x-ray view of the wr 38 wolf-rayet cluster |
superbubbles are powered by the stellar winds and subsequent supernovae of a massive stellar population and are often argued as strong candidates for galactic cosmic-ray acceleration sites. the recent detection of tev gamma-rays from 30 dor c in the large magellanic cloud by the high energy stereoscopic system (h.e.s.s.) has shown that superbubbles can and do accelerate particles up to very high cosmic-ray energies, and are a new and important source class in tev astronomy. however, the dominant production mechanism (i.e., hadronic or leptonic) is still unclear. the answer to this question is locked in the unique synchrotron x-ray shell of 30 dor c. the widths of the synchrotron emission regions are directly related to the magnetic field, which is a crucial parameter assessing dominant gamma-ray emission mechanism. in this talk we will present a study of the synchrotron emission region widths in 30 dor c using several hundred ks of archival x-ray data from xmm-newton. we constructed radial emission profiles from various regions of the synchrotron shell, fitted emission models to determine the widths, and derived b-field values in the downstream regions using appropriate models. the resulting low b-field estimates, of the order of a few micro g, favour a leptonic origin for the gamma-ray emission. hadronic cosmic rays are likely to be accelerated as well, but the low density inside the bubble suppresses their emissivity. | magnetic field estimates from the synchrotron x-ray shell of 30 dor c, the first tev superbubble |
supernova remnants (snrs) are a very well studied class of objects in our galaxy and are closely related to the origin of cosmic rays (crs), being candidates to host the acceleration process of galactic crs. accelerated particles in snrs can produce γ-rays through interactions with gas (nucleon-nucleon interactions or e± bremsstrahlung) or low-energy photons (inverse compton scattering by electrons). in more than eight years of data taking, the large area telescope (lat) onboard the fermi satellite, has detected more than 30 snrs in the γ-ray energy band. the energy range in which fermi-lat is sensitive, namely from less than 100 mev up to a few hundred gev, is crucial to provide information on the physical processes occurring at the source and disentangle between lepton-based and hadron-based interpretation models. the fermi-lat collaboration has recently performed a systematic study of the known snrs, producing the first supernova remnant catalog in the gev energy range. the spatial and spectral information obtained allow a systematic study of the snr characteristics, which, together with multi-wavelength information, provide more general constraints on the cr population of our galaxy. we present here the latest results from the observations of galactic snrs by fermi-lat, with a particular focus on the recent results obtained in the first snr catalog. | fermi-lat highlights on supernova remnants |
voyager 1 (v1), before it entered the local interstellar medium (lism) in the summer of 2012, observed a series of increases and decreases in the galactic cosmic ray (gcr) nuclei (mainly protons with energies exceeding 70 mev) fluxes. this remarkable feature was accompanied by the corresponding decreases and increases in the anomalous cosmic ray fluxes. we argue that these observations may be due to mhd instabilities and/or magnetic reconnection near the nose of the heliopause (hp), which created a possibility for v1 to cross the regions occupied by the solar wind and lism plasma consecutively. it has been shown previously that the v1 observation of a jump-like increase in the gcr flux during its final penetration into the lism could only occur if both pitch angle scattering and perpendicular diffusion were greatly reduced in the lism. we demonstrate the effect of the solar wind and lism turbulence, the properties of which are derived from 48 s averaged v1 measurements, on the hp instability. since v1 was crossing the regions magnetically connected either to the sun or to the lism, the observed gcr fluxes were substantially affected. we present numerical simulations illustrating such behavior. | heliopause instability and its relation to variations in the galactic cosmic ray flux at voyager 1 |
supernova remnants (snrs) have long been thought to be the main source of galactic cosmic rays up to pev energies, and many of them have been shown to accelerate particles to very high energies. but which of them do indeed accelerate a significant number of protons and nuclei? and up to which energies can they accelerate these particles? non-thermal photon emission, especially in the x-ray and gamma-ray range, is of crucial help in answering these questions. this presentation will focus on multi-wavelength observations of the cygnus region, a star-forming region including the gamma cygni supernova remnant, a middle-aged snr in the cygnus region. we will use the vhe gamma-ray emission measured by the high-altitude water cherenkov (hawc) gamma-ray observatory as well as measurements from other instruments to obtain information about the underlying particle populations producing this emission. see https://www.hawc-observatory.org/collaboration/#acknowledgments. | the gamma cygni supernova remnant at the highest energies |
galaxy clusters are predicted to produce gamma-ray emission, through cosmic ray interaction and/or dark matter annihilation, potentially detectable by the fermi large area telescope (fermi-lat). specifically, cosmic ray interactions with the intra-cluster gas results in neutral pion decay, producing gamma-rays. as yet, this emission has not been detected using small samples of clusters. we present a new, independent stacking analysis of fermi-lat photon count maps using the 78 richest nearby clusters (z < 0.12) from the two micron all-sky survey (2mass) cluster catalog. our initial search yields non-detections of gamma-ray emission from galaxy clusters but we achieve the lowest upper limits on the photon flux to date. scaling to recent cosmic ray acceleration and gamma-ray emission models, we find that cosmic rays represent a negligible contribution to the intra-cluster energy density and gas pressure. furthermore, either merger shocks must have lower mach numbers than inferred from radio emission, so < 2 - 4, or significantly less than 50% of the baryon mass has been processed through such shocks, and thus, the majority of baryons should be assembled through minor mergers or through cold accretion. | new limits on gamma-ray emission from galaxy clusters |
voyager 1 continues to observe time-varying enhancements and reductions in galactic cosmic-ray protons related to solar-induced transient events in the very local interstellar medium. the intensity reductions are characterized by a depletion of particles with pitch angles near 90-deg, while other directions remain generally uniform. from 2012 to 2017, voyager 1 observed three large-scale anisotropy intervals lasting from 100 to 630 days, measured by both the low energy charged particle instrument in its > 211 mev proton channel and by the cosmic ray subsystem in its omnidirectional (>20 mev) and bi-directional (>70 mev) proton rates. an unexpected finding is that while protons show clear evidence of the pitch angle anisotropy in these intervals, electrons do not. if the physical mechanism responsible for the anisotropy is species-independent, equivalent or larger count rate reductions would be expected in the cosmic ray subsystem's highest-energy unidirectional cosmic-ray electron rates (~18 to ~70 mev and ~5 to ~105 mev). however, these reductions appear negligible compared to protons, indicating that additional processes must be at work. in this study, we analyze the electron observations in detail and examine how they yield further insights into the cosmic-ray anisotropies and physical processes that govern them in the very local interstellar medium. | voyager 1 galactic cosmic-ray anisotropies: electron observations in the very local interstellar medium |
in about eight years of data taking, the large area telescope (lat) onboard the fermi satellite proved to be an excellent instrument to detect and observe supernova remnants (snrs) in the γ-ray energy band, from less than one hundred mev to a few hundred gev. this energy range is crucial to provide information on the physical processes occurring at the source, which involve both accelerated leptons and hadrons. the understanding of these processes is essential in the study of the mechanisms responsible for the primary cosmic ray acceleration. we present the latest results from observations of galactic snrs with the fermi lat, highlighting how the environment in which the snr is expanding affects the interpretation of its γ-ray emission. | fermi-lat observations of supernova remnants |
this lecture reviews recent investigations of the dynamical effects of cosmic rays (crs) in the interstellar medium of disk galaxies. we focus on the role of crs for generation of galactic magnetic fields as well as galactic winds. recent simulation models of magnetised interstellar medium, including the cr gas described by the diffusion-advection equation, indicate that cosmic rays accelerated in supernova remnants play a significant role as drivers of magnetic field amplification in galaxies. it has been demonstrated that weak dipolar magnetic fields supplied on small sn-remnant scales can be amplified exponentially, by the cr-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic-scales. the resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals a so called x-shaped structure in the edge-on view. those x-shaped structures in synchrotron radio maps result from the advection of disk magnetic fields by galactic winds. driven by the additional pressure gradient of the cr relativistic fluid, the wind speed can exceed the escape velocity of the galaxy. the global mass loading, i.e. the ratio of the mass of gas leaving the galactic disk in the cr-driven wind to the star formation rate, becomes of order unity. these winds help in explaining the low efficiencies for the conversion of gas into stars in galaxies, as well as the early enrichment of the intergalactic medium with metals. | galactic magnetic fields, cosmic rays and winds |
