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bismuth germanium oxide (bi4ge3o12, bgo) scintillation crystals are widely used as detectors in the fields of particle physics and astrophysics due to their high density, and thus higher efficiency for gamma-ray detection. owing to their good chemical stability, they can be used in any environment. for rare-event searches, such as dark matter and coherent elastic neutrino-nucleus scattering, bgo crystals are essential to comprehend the response of nuclear recoil. in this study, we have analyzed the events of neutron elastic scattering with oxygen in bgo crystals. then, we have measured the quenching factor for oxygen recoil energy in the bgo crystal as a function of recoil energy by using a monoenergetic neutron source. | a method to measure the quenching factor for recoil energy of oxygen in bismuth germanium oxide scintillators |
proper interpretation of past, current, and future data on lepton-nucleus reactions requires a clear separation between quantum electrodynamics and strong interaction effects inside the nucleus. first studies of qed in-medium lepton dynamics have set a theoretical framework to derive electron-nucleus and (anti)neutrino-nucleus cross section corrections. we employ this approach to quantitatively compute the effects of glauber photon-mediated multiple rescattering within the nuclear medium. we find that the relativistic charged lepton acquires momentum of order 10 mev transverse to its direction of propagation inside the nucleus. this broadening sizably deflects expected electron tracks and suppresses scattering cross sections. precise extraction of the nucleon and nuclear structure by electron and muon probes should, thus, take the qed nuclear medium angular redistribution of particles into account. our results further show that the associated effects in (anti)neutrino-nucleus scattering with fixed final-lepton energy are significant only at the kinematical end points. | broadening of particle distributions in electron-, neutrino-, and antineutrino-nucleus scattering from qed interactions |
since many of the dark-sector particles interact with standard model (sm) particles in multiple ways, they can appear in experimental facilities where sm particles appear in abundance. in this study, we explore a particular class of longer-lived mediators that are produced from photons, charged mesons, neutral mesons, and $e^\pm$ that arise in proton-beam fixed-target-type neutrino experiments. this class of mediators encompasses light scalars that appear in theories like extended higgs sectors, muon(electro)philic scalars, etc. we evaluate the sensitivities of these mediators at beam-based neutrino experiments such as the finished argoneut, ongoing microboone, sbnd, icarus, and the upcoming dune experiment. we realize that scalars are more enhanced while produced from three-body decay of charged mesons, especially if they are muonphilic in nature. for scenarios that contain muonphilic scalars, these experiments can probe unexplored regions of parameter space that can explain the current discrepancy in the anomalous magnetic moment of muons. the sensitivity of electrophilic scalars at the dune near detector can explore new regions. we also show that bethe-heitler scattering processes can be used to probe flavor-specific lepton final states even for the mediator masses below twice the lepton mass. | longer-lived mediators from charged mesons and photons at neutrino experiments |
we investigate the inelastic signatures of dark matter-nucleus interactions, explicitly focusing on the ramifications of polarization, dark matter splitting, and the migdal effect. direct detection experiments, crucial for testing the existence of dark matter, encounter formidable obstacles such as indomitable neutrino backgrounds and the elusive determination of dark matter spin. to overcome these challenges, we explore the potential of polarized-target dark matter scattering, examining the impact of nonvanishing mass splitting and the role of the migdal effect in detecting light dark matter. our findings significantly contribute to understanding direct detection experiments, unveiling new insights into the behavior of dark matter and its inelastic nature. | probing inelastic signatures of dark matter detection via polarized nucleus |
in this work, we introduce the theoretical framework of the phonon-mediated migdal effect for neutrino-nucleus scattering in semiconductors, considering both the standard model and the presence of the neutrino magnetic moment. we calculate the rate of electron excitation resulting from the migdal effect and observe a substantial coherent enhancement compared to ordinary neutrino-electron scattering. furthermore, we provide numerical sensitivities for detecting the migdal effect and constraints on the neutrino magnetic moment, utilizing an experimental setup with reactor neutrinos. | migdal effect of phonon-mediated neutrino nucleus scattering in semiconductor detectors |
we investigate the enhancement of dark sector particle production within the scattering dominant regime. these particles typically exhibit a slight mixing with standard model particles through various portals, allowing for their generation through in-medium oscillation from standard model particle sources. our analysis reveals that in the scattering dominance regime, with a significantly smaller scattering mean free path $\lambda_{\rm sca}$ compared to the absorption mean free path $\lambda_{\rm abs}$, the non-resonant production of sterile states can experience an enhancement by a factor of $\lambda_{\rm abs}/\lambda_{\rm sca}$. this phenomenon is demonstrated within the context of kinetic mixing dark photon production at a reactor, precisely satisfying this condition. by incorporating this collisional enhancement, we find that the current sensitivity to the mixing parameter $\epsilon$ for dark photons in the texono experiment can be significantly improved across a range spanning from tens of ev to mev. this advancement establishes the most stringent laboratory constraint within this mass spectrum for the dark photon. sterile neutrino production, however, does not exhibit such enhancement, either due to the failure to meet the scattering dominance criterion or the neutrino damping in resonant production. | amplifying non-resonant production of dark sector particles in scattering dominance regime |
in certain conditions a macroscopic quantum-mechanical scattering may occur, which may lead to a coherent cross-section on a macroscopic scale in a monocrystal. the conditions are satisfied by neutrinos, but not satisfied by other projectiles, with a higher cross-section. this may explain weber-type experiments of neutrino detection by a perfect, stiff sapphire monocrystal. the occurrence of coherence domains for quantum-mechanical scattering and classical diffraction is analyzed, and the force exerted upon a macroscopic target is estimated. it is concluded that neutrinos exhibit a distinctive feature in this respect, due precisely to their very small cross-section. | macroscopic quantum-mechanical scattering |
there are profound connections between neutrino physics and nuclear experiments. exceptionally precise measurements of single and double beta-decay spectra illuminate the scale and nature of neutrino mass and may finally answer the question of whether neutrinos are their own antimatter counterparts. neutrino-nucleus scattering underpins oscillation experiments and probes nuclear structure, neutrinos offer a rare vantage point into collapsing stars and nuclear fission reactors, and techniques pioneered in neutrino nuclear-physics experiments are advancing quantum-sensing technologies. in this article, we review current and planned efforts at the intersection of neutrino and nuclear experiments. | experimental neutrino physics in a nuclear landscape |
the icecube neutrino observatory deployed 5160 digital optical modules (doms) in a cubic kilometer of deep, glacial ice below the geographic south pole, recording the cherenkov light of passing charged particles. while the optical properties of the undisturbed ice are nowadays well understood, the properties of the refrozen drill holes still pose a challenge. from camera observations, we expect a central, strongly scattering column shadowing a part of the doms' sensitive area. in mc simulation, this effect is commonly modeled as a modification to the doms' angular acceptance curve, reducing the forward sensitivity of the doms. the associated uncertainty is a dominant detector systematic for neutrino oscillation studies as well as high-energy cascade reconstructions. over the years, several measurements and fits of the drill holes' optical properties and of the angular acceptance curve have been proposed, some of which are in tension. here, we present a principle component analysis, which allows us to interpolate between all suggested scenarios, and thus provide a complete systematic variation within a unified framework at analysis level. | a model independent parametrization of the optical properties of the refrozen icecube drill holes |
solar neutrino measurements have recently reached a level of sensitivity such that cno fluxes can now be experimentally determined. while these first measurements are still only sensitive to the higher energy neutrinos resulting from the β+ decays of 15o produced by the 14n(p ,γ )15o reaction, future measurements will work towards detection of neutrinos from the β+ decay of 13n from the 12c(p ,γ )13n reaction. this paper reports on a recent measurement of the 12c(p ,γ )13n reaction covering a broad laboratory energy range between 1.0 and 2.5 mev. the measurement was made to better determine the overall normalization of the absolute cross section and to explore the interference effects between the two broad, overlapping resonances at proton energies of 0.460 and 1.689 mev and the direct capture to the ground state of 13n in the framework of a multichannel r -matrix analysis. this work takes into account previous radiative capture as well as elastic 12c(p ,p )12c scattering data, making uncertainty estimations using a bayesian framework, to determine a reliable extrapolation of the low energy s factor towards the stellar energy range of cno hydrogen burning. these new experimental results, and a detailed investigation of the past literature data, suggest that the resonant component of the cross section should be 30% lower than previously accepted. | absolute cross section of the 12c(p ,γ )13n reaction |
a portable monoenergetic 24 kev neutron source based on the 124sb-9be photoneutron reaction and an iron filter has been constructed and characterized. the coincidence of the neutron energy from sbbe and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from 124sb decays while letting through the neutrons. to increase the 124sb activity and thus the neutron flux, a >1 gbq 124sb source was produced by irradiating a natural sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. the design of the source shielding structure makes for easy transportation and deployment. a hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a nai detector is used for gamma background characterization. at the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20-25 kev to be 6.00±0.30 neutrons per cm2 per second and the total gamma flux to be 245±8 gammas per cm2 per second (numbers scaled to 1 gbq activity of the 124sb source). a liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 kev, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. this photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments. | a portable and monoenergetic 24 kev neutron source based on 124sb-9be photoneutrons and an iron filter |
introduction: the recent discovery of coherent elastic neutrino-nucleus scattering (cevns) has created new opportunities to detect and study neutrinos. the interaction cross section in cevns scales quadratically with the number of neutrons, making heavy-nuclei targets such as active lead-based detectors ideal. lead perovskites have emerged in the last decade as revolutionary materials for radiation detection due to their heavy and flexible element composition and their unique optoelectronic properties that result in an excellent energy resolution at an economic cost.methodology: in this study, we discuss, for the first time, the physics potential and feasibility of building neutrino detectors using semiconductor lead perovskite crystals as a target.results and discussion: we indicate that existing data with x-rays suggest the suitability of existing lead perovskite sensors to study cevns using neutrinos from π decay at rest (π- dar) sources. although dedicated research and development will be necessary, we have found significant benefits and no inherent obstacles for the development of lead perovskites as cevns detectors. | lead perovskites as ceνns detectors |
the elastic and inelastic neutral current ν (ν ¯) scattering off the polarized nucleon is discussed. the inelastic scattering concerns the single-pion production process. we show that the spin asymmetries' measurement can help to distinguish between neutrino and antineutrino neutral current scattering processes. the spin asymmetries also encode information about a type of target. eventually, detailed studies of the inelastic spin asymmetries can improve understanding of the resonant-nonresonant pion production mechanism. | neutral current neutrino and antineutrino scattering off the polarized nucleon |
inverse muon decay (νμe-→νeμ- ) is a promising tool to constrain neutrino fluxes with energies eν≥10.9 gev . radiative corrections introduce percent-level distortions to energy spectra of outgoing muons and depend on experimental details. in this paper, we calculate radiative corrections to the scattering processes νμe-→νeμ- and ν¯ee-→ν¯μμ-. we present the muon energy spectrum for both channels, double-differential distributions in muon energy and muon scattering angle and in photon energy and photon scattering angle, and the photon energy spectrum for the dominant νμe-→νeμ- process. our results clarify and extend the region of applicability of previous results in the literature for the double differential distribution in muon energy and photon energy, and in the muon energy spectrum with a radiated photon above a threshold energy. we provide analytic expressions for single, double, and triple differential cross sections, and discuss how radiative corrections modify experimentally interesting observable distributions. | radiative corrections to inverse muon decay for accelerator neutrinos |
we present an analysis on the sensitivity to the active-sterile neutrino mixing with germanium (ge) and silicon (si) detectors in the context of the proposed coherent elastic neutrino-nucleus experiment in india. the study has been carried out with 3 (active )+1 (sterile ) neutrino oscillation model. it is observed that the measurements that can be carried out with the ge detector exhibit better sensitivity to the active-sterile neutrino mixing as compared to the si detector. both detectors are able to exclude most of the anomaly regions observed by the gallium experiment. the ge detector with mass 10 kg, can observe the active-sterile neutrino oscillation at 95% confidence level, provided that sin22 θ14≥0.09 at δ m412=1.0 ev2 for an exposure of 1-yr. at higher values of δ m412, a better sensitivity is obtained at a short baseline. it is also found that the threshold as well as resolution of the detectors play a crucial role on the measurements of active-sterile neutrino mixing parameters. | sterile neutrino searches with reactor antineutrinos using coherent neutrino-nucleus scattering experiments |
at leading order in weak and electromagnetic couplings, cross sections for (anti)neutrino-nucleon elastic scattering are determined by vector and axial-vector form factors. radiative corrections in the standard model, and potential new physics contributions beyond the standard model, generate additional operators with corresponding invariant amplitudes. we provide the definition of these amplitudes and study constraints from existing experimental data. we explore the impact of modern and future cross-section measurements, considering both unpolarized and polarized observables, on constraining these amplitudes and discuss the effects of radiative corrections on the observables of interest. | invariant amplitudes, unpolarized cross sections, and polarization asymmetries in neutrino-nucleon elastic scattering |
complete monte carlo (mc) simulation of a neutrino experiment typically involves the lengthy and cpu-intensive process of integrating models of incoming neutrino fluxes, event generation, and detector setup. we describe a fast, geometry-independent, genie-based system known as nusmear which provides preliminary simulation of energy smearing and angular smearing for neutrino-nucleon interactions. we discuss nusmear's simulation methodology, explaining its calculation of reconstructed values through its model-based resolution computation, smearing distributions, and particle detection dependencies. we go on to validate nusmear's performance as a fast simulation system through a series of internal and external comparisons testing its predictive accuracy and model-adherence. finally, we briefly explore the potential for future user-customization in nusmear. | nusmear: fast simulation of energy smearing and angular smearing for neutrino-nucleon scattering events in the genie event generator |
the detection of coherent elastic neutrino-nucleus scattering (ce$\nu$ns) opens new possibilities for neutrino physics within and beyond the standard model. following the initial discovery in 2017, several experimental attempts have emerged allowing this reaction channel to be studied with the full repertoire of modern detection technologies. as one of several reactor experiments, conus aims for an observation with antineutrinos emitted from the powerful $3.9$ gw$_{th}$ reactor of the nuclear power plant in brokdorf (germany). in particular, the application of ultra-low threshold, high-purity germanium detectors within a sophisticated shield design in close proximity to a nuclear reactor core represents an important step towards high-statistics neutrino detection with small-scale detectors. in addition to the conventional interaction, typical extensions of the standard model neutrino sector can be investigated with data provided from different neutrino sources and several target materials. among these, new neutrino interactions as well as electromagnetic neutrino properties are of particular interest. this talk gives an overview of existing ce$\nu$ns results and highlights the advantage of using different neutrino sources and target materials. the example of conus is used to demonstrate the various capabilities of recent and future ce$\nu$ns measurements. | coherent elastic neutrino-nucleus scattering -- first constraints/observations and future potential |
we suggest an empirical rule-of-thumb for calculating the cross sections of charged-current quasielastic (ccqe) and ccqe-like interactions of neutrinos and antineutrinos with nuclei. the approach is based on the standard relativistic fermi-gas model and on the notion of neutrino energy dependent axial-vector mass of the nucleon, governed by a couple of adjustable parameters, one of which is the conventional charged-current axial-vector mass. the inelastic background contributions and final-state interactions are therewith simulated using genie 3 neutrino event generator. an extensive comparison of our calculations with earlier and current accelerator ccqe and ccqe-like data for different nuclear targets shows good or at least qualitative overall agreement over a wide energy range. we also discuss some problematical issues common to several competing contemporary models of the ccqe (anti)neutrino-nucleus scattering and to the current neutrino interaction generators. | running axial mass of the nucleon as a phenomenological tool for calculating qe neutrino-nucleus cross sections |
we discuss cross sections for $\nu_{\tau}$ and ${\overline \nu}_{\tau}$ production from the direct $d_s^{\pm} \to \nu_{\tau}/{\overline \nu}_{\tau}$ and chain $d_s^{\pm} \to \tau^+/\tau^- \to \nu_{\tau}/{\overline \nu}_{\tau}$ decays in $p\!+^{96}\!\mathrm{mo}$ scattering with proton beam $e_{\mathrm{lab}}$ = 400 gev \textit{i.e.} at $\sqrt{s}_{nn}$ = 27.4 gev. in our calculations we include $d_s^{\pm}$ from charm fragmentation $c \to d_s^{+}$ and $\bar c \to d_s^-$ as well as those from subleading fragmentation of strange quarks/antiquarks $s \to d_s^-$ and $\bar s \to d_s^+$. the different contributions to $d_s^{\pm}$ and $\nu_{\tau} / {\overline \nu}_{\tau}$ production rates are shown explicitly. estimates of a number of observed $\nu_{\tau} / \overline{\nu}_{\tau}$ in the $\nu_{\tau} / \overline{\nu}_{\tau} +^{208}\!\mathrm{pb}$ reaction, with 2m long target are given. | production of \\nu_{\\tau} neutrinos and {/line \\nu}_{\\tau} antineutrinos - elaborate calculation for a fixed target experiment ship |
the public galprop code gives a fully numerical solution for the spectrum of cosmic rays propagating through a linear galactic wind directed outward from the galactic plane in the framework of a cylindrical diffusion model. alternatively, for the linear galactic wind case, we present a semianalytical solution of the two-zone cylindrical model that describes the spectrum of cosmic-ray antiprotons produced from the primary sources throughout the dark matter (dm) halo. while the secondary antiprotons can be generated by, e.g., the galprop webrun, consistently using this semianalytical solution for the primary ones would be helpful to build a suited dm model, which may be sophisticated, and then to perform a statistical analysis when comparing it with data. as an example, using the obtained formula, we study the possible dm signal through the channel $\mathrm{dm}\,\mathrm{dm}\to \bar{b}b$ and its constraint from the measurement of the ams-02 antiproton-to-proton ratio. the indication of the dm signal is discussed. the advantages of the semianalytical approach and its comparison with the galprop model are presented. | diffusion of cosmic antiprotons generated throughout the dark matter halo-a semianalytical solution for a linear galactic wind model |
we consider anisotropic diffusion of galactic cosmic rays in the galactic magnetic field, using the jansson-farrar model for the field. in this paper we investigate the influence of source position on the cosmic ray flux at earth in two ways: [1] by considering the contribution from cosmic ray sources located in different intervals in galacto-centric radius, and [2] by considering the contribution from a number of specific and individual close-by supernova remnants. our calculation is performed by using a fully three-dimensional stochastic method. this method is based on the numerical solution of a set of stochastic differential equations, equivalent to ito formulation, that describes the propagation of the galactic cosmic rays. | the contribution of nearby supernova remnants on the cosmic ray flux at earth |
the origin and nature of the ultrahigh energy cosmic rays (uhecrs) are still unknown. however, great progress has been achieved in past years due to the observations performed by the pierre auger observatory and telescope array. above $10^{18}$ ev the observed energy spectrum presents two features: a hardening of the slope at about $10^{18.7}$ ev, which is known as the ankle and a suppression at approximately $10^{19.6}$ ev. the composition inferred from the experimental data, interpreted by using the current high energy hadronic interaction models, seems to be light below the ankle, showing a trend to heavier nuclei for increasing values of the primary energy. current high energy hadronic interaction models, updated by using large hadron collider data, are still subject to large systematic uncertainties, which makes difficult the interpretation of the experimental data in terms of composition. on the other hand, it is very well known that gamma rays and neutrinos are produced by uhecrs during propagation from their sources, as a consequence of their interactions with the radiation field present in the universe. the flux at earth of these secondary particles depends on the source models of uhecrs including the chemical composition at injection. therefore, both gamma-ray and neutrino observations can be used to constrain source models of uhecrs, including the composition in a way which is independent of the high energy hadronic interaction models. in this article i will review recent results obtained by using the latest gamma-ray and neutrino observations. | implications of gamma-ray and neutrino observations on source models of ultrahigh energy cosmic rays |
using a setup for testing a prototype for a satellite-borne cosmic-ray ion detector, we have operated a stack of scintillator and silicon detectors on top of the princess sirindhorn neutron monitor (psnm), an nm64 detector at 2560-m altitude at doi inthanon, thailand (18.59∘n, 98.49∘e). monte carlo simulations have indicated that about 15% of the neutron counts by psnm are due to interactions (mostly in the lead producer) of gev-range protons among the atmospheric secondary particles from cosmic ray showers, which can be detected by the scintillator and silicon detectors. those detectors can provide a timing trigger for measurement of the propagation time distribution of such neutrons as they scatter and propagate through the nm64, processes that are similar whether the interaction was initiated by an energetic proton (for 15% of the count rate) or neutron (for 80% of the count rate). this propagation time distribution underlies the time delay distribution between successive neutron counts, from which we can determine the leader fraction (inverse multiplicity), which has been used to monitor galactic cosmic ray spectral variations over ∼1-40 gv. here we have measured and characterized the propagation time distribution from both the experimental setup and monte carlo simulations of atmospheric secondary particle detection. we confirm a known propagation time distribution with a peak (at ≈70 μs) and tail over a few ms, dominated by neutron counts. we fit this distribution using an analytic model of neutron diffusion and absorption, for both experimental and monte carlo results. in addition we identify a group of prompt neutron monitor pulses that arrive within 20 μs of the charged-particle trigger, of which a substantial fraction can be attributed to charged-particle ionization in a proportional counter, according to both experimental and monte carlo results. prompt pulses, either due to neutrons or charged-particle ionization, are associated with much higher mean multiplicity than typical pulses. these results validate and point the way to some improvements in monte carlo simulations and the resulting yield functions used to interpret the neutron monitor count rate and leader fraction. | measurement and simulation of the neutron propagation time distribution inside a neutron monitor |
cosmic rays are nowadays a crucial tool to study the astrophysics of extreme objects in the universe, the cosmic environmental plasma (both galactic and extra-galactic), the physics of nuclear interactions or the properties of elementary particles at very high energies and even cosmological problems such as the dark matter puzzle. in this thesis, the phenomenology on the transport of galactic cosmic rays is studied in light of the most recent experimental data in the field and new analyses are presented in order to obtain better constraints. throughout the thesis, secondary particles produced from collisions of cosmic rays with the interstellar gas, such as secondary cosmic ray nuclei (b, be and li), antiprotons and gamma rays, are treated in order to adjust and test our models and probe different scenarios, such as possible signatures of dark matter decay or annihilation. a preliminary version of the upcoming dragon2 code has been used to perform the propagation computations. with the increasing accuracy of cr data a number of anomalies have appear with respect to the standard paradigm of propagation of charged particles in the galaxy. in this thesis, we demonstrate that some of these anomalies disappear by taking into account the systematic uncertainties involving these kind of analyses, specially cross sections uncertainties. | cosmic-ray propagation and production of secondary particles in the galaxy |