we present energetic particle measurements made at voyager 2 (helioradius 119 au, lat s32°, long 218°) in the heliosheath and at voyager 1 (helioradius 144 au, lat n35°, long 175°) in the local interstellar medium. data are from the lecp instruments on the two spacecraft during mainly the 2017-18 period. voyager 2 is now 35 au beyond its termination shock crossing (at 84 au in august 2007), indicating a heliosheath at voyager 2 at least 7-8 au wider than that (28 au) traversed by voyager 1. this is not surprising, since voyager 1 penetrated the heliosheath near the heliosphere's nose, while voyager 2 is doing so more toward its flank, i.e., at a longitude tailward from nose by about 45° (see dialynas et al., this session, for discussion of heliosheath thickness and the voyagers). at voyager 2 during 2015-18, intensities of heliosheath electrons >20 kev and low-energy ions >30 kev remain elevated, with the latter showing broad transient variations, with intensities a factor ≈5 or more above those measured during the 2013 intensity minimum. pressure in the low-energy ions during 2015-18 is (1.2 ± 0.2) × 10-13 dyne cm-2, comparable to high levels measured in the heliosheath at voyager 2 during 2009 through 2011. data taken through mid-2018 show no signs that voyager 2 has, or very soon will, cross the heliopause, particularly when compared to data from voyager 1 taken prior to and during its heliopause crossing (at 122 au in august 2012). voyager 1 is now about 22 au upstream of where it crossed the heliopause nose. intensities of low-energy ions and electrons and of anomalous cosmic rays remain at background levels. angular distributions of galactic cosmic ray protons >211 mev continue to depart from isotropy, showing broad (0.3-0.8 year) episodes of intensity depletions of protons gyrating nearly perpendicular to the magnetic field. data taken during august 2017 through early february 2018 show small, irregular departures from isotropy. thereafter, the anisotropy increases steadily, but remains relatively small, reaching an amplitude ≈3% by mid-2018. these data are relevant to plasma oscillation events measured by the voyager 1 plasma wave (pws) instrument during august 2017 and early june 2018 (see gurnett et al., this session, for discussion of these pws data). | recent energetic particle activity at voyagers 1 and 2 |
measurements of the growth of cosmic structure from galaxy cluster surveys are one of the most powerful and promising cosmological probes currently available. while the fundamental observation is the number of clusters detected as a function of redshift with a given survey observable (e.g. x-ray luminosity, sunyaev-zel'dovich flux, optical richness), these studies benefit significantly from follow-up data, which is used to calibrate the scaling relation between the survey observable and cluster mass. the best additional information of this type comes in two forms: x-ray measurements of gas mass and temperature, used to precisely determine the relative masses of clusters; and weak gravitational lensing data, used to accurately set the absolute mass scale of the cluster survey. both the relative and absolute mass information is critical to extracting tight constraints on dark energy from these data. equally important is that the analysis incorporate this auxiliary information in an internally consistent way, which is necessary to fully account for selection biases. the planck survey has provided a catalog of massive clusters, spanning the whole sky and extending to high redshifts, detected through the sunyaev-zel'dovich (sz) effect. while the cluster cosmology analyses published by the planck team incorporate information on absolute and relative cluster masses, they do so in a relatively crude way, by adopting priors from external work on the parameters of the mean mass-observable scaling relation, rather than using x-ray and weak lensing measurements for individual clusters in the survey directly. this simple approach does not allow selection effects to be fully modeled and thus accounted for, nor does it optimally make use of the available mass information. we propose to independently re-analyze the planck cluster sample, obtaining new and improved cosmological constraints. to accomplish this, we will modify the analysis code previously developed and used by the proposing team to analyze rosat all-sky survey clusters to the case of planck sz selection. we will derive x-ray gas masses and temperatures from all available chandra and xmm-newton data for planck-selected clusters, incorporating this relative mass information self-consistently into the cosmology analysis. finally, working with the dark energy survey (des) team, we will incorporate weak lensing data from des, which will provide the most direct, accurate and precise absolute mass calibration yet applied to the planck catalog. a self-consistent analysis of the planck clusters that incorporates all these additional data will result in tighter and more robust constraints on dark energy parameters, as well as the cosmic matter density, the amplitude of the power spectrum, and (in combination with the primary cmb) neutrino masses. the proposed program addresses key issues in fundamental physics and cosmology, most pertinently the cause of the accelerating expansion of the universe. | optimized cluster cosmology with the planck satellite |
star-forming galaxies are the first extragalactic sources whose total emission, or at least a large amount of it, comes from the cosmic rays interactions accelerated by shock fronts in a young stellar population environment but not from the active galactic nuclei. a strong evidence of this fact is the quasi-linear correlation between the -ray luminosity of these galaxies and different indicators of their star formation rate. in this work, we report a detailed analysis of this correlation, by quantifying its nonlinearity in the different energy bands provided by the fermi catalog. we discarded the linearity with a high level of confidence and we observed possibles variation with the energy. these results raise the question of the origin of the correlation, which answer required the development of theoretical models that describe the cosmic rays production inside these galaxies and the -ray emission due to the cosmic rays interacting with their matter and radiation fields. | galaxias con formación estelar activa como emisores de radiación gamma |
galactic cosmic rays are observed at pev energies, so at least a few sources that accelerate to these energies are expected to exist. however, only one such source has been identified: the galactic center. since one of the signatures of a pevatron is a hadronic, hard spectrum that extends without any apparent spectral cutoff, high-energy (> 50 tev) gamma-ray observations are important in identifying and studying pevatron candidates. the high altitude water cherenkov (hawc) observatory, located at 4100 m in puebla, mexico, has sensitivity to gamma rays at these previously largely unexplored energies. with an instantaneous field of view of 2sr and a duty cycle > 95 %, it is well suited to performing all-sky surveys. i will discuss high-energy sources seen in the galactic plane in the first 30 months of data from hawc and discuss which ones may be identified as pevatron candidates. i will also briefly discuss the energy estimation method used by hawc. | pevatron candidates in the first 30 months of hawc data |
voyager 1 (v-1) crossed the heliopause in 2012 august, gathering measurements of particle flux as a function of time. with this data, heliophysicists have observed anisotropy in the flux of galactic cosmic rays (gcrs); following the st. patrick solar event in 2013 march, they calculated small increases in the flux of higher-energy gcrs as well as linear depletion of gcr flux for particles with energies above approximately 200 mev as the particles approached perpendicular pitch angles. given these observations, the motivation for studying this anisotropy is to attempt to explain the lack of gyrating particles outside the heliopause with pitch angles approximately perpendicular to the magnetic field in relation to streaming particles with pitch angles approximately parallel to the magnetic field. in this project, we adapt existing code in order to create a model of the outer surface of the heliopause superimposed with the calculated trajectory of a gcr with respect to a given starting point in the model. the model predicts a magnetic trap in close proximity to the heliopause. though magnetic traps near the heliopause have been predicted before, there is no observational verification of their existence. not only will our model help future scientists study the observed anisotropy, but it may be useful for future exploration of questions regarding charged particle behavior in magnetic traps with different geometries. | a study of cosmic rays around the surface of the heliopause |
post-pericenter mergers of galaxy clusters may provide a unique window into the behavior of dark matter by acting as "dark matter colliders." mergers may also play a role in the evolution of cluster member galaxies and other astrophysical processes such as cosmic ray acceleration. to quantify these connections, we need reliable estimates of the basic dynamics of each observed merger: the time since pericenter, the maximum relative speed of the merging subclusters, pericenter distance, the merger phase (outbound vs returning for second pericenter), and the viewing angle (which is critical for determining the 3-d velocity and separation today, given that we measure only line-of-sight velocities and projected separations). we describe a new technique: finding analog systems in cosmological n-body simulations and extracting these parameters from the simulation. this eliminates many of the approximations used in the classic "timing argument" approach for estimating these parameters: assuming purely radial trajectories, assuming a specific mass profile or even point masses, neglecting substructure and surrounding large-scale structure, etc. we find analogs for 10 observed systems and show that we can distinguish between old and young systems, fast and slow, outbound and returning. | dynamics of merging galaxy clusters: what can simulated analogs tell us? |