at very high energies (vhe), the emission of $\gamma$ rays is dominated by discrete sources. due to the limited resolution and sensitivity of current-generation instruments, only a small fraction of the total galactic population of vhe $\gamma$-ray sources has been detected significantly. the larger part of the population can be expected to contribute as a diffuse signal alongside emission originating from propagating cosmic rays. without quantifying the source population, it is not possible to disentangle these two components. based on the h.e.s.s. galactic plane survey, a numerical approach has been taken to develop a model of the population of galactic vhe $\gamma$-ray sources, which is shown to account accurately for the observational bias. we present estimates of the absolute number of sources in the galactic plane and their contribution to the total vhe $\gamma$-ray emission for five different spatial source distributions. prospects for cta and its ability to constrain the model are discussed. finally, first results of an extension of our modelling approach using machine learning to extract more information from the available data set are presented. | exploring the population of galactic very-high-energy gamma-ray sources |
we study the effects of drift motions and the advection by a galactic wind on the propagation of cosmic rays in the galaxy. we employ a simplified magnetic field model, based on (and similar to) the jansson-farrar model for the galactic magnetic field. diffusion is allowed to be anisotropic. the relevant equations are solved numerically, using a set of stochastic differential equations. inclusion of drift and a galactic wind significantly shortens the residence time of cosmic rays, even for moderate wind speeds. | the effects of drift and winds on the propagation of galactic cosmic rays |
cosmic rays (crs) are an integral component of the interstellar medium, producing broadband emission while interacting with other galactic matter components like the interstellar gas or magnetic fields. in addition to observations, numerical simulations of cr propagation through the galaxy help to increase the level of understanding of galactic cr transport and diffuse γ-ray emission as seen by different experiments. up to now, the standard approach at modelling source distributions used as input for such transport simulations often rely on radial symmetry and analytical functions rather than individual, observation-based sources. we aim at a redefinition of existing cr source distributions by combining sources observed with the h.e.s.s. experiment and simulated random sources, which follow the matter density in the milky way. as a result, h.e.s.s.-inspired galactic cr source distributions are inferred. we use the picard code to perform 3d-simulations of nuclei and electrons in cr propagation using our hybrid source distribution models. furthermore, also gamma-ray maps and spectra, simulated with the redefined source models, are evaluated in different regions in the galaxy and compared with each other to determine the statistical scatter of the underlying distributions. we find global consistency between our models and in comparison to previous simulations, with only some localised fluctuations, e.g. in the spiral arms. this implementation of a three-dimensional source model based on observations and simulations enables a new quality of propagation modelling. it offers possibilities for more realistic cr transport scenarios beyond radial symmetry and delivers meaningful results in both the arm and interarm regions of the galaxy. this gives a more realistic picture of the galactic γ-ray sky by including structures from the source model and not just the gas distributions. | cosmic-ray propagation under consideration of a spatially resolved source distribution |
high-velocity clouds moving towards the disc will reach the galactic plane and will inevitably collide with the disc. in these collisions, a system of two shocks is produced, one propagating through the disc and the other develops within the cloud. the shocks produced within the clouds in these interactions have velocities of hundreds of kilometres per second. when these shocks are radiative they may be inefficient in accelerating fresh particles; however, they can reaccelerate and compress galactic cosmic rays from the background. in this work, we investigate the interactions of galactic cosmic rays within a shocked high-velocity cloud, when the shock is induced by the collision with the disc. this study is focused in the case of radiative shocks. we aim to establish under which conditions these interactions lead to significant non-thermal emission, especially gamma-rays. we model the interaction of cosmic ray protons and electrons reaccelerated and further energized by compression in shocks within the clouds, under very general assumptions. we also consider secondary electron-positron pairs produced by the cosmic ray protons when colliding with the material of the cloud. we conclude that nearby clouds reaccelerating galactic cosmic rays in local shocks can produce high-energy radiation that might be detectable with existing and future gamma-ray detectors. the emission produced by electrons and secondary pairs is important at radio wavelengths, and in some cases it may be relevant at hard x-rays. concerning higher energies, the leptonic contribution to the spectral energy distribution is significant at soft gamma-rays. | gamma-rays from reaccelerated cosmic rays in high-velocity clouds colliding with the galactic disc |
the dark matter particle explorer (dampe) has been undergoing a stable on-orbit operation for more than 6 yr and acquired observations of over 11 billion events. a better understanding of the overall radiation environment of the dampe orbit is crucial for both simulation data production and flight data analysis. in this work, we study the radiation environment at low earth orbit and develop a simulation software package using the framework of atmnc3, in which state-of-the-art full 3d models of the earth's atmospheric and magnetic-field configurations are integrated. we consider in our monte carlo procedure event-by-event propagation of cosmic rays in the geomagnetic field and their interaction with the earth's atmosphere, focusing on the particles above gev that are able to trigger the dampe data acquisition system. we compare the simulation results with the cosmic-ray electron and positron (cre) flux measurements made by dampe. the overall agreement on both the spectral and angular distribution of the cre flux demonstrates that our simulation is well established. our software package could be of more general usage for simulation of the radiation environment of low earth orbit at various altitudes. | a study on monte carlo simulation of the radiation environment above gev at the dampe orbit |
cosmic rays are charged particles accelerated in supernova shocks, exerting pressure on gas and heating it. as these effects can alter both the star formation and the multiphase structure of galaxies, they are likely an important feedback channel in galaxy evolution. using radiation-magneto-hydrodynamics simulations of three isolated and idealised disk galaxies of different masses, we investigate the impact of cosmic ray feedback on galaxy evolution. we find that cosmic rays have a mild effect in reducing star formation, by at most a factor two, and with decreasing efficiency in increasingly massive galaxies. at any galaxy mass however, cosmic ray pressure support increases galactic outflows, which are also much colder than when cosmic rays are excluded. we find that both the increase in outflows and their temperature are sensitive to the adopted cosmic ray diffusion coefficient, revealing the importance of the detailed modelling of cosmic ray propagation. | the role of cosmic ray feedback in the evolution of galaxies |
the center of the milky way is a prime site to search for signals of dark matter (dm) annihilation due to its proximity and expected high concentration of dm. the amplification of the dispersion velocity of dm particles in the galactic center (gc), caused by baryonic contraction and feedback, makes this particular region of the sky an even more promising target for exploring velocity-dependent dm models. here we demonstrate that current gc observations with the h.e.s.s. telescope, presently the most sensitive tev-scale gamma-ray telescope in operation in this region of the sky, set the strongest constraints on velocity-dependent annihilating dm particles with masses above 200 gev. for p-wave annihilations, they improve the current constraints by a factor of ∼4 for a dm mass of 1 tev. for the spatial distribution of dm, we use the results of the latest fire-2 zoom cosmological simulation of milky way-size halos. in addition, we utilize the newest version of the galprop cosmic-ray propagation framework to simulate the galactic diffuse gamma-ray emission in the gc. we have found that p-wave (d-wave) dm particles with a mass of approximately 1.7 tev and annihilating into the w+w- channel exhibit a velocity-weighted annihilation cross-section upper limit of 4.6 ×10-22 cm3 s-1 (9.2 ×10-17 cm3 s-1 ) at a 95% confidence level. this is about 460 (2 ×106 ) times greater than the thermal relic cross section for p-wave (d-wave) dm models. | tev gamma-ray sensitivity to velocity-dependent dark matter models in the galactic center |
m-dwarf stars have been preferred targets of exoplanet search due to the favourable parameters of the system for remote characterisation. however, planets in the habitable zones of these stars are expecting to experience intense radiation. we present the increase project (influence of strong stellar particle events and galactic cosmic rays on exoplanetary atmospheres), aiming at modelling the effect of energetic particles on the atmosphere of terrestrial exoplanets. the increase model suite is an almost self-consistent simulation chain coupling the state-of-the-art magnetospheric and atmospheric propagation and interaction models planetocosmics (desorgher et al. 2006) and atris (banjac57 et al. 2019) with the atmospheric chemistry and climate models 1d-terra (e.g., wunderlich et al. 2020) and exotic. finally, spectral characterisation is done using the garlic line by line radiative transfer model. by combining these models, we are able to constrain the habitability of such planets, the stability of their atmosphere as well as simulating observational features. | effect of energetic particles on the atmosphere of terrestrial exoplanets |
detailed measurements of the spectral structure of cosmic-ray electrons and positrons from 10.6 gev to 7.5 tev are presented from over 7 years of observations with the calorimetric electron telescope (calet) on the international space station. the instrument, consisting of a charge detector, an imaging calorimeter, and a total absorption calorimeter with a total depth of 30 radiation lengths at normal incidence and a fine shower imaging capability, is optimized to measure the all-electron spectrum well into the tev region. because of the excellent energy resolution (a few percent above 10 gev) and the outstanding e /p separation (105), calet provides optimal performance for a detailed search of structures in the energy spectrum. the analysis uses data up to the end of 2022, and the statistics of observed electron candidates has increased more than 3 times since the last publication in 2018. by adopting an updated boosted decision tree analysis, a sufficient proton rejection power up to 7.5 tev is achieved, with a residual proton contamination less than 10%. the observed energy spectrum becomes gradually harder in the lower energy region from around 30 gev, consistently with ams-02, but from 300 to 600 gev it is considerably softer than the spectra measured by dampe and fermi-lat. at high energies, the spectrum presents a sharp break around 1 tev, with a spectral index change from −3.15 to −3.91 , and a broken power law fitting the data in the energy range from 30 gev to 4.8 tev better than a single power law with 6.9 sigma significance, which is compatible with the dampe results. the break is consistent with the expected effects of radiation loss during the propagation from distant sources (except the highest energy bin). we have fitted the spectrum with a model consistent with the positron flux measured by ams-02 below 1 tev and interpreted the electron +positron spectrum with possible contributions from pulsars and nearby sources. above 4.8 tev, a possible contribution from known nearby supernova remnants, including vela, is addressed by an event-by-event analysis providing a higher proton-rejection power than a purely statistical analysis. | direct measurement of the spectral structure of cosmic-ray electrons+positrons in the tev region with calet on the international space station |
electron and positron fluxes in cosmic rays are currently measured with unprecedented precision by ams-02 up to tev energies, and represent unique probes for the local properties of our galaxy. the interpretation of their spectra is at present still debated, especially for the excess of positrons above 10 gev. the hypothesis that pulsars can significantly contribute to this excess has been consolidated after the observation of gamma-ray halos at tev energies of a few degree size around geminga and monogem pulsars. however, the spatial and energetic galactic distribution of pulsars and the details of the positron production, acceleration and release from these sources are not yet fully understood. i will describe how we can use the high-precision ams-02 positron data to constrain the main properties of the galactic pulsar population and of the positron acceleration needed to explain the observed fluxes. this is achieved by simulating a large number of galactic pulsar populations, following the most recent self-consistent modelings for the pulsar spin-down and evolution properties, calibrated on catalog observations. by fitting the positron ams-02 data together with a secondary component due to collisions of primary cosmic rays with the interstellar medium, we determine the physical parameters of the pulsars dominating the positron flux, and assess the impact of different assumptions on radial distributions, spin-down properties, galactic propagation scenarios and positron emission time. | constraints on the positron emission from pulsar populations with ams-02 data |