we present evidence for jets from the nearby pulsar, b2224+65, based on three epochs of chandra x-ray observations, separated by 6 years from each other. this relatively slow rotating pulsar is well known for its extreme velocity of proper motion and associated "guitar"-shaped optical nebula in the opposite direction. the main jet-like x-ray-emitting feature is extremely narrow and significantly curved near the pulsar, but further away remains amazingly straight and is directed about 62 degrees away from the nebula, the x-ray emission of which is also detected. we find the consistent proper motions of the pulsar and the feature. the substructure of the feature varies among the epochs, while its spectrum is well characterized by a power law with a photon index of 1.2, is significantly harder than that of the pulsar, and remains remarkably consistent spatially and with the time. these results can be explained most intuitively by ballistic, relativistic, and probably magnetic field-dominated jets from the pulsar, similar to those from active galactic nuclei. indeed, we also detect the extended x-ray emission from the putative counter-jet, albeit at a much fainter level and a much smaller scale. the luminosity of these features is 7e30 erg/s in the chandra band, accounting for about 1% of the spin-down energy rate of the pulsar. because of the flat nonthermal x-ray spectrum, this fraction increases with the photon energy. the total power required to generate the jets is likely greater than 10% of the rate. much of the acceleration of the particles for the (synchrotron) x-ray emission to energies > 100 tev likely occurs within the jets, probably via magnetic field re-connection. this jet scenario and the underlying physics can be further tested by a carefully designed x-ray monitoring of the substructure and by a measurement of the radio polarization of the pulsar, as its spin axis is expected to be aligned with the jets. we speculate that the energetic jet ejection from b2224+65 may represent a common phenomenon of pulsars, young and old, and an important source of cosmic-rays. the understanding of the ejection could also shed lights into the nature of extragalactic jets. | energetic x-ray-emitting jets from the fast-moving middle-aged pulsar b2224+65 |
recent very high energy observations of the galactic centre region performed by h.e.s.s. revealed the presence of a powerful pevatron. this is the first of such objects detected, and its most plausible counterpart seems to be associated to sgr a*, the supermassive black hole in the centre of our galaxy. the implications of this discovery will be discussed, in particular in the context of the problem of the origin of galactic cosmic rays. | acceleration of particles up to pev energies at the galactic centre |
high-energy particles enter the solar atmosphere from galactic or solar sources, producing gamma-ray "albedo'' radiations. these emissions come from the quiet sun and from the large-scale corona, as well as from the vicinity of flares, and have been observed across a wide range of photon energies (mev to gev). the interaction of high-energy particles in the solar atmosphere depends essentially upon the joint variation of the magnetic field and the gas, and this has heretofore generally been characterized parametrically as p ~ balpha (zweibel & haber 1983), with p the gas pressure and b the magnitude of the magnetic field. we have checked this relationship with a bifrost 3d mhd model, approximating the particle transport as a guiding-center motion along "open'' (large-scale) fieldlines. we find alpha ~ 2.2 in the strongest (kg) fields in the simulation, but individual field structures have widely disparate relationships. the scatter corresponds to the strong meandering of the open-field flux tubes in the lower atmosphere and to their incessant dynamics. we discuss this and other aspects of the interactions of high-energy particles with the sun (the "solar størmer problem''). | cosmic rays across the rainbow bridge: particle interactions in a magnetized plasma atmosphere |
the supernova remnant (snr) w49b originated from a core-collapse supernova that occurred few thousands years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (mc). snr/mc associations are particularly interesting for probing the acceleration of hadrons in snrs and consequently the origin of galactic cosmic rays. the molecular material in the vicinity of the source acts as an efficient target material for accelerated particles. these interactions can lead to gamma-ray emission, making snr/mc a prime target for current gamma-ray observatories. w49b has been detected in gamma rays at high energies (he, 0.1-100 gev) and very high energies (vhe, >100 gev) with the fermi large area telescope (fermi-lat) and the high energy stereoscopic system (h.e.s.s.), respectively. the latest results obtained on w49b with these instruments will be presented. in particular, the spectrum shows a break at low energies, similar to previous observations by the fermi-lat in other snrs and interpreted as the signature of pion-decay gamma-ray emission. the implications of these results on the population of particles at the origin of the gamma-ray emission will be discussed. | observation of the w49b supernova remnant with fermi-lat and h.e.s.s. |
the signatures of laser wakefields have become increasingly important in recent years due to the invention of a novel laser compression technique that may enable the creation of single cycle x-ray pulses. this x-ray driver may be able to utilize solid density targets to create acceleration gradients of up to tev/cm. on the other hand, laser wakefield acceleration (lwfa) has been identified as a potential mechanism for the generation of extreme high energy cosmic rays (ehecr) in active galactic nuclei (agn). though these disparate density regimes may include different physics, by investigating scalings of the ratio ncr/ne we are able to survey a wide range of parameters to gain insight into particle acceleration and photon emission properties. the scaling of electron acceleration and photon radiation from wakefields as a function of the parameter ncr/ne has been studied. further, acceleration gradient as well as other scalings were investigated in solid density channels and compared to gas plasma. funded in part by the norman rostoker fund. | laser wakefield signatures: from gas plasma to nanomaterials |
i begin this study by presenting an overview of the theory of magnetohydrodynamics and the necessary conditions to justify the fluid treatment of a plasma. upon establishing the fluid description of a plasma we move on to a discussion of magnetohydrodynamics in both the ideal and hall regimes. this framework is then extended to include multiple plasmas in order to consider two problems of interest in the field of theoretical space physics. the first is a study on the evolution of a partially ionized plasma, a topic with many applications in space physics. a multi-fluid approach is necessary in this case to account for the motions of an ion fluid, electron fluid and neutral atom fluid; all of which are coupled to one another by collisions and/or electromagnetic forces. the results of this study have direct application towards an open question concerning the cascade of kolmogorov-like turbulence in the interstellar plasma which we will discuss below. the second application of multi-fluid magnetohydrodynamics that we consider in this thesis concerns the amplification of magnetic field upstream of a collisionless, parallel shock. the relevant fluids here are the ions and electrons comprising the interstellar plasma and the galactic cosmic ray ions. previous works predict that the streaming of cosmic rays lead to an instability resulting in significant amplification of the interstellar magnetic field at supernova blastwaves. this prediction is routinely invoked to explain the acceleration of galactic cosmic rays up to energies of 1015 ev. i will examine this phenomenon in detail using the multi-fluid framework outlined below. the purpose of this work is to first confirm the existence of an instability using a purely fluid approach with no additional approximations. if confirmed, i will determine the necessary conditions for it to operate. | multi-fluid problems in magnetohydrodynamics with applications to astrophysical processes |
cosmic rays represent only about a billionth of the interstellar gas in galaxies by number, but their energy density is equivalent to that of the thermal gas, although virtually collisionless, they exchange energy and momentum with the thermal gas through their coupling to the interstellar magnetic field, thus playing a critical role in interstellar gas dynamics and energy balance. cosmic ray driven galactic outflows, or winds, are one of their most dramatic and consequential signatures. because cosmic rays are believed to be accelerated by stellar explosions, and removing gas in a wind reduces the rate of star formation, cosmic ray driven winds are considered a form of ``feedback''. i will discuss the physical basis for magnetically mediated cosmic ray - thermal gas coupling, which spans scales from astronomical units to thousands of light years, in galaxies of many types as they evolve over cosmic time. the university of wisconsin and the national science foundation. | maxwell prize: the basis for cosmic ray feedback: written on the wind |
in a growing number of galaxy clusters diffuse elongated radio sources have been found, so-called radio relics. these megaparsec relics are usually located in the low-density outskirts of merging clusters. the existence of these radio sources implies the presence of relativistic particles and magnetic fields in the intracluster medium. the idea is that these radio relics trace cluster merger shocks, where particles are accelerated to relativistic energies, causing them to emit synchrotron radiation observable at radio wavelengths. however, a problem is that cluster merger shocks should have low-mach numbers, for which particle acceleration is thought to be very inefficient. this is hard to reconcile with the observed synchrotron radiation. current x-ray observations lack the sensitivity to determine accurate shock properties, since these relics are located in the faint outskirts of clusters. observations with the x-ray surveyor will for the first time provide accurate measurements of the mach number of these shocks, both using the temperature and surface brightness. this will provide crucial information to determine the nature of the particle acceleration mechanism that operates this intracluster plasma. | probing the physics of particle acceleration in dilute cosmic plasmas |
the origin of cosmic rays remains a mystery, even over 100 years since their discovery. neutron stars (nss) are considered textbook cases of particle acceleration sites in our galaxy, but many unresolved numerical problems remain. searches for new acceleration sites are crucial for astrophysics. the magnetized white dwarfs (mwds) have the same kind of rotating magnetosphere as nss, and may be the source of up to 10% of galactic cosmic ray electrons. in the parallel session of the "white dwarf pulsars and rotating white dwarf theory", we focus on the current observational results on white dwarf pulsars, related theories of the radiation process both in white dwarfs and neutron stars, and the origin and rule of white dwarf pulsars, as well as surveying on the current theories of the internal structure and the equation of state of white dwarfs. | summary of the session, white dwarf pulsars and rotating white dwarf theory |
in recent years, the detection of star forming galaxies at gev and tev energies by fermi and cherenkov (h.e.s.s. y veritas) observatories, respectively, has opened a new era for the study of the cosmic-ray population of galaxies. the fermi survey is still small, so far just five galaxies outside the local group have been detected. given that there are more than one thousand of unidentified fermi sources, we propose to increase this sample by doing a cross-correlation search of the last fermi catalog with different galaxies catalogs. here we report our preliminary results, and discuss the contribution of our results to the picture of cosmic-ray production in these objects. | emisión de altas energías de galaxias con fomación estelar activa |
the grapes-3 experiment is a compact, high density extensive air shower (eas) array of ∼ 400 scintillator detectors operating in conjunction with a 560 m2 tracking muon telescope with a threshold of eμ > 1 gev. it is being operated in ooty, india since 1 january 2000. the implementation of precise corrections for the effects of the variation in the pressure, and temperature of the atmosphere has permitted the muon telescope to deliver an accurate estimate of the intensity of the galactic cosmic rays (gcrs) as a function of direction. the muon telescope has been successfully used to study acceleration of muons during large thunderstorm events. the discovery of the transient weakening of earth's magnetic field through the detection of a muon burst was undoubtedly the highlight of the grapes-3 experiment. at present the expansion of the muon telescope is ongoing to increase its area by 570 m2 to significantly enhance its capability. | a review of the recent results from the grapes-3 experiment |
the bulk of the dark matter in the galaxy is believed to have velocity of order several hundred km/s. however, it has recently been shown that cosmic ray collisions with dark matter may accelerate a small fraction of the galactic dark matter to much higher velocities. this boosted dark matter would transfer far more energy to target nuclei or electrons in a detector than it would if it were traveling at the typical dark matter speed in the galaxy. this has recently been used to place constraints on low-mass dark matter, to which direct detection experiments are usually blind because of their threshold energy. we explore various avenues to improve the sensitivity of these studies. this work of cvc and jfb is supported by nsf grant phy-1714479. | constraining dark matter with cosmic ray interactions |
we present the high altitude water cherenkov (hawc) observatory's first catalog of gamma-ray sources emitting at the highest energies (above 50 tev and 100 tev). hawc consists of an array of 300 water cherenkov detectors located in puebla, mexico and is well-suited to performing all-sky surveys due to its high duty cycle (>90%) and wide instantaneous field-of-view ( 2 sr). there are a total of seven sources in these catalogs: six in the galactic plane, as well as the crab nebula. these sources may have implications for the sources of galactic cosmic rays. since galactic crs have been observed up to pev energies, sources accelerating particles to these energies (``pevatrons'') are expected to exist. the corresponding gamma-ray spectrum would be hard and extend to the highest energies without any spectral break or cutoff. we will compute the spectrum of these seven highest-energy sources and explore whether any of them can be considered pevatron candidates. we will also consider the relevance of these highest-energy sources to probing violations of lorentz invariance. | the hawc observatory's first catalog of sources emitting above 50 tev and 100 tev |
constraints on galactic cosmic-ray origins from elemental composition measurements r.a. mewaldt1, w.r. binns2, e.r. christian3, a.c. cummings1, g.a. de nolfo3, m.h. israel2, k.a. lave2 r.a. leske1, e.c. stone1, t.t. von rosenvinge3, m.e. wiedenbeck41california institute of technology, pasadena, ca 91125 usa2washington university, st. louis, mo 63130 usa3nasa/goddard space flight center, greenbelt, md 20771 usa4jet propulsion laboratory, pasadena, california institute of technology, ca 91109 usawe present measurements of the abundances of ultra-heavy (z>29) cosmic rays made by the cris instrument on nasa's ace satellite. the data set corresponds to >7000 days of data collection beginning december 4, 1997 through january 10, 2018. the charge resolution shows essentially complete separation of charges in the z>28 range. we have detected more than 1100 events over the charge range of z=30-40. our measurements show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to a mix of massive star outflow and sn ejecta with normal interstellar material (ism), rather than with pure ism. in addition, the refractory and volatile elements have similar slopes and refractory elements are preferentially accelerated by a factor of ∼4. the measured abundances support a model in which cosmic-ray source material is a mix of material from massive star outflow and ejecta and normal ism. this research is supported by nasa under grant # nnx13ah66g. | constraints on galactic cosmic-ray origins from elemental composition measurements |
we report on variations in the intensities and angular distributions of energetic (>28 kev) ions and (>22 kev) electrons, and > 213 mev galactic cosmic ray protons, all measured during the passage of voyager 2 from the heliosheath into the local interstellar medium. intensity drops of low-energy heliosheath ions are consistent with the heliopause crossing occurring on or about 5 nov. (doy 309) of 2018, at a helioradius of about 119.0 au, heliographic latitude of -32 deg., and longitude of about 45 deg. from that of voyager 1, which is near the nose of the heliosphere. we compare these voyager 2 data with those taken during the voyager 1 heliopause crossing in aug. of 2012 at about 121.6 au. compared to the voyager 1 observations made during its heliosheath to interstellar medium transition, those at voyager 2 show lower levels of interstellar magnetic field and galactic cosmic ray intrusion into the pre-heliopause heliosheath, and longer decay times and markedly different pitch angle distributions of heliosheath suprathermal and anomalous cosmic ray ions that penetrate into the post-heliopause local interstellar medium. a notable similarity is that at both voyagers the intensities of ~ 50 kev heliosheath electrons began decreasing rapidly roughly an au prior the heliopause, dropping to background levels before the crossings. angular distributions of >213 mev galactic cosmic ray protons measured at voyager 2 in the heliosheath show a small and varying anisotropy within about 0.4 au of heliopause, but thereafter in the local interstellar medium distributions are more nearly isotropic. | voyager 2 measurements of energetic particles across the heliopause |
on december 8, 2012 the supertiger (super trans-iron galactic element recorder) instrument was launched from williams field, antarctica on a long-duration balloon flight that lasted 55 days and maintained a mean altitude of 125,000 feet. supertiger measured the relative abundances of galactic cosmic-ray (gcr) nuclei with high statistical precision and well resolved individual element peaks from $_{10}$ne to $_{40}$zr. supertiger also made exploratory measurements of the relative abundances up to $_{56}$ba. the supertiger data analysis reported in murphy et al. 2016 was performed prior to the antarctic recovery effort in 2015 and only included data transmitted during line-of-site periods and via satellite telemetry. the current analysis includes additional data saved to on-board solid-state drives that were retrieved during recovery. although the statistics are low for elements heavier than $_{40}$zr, we show relative abundances of charges z=41-56 with individual element resolution. extending the range of gcr relative abundance measurements past $_{40}$zr further tests the preferential acceleration of refractory over volatile elements and constrains the charge dependence seen in gcr acceleration for both refractory and volatile elements. the relative abundances of elements $_{40}$zr through $_{60}$nd are of particular interest because they are likely formed both by supernova explosions and binary neutron star mergers. a well resolved measurement of this charge range may constrain the contributions to the gcr composition from both these possible sources. this work was supported by nasa grant nnx15ac23g and 80nssc20k0405, the peggy and steve fossett foundation and the mcdonnell center for the space sciences. | supertiger abundances of galactic cosmic rays for the charge interval z=41-56 |