observations of oh+ are used to infer the interstellar cosmic ray ionization rate in diffuse atomic clouds, thereby constraining the propagation of cosmic rays through and the shielding by interstellar clouds, as well as the low energy cosmic ray spectrum. in regions where the h2-to-h number density ratio is low, dissociative recombination (dr) is the dominant destruction process for oh+ and the dr rate coefficient is important for predicting the oh+ abundance and inferring the cosmic ray ionization rate. we have experimentally studied dr of electronically and vibrationally relaxed oh+ in its lowest rotational levels, using an electron-ion merged-beams setup at the cryogenic storage ring. from these measurements, we have derived a kinetic temperature rate coefficient applicable to diffuse cloud chemical models, i.e., for oh+ in its electronic, vibrational, and rotational ground level. at typical diffuse cloud temperatures, our kinetic temperature rate coefficient is a factor of ~5 times larger than the previous experimentally derived value and a factor of ~33 times larger than the value calculated by theory. our combined experimental and modeling results point to a significant increase for the cosmic ray ionization rate inferred from observations of oh+ and h2o+, corresponding to a geometric mean of (6.6 ± 1.0) × 10-16 s-1, which is more than a factor of 2 larger than the previously inferred values of the cosmic ray ionization rate in diffuse atomic clouds. combined with observations of diffuse and dense molecular clouds, these findings indicate a greater degree of cosmic ray shielding in interstellar clouds than has been previously inferred. | dissociative recombination of rotationally cold oh+ and its implications for the cosmic ray ionization rate in diffuse clouds |
when high-energy particles originating from space penetrate the atmosphere, they may interact with atoms and molecules, initiating air showers composed of secondary and tertiary particles propagating towards the ground. they can cause ionization of the atmosphere and contribute to the radiation dose at low altitudes. this work uses the geant-4-based atmospheric radiation interaction simulator (atris) toolkit to compute these quantities in the earth's atmosphere. we take advantage of the unique planet specification file (psf) of the atmospheric radiation interaction simulator (atris) to investigate the effect of the state of the atmosphere on the resulting induced ionization and absorbed dose rates from the top of the atmosphere (at 100 km) down to the surface. the atmospheric profiles (density, pressure, temperature, and composition) are computed with the nrlmsise-00 model at various latitudes and for every month of 2014, corresponding to the last maximum of solar activity. the resulting ionization and dose rates present different profiles that vary with latitude in the atmosphere, with the relative difference between equatorial and high latitude ionization rates reaching 68% in the pfotzer maximum. we obtain differences of up to 59% between the equator and high latitudes observed at commercial flight altitudes for the radiation dose. both ionization and absorbed dose rates also feature anti-phased seasonal variations in the two hemispheres throughout 2014. based on these results, we computed global maps of the ionization and dose rates at fixed altitudes in the atmosphere by using precomputed maps of the effective vertical cutoff rigidities and the results of three atris simulations to consider the effect of latitude. while sharing the same general structure as maps created with a single profile, these new maps also show a clear asymmetry in the ionization and absorbed dose rates in the polar regions. | the atmospheric influence on cosmic-ray-induced ionization and absorbed dose rates |
in the standard picture of cosmic ray transport the propagation of charged cosmic rays through turbulent magnetic fields is described as a random walk with cosmic rays scattering on magnetic field turbulence. this is in good agreement with the highly isotropic cosmic ray arrival directions as this diffusion process effectively isotropizes the cosmic ray distribution. high-statistics observatories like icecube and hawc have however observed significant deviations from isotropy down to very small angular scales. this is in strong tension with this standard picture of cosmic ray propagation. while large scale multipoles arise naturally, for example due to the earth's motion relative to the isotropic cosmic ray distribution, there is no intuitive mechanism to account for the observed anisotropies at smaller angular scales. by relaxing one of the standard assumptions of quasi linear theory and treating correlations between fluxes of cosmic rays from different directions explicitly we show that higher multipoles also are to be expected from particle propagation through turbulent magnetic fields. we present a first analytical calculation of the angular power spectrum assuming a physically motivated model of the magnetic field turbulence and find good agreement with numerical simulations. | cosmic ray small-scale anisotropies in slab turbulence |
with tantalizing evidence of the recent e-rosita mission, re-discovering very soft x-rays and extreme-ultraviolet (euv) radiation from a cluster of galaxies or its environment, the question of the origin of cluster euv excess is revisited in this work. it will be shown that the gas temperature, density, and frozen-in magnetic field of the intracluster medium, collectively support the emission and propagation of coherent c̆erenkov radiation, which is low frequency and large amplitude radiation capable of accelerating charged particles to relativistic speeds. owing to the spectrum of c̆erenkov radiation, most of the incipient relativistic electrons undergo inverse-compton scattering with the cosmic microwave background. it turns out the scattered radiation has observable ramifications only in the euv band, of photon energy 70-100 ev, having a luminosity ≈1044 ergs s-1. this luminosity is on par with the euv excess level detected from abell 1795 and the coma cluster. it should be stressed, as caveat emptor, that although the main subject is the putative large amplitude coherent c̆erenkov modes which are highly non-linear, the results presented were derived using a quasi-linear approach to highlight the observable features of the phenomenon, namely, the euv emission. | a model of euv emission from clusters of galaxies |
cosmic rays represent one of the most important energy transformation processes of the universe. they bring information about the surrounding universe, our galaxy, and very probably also the extragalactic space, at least at the highest observed energies. more than one century after their discovery, we have no definitive models yet about the origin, acceleration and propagation processes of the radiation. the main reason is that there are still significant discrepancies among the results obtained by different experiments located at ground level, probably due to unknown systematic uncertainties affecting the measurements. in this document, we will focus on the detection of galactic cosmic rays from ground with air shower arrays up to 10$^{18}$ ev. the aim of this paper is to discuss the conflicting results in the 10$^{15}$ ev energy range and the perspectives to clarify the origin of the so-called `knee' in the all-particle energy spectrum, crucial to give a solid basis for models up to the end of the cosmic ray spectrum. we will provide elements useful to understand the basic techniques used in reconstructing primary particle characteristics (energy, mass, and arrival direction) from the ground, and to show why indirect measurements are difficult and results are still conflicting. | measurement of energy spectrum and elemental composition of pev cosmic rays: open problems and prospects |
the alpha magnetic spectrometer (ams) is a cosmic ray detector operating onboard the international space station since may 2011 conducting a unique, long-duration mission of fundamental physics research in space. the physics objectives include the precise studies of the origin of dark matter, antimatter, and cosmic rays as well as the exploration of new phenomena. a description of the detector and the main results obtained over 10 years of data taking are presented. this includes the fluxes of positrons, electrons, antiprotons, protons, and nuclei. these results provide unexpected information, which cannot be explained by the current theoretical models. the accuracy and characteristics of the data, simultaneously from many different types of cosmic rays, provide unique input to the understanding of origins, acceleration, and propagation of cosmic rays. the experiment ams-02, thanks to the repair carried out in 2020, will continue to collect data for the lifetime of the international space station promising more interesting physics results on antimatter, cosmic rays particles and last but not least provide hints on dark matter search. | the ams experiment on the international space station |
recent studies have indicated that cosmic ray acceleration by a first-order fermi process in magnetic reconnection current sheets can be efficient enough in the surrounds of compact sources. in this work, we discuss this acceleration mechanism operating in the core region of galactic black hole binaries (or microquasars) and show the conditions under which this can be more efficient than shock acceleration. in addition, we compare the corresponding acceleration rate with the relevant radiative loss rates obtaining the possible energy cut-off of the accelerated particles and also compute the expected spectral energy distribution (sed) for two sources of this class, namely cygnus x-1 and cygnus x-3, considering both leptonic and hadronic processes. the derived seds are comparable to the observed ones in the low- and high-energy ranges. our results suggest that hadronic non-thermal emission due to photomeson production may produce the very high energy gamma-rays in these microquasars. | a magnetic reconnection model for explaining the multiwavelength emission of the microquasars cyg x-1 and cyg x-3 |
recently, active galactic nuclei (agn) have been proposed as "standardizable candles," thanks to an observed nonlinear relation between their x-ray and optical-ultraviolet (uv) luminosities, which provides an independent measurement of their distances. in this paper, we use these observables for the first time to estimate the parameters of f (r ) gravity models (specifically, the hu-sawicki and the exponential models) together with the cosmological parameters. the importance of these types of modified gravity theories lies in the fact that they can explain the late time accelerated expansion of the universe without the inclusion of a dark energy component. we have also included other observable data to the analyses such as estimates of the hubble parameter h (z ) from cosmic chronometers (ccs), the pantheon type ia (snia) supernovae compilation, and baryon acoustic oscillation (bao) measurements. the 1 σ inferred constraints using all datasets are b ≤0.276 , ωm=0.30 4-0.011+0.010, and h0=67.55 3-0.936+1.242 for the hu-sawicki model, and b =0.78 5-0.606+0.409 ωm=0.30 5-0.010+0.011 and h0=68.34 8-0.760+0.959 for the exponential one, but we stress that for both f (r ) models results within 2 σ are consistent with the λ cold dark matter (cdm) model. our results show that the allowed space parameter is restricted when both agn and bao data are added to cc and snia data, with the bao dataset being the most restrictive one. we can conclude that both the λ cdm model and small deviations from general relativity given by the f (r ) models studied in this paper are allowed by the considered observational datasets. | testing f (r ) gravity models with quasar x-ray and uv fluxes |
the study of cosmic expansion history and the late time cosmic acceleration from observational data depends on the nuisance parameters associated with the data. for example, the absolute peak magnitude of type ia supernova associated with the type ia supernova observations and the comoving sound horizon at the baryon drag epoch associated with baryon acoustic oscillation observations are two nuisance parameters. the nuisance parameters associated with the gamma-ray bursts data are also considered. these nuisance parameters are constrained by combining the cosmological observations using the gaussian process regression method with minimal model dependence. the bounds obtained in this method can be used as the prior for the data analysis while considering the observational data accordingly. along with these nuisance parameters, the cosmic curvature density parameter is also constrained simultaneously. we find that the constraints on the cosmic curvature density parameter show no significant deviations from a flat universe. | minimal model-dependent constraints on cosmological nuisance parameters and cosmic curvature from combinations of cosmological data |
we probed the dynamical mass profiles of ten galaxy clusters from the highest x-ray flux galaxy cluster sample (hiflugcs) using galaxy kinematics. we numerically solved the spherical jeans equation and parameterize the dynamical mass profile and the galaxy velocity anisotropy profile using two general functions to ensure that our results are not biased toward any specific model. the mass-velocity anisotropy degeneracy is ameliorated by using two "virial shape parameters" that depend on the fourth moment of velocity distribution. the resulting velocity anisotropy estimates consistently show a nearly isotropic distribution in the inner regions, with an increasing radial anisotropy toward large radii. we compared our derived dynamical masses with those calculated from x-ray gas data assuming hydrostatic equilibrium, finding that massive and rich relaxed clusters generally present consistent mass measurements, while unrelaxed or low-richness clusters have systematically larger total masses than hydrostatic masses by, on average, 50%. this might help alleviate current tensions in the measurement of σ8, but it also leads to cluster baryon fractions below the cosmic value. finally, our approach probes accelerations as low as 10−11 m s−2, comparable to the outskirts of individual late-type galaxies. we confirm that galaxy clusters deviate from the radial acceleration relation defined by galaxies. | measuring galaxy cluster mass profiles into the low-acceleration regime with galaxy kinematics |