star formation proceeds inefficiently in galaxies for reasons that remain under debate. in the local ism it is known that the cosmic rays (crs) provide a significant fraction of total ism pressure and therefore contribute to hydrostatic balance. here we develop a model for the dynamical effect of crs, directly accelerated as a result of star formation itself, on the ism gas column. we determine the critical cr fluxes - and corresponding star formation rate surface densities - above which hydrostatic equilibrium within a given galaxy is precluded because crs drive the gas off in a wind or render it unstable. the locus of this cr stability curve patrols the high side of the observed distribution of galaxies in the kennicutt-schmidt parameter space of star formation rate versus gas surface density for normal spirals and dwarfs. we thus conclude that cr feed-back sets an ultimate limit to the star formation efficiency of most 'ordinary' galaxies. at the higher surface densities pertinent to star burst systems, however, pionic losses imply that crs are dynamically unimportant on global scales while, at the same time, guaranteeing that such galaxies are luminous gamma-ray sources. | cosmic ray feedback in star-formation and implications for gamma-ray emission from starbursts |
the intra-cluster medium (icm), the x-ray emitting hot plasmas associated with individual clusters of galaxies, is the most dominant form of all known cosmic baryons. confined by gravity in a hydrostatic manner, the icm is considered to be free from most of instabilities, except the radiative thermal instability on large scales. that is, by emitting x-rays, the icm at the center of each cluster will cool on the hubble time, and the consequent reduction in the central plasma pressure will drive a slow inward plasma flow, which will further enhance the central icm density and accelerate the cooling. this thermal instability, called "cooling flows", was apparently supported by many x-ray observations made before the early 1990s. however, improved x-ray instrumentations in the middle 1990's have observationally revealed that the predicted cooling flow is absent essentially in all clusters (makishima et a. 2001). therefore, the icm must be somehow heated against the radiative cooling. since then, the necessary heating mechanism has long been sought for. among several candidates, we have constructed a very promising scenario, that the icm is being heated as member galaxies of each cluster move through it with a transonic speed, and transfer, via various plasma interactions, a fraction of their dynamical energy to the icm. this mechanism is expected to heat the icm, and make the galaxies to gradually fall to the center of the gravitational potential. through extensive x-ray and optical observations of clusters at various redshifts from z=0 to z=1, we have discovered (gu et al. 2013, 2016) that the galaxies in typical clusters have actually been falling to the potential centers on a cosmological time scale, and the galaxies' energy loss through this process is sufficient to counter-balance the radiative cooling. the process is considered as one of the largest energy flows in the universe, after the large-scale structure was formed. in addition, this scenario can also explain many unanswered facts about the icm, including its uniform metallization, the two-temperature structure observed in the cluster core regions, the origin of so-called environmental effects working on galaxies, and the relatively mild icm turbulence as revealed by the hitomi mission (hitomi collaboration 2016). details of the galaxy vs. icm interaction are expected to provide interesting research subjects to modern plasma astrophysics. | how the hot plasmas in clusters of galaxies are thermally stabilized |
understanding the complete nature of galactic sources that accelerate cosmic rays up to $10^{15}$ ev energy (galactic pevatrons) is still an unsolved problem in high-energy astrophysics. although supernova remnants have long been considered as the best candidates for galactic pevatrons, a clear association of snrs with pevatrons needs further exploration. recently, the lhaaso collaboration published its first catalog of 90 very high energy (vhe) gamma-ray sources, and a few of them have no obvious counterparts at other wavelengths. here, we will present morphology and spectral analysis of one such unassociated source lhaaso j2108+5157 using veritas and hawc data. | veritas and hawc observations of unidentified source lhaaso j2108+5157 |
a well-known paradigm about the origin of galactic cosmic rays (crs) is that these high-energy particles are accelerated in the process of diffusive shock acceleration (dsa) at collisionless shocks (at least up to the so-called "knee"energy of $10^{15}$ ev). knowing the details of injection of electrons, protons and heavier nuclei into the dsa, their initial and the resulting spectrum, is extremely important in many "practical" applications of the cr astrophysics, e.g. in modelling of the gamma or synchrotron radio emission of astrophysical sources. in this contribution i we will give an overview of the dsa theory and the results of observations and kinetic particle-in-cell (pic) simulations that support the basic theoretical concepts. pic simulations of quasi-parallel collisionless shocks show that thermal and supra-thermal proton distribution functions at the shock can be represented by a single quasi-thermal distribution - the $\kappa$-distribution that is commonly observed in out-of-equilibrium space plasmas. farther downstream, index $\kappa$ increases and the low-energy spectrum tends to maxwell distribution. on the other hand, higher-energy particles continue through the acceleration process and the non-thermal particle spectrum takes a characteristic power-law form predicted by the linear dsa theory. in the end, i will show what modification of the spectra is expected in the non-linear dsa, when cr back-reaction to the shock is taken into account. | diffusive shock acceleration of cosmic rays - quasi-thermal and non-thermal particle distributions |
star-forming galaxies (sfgs) have been established as an important source population in the extra-galactic $\gamma$-ray background (egb). their intensive star-formation creates an abundance of environments able to accelerate particles, and these build-up a rich sea of cosmic rays (crs). above gev energies, cr protons can undergo hadronic interactions with their environment to produce $\gamma$-rays. sfgs can operate as cr proton "calorimeters", where a large fraction of the cr energy is converted to $\gamma$-rays. however, crs also deposit energy and momentum to modify the thermal and hydrodynamic conditions of the gas in sfgs, and can become a powerful driver of outflows. such outflows are ubiquitous among some types of sfgs, and have the potential to severely degrade their cr proton calorimetry. this diminishes their contribution to the egb. in this work, we adopt a self-consistent treatment of particle transport in outflows from sfgs to assess their calorimetry. we use 1d numerical treatments of galactic outflows driven by crs and thermal gas pressure, accounting for the dynamical effects and interactions of crs. we show the impact cr-driven flows have on the relative contribution of sfg populations to the egb, and investigate the properties of sfgs that contribute most strongly. | cosmic ray calorimetry in star-forming galaxy populations and implications for their contribution to the extra-galactic $\\gamma$-ray background |
anisotropic diffusion is imperative in understanding cosmic ray diffusion across the galaxy, the heliosphere, and the interplay of cosmic rays with the galactic magnetic field. this diffusion term contributes to the highly stiff nature of the cosmic ray transport equation. to conduct numerical simulations of time-dependent cosmic ray transport, implicit integrators (namely, crank-nicolson (cn)) have been traditionally favoured over the cfl-bound explicit integrators in order to be able to take large step sizes. we propose exponential methods to treat the linear anisotropc diffusion equation in the presence of advection and time-independent and time-dependent sources. these methods allow us to take even larger step sizes that can substantially speed-up the simulations whilst generating highly accurate solutions. in or subsequent work, we will use these exponential solvers in the picard code to study anisotropic cosmic ray diffusion and we will consider additional physical processes such as continuous momentum losses and reacceleration. | efficient numerical methods for anisotropic diffusion of galactic cosmic rays |
organic features lead to two distinct types of class 0/i low-mass protostars: hot corino sources, and warm carbon-chain chemistry (wccc) sources. some observations suggest that the chemical variations between wccc sources and hot corino sources are associated with local environments, as well as the luminosity of protostars. we conducted gas-grain chemical simulation in collapsing protostellar cores, and found that the fiducial model predicts abundant carbon-chain molecules and coms, and reproduces wccc and hot corino chemistry in the hybrid source l483. by changing values of some physical parameters, including the visual extinction of ambient clouds ($a_{\rm v}^{\rm amb}$), the cosmic-ray ionization rate ($\zeta$), the maximum temperature during the warm-up phase ($t_{\rm max}$), and the contraction timescale of protostars ($t_{\rm cont}$), we found that uv photons and cosmic rays can boost wccc features by accelerating the dissociation of co and ch$_4$ molecules. on the other hand, uv photons can weaken the hot corino chemistry by photodissociation reactions, while the dependence of hot corino chemistry on cosmic rays is relatively complex. the $t_{\rm max}$ does not affect wccc features, while it can influence hot corino chemistry by changing the effective duration of two-body surface reactions for most coms. the long $t_{\rm cont}$ can boost wccc and hot corino chemistry, by prolonging the effective duration of wccc reactions in the gas phase and surface formation reactions for coms, respectively. subsequently, we ran a model with different physical parameters to reproduce scarce coms in prototypical wccc sources. the scarcity of coms in prototypical wccc sources can be explained by insufficient dust temperature in the inner envelopes to activate hot corino chemistry. meanwhile, the high $\zeta$ and the long $t_{\rm cont}$ favors the explanation for scarce coms in these sources. | chemical differences among collapsing low-mass protostellar cores |
galaxy clusters are the largest and most massive gravitationally bound structures known in the universe. cosmic-ray (cr) hadrons accelerated at structure formation shocks and injected by galaxies, are confined in galaxy clusters where they accumulate for cosmological times. the presence of diffuse synchrotron radio emission in several clusters proves the existence of high-energy electrons, and magnetic fields. however, a direct proof of cr proton acceleration is missing. the presence of cr protons can be probe through the diffuse gamma-ray emission induced by their hadronic interaction with the intra-cluster medium (icm). the perseus cluster, a nearby cool-core cluster, has been identified to be among the best candidates to detect such emission. we present here the results of a very deep observation of the perseus cluster with the magic telescopes, accumulating about 250 hours of data from 2009 to 2014. no evidence of large-scale very-high-energy gamma-ray emission from cr-icm interactions has been detected. the derived flux upper limits in the tev regime allow us to put stringent constraints on the physics of cluster crs, in particular on the cr-to-thermal pressure, the cr acceleration efficiency at formation shocks and the magnetic field of the central cluster region. | constraints on the cosmic ray cluster physics from a very deep observation of the perseus cluster with magic |
the local interstellar energy spectra of galactic cosmic rays down to a few mev/nucleon were directly measured in the experiment on the board of the voyager 1 spacecraft. we suggest interpretation of these data based on our models of cosmic ray acceleration in supernova remnants and the diffusion in galactic wind where diffusion coefficient is determined by the cosmic ray streaming instability. the dependence of wind velocity on distance above the galactic disk is determined. | interpretation of voyager 1 data on low energy cosmic rays in galactic wind model |
supernova remnants (snrs) are nowadays considered as the favoured sources of galactic cosmic rays. when accelerated protons encounter the interstellar material they produce neutral pions, which in turn decay into gamma rays. the observation of the g-ray emission from snrs therefore is a compelling way to identificate and locate the acceleration sites of the protons. spatial extension of g-ray sources is an important characteristic for correctly associating their g emission with their counterparts at other wavelengths and for obtaining an unbiased model of their spectra. the purpose of the analyses performed in this thesis is the test of the new fermi pass 8 data for the study of the emission of extended sources. the paradigmatic example of w44, one of the brightest extended sources in the g-ray sky, was chosen as case of study. this thesis is structured in four chapters: chapter 1 provides an overview of the fermi-lat technical characteristics and of the process of selection of the data that are then available for the analysis. attention is focused on the new event types (based on the quality of the reconstructed energy and direction) that comes with the pass 8 release. chapter 2 describes the fermi science tools, the standard instrument for the data analysis in the fermi-lat collaboration. the steps followed in a standard likelihood analysis are also presented. chapter 3 resumes the literature on w44, pointing out the features of the spectral and spatial models used for describing its g-ray emission. chapter 4 finally presents the results obtained with pass 8 data analysis on w44 snr. | fermi-lat analysis of extended supernova remnants with the new pass 8 data |
we propose that the recently observed diffuse neutrinos by icecube with energies above 1 pev might have originated from sagittarius $\mathrm{a}^{\star}$ located in the galactic disk. this implies that the astrophysical settings of sagittarius $\mathrm{a}^{\star}$ need to accelerate hadronic cosmic rays to energies of $\sim 100$ pev or more. then, the hadronic emission scenario argues that this galactic neutrino source is also a pev gamma-ray source. recent observation of galactic diffuse pev gamma-rays with energies $\sim 1$ pev by large high altitude air shower observatory has also advocated this conjecture. in the present paper, we demonstrate that if protons are accelerated to energies of $\sim 100$ pev or more as reported by osmanov {\it et al.} (astrophys. j. {\bf 835} 164:2017) in sagittarius $\mathrm{a}^{\star}$ environment, then they might generate pev neutrinos and gamma rays through cosmic rays-gas/interstellar matter ({\it e.g.} $pp$) interactions. we estimate theoretically the diffuse neutrino flux due to back-to-back charged pion decays and the accompanying gamma-ray flux from neutral pion decays. these results suggest that a fraction ($\simeq 1\%$) of the pev diffuse neutrino flux observed by icecube can be explained by the neutrino emission from sagittarius $\mathrm{a}^{\star}$. upcoming icecube gen2 and cherenkov telescope array could be able to test our scenario for pev neutrino and gamma-ray emissions from the only known galactic pevatron sagittarius $\mathrm{a}^{\star}$ with cr energies more than $100$ pev. | sagittarius $\\mathrm{a}^{\\star}$ as a plausible source candidate for pev neutrinos |
galaxy clusters represent the last step of the formation of large-scale structures in the universe. they are both useful cosmological probes and unique astrophysical laboratories. the clusters grow by accretion of surrounding structures and from the merging of subclusters, in very energetic events, eventually forming a diffuse gas phase made of a hot thermal component, but also leading to particle acceleration up to very high energies. one of the key science projects of the cherenkov telescope array (cta), the next generation array of imaging atmospheric cherenkov telescopes, being built in la palma (spain) and paranal (chile), consists of the first unambiguous measurement of the diffuse gamma-ray emission associated with the interaction between the cluster cosmic rays protons and the thermal gas. prospects for probing such a signal using cta are discussed and we highlight what can be learned about cluster physics from such observations. | search for diffuse gamma-ray emission from galaxy clusters with the cherenkov telescope array |
detailed modelling of the evolution of neutral hydrogen in the intergalactic medium during the epoch of reionization, $5 \leq z \leq 20$, is critical in interpreting the cosmological signals from current and upcoming 21-cm experiments such as low-frequency array (lofar) and the square kilometre array (ska). numerical radiative transfer codes offer the most physically motivated approach for simulating the reionization process. however, they are computationally expensive as they must encompass enormous cosmological volumes while accurately capturing astrophysical processes occurring at small scales ($\lesssim\rm mpc$). here, we present pyc$^2$ray, an updated version of the massively parallel ray-tracing and chemistry code, c$^2$ray, which has been extensively employed in reionization simulations. the most time-consuming part of the code is calculating the hydrogen column density along the path of the ionizing photons. here, we present the accelerated short-characteristics octhaedral raytracing (asora) method, a ray-tracing algorithm specifically designed to run on graphical processing units (gpus). we include a modern python interface, allowing easy and customized use of the code without compromising computational efficiency. we test pyc$^2$ray on a series of standard ray-tracing tests and a complete cosmological simulation with volume size $(349\,\rm mpc)^3$, mesh size of $250^3$ and approximately $10^6$ sources. compared to the original code, pyc$^2$ray achieves the same results with negligible fractional differences, $\sim 10^{-5}$, and a speedup factor of two orders of magnitude. benchmark analysis shows that asora takes a few nanoseconds per source per voxel and scales linearly for an increasing number of sources and voxels within the ray-tracing radii. | pyc$^2$ray: a flexible and gpu-accelerated radiative transfer framework for simulating the cosmic epoch of reionization |
the knee of cosmic ray spectra reflects the maximum energy accelerated by galactic cosmic ray sources or the limit to the ability of galaxy to bind cosmic rays. the measuring of individual energy spectra is a crucial tool to ascertain the origin of the knee. the extensive air shower of cosmic rays in the knee energy region is simulated via corsika software. the energy resolution for different secondary components and primary nuclei identification capability are studied. the energy reconstruction by using electromagnetic particles in the energy around knee is better than by using other secondary particles. the resolution is 10-19 percent for proton, and 4-8 percent for iron. for the case of primary nuclei identification capability, the discriminability of density of muons is best both at low (around 100 tev) and high (around 10 pev) energy, the discriminability of the shape of lateral distribution of electron and gamma-rays are good at low energy and the discriminability of density of neutrons is good at high energy. the differences between the lateral distributions of secondary particles simulated by epos-lhc and qgsjet-ii-04 hadronic model are also studied. the results in this work can provide important information for selecting the secondary components and detector type during energy reconstruction and identifying the primary nuclei of cosmic rays in the knee region. | properties of secondary components in extensive air shower of cosmic rays in knee energy region |
a new parametrization of the phenomenological hubble parameter is proposed to explore the issue of the cosmological landscape. the constraints on model parameters are derived through the markov chain monte carlo (mcmc) method by employing a comprehensive union of datasets such as 34 data points from cosmic chronometers (cc), 42 points from baryonic acoustic oscillations (bao), a recently updated set of 1701 pantheon$^+$ (p22) data points derived from type ia supernovae (sneia), and 162 data points from gamma-ray bursts (grb). the kinematic behavior of the models is also investigated by encompassing the transition from deceleration to acceleration and the evolution of the jerk parameter. from the analysis of the parametric models, it is strongly indicated that the universe is currently undergoing an accelerated phase. furthermore, the models are compared by using the akaike information criterion (aic) and bayesian information criterion (bic), so that a comparative assessment of model performance can be available. | governing accelerating universe via newly reconstructed hubble parameter by employing empirical data simulations |