radio relics are synchrotron emission found on the periphery of galaxy clusters. from the position and the morphology, it is often believed that the relics are generated by cosmic-ray (cr) electrons accelerated at shocks through a diffusive shock acceleration (dsa) mechanism. however, some radio relics have harder spectra than the prediction of the standard dsa model. one example is observed in the cluster 1rxs j0603.3+4214, which is often called the “toothbrush cluster.” interestingly, the position of the relic is shifted from that of a possible shock. in this study, we show that these discrepancies in the spectrum and the position can be solved if turbulent (re)acceleration is very effective behind the shock. this means that for some relics turbulent reacceleration may be the main mechanism to produce high-energy electrons, contrary to the common belief that it is the dsa. moreover, we show that for efficient reacceleration, the effective mean free path of the electrons has to be much smaller than their coulomb mean free path. we also study the merging cluster 1e 0657-56, or the “bullet cluster,” in which a radio relic has not been found at the position of the prominent shock ahead of the bullet. we indicate that a possible relic at the shock is obscured by the observed large radio halo that is generated by strong turbulence behind the shock. we propose a simple explanation of the morphological differences of radio emission among the toothbrush, the bullet, and the sausage (ciza j2242.8+5301) clusters. | turbulent cosmic-ray reacceleration at radio relics and halos in clusters of galaxies |
spatially compact stellar profiles and old stellar populations have established compact elliptical galaxies (cegs) as local analogs of the high-redshift “red nuggets” thought to represent the progenitors of today’s early-type galaxies (etgs). to address whether the structure of the dark matter (dm) halo in a ceg also reflects the extremely quiescent and isolated evolution of its stars, we use a new ≈122 ks chandra observation together with a shallow ≈13 ks archival observation of the ceg mrk 1216 to perform a hydrostatic equilibrium analysis of the luminous and relaxed x-ray plasma emission extending out to a radius 0.85r 2500. we examine several dm model profiles and in every case obtain a halo concentration (c 200) that is a large positive outlier in the theoretical λcdmc 200-m 200 relation; i.e., ranging from 3.4σ to 6.3σ above the median λcdm relation in terms of the intrinsic scatter. the high value of c 200 we measure implies an unusually early formation time that firmly establishes the relic nature of the dm halo in mrk 1216. the highly concentrated dm halo leads to a higher dm fraction and smaller total mass slope at 1 recompared to nearby normal etgs. in addition, the highly concentrated total mass profile of mrk 1216 cannot be described by modified newtonian dynamics without adding dm, and it deviates substantially from the radial acceleration relation. our analysis of the hot plasma indicates that the halo of mrk 1216 contains ≈80% of the cosmic baryon fraction within r 200. the radial profile of the ratio of cooling time to freefall time varies within a narrow range (t c/t ff ≈ 14-19) over a large central region (r ≤ 10 kpc), suggesting “precipitation-regulated active galactic nucleus feedback” for a multiphase plasma, although there is little evidence at present for cool gas in mrk 1216. finally, other than its compact stellar size, the stellar, gas, and dm properties of mrk 1216 are remarkably similar to those of the nearby fossil group ngc 6482. | the extremely high dark matter halo concentration of the relic compact elliptical galaxy mrk 1216 |
next-generation optical imaging surveys will revolutionize the observations of weak gravitational lensing by galaxy clusters and provide stringent constraints on growth of structure and cosmic acceleration. in these experiments, accurate modelling of covariance matrices of cluster weak lensing plays the key role in obtaining robust measurements of the mean mass of clusters and cosmological parameters. we use a combination of analytical calculations and high-resolution n-body simulations to derive accurate covariance matrices that span from the virial regime to linear scales of the cluster-matter cross-correlation. we validate this calculation using a public ray-tracing lensing simulation and provide a software package for calculating covariance matrices for a wide range of cluster and source sample choices. we discuss the relative importance of shape noise and density fluctuations, the impact of radial bin size, and the impact of off-diagonal elements. for a weak lensing source density ns = 10 arcmin-2, shape noise typically dominates the variance on comoving scales r_p≲ 5 h^{-1} mpc. however, for ns = 60 arcmin-2, potentially achievable with future weak lensing experiments, density fluctuations typically dominate the variance at r_p≳ 1 h^{-1} mpc and remain comparable to shape noise on smaller scales. | covariance matrices for galaxy cluster weak lensing: from virial regime to uncorrelated large-scale structure |
the intracluster medium (icm) is expected to experience on average about three passages of weak shocks with low sonic mach numbers, m ≲ 3, during the formation of galaxy clusters. both protons and electrons could be accelerated to become high energy cosmic rays (crs) at such icm shocks via diffusive shock acceleration (dsa). we examine the effects of dsa by multiple shocks on the spectrum of accelerated crs by including in situ injection/acceleration at each shock, followed by repeated re- acceleration at successive shocks in the test-particle regime. for simplicity, the accelerated particles are assumed to undergo adiabatic decompression without energy loss and escape from the system, before they encounter subsequent shocks. we show that in general the cr spectrum is flattened by multiple shock passages, compared to a single episode of dsa, and that the acceleration efficiency increases with successive shock passages. however, the decompression due to the expansion of shocks into the cluster outskirts may reduce the amplification and flattening of the cr spectrum by multiple shock passages. the final cr spectrum behind the last shock is determined by the accumulated effects of repeated re-acceleration by all previous shocks, but it is relatively insensitive to the ordering of the shock mach numbers. thus multiple passages of shocks may cause the slope of the cr spectrum to deviate from the canonical dsa power-law slope of the current shock. | diffusive shock acceleration by multiple weak shocks |
we report a discovery of a double radio relic in the cluster merger zwcl1447.2+2619 (z = 0.376) with ugmrt observations at 420 mhz and 700 mhz. the linear sizes of the northern and southern relics are ~0.3 mpc and ~1.2 mpc, respectively, which is consistent with the theoretical expectation that a larger relic is produced in the less massive subcluster side. however, zwcl1447.2+2619 is unlike other known double radio relic systems, where the larger relics are much more luminous by several factors. in this merger, the higher surface brightness of the smaller northern relic makes its total radio luminosity comparable to that of the much larger southern relic. the surface brightness ratio ~0.1 between the two radio relics differs significantly from the relation observed in other double radio relic systems. from our radio spectral analysis, we find that both relics signify similar weak shocks with mach numbers of 2.9 ± 0.8 and 2.0 ± 0.7 for the northern and southern relics, respectively. moreover, the northern relic is connected to a discrete radio source with an optical counterpart, which indicates the possible presence of cosmic-ray injection and reacceleration. therefore, we propose that this atypical surface brightness ratio can be explained with the particle acceleration efficiency precipitously dropping in the weak shock regime and/or with reacceleration of fossil cosmic rays. our multi-wavelength analysis and numerical simulation suggest that zwcl1447.2+2619 is a postmerger, which has experienced a near head-on collision ~0.7 gyr ago. | discovery of a double radio relic in zwcl1447.2+2619: a rare testbed for shock-acceleration models with a peculiar surface-brightness ratio |
massive stars blow powerful winds and eventually explode as supernovae. by doing so, they inject energy and momentum in the circumstellar medium, which is pushed away from the star and piles up to form a dense and expanding shell of gas. the effect is larger when many massive stars are grouped together in bound clusters or associations. large cavities form around clusters as a result of the stellar feedback on the ambient medium. they are called superbubbles and are characterised by the presence of turbulent and supersonic gas motions. this makes star clusters ideal environments for particle acceleration, and potential contributors to the observed galactic cosmic ray intensity. | cosmic rays from star clusters |
following evidence for an east-west elongated virial ring around the coma galaxy cluster in a ∼220 gev veritas mosaic, we search for corresponding signatures in >gev γ-rays from fermi-large area telescope (lat), and in soft, ∼0.1 kev x-rays from rosat. for the ring elongation and orientation inferred from veritas, we find a nominal 3.4σ lat excess, and the expected signature (> 5σ ) in rosat bands r1 and r1+r2. the significances of both lat and rosat signals are maximal near the veritas ring parameters. the intensities of the rosat, fermi, and veritas signals are consistent with the virial shock depositing ∼ 0.3 % (with an uncertainty factor of ∼3) of its energy over a hubble time in a nearly flat, p\equiv -d{ln}{n}e/d{ln}e≃ 2.0{--}2.2 spectrum of cosmic-ray electrons. the sharp radial profiles of the lat and rosat signals suggest preferential accretion in the plane of the sky, as indicated by the distribution of neighboring large-scale structures. the x-ray signal gauges the compression of cosmic-rays as they are advected deeper into the cluster. | evidence for an x-ray to gamma-ray virial shock signal from the coma cluster |
we use 1d and 3d two-fluid cosmic ray (cr) hydrodynamic simulations to investigate the role of crs in the vicinity of a compact young star cluster. we model a self-gravitating cloud (density profile ρ∝r-1), include important thermal and non-thermal processes, and explore two different cr injection scenarios. we show that if internal shocks in the wind-driving region are the main site for cr acceleration, then the resulting γ-ray luminosity (lγ) can reach ≈5 per cent of the mechanical luminosity (lw), independent of the fraction of wind energy (∼1-20 per cent) injected into crs. in contrast, if the forward/reverse shock of a bubble is the injection site then lγ increases linearly with the cr injection fraction, as expected analytically. we find that the x-ray luminosity (lx) in the forward/reverse shock injection scenario is ≳ 10-3lw, which is ∼10 times larger than in the central wind-driving injection case. we predict the corresponding range of the synchrotron radio luminosity. we show how multi-wavelength observations can constrain the cr parameters. comparing the predicted multi-wavelength luminosities with those of 30 doradus and westerlund 2 we identify the reverse shock as the most probable cr injection site. we do not find significant dynamical impact of crs in our models. | constraining cosmic ray acceleration in young star clusters using multi-wavelength observations |
it has often been thought that the northern radio relic in the galaxy cluster ciza j2242.8+5301 (the "sausage" cluster) is associated with cosmic ray (cr) electrons that are accelerated at a shock through the diffusive shock acceleration (dsa) mechanism. however, recent radio observations have shown that the radio spectrum is curved, which is inconsistent with the prediction of a simple dsa model. moreover, the cr electron spectrum before being affected by radiative cooling seems to be too hard for dsa. in this study, we show that these facts are natural consequences if the electrons are reaccelerated in turbulence downstream of the shock. in this model, dsa is not the main mechanism for generating high-energy electrons. we find that the mean free path of the electrons should be much shorter than the coulomb mean free path for efficient reacceleration. the scale of the turbulent eddies must be smaller than the width of the relic. we also predict hard x-ray spectra of inverse compton scattering of photons. | turbulent cosmic ray reacceleration and the curved radio spectrum of the radio relic in the sausage cluster |
we propose semi-analytic models for the electron momentum distribution in weak shocks that accounts for both in situ acceleration and re-acceleration through diffusive shock acceleration (dsa). in the former case, a small fraction of incoming electrons is assumed to be reflected at the shock ramp and pre-accelerated to the so-called injection momentum, p_inj, above which particles can diffuse across the shock transition and participate in the dsa process. this leads to the dsa power-law distribution extending from the smallest momentum of reflected electrons, p_ref, all the way to the cutoff momentum, p_eq, constrained by radiative cooling. in the latter case, fossil electrons, specified by a power-law spectrum with a cutoff, are assumed to be re-accelerated from pref up to p_eq via dsa. we show that, in the in situ acceleration model, the amplitude of radio synchrotron emission depends strongly on the shock mach number, whereas it varies rather weakly in the re-acceleration model. considering the rather turbulent nature of shocks in the intracluster medium, such extreme dependence for the in situ acceleration might not be compatible with the relatively smooth surface brightness of observed radio relics. | semi-analytic models for electron acceleration in weak icm shocks |
observations of diffuse radio emission in galaxy clusters indicate that cosmic-ray electrons are accelerated on ∼ mpc scales. however, protons appear to be accelerated less efficiently since their associated hadronic γ-ray emission has not yet been detected. inspired by recent particle-in-cell simulations, we study the cosmic-ray production and its signatures under the hypothesis that the efficiency of shock acceleration depends on the mach number and on the shock obliquity. for this purpose, we combine enzo cosmological magneto-hydrodynamical simulations with a lagrangian tracer code to follow the properties of the cosmic rays. our simulations suggest that the distribution of obliquities in galaxy clusters is random to first order. quasi-perpendicular shocks are able to accelerate cosmic-ray electrons to the energies needed to produce observable radio emission. however, the γ-ray emission is lowered by a factor of a few, ∼3 , if cosmic-ray protons are only accelerated by quasi-parallel shocks, reducing (yet not entirely solving) the tension with the non-detection of hadronic γ-ray emission by the fermi-satellite. | studying the effect of shock obliquity on the γ-ray and diffuse radio emission in galaxy clusters |
while it is well known that cosmic rays (crs) can gain energy from turbulence via second-order fermi acceleration, how this energy transfer affects the turbulent cascade remains largely unexplored. here, we show that damping and steepening of the compressive turbulent power spectrum are expected once the damping time ${t}_{\mathrm{damp}}\sim \rho {v}^{2}/{\dot{e}}_{\mathrm{cr}}\propto {e}_{\mathrm{cr}}^{-1}$ becomes comparable to the turbulent cascade time. magnetohydrodynamic simulations of stirred compressive turbulence in a gas-cr fluid with diffusive cr transport show clear imprints of cr-induced damping, saturating at ${\dot{e}}_{\mathrm{cr}}\sim \tilde{\epsilon }$ , where $\tilde{\epsilon }$ is the turbulent energy input rate. in that case, almost all of the energy in large-scale motions is absorbed by crs and does not cascade down to grid scale. through a hodge-helmholtz decomposition, we confirm that purely compressive forcing can generate significant solenoidal motions, and we find preferential cr damping of the compressive component in simulations with diffusion and streaming, rendering small-scale turbulence largely solenoidal, with implications for thermal instability and proposed resonant scattering of e ≳ 300 gev crs by fast modes. when cr transport is streaming dominated, crs also damp large-scale motions, with kinetic energy reduced by up to 1 order of magnitude in realistic e cr ~ e g scenarios, but turbulence (with a reduced amplitude) still cascades down to small scales with the same power spectrum. such large-scale damping implies that turbulent velocities obtained from the observed velocity dispersion may significantly underestimate turbulent forcing rates, i.e., $\tilde{\epsilon }\gg \rho {v}^{3}/l$ . | cosmic-ray drag and damping of compressive turbulence |
sagittarius a* (sgr a*) is a potential very high energy (vhe) γ-ray and cosmic-ray source. we examine limits to gap-type particle acceleration in the magnetosphere of sgr a*, showing that in the current phase of activity proton acceleration to pev energies is possible, with injection powers into the environment usually limited to several 1036 erg s-1. compton upscattering of ambient soft photons by gap-accelerated electrons could yield tev emission compatible with the detected vhe point source. we explore the dependency of the results on changes in the accretion rate showing that higher stages in the past are unlikely to increase the power output unless the inner accretion flows itself changed its configuration. | constraining cosmic-ray acceleration in the magnetospheric gaps of sgr a* |
galaxy clusters accrete mass through large-scale, strong, structure-formation shocks. such a virial shock is thought to deposit fractions ξe and ξb of the thermal energy in cosmic-ray electrons (cres) and magnetic fields, respectively, thus generating a leptonic virial ring. however, the expected synchrotron signal was not convincingly established until now. we stack low-frequency radio data from the ovro-lwa around the 44 most massive, high latitude, extended mcxc clusters, enhancing the ring sensitivity by rescaling clusters to their characteristic, r500 radii. both high (73 mhz) and co-added low (36-68 mhz) frequency channels separately indicate a significant (4-5σ) excess peaked at (2.4-2.6)r500, coincident with a previously stacked fermi γ-ray signal interpreted as inverse-compton emission from virial-shock cres. the stacked radio signal is well fit (ts-test: 4-6σ at high frequency, 4-8σ at low frequencies, and 8-10σ joint) by virial-shock synchrotron emission from the more massive clusters, with $\dot{m}\xi _e\xi _b\simeq (1\!-\!4)\times 10^{-4}$, where $\dot{m}\equiv \dot{m}/(mh)$ is the dimensionless accretion rate for a cluster of mass m and a hubble constant h. the inferred cre spectral index is flat, p ≃ 2.0 ± 0.2, consistent with acceleration in a strong shock. assuming equipartition or using $\dot{m}\xi _e\sim 0.6~{{\ \rm per\ cent}}$ inferred from the fermi signal yields $\xi _b\simeq (2\!-\!9)~{{\ \rm per\ cent}}$, corresponding to b ≃ (0.1-0.3) $\mu$g magnetic fields downstream of typical virial shocks. preliminary evidence suggests non-spherical shocks, with factor 2-3 elongations. | synchrotron emission from virial shocks around stacked ovro-lwa galaxy clusters |
radio relics are diffuse synchrotron sources that illuminate shock waves in the intracluster medium. in recent years, radio telescopes have provided detailed observations about relics. consequently, cosmological simulations of radio relics need to provide a similar amount of detail. in this methodological work, we include information on adiabatic compression and expansion, which have been neglected in the past in the modelling of relics. in a cosmological simulation of a merging galaxy cluster, we follow the energy spectra of shock accelerated cosmic-ray electrons using lagrangian tracer particles. on board of each tracer particle, we compute the temporal evolution of the energy spectrum under the influence of synchrotron radiation, inverse compton scattering, and adiabatic compression and expansion. exploratory tests show that the total radio power and, hence, the integrated radio spectrum are not sensitive to the adiabatic processes. this is attributed to small changes in the compression ratio over time. | modelling the energy spectra of radio relics |
the debate on the nature of the gamma-ray emission from young supernova remnants is still open. ascribing such emission to hadronic rather than leptonic processes would provide an evidence for the acceleration of protons and nuclei, and this fact would fit with the very popular (but not proven) paradigm that supernova remnants are the sources of galactic cosmic rays. here, we discuss this issue with a particular focus on the best studied gamma-ray-bright supernova remnant: rx j1713.7-3946. | gamma-ray emission from young supernova remnants: hadronic or leptonic? |
we perform spatial and spectral analyses of the lmc gamma-ray emission collected over 66 months by the fermi gamma-ray space telescope. in our spatial analysis, we model the lmc cosmic-ray distribution and gamma-ray production using observed maps of the lmc interstellar medium, star formation history, interstellar radiation field, and synchrotron emission. we use bootstrapping of the data to quantify the robustness of spatial model performance. we model the lmc gamma-ray spectrum using fitting functions derived from the physics of π0 decay, bremsstrahlung, and inverse compton scattering. we find the integrated gamma-ray flux of the lmc from 200 mev to 20 gev to be 1.37 ± 0.02 × 10-7 ph cm-2 s-1, of which we attribute about 6% to inverse compton scattering and 44% to bremsstrahlung. from our work, we conclude that the spectral index of the lmc cosmic-ray proton population is 2.4 ± 0.2, and we find that cosmic-ray energy loss through gamma-ray production is concentrated within a few 100 pc of acceleration sites. assuming cosmic-ray energy equipartition with magnetic fields, we estimate lmc cosmic rays encounter an average magnetic field strength ∼3 μg. | spatial and spectral modeling of the gamma-ray distribution in the large magellanic cloud |
supernova remnants (snrs) are prime candidates for efficient particle acceleration up to the knee in the cosmic ray particle spectrum. in this work we present a new method for a systematic search for new tev-emitting snr shells in 2864 hours of h.e.s.s. phase i data used for the h.e.s.s. galactic plane survey. this new method, which correctly identifies the known shell morphologies of the tev snrs covered by the survey, hess j1731-347, rx 1713.7-3946, rcw 86, and vela junior, reveals also the existence of three new snr candidates. all three candidates were extensively studied regarding their morphological, spectral, and multi-wavelength (mwl) properties. hess j1534-571 was associated with the radio snr candidate g323.7-1.0, and thus is classified as an snr. hess j1912+101 and hess j1614-518, on the other hand, do not have radio or x-ray counterparts that would permit to identify them firmly as snrs, and therefore they remain snr candidates, discovered first at tev energies as such. further mwl follow up observations are needed to confirm that these newly discovered snr candidates are indeed snrs. | discovery of new tev supernova remnant shells in the galactic plane with h.e.s.s. |
galaxy clusters are known to host many active galaxies (agns) with radio jets, which could expand to form radio bubbles with relativistic electrons in the intracluster medium (icm). it has been suggested that fossil relativistic electrons contained in remnant bubbles from extinct radio galaxies can be re-accelerated to radio-emitting energies by merger-driven shocks via diffusive shock acceleration (dsa), leading to the birth of radio relics detected in clusters. in this study we assume that such bubble consist primarily of thermal gas entrained from the surrounding medium and dynamically-insignificant amounts of relativistic electrons. we also consider several realistic models for magnetic fields in the cluster outskirts, including the icm field that scales with the gas density as b_{icm}∝ n_{icm}^{0.5}. then we perform time-dependent dsa simulations of a spherical shock that runs into a lower-density but higher-temperature bubble with the ratio n_{b}/n_{icm} ≈ t_{icm}/t_{b}≈ 0.5. we find that inside the bubble the shock speed increases by about 20 %, but the mach number decreases by about 15% in the case under consideration. in this re-acceleration model, the observed properties of a radio relic such as radio flux, spectral index, and integrated spectrum would be governed mainly by the presence of seed relativistic electrons and the magnetic field profile as well as shock dynamics. thus it is crucial to understand how fossil electrons are deposited by agns in the icm and how the downstream magnetic field evolves behind the shock in detailed modeling of radio relics.} | re-acceleration of fossil electrons by shocks encountering hot bubbles in the outskirts of galaxy clusters |
we report on results of our upgraded giant metrewave radio telescope (ugmrt) observations for an early-stage merging galaxy cluster, ciza j1358.9-4750 (ciza1359), in band-3 (300-500 mhz). we achieved the image dynamic range of ~38000 using the direction dependent calibration and found a candidate of diffuse radio emission at 4σrms significance. the flux density of the candidate at 400 mhz, 24.04 ± 2.48 mjy, is significantly positive compared to noise, where its radio power, 2.40 × 1024 w hz-1, is consistent with those of typical diffuse radio sources of galaxy clusters. the candidate is associated with a part of the x-ray shock front at which the mach number reaches its maximum value of $\mathcal {m}\sim 1.7$. the spectral index (fν ∝ να) of the candidate, α = -1.22 ± 0.33, is in agreement with an expected value derived from the standard diffusive shock acceleration (dsa) model. however, such a low mach number with a short acceleration time would require seed cosmic rays supplied from active galactic nucleus (agn) activities of member galaxies, as suggested in some other clusters. indeed, we found seven agn candidates inside the diffuse source candidate. assuming the energy equipartition between magnetic fields and cosmic rays, the magnetic field strength of the candidate was estimated to be 2.1 μg. we also find head-tail galaxies and radio phoenixes or fossils near ciza1359. | diffuse radio source candidate in ciza j1358.9-4750 |
amongst the population of tev gamma-ray sources detected with the high energy stereoscopic system (h.e.s.s.) in the galactic plane, clearly identified supernova remnant (snr) shells constitute a small but precious source class. tev-selected snrs are prime candidates for sources of efficient cosmic-ray acceleration. in this work, we present new snr candidates that have been identified in the entire h.e.s.s. phase i data set of the galactic plane recorded over the past ten years. identification with a known snr shell candidate was successful for one new source, hess j1534-571. in other cases, tev-only shell candidates are challenging to firmly identify as snrs due to their lack of detected non-thermal emission in lower energy bands. we will discuss how these objects may present an important link between young and evolved snrs, since their shell emission may be dominated by hadronic processes. | search for new supernova remnant shells in the galactic plane with h.e.s.s. |
we report on the search for steady point-like sources of neutral particles around 1018 ev between 2008 and 2013 may with the scintillator sd of the telescope array experiment. we found overall no significant point-like excess above 0.5 eev in the northern sky. subsequently, we also searched for coincidence with the fermi bright galactic sources. no significant coincidence was found within the statistical uncertainty. hence, we set an upper limit on the neutron flux that corresponds to an averaged flux of 0.07 km-2 yr-1 for e\gt 1 eev in the northern sky at the 95% confidence level. this is the most stringent flux upper limit in a northern sky survey assuming point-like sources. the upper limit at the 95% confidence level on the neutron flux from cygnus x-3 is also set to 0.2 km-2 yr-1 for e\gt 0.5 eev. this is an order of magnitude lower than previous flux measurements. | a northern sky survey for point-like sources of eev neutral particles with the telescope array experiment |
cosmic rays (crs) play an important role in many astrophysical systems. acting on plasma scales to galactic environments, crs are usually modelled as a fluid, using the cr energy density as the evolving quantity. this method comes with the flaw that the corresponding cr evolution equation is not in conservative form as it contains an adiabatic source term that couples crs to the thermal gas. in the absence of non-adiabatic changes, instead evolving the cr entropy density is a physically equivalent option that avoids this potential numerical inconsistency. in this work, we study both approaches for evolving crs in the context of magnetohydrodynamic (mhd) simulations using the massively parallel moving-mesh code arepo. we investigate the performance of both methods in a sequence of shock-tube tests with various resolutions and shock mach numbers. we find that the entropy-conserving scheme performs best for the idealized case of purely adiabatic crs across the shock while both approaches yield similar results at lower resolution. in this set-up, both schemes operate well and almost independently of the shock mach number. taking active cr acceleration at the shock into account, the energy-based method proves to be numerically much more stable and significantly more accurate in determining the shock velocity, in particular at low resolution, which is more typical for astrophysical large-scale simulations. for a more realistic application, we simulate the formation of several isolated galaxies at different halo masses and find that both numerical methods yield almost identical results with differences far below common astrophysical uncertainties. | comparing energy and entropy formulations for cosmic ray hydrodynamics |