kepler's supernova remnant (snr) which is produced by the most recent naked-eye supernova in our galaxy is one of the best studied snrs, but its gamma-ray detection has eluded us so far. observations with modern imaging atmospheric cherenkov telescopes (iact) have enlarged the knowledge about nearby snrs with ages younger than 500 years by establishing cassiopeia a and tycho's snrs as very high energy (vhe) gamma-ray sources and setting a lower limit on the distance to kepler's snr. this snr is significantly more distant than the other two and expected to be one of the faintest gamma-ray sources within reach of the iact arrays of this generation. we report strong evidence for a vhe signal from kepler's snr based on deep observations of the high energy stereoscopic system (h.e.s.s.) with an exposure of 152 hours, including 122 hours accumulated in 2017-2020. we further discuss implications of this result for cosmic-ray acceleration in young snrs. | deep observations of kepler's snr with h.e.s.s. |
although the existence and importance of magnetic fields and cosmic rays are widely recognized in the current universe, their origins in the early universe are not unrevealed yet. motivated by the recent studies that suggest the acceleration of cosmic rays in the supernova remnants of first stars, we propose a new generation mechanism of magnetic fields in the early universe induced by first cosmic rays. in this mechanism, magnetic fields are generated by the biermann battery effect driven by streaming cosmic rays. as the joule heating is induced by streaming of cosmic rays, if cosmic rays stream inhomogeneously, the plasma is heated inhomogeneously and temperature and pressure inhomogeneities are produced. since this pressure inhomogeneity does not necessarily coincide with that of electron density, baroclinicity ∇ n_e × ∇ p_e arises, and magnetic fields are generated by the biermann battery effect. we estimate the field strength achieved by this mechanism for a typical environment in the early universe and show that it is sufficient for the seed field to be amplified by the subsequent dynamo mechanisms up to the currently observed field strength in galaxies. we also compare it with other previously proposed mechanisms and clarify which of these becomes dominant for different environments. | a new magnetic field generation mechanism induced by streaming cosmic rays |
the galactic center excess (gce), one of the most remarkable discoveries by fermi-lat, has prompted extensive exploration over the past decade, often attributed to dark matter or millisecond pulsars. this work proposes a novel interpretation on the origin of the gce, focusing on the observed spectral shape. protons are accelerated at the galactic center and collide with the neutron cluster on the surface of the nonrotating neutron stars. due to the gluon condensation in nucleons, these collisions produce a large number of mesons, which have reached to the saturation state and subsequently generate the broken power law in the gamma ray spectra. we explained the spectral shape of gce using the gluon condensation and an assumption of existing the nonrotating neutron stars at the galactic center. this example of the gluon condensation mechanism not only expands the applications of the hadronic scenario in the cosmic gamma ray spectra but also provides a new evidence of the gluon condensation. | gluon condensation: from nucleon to galactic center |
supernova remnants (snrs) have been considered as the dominant contributors to galactic cosmic rays (crs). however, the relation between high-energy particles accelerated in snrs and cosmic rays observed at the earth remains obscure. we fit the spectral energy distributions of 35 snrs with a simple one-zone emission model and find some correlations of model parameters which can uncover the evolution of high-energy particle distribution in snrs. we also comment on the implications of these results on the snr origin of galactic cosmic rays. | evolution of high-energy particle distribution in supernova remnants |
we present the discovery of ringlike diffuse radio emission structures in the peripheral regions of the bullet cluster 1e 0657$-$55.8. ring formations are spanning between 1--3 mpc away from the center of the cluster, significantly further away from the two already reported relics. integrated fluxes of four of the sub-regions in the inner `ring' from 4.5 to 10 ghz have also been reported. to understand the possible origin of these structures, here we present a maiden attempt of numerical modelling of a 3d and realistic `bullet' like event in a full cosmological ($\lambda$cdm) environment with n-body plus hydrodynamics code. we report a simulated `bullet' found inside a (128 mpc)$^3$ volume simulation with a speed of 2700 km s$^{-1}$, creating a high supersonic bow shock of mach $m=3.5$ and a clear evidence of temporal separation of dark matter and baryons, assuring no challenge to $\lambda$cdm cosmology from the bullet event as of now. we are also able to unveil the physics behind the formation of these observed multiple shock structures. modelled radio emissions in our simulation support a complex combination of merger-associated processes that accelerates and re-accelerates fossil and cosmic-ray electrons. with a time evolution study and the computed radio emissions, we have shown that the ring like formation around the bullet is originated due to the interaction of the strong merger shocks with the accretion shocks at the periphery. the multiple shock structures observed are possibly originated from multiple mergers that have taken place at different times and much before the bullet event. | `rings' of diffuse radio emission surrounding the bullet cluster |
recent observations of the diffuse galactic gamma-ray emission by the fermi-lat satellite have shown significant deviations from models which assume the same diffusion properties for cosmic rays (cr) throughout the galaxy. we explore the possibility that a fraction of this diffuse galactic emission could be due to hadronic interactions of crs self-confined in the region around their sources. in fact, freshly accelerated crs that diffuse away from the acceleration region can trigger the streaming instability able to amplify magnetic disturbance and to reduce the particle diffusion. when this happen, crs are trapped in the near source region for a time longer than expected and an extended gamma-ray halo is produces around each source. here we calculate the contribution to the diffuse gamma-ray background due to the overlap along lines of sight of several of these extended halos. we find that if the density of neutrals is low, the halos can account for a substantial fraction of the diffuse emission observed by fermi-lat, depending on the orientation of the line of sight with respect to the direction of the galactic center. | contribution to diffuse gamma-ray emission coming from self-confined crs around their galactic sources |
we apply the ultrarelativistic generalized lorentzian quasi-equilibrium thermodynamic energy distribution to the energy spectrum of galactic cosmic ray fluxes. the inferred power law slopes contain a component which evolves with cosmic ray energy in steps of thirds, resembling the sequence of structure functions in fully developed kolmogorov turbulence. within the generalized thermodynamics the chemical potential can be estimated from the deviation of the fluxes at decreasing energy. both may throw some light on the cosmic ray acceleration mechanism to very high energies. | ultrarelativistic generalized lorentzian thermodynamics and the differential cosmic ray energy flux |
trace charge imbalances can explain puzzling cosmological observations such as the large `missing' fraction of electrons in cosmic rays and their contrast to the charge-neutral solar wind, the extreme energy sources that sustain pulsars, quasars, galactic jets and active galactic nuclei (agn), the origin and nature of `dark matter' galaxy haloes, and the apparent acceleration of the expansion of the universe. when there are $\sim \num{9e-19}$ amounts of excess $\ce{h3+}$ or $\ce{h-}$ within cold diffuse clouds of $\ce{h2}$, residual repulsive coulomb forces between these few unbalanced charges are comparable to the gravitational attractions between the many nucleons. thus, trace-charged dark matter is inert with respect to static electrogravitional self-attractions, but responds to electromagnetic fields and gravitational attractions with uncharged matter. trace charge is also the ionic catalyst that keeps dark matter in the state of unseen clouds of cold molecular hydrogen plus trace $\ce{h3+}$. once warm enough to partially ionize, bright matter preferentially expels its net charge to become nearly charge-neutral. planets surrounding stars become charge neutral as they bathe in a charge-neutral stellar wind. in contrast, around trace-charged agns, black holes, and pulsars,newly ionized protons along with a significant fraction of entrained dark matter are coulomb-expelled to relativistic velocities in polar jets. extrasolar cosmic rays generated by these would be strongly proton-dominated, as observed. initial trace charge imbalances could originate at the onset of the the big bang by segregation of an electron-rich shell to peripheral expanding matter of the universe. | cosmological implications of trace-charged dark matter |