it is recently proposed that cosmic rays generate a seed magnetic field in the early universe. in this paper, we propose another generation mechanism of magnetic fields by cosmic rays, which is the biermann battery driven by resistive heating induced by the streaming of cosmic rays. this mechanism is dominant in small-scale, low-temperature, and strongly ionized regions, compared with other previously proposed mechanisms. because cosmic rays are expected to be accelerated after the death of the first stars, this mechanism can work during structure formation in the early universe. we show that it makes the seed magnetic field with sufficient strength for the subsequent dynamo to amplify it to the micro gauss level in the current galaxies. | biermann battery powered by resistive heating induced by cosmic ray streaming |
the ultrarelativistic generalized lorentzian quasi-equilibrium thermodynamic energy distribution is tentatively applied to the energy spectrum of galactic cosmic ray fluxes. it is found that 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 is estimated from the deviation of the fluxes at decreasing energy, presumably throwing light on the cosmic ray acceleration mechanism. a relation between involved turbulent volumina and structure functions is obtained. the conclusions drawn hold only within the realm of applicability of thermodynamics to cosmic ray spectra. | the differential cosmic ray energy flux in the light of an ultrarelativistic generalized lorentzian thermodynamics |
we present the results of suzaku and chandra observations of the galaxy cluster rxc j1053.7+5453 (z = 0.0704), which contains a radio relic. the radio relic is located at a distance of ∼540 kpc from the x-ray peak toward the west. we measured the temperature of this cluster for the first time. the resultant temperature in the center is ∼1.3 kev, which is lower than the value expected from the x-ray luminosity-temperature and the velocity dispersion-temperature relations. though we did not find a significant temperature jump at the outer edge of the relic, our results suggest that the temperature decreases outward across the relic. assuming the existence of the shock at the relic, its mach number becomes m ≃ 1.4. a possible spatial variation of mach number along the relic is suggested. additionally, a sharp surface brightness edge is found at a distance of ∼160 kpc from the x-ray peak toward the west in the chandra image. we performed x-ray spectral and surface brightness analyses around the edge with the suzaku and chandra data, respectively. the obtained surface brightness and temperature profiles suggest that this edge is not a shock but likely a cold front. alternatively, it cannot be ruled out that thermal pressure is really discontinuous across the edge. in this case, if the pressure across the surface brightness edge is in equilibrium, other forms of pressure sources, such as cosmic-rays, are necessary. we searched for the non-thermal inverse compton component in the relic region. assuming a photon index γ = 2.0, the resultant upper limit of the flux is 1.9 × 10-14 erg s-1 cm-2 for a 4.50 × 10-3 deg2 area in the 0.3-10 kev band, which implies that the lower limit of magnetic field strength becomes 0.7 μg. | suzaku and chandra observations of the galaxy cluster rxc j1053.7+5453 with a radio relic |
experimental evidence has accumulated to indicate that wakefield acceleration (wfa) accompanies intense and sometimes coherent emission of radiation such as from betatron radiation. the investigation of this issue has additional impetus nowadays because we are learning (1) there is an additional acceleration process of the ponderomotive acceleration; (2) wfa may become relevant in much higher density regimes; (3) wfa has been proposed as the mechanism for extreme high energy cosmic ray acceleration and gamma ray bursts for active galactic nuclei. these require us to closely examine the radiative mechanisms in wfa anew. we report studies of radiation from wakefield (self-injected betatron) and ponderomotive (laser field) mechanisms in scalings of the frequency and intensity of the driver, as well as the plasma density. | high energy photon emission from wakefields |
the large gap between a galactic dark matter subhalo's velocity and its own gravitational binding velocity creates the situation that small subhalos can be evaporated before dark matter thermalize with baryons due to the low binding velocity. in case dark matter acquires an electromagnetic dipole moment, the survival of low-mass subhalos requires stringent limits on the photon-mediated soft scattering. the current stringent direct detection limits indicate for a small dipole moment, which lets dm decouple early and allows small subhalos to form. we calculate the dm kinetic decoupling temperature in the early universe and evaluate the smallest protohalo mass. in the late universe, low-mass subhalos can be evaporated via soft collision by ionized gas and accelerated cosmic rays. we calculate the subhalos evaporation rate and show that subhalos lighter than 10-5m⊙ in the gaseous inner galactic region are subject to evaporation via dark matter's effective electric and magnetic dipole moments below current direct detection limits, which potentially affects the low-mass subhalos distribution in the galactic center. | soft scattering evaporation of dark matter subhalos by inner galactic gases |
it is suggested that the decline with energy of the boron-to-carbon abundance ratio in galactic cosmic rays is due, in part, to a correlation between the maximum energy attainable by shock acceleration in a given region of the galactic disk and the grammage traversed before escape. in this case the energy dependence of the escape rate from the galaxy may be less than previously thought and the spectrum of antiprotons becomes easier to understand. | an alternative explanation of the varying boron-to-carbon ratio in galactic cosmic rays |
supernova remnants are supposed to be the most possible sources of cosmic rays. however, alternative sources of cosmic rays, such as an active galactic nucleus, gamma-ray bursts, and pulsars, have not be excluded. in this study, we investigate the possibility of cosmic rays being generated by pulsars. the pulsar is simply described as a rotational magnetic dipole, the so-called hertzian magnetic dipole, an exact solution of the d'alembert equations. in the rotational magnetic dipole field, charged particles experience an accelerated electric field with their radiation reaction. the particles, which are initially static out of the light cylinder radius, can be accelerated up to a high energy. * supported by grants from nsfc (11675182, 11690022) | particles accelerated in hertzian magnetic dipole field of a pulsar |
superclusters and galaxy clusters offer a wide range of astrophysical science topics with regards to studying the evolution and distribution of galaxies, intra-cluster magnetization mediums, cosmic ray accelerations and large scale diffuse radio sources all in one observation. recent developments in new radio telescopes and advanced calibration software have completely changed data quality that was never possible with old generation telescopes. hence, radio observations of superclusters are a very promising avenue to gather rich information of a large-scale structure (lss) and their formation mechanisms. these newer wide-band and wide field-of-view (fov) observations require state-of-the-art data analysis procedures, including calibration and imaging, in order to provide deep and high dynamic range (dr) images with which to study the diffuse and faint radio emissions in supercluster environments. sometimes, strong point sources hamper the radio observations and limit the achievement of a high dr. in this paper, we have shown the dr improvements around strong radio sources in the meerkat observation of the saraswati supercluster by applying newer third-generation calibration (3gc) techniques using cubical and killms software. we have also calculated the statistical parameters to quantify the improvements around strong radio sources. this analysis advocates for the use of new calibration techniques to maximize the scientific returns from new-generation telescopes. | third-generation calibrations for meerkat observation |
the dependence of the cosmic ray intensity on galactocentric distance is known to be much less rapid than that of the thought-to-be sources: supernova remnants. this is an old problem ('the radial gradient problem') which has led to a number of possible 'scenarios'. here, we use recent data on the supernova remnant's radial distribution and correlate it with the measured hii electron temperature (t). we examined two models of cosmic ray injection and acceleration and in both of them the injection efficiency increases with increasing ambient temperature t. the increase is expected to vary as a high power of t in view of the strong temperature-dependence of the tail of the maxwell-boltzmann distribution of particle energies. writing the efficiency as proportional to tn we find n ≈ 8.4 . there is thus, yet another possible explanation of the radial gradient problem. | the radial gradient of cosmic ray intensity in the galaxy |
we examine the new galactic supernova remnant (snr) candidate, g23.11+0.18, as seen by the murchison widefield array radio telescope. we describe the morphology of the candidate and find a spectral index of -0.63 ± 0.05 in the 70-170 mhz domain. coincident tev gamma-ray detection in high energy stereoscopic system (hess) data supports the snr nature of g23.11+0.18 and suggests that g23.11+0.18 is accelerating particles beyond tev energies, thus making this object a promising new cosmic-ray hadron source candidate. the remnant cannot be seen in current optical, infrared and x-ray data sets. we do find, however, a dip in co-traced molecular gas at a line-of-sight velocity of ∼85 km s-1, suggesting the existence of a g23.11+0.18 progenitor wind-blown bubble. furthermore, the discovery of molecular gas clumps at a neighboring velocity toward hess j1832-085 adheres to the notion that a hadronic gamma-ray production mechanism is plausible toward the north of the remnant. based on these morphological arguments, we propose an interstellar medium association for g23.11+0.18 at a kinematic distance of 4.6 ± 0.8 kpc. | a supernova remnant counterpart for hess j1832-085 |
recent discovery of fast blue optical transients (fbots)—a new class of energetic transient sources—can shed light on the long-standing problem of supernova—long gamma-ray burst connections. a distinctive feature of such objects is the presence of modestly relativistic outflows which place them in between the non-relativistic and relativistic supernovae-related events. here we present the results of kinetic particle-in-cell and monte carlo simulations of particle acceleration and magnetic field amplification by shocks with the velocities in the interval between 0.1 and 0.7 c. these simulations are needed for the interpretation of the observed broad band radiation of fbots. their fast, mildly to moderately relativistic outflows may efficiently accelerate relativistic particles. with particle-in-cell simulations we demonstrate that synchrotron radiation of accelerated relativistic electrons in the shock downstream may fit the observed radio fluxes. at longer timescales, well beyond those reachable within a particle-in-cell approach, our nonlinear monte carlo model predicts that protons and nuclei can be accelerated to petaelectronvolt (pev) energies. therefore, such fast and energetic transient sources can contribute to galactic populations of high energy cosmic rays. | particle acceleration in mildly relativistic outflows of fast energetic transient sources |
one of the primary current astrobiological goals is to understand the limits of microbial resistance to extraterrestrial conditions. much attention is paid to ionizing radiation, since it can prevent the preservation and spread of life outside the earth. the aim of this research was to study the impact of accelerated he ions (150 mev/n, up to 1 kgy) as a component of the galactic cosmic rays on the black fungus c. antarcticus when mixed with antarctic sandstones—the substratum of its natural habitat—and two martian regolith simulants, which mimics two different evolutionary stages of mars. the high dose of 1 kgy was used to assess the effect of dose accumulation in dormant cells within minerals, under long-term irradiation estimated on a geological time scale. the data obtained suggests that viable earth-like microorganisms can be preserved in the dormant state in the near-surface scenario for approximately 322.000 and 110.000 earth years within martian regolith that mimic early and present mars environmental conditions, respectively. in addition, the results of the study indicate the possibility of maintaining traces within regolith, as demonstrated by the identification of melanin pigments through ultraviolet-visible (uv-vis) spectrophotometric approach. | the responses of the black fungus cryomyces antarcticus to high doses of accelerated helium ions radiation within martian regolith simulants and their relevance for mars |