studying gamma-ray emission by galactic objects is key to understanding the origins and acceleration mechanisms of galactic cosmic ray electrons and hadrons. the hawc observatory provides an unprecedented view of the gamma-ray sky at tev energies and is particularly suited for the study of galactic objects. however, the interpretation of the measured data poses several challenges. the high density of sources and source candidates can cause source confusion and make it harder to disentangle the origin of the emission. the relatively low angular resolution of hawc, compared to instruments in optical or radio wavelengths, can further cause the emission of neighboring sources to bleed into each other or even make them look like one extended source. on the other hand, with its wide field of view, hawc is uniquely suited for the study of extended sources. however, this requires the simultaneous modeling of both their morphology and emission spectrum. joint likelihood fits to data taken over a larger range of energies can help overcome these challenges and achieve the full potential of the hawc detector. in this presentation, we will discuss how systematic uncertainties related to joint likelihood fits can affect the measurements. | joint likelihood fits for the study of galactic objects with hawc |
despite centuries of rigorous theoretical and observational research, the origin and acceleration mechanism of galactic cosmic rays (gcrs) remain a mystery. in 1949, fermi proposed a diffusive shock acceleration model that includes a prominent mechanism for gcr acceleration. however, observational evidence, on the other hand, remains elusive. here, we provided the first apparent verification of gcr acceleration at 1 au using measurements from the cris instrument onboard the ace spacecraft. | observational validation of cosmic ray acceleration hypothesis |
cool outflows are now commonly observed in galaxies, but their physical origin and driving mechanism remain unclear. active galactic nucleus (agn) feedback can potentially accelerate cool galactic outflows via cosmic rays (cr) and radiation pressure on dust. here we investigate the relative importance of cr and radiation feedback in agns, and we analyse the physical conditions for outflow launching as a function of the black hole accretion flow mode. we assume crs from agn jet origin and consider the analogy with galactic x-ray binaries, whereby the jet is prominent at low accretion rates (hard state) and quenched at high accretion rates (soft state). we show that cr-driven outflows can be powered at low accretion rates and at large radii, whereas radiation pressure-driven outflows dominate at high accretion rates and small radii. thus the two agn feedback mechanisms - crs and radiation pressure on dust - may play complementary roles in driving cool outflows on galactic scales. the transition from radiation pressure-driven outflows at higher accretion rates to cr-driven outflows at lower accretion rates likely corresponds to a transition in the underlying accretion flow modes (from a radiatively efficient accretion disc to a radiatively inefficient jet-dominated flow) over cosmic time. | agn cool feedback and analogy with x-ray binaries: from radiation pressure to cosmic ray-driven outflows |
cosmic ray electron (cre) acceleration and cooling are important physical processes in astrophysics. we develop an approximative framework to treat cre physics in the parallel smoothed particle hydrodynamics code gadget-3. in our methodology, the cre spectrum of each fluid element is approximated by a single power-law distribution with spatially varying amplitude, upper cut-off, lower cut-off, and spectral index. we consider diffusive shock acceleration to be the source of injection, and oppositely the sinking processes is attributed to synchrotron radiation, inverse compton scatters, and coulomb scatters. the adiabatic gains and losses are also included. we show that our formalism produces the energy and pressure with an accuracy of $ > 90\%$ for a free cooling cre spectrum. both slope and intensity of the radio emission computed from the cre population given by our method in cosmological hydro-simulation coincide well with observations, and our results also show that relaxed clusters have lower fluxes. finally, we investigate several impacts of the cre processes on the cosmological hydro-simulation, we find that: (1) the pressure of the cre spectrum is very small and can be ignored in hydro-simulation, (2) the impacts of the cre processes on the gas phase-space state of hydro-simulation is up to $3\%$, (3) the cre processes induce a $5\%$ influence on the mass function in the mass range $10^{12} -10^{13} h^{-1} m_{\odot}$, (4) the gas temperature of massive galaxy cluster is influenced by the cre processes up to $\sim 10\%$. | modelling cosmic ray electron physics in cosmological smoothed particle hydrodynamics simulation |
recent measurements revealed the presence of several features in the cosmic ray spectrum. in particular, the proton and helium spectra exhibit a spectral hardening at $\approx$ 300 gv and a spectral steeping at $\approx$ 15 tv, followed by the well known knee-likefeature at $\approx$ 3 tv. the spectra of heavier nuclei also harden at $\approx$ 300 gv, while no claim can be currently done about the presence of the $\approx$ 15 tv softening, due to low statistics. in addition, the b/c ratio flattens at $\approx$ 1 tev/n. we present a novel scenario for cosmic ray sources and transport in the galaxy that may explain all of the observed spectral features. the proposed scenario is based mainly on two assumptions. first, in the galactic disk, where magnetic field lines are mainly oriented along the galactic plane, particle scattering is assumed to be very inefficient. therefore, the transport of cosmic rays from the disk to the halo is set by the magnetic field line random walk induced by large scale turbulence. second, we propose that the spectral steepening at $\approx$ 15 tv is related to the typical maximum rigidity reached in the acceleration of cosmic rays by the majority of supernova remnants, while we assume that only a fraction of sources, contributing to $\approx$ 10-20% of the cosmic ray population, can accelerate particles up to $\sim$ pv. we show that, within this framework, it is possible to reproduce the proton and helium spectra from gv to multi-pv, and the p/he ratio, the spectra of cosmic ray from lithium to iron, the $\bar{p}$ flux and the $\bar{p}$/p ratio and the abundance ratios b/c, b/o, c/o, be/c, be/o, be/b. we also discuss the $^{10}$be/ $ ^9$be ratio in view of the recent ams02 preliminary measurements. | on the origin of the spectral features observed in the cosmic ray spectrum |
clusters of galaxies are the most massive virialized structures in the universe. the microphysical properties of the intracluster plasma can affect dynamical processes over an enormous range: from the feedback of active galactic nuclei to shock acceleration in merging clusters. all the major cosmological simulations assume the astrophysical plasma to be inviscid. it is critical to measure microphysical properties of the intracluster plasma to truly understand the physical processes that drive the cosmic evolution. tremendous progress has been made by comparing high spatial resolution x-ray images to (magneto-)hydrodynamic simulations. future x-ray missions with calorimeters promise a direct measurement of transport coefficients and gas motions, providing a more realistic benchmark for cosmological simulations. | astro2020 science white paper: a unification of the micro and macro physics in the intracluster medium of nearby clusters |
supernova remnants (snrs) that exhibit x-ray spectra dominated by synchrotron radiation are crucial laboratories for the study of cosmic-ray acceleration by this class of sources. however, despite the discovery of synchrotron x-ray emission from the archetypal source sn 1006 over two decades ago, the number of galactic snrs of this class remains small. combining x-ray observations of candidate members of this class with long wavelength radio observations holds the promise of applying robust constraints on fits to extracted x-ray spectra. such fits can provide estimates of the maximum energies of cosmic-ray electrons accelerated by these sources and thus investigate the association between snrs and the knee energy of the cosmic-ray spectrum. in this presentation, we describe new l-band (1500 mhz) and p-band (300 mhz) observations made with the vla of four candidate and known galactic snrs, g22.0+0.0, g23.5+0.1, g28.6-0.1, and g32.4+0.1, that are believed to exhibit x-ray spectra that are dominated by synchrotron emission. we have extracted x-ray spectra for these sources using archival observations made by chandra, suzaku, and xmm-newton, and applied synchrotron models to these spectra using constraints; namely, derived flux densities and spectral indices obtained from the l-band and p-band observations. we have also analyzed the long wavelength radio properties of known snrs, specifically 3c 391, kes 69, and w41, that were serendipitously detected by these radio observations. initial results will be presented and discussed. | l-band and p-band observations of galactic supernova remnants with synchrotron x-ray-dominated spectra |
the galactic supernova remnant (snr) g28.6-0.1 belongs to the remarkable class of snrs that exhibit x-ray spectra that are dominated by synchrotron radiation emitted by extremely energetic accelerated cosmic-ray particles. detailed spatially resolved spectroscopic studies of these snrs are crucial in yielding insights into how these sources accelerate these particles to such high energies that approach the so-called "knee" energy of the cosmic-ray spectrum. amongst the synchrotron x-ray-dominated galactic snrs, g28.6-0.1 is unique in that the synchrotron x-ray emission originates from interior diffuse emission rather than from localized rims, which is typical for snrs of this class. we are conducting a spatially resolved x-ray spectroscopic analysis of g28.6-0.1 using archival chandra observations of this snr. to constrain the fits to the synchrotron x-ray emission from different regions of g28.6-0.1, we have supplemented our analysis with new l-band and p-band observations of this snr using the jvla. these jvla observations have facilitated a more sophisticated measurement of the flux densities and spectral indices of particular structures of g28.6-0.1 as well as for the whole snr. initial results of our analysis will be presented and discussed. | an x-ray and radio analysis of the peculiar galactic supernova remnant g28.6-0.1 |
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