an introduction is given to a meeting on the role of massive and stellar black holes in powering non-thermal activity in a rich variety of cosmic sources. relevant properties of magnetized, spinning black holes are summarized and their observational expression, within galactic nuclei, in terms of radio loudness and fanaroff-riley class, is briefly described. the dependence of the accretion mode on the rate and manner of the mass supply beyond the black hole sphere of influence is also discussed. it is argued that hydromagnetic outflows from accretion disks are generally expected over as many as six decades of radius and that they may be the source of emission line gas. these outflows collimate the relativistic jets which are probably generated in an electromagnetic form but become hydromagnetic as they entrain gas through boundary layers where most of the initial nonthermal emission occurs. it is proposed that the particle acceleration close to the hole emphasizes the proton channel which allows secondary pairs to be created at far higher energies than is possible from direct acceleration. these pairs radiate synchrotron gamma-rays which can escape along the jet because the outflow effectively shields them from pair-producing, soft photons. jets are subject to helical instabilities which can tangle their magnetic field and may destroy them. the jet should become plasma-dominated through intermittent, "magnetoluminescent" untangling of the field which causes nonthermal emission all along its length. powerful jets remain supersonic out to the "hot spots" at the extremities of the source; weaker jets become subsonic plumes or bubbles. the prospects for learning much more about the nature and operation of jets over the next decade are excellent. | black holes as cosmic dynamos |
based on the collective linear and nonlinear processes in a magnetized plasma surrounding the black hole at the galactic center (gc), an acceleration mechanism is proposed to explain the recent detection/discovery of pev protons. in a two-stage process, the gravitation energy is first converted to the electrical energy in fast-growing langmuir waves, and then the electrical energy is transformed to the particle kinetic energy through landau damping of waves. it is shown that, for the characteristic parameters of gc plasma, proton energy can be boosted up to 5 pev. | on the rotationally driven pevatron in the center of the milky way |
galaxy clusters are the largest and most massive bound objects resulting from cosmic hierarchical structure formation. baryons account for somewhat more than 10% of that mass, with roughly 90% of the baryonic matter distributed throughout the clusters as hot ($t>1$ kev), high-$\beta$, very weakly collisional plasma; the so-called "intracluster medium" (icm). cluster mergers, close gravitational encounters and accretion, along with violent feedback from galaxies and relativistic jets from active galactic nuclei, drive winds, gravity waves, turbulence and shocks within the icm. those dynamics, in turn, generate cluster-scale magnetic fields and accelerate and mediate the transport of high-energy charged particles. kinetic-scale, collective plasma processes define the basic character and fundamental signatures of these icm phenomena, which are observed primarily by x-ray and radio astronomers. | plasma 2020 - intracluster medium plasmas |
hessj1826-130 is an unidentified hard spectrum source discovered by h.e.s.s. along the galactic plane, the spectral index being γ = 1.6 with an exponential cut-off at about 12 tev. while the source does not have a clear counterpart at longer wavelengths, the very hard spectrum emission at tev energies implies that electrons or protons accelerated up to several hundreds of tev are responsible for the emission. in the hadronic case, the vhe emission can be produced by runaway cosmic-rays colliding with the dense molecular clouds spatially coincident with the h.e.s.s. source. | hess j1826-130: a very hard γ-ray spectrum source in the galactic plane |
supernovae (sne) are the dominant source of chemical enrichment of galaxies, and they are an important source of energy to heat the interstellar medium and accelerate cosmic rays. our knowledge of sne in the milky way is based mostly on the study of galactic supernova remnants (snrs), providing an (incomplete) record to sn activity over the last ~100 000 yr. here, we report on an investigation of the spatial distribution of galactic snrs. given the limited number of snrs, it is common to assume a functional form for the galactocentric distribution of snrs. however, several functional forms have been used in the past, without much justification for the radial distribution. for example, one often used functional form implies that no sn activity is present in the galactic centre region. however, the presence of a magnetar and an snr near the galactic centre suggests that a spatial distribution with zero snrs at the galactic centre is not realistic. in light of these concerns, we re-evaluate the galactic snr distribution. we provide a brief outline of the main detection biases in finding snrs and we investigate whether or not the use of the most common functional form is justified and how it compares to other models for the snr distribution. we do this by analysing the longitudinal distribution of snrs. we find that a simple exponential distribution is the most consistent and simplest model for describing the radial snr distribution in the galaxy and draw comparisons with the massive star formation and metallicity distributions. | the radial supernova remnant distribution in the galaxy |
we report the emergence of a new h i 21-cm absorption at zabs = 1.172 635 in the damped lyα absorber (dla) towards the γ-ray blazar pks 2355-106 (zem~1.639) using science verification observations (2020 june) from the meerkat absorption line survey (mals). since 2006, this dla is known to show a narrow h i 21-cm absorption at zabs = 1.173019 coinciding with a distinct metal absorption-line component. we do not detect significant h i 21-cm optical depth variations from this known h i component. a high-resolution optical spectrum (2010 august) shows a distinct mg i absorption at the redshift of the new h i 21-cm absorber. however, this component is not evident in the profiles of singly ionized species. we measure the metallicity ([zn/h] = -(0.77 ± 0.11) and [si/h]= -(0.96 ± 0.11)) and depletion ([fe/zn] = -(0.63 ± 0.16)) for the full system. using the apparent column density profiles of si ii, fe ii, and mg i, we show that the depletion and the n(mg i)/n(si ii) column density ratio systematically vary across the velocity range. the region with high depletion tends to have a slightly larger n(mg i)/n(si ii) ratio. the two h i 21-cm absorbers belong to this velocity range. the emergence of zabs = 1.172 635 can be understood if there is a large optical depth gradient over a length-scale of ~0.35 pc. however, the gas producing the zabs = 1.173 019 component must be nearly uniform over the same scale. systematic uncertainties introduced by the absorption-line variability has to be accounted for in experiments measuring the variations of fundamental constants and cosmic acceleration even when the radio emission is apparently compact as in pks 2355-106. | emergence of a new h i 21-cm absorption component at z 1.1726 towards the γ-ray blazar pks 2355-106 |
pair cascades from millisecond pulsars (msps) may be a primary source of galactic electrons and positrons that contribute to the increase in positron flux above 10 gev as observed by pamela and ams-02. the fermi large area telescope (lat) has increased the number of detected gamma-ray msps tremendously. light curve modelling furthermore favours abundant pair production in msp magnetospheres, so that models of primary cosmic-ray positrons from pulsars should include the contribution from the larger numbers of msps and their potentially higher positron output per source. we model the contribution of galactic msps to the terrestrial cosmic-ray electron / positron flux by using a population synthesis code to predict the source properties of present-day msps. we simulate pair spectra assuming an offset-dipole magnetic field which boosts pair creation rates. we also consider positrons and electrons that have additionally been accelerated to very high energies in the strong intrabinary shocks in black widow (bw) and redback (rb) binary systems. we transport these particles to earth by calculating their diffusion and the radiative energy losses they suffer in the galaxy using a model. our model particle flux increases for non-zero offsets of the magnetic polar caps. we find that pair cascades from msp magnetospheres contribute only modestly around a few tens of gev to the measured fluxes. bw and rb fluxes may reach a few tens of percent of the observed flux up to a few tev. future observations should constrain the source properties in this case. | the millisecond pulsar contribution to the rising positron fraction |
context. the diffusive shock acceleration mechanism has been widely accepted as the acceleration mechanism for galactic cosmic rays. while self-consistent hybrid simulations have shown how power-law spectra are produced, detailed information on the interplay of diffusive particle motion and the turbulent electromagnetic fields responsible for repeated shock crossings are still elusive.aims: the framework of test-particle theory is applied to investigate the effect of diffusive shock acceleration by inspecting the obtained cosmic-ray energy spectra. the resulting energy spectra can be obtained this way from the particle motion and, depending on the prescribed turbulence model, the influence of stochastic acceleration through plasma waves can be studied.methods: a numerical monte-carlo simulation code is extended to include collisionless shock waves. this allows one to trace the trajectories of test particle while they are being accelerated. in addition, the diffusion coefficients can be obtained directly from the particle motion, which allows for a detailed understanding of the acceleration process.results: the classic result of an energy spectrum with e-2 is only reproduced for parallel shocks, while, for all other cases, the energy spectral index is reduced depending on the shock obliqueness. qualitatively, this can be explained in terms of the diffusion coefficients in the directions that are parallel and perpendicular to the shock front. | cosmic-ray acceleration at collisionless astrophysical shocks using monte-carlo simulations |
we consider cosmic ray (cr) modified shocks with both streaming and diffusion in the two-fluid description. previously, numerical codes were unable to incorporate streaming in this demanding regime, and have never been compared against analytic solutions. first, we find a new analytic solution highly discrepant in acceleration efficiency from the standard solution. it arises from bi-directional streaming of crs away from the subshock, similar to a zeldovich spike in radiative shocks. since fewer crs diffuse back upstream, this results in a much lower acceleration efficiency, typically $\sim 10\%$ as opposed to $\sim 50\%$ found in previous analytic work. at mach number $\gtrsim 10$, the new solution bifurcates into 3 branches, with efficient, intermediate and inefficient cr acceleration. our two-moment code (jiang & oh 2018) accurately recovers these solutions across the entire parameter space probed, with no ad hoc closure relations. for generic initial conditions, the inefficient branch is the most robust and preferred solution. the intermediate branch is unstable, while the efficient branch appears only when the inefficient branch is not allowed (for cr dominated or high plasma $\beta$ shocks). cr modified shocks have very long equilibration times ($\sim 1000$ diffusion time) required to develop the precursor, which must be resolved by $\gtrsim 10$ cells for convergence. non-equilibrium effects, poor resolution and obliquity of the magnetic field all reduce cr acceleration efficiency. shocks in galaxy scale simulations will generally contribute little to cr acceleration without a subgrid prescription. | fluid simulations of cosmic ray modified shocks |
the x-ray emission from the knots of the kiloparsec scale jet of active galactic nuclei (agn) suggests the high energy emission process is different from the radio/optical counterpart. interpretation based on the inverse compton scattering of cosmic microwave photons has been ruled out through fermi γ-ray observations for low-redshift sources. as an alternate explanation, synchrotron emission from a different electron population is suggested. we propose a model considering the advected electron distribution from the sites of particle acceleration in agn knots. this advected electron distribution is significantly different from the accelerated electron distribution and satisfies the requirement of the second electron population. the synchrotron emission from the accelerated and the advected electron distribution can successfully reproduce the observed radio-to-x-ray fluxes of the knots of 3c 273. for the chosen combination of the model parameters, the spectrum due to inverse compton scattering of cosmic microwave photons falls within the fermi γ-ray upper limits. | advection of accelerated electrons in radio/x-ray knots of agn jets |
we investigate the production of magnetic flux from rotating black holes in active galactic nuclei (agns) and compare it with the upper limit of ultrahigh energy cosmic ray (uhecr) luminosities, calculated from observed integral flux of gev-tev gamma rays for nine uhecr agn sources. we find that, for the expected range of black hole rotations (0.44 <a <0.80 ), the corresponding bounds of theoretical magnetic luminosities from agns coincides with the calculated uhecr luminosity. we argue that such result possibly can contribute to constrain agn magnetic and dynamic properties as phenomenological tools to explain the requisite conditions to proper accelerate the highest energy cosmic rays. | luminosity of ultrahigh energy cosmic rays and bounds on magnetic luminosity of radio-loud active galactic nuclei |
in this paper, we study centrifugal acceleration of particles moving along a prescribed rotating curved trajectories. we consider the physical system embedded in an isotropic photon field and study the influence of the photon drag force on the acceleration process. for this purpose, we study three major configurations of the field lines: the straight line, the archimede spiral and the dipolar field line configuration. by analyzing dynamics of particles sliding along the field lines in the equatorial plane, we have found several interesting features of motion. in particular, it has been shown that for rectilinear field lines, the particles reach the light cylinder (area where the linear velocity of rotation exactly equals the speed of light) zone relatively slowly for bigger drag forces. considering the archimedes’ spiral, we have found that in cases when the field lines lag behind the rotation, the particles achieve the force-free regime of dynamics regardless of the drag force. unlike this scenario, when the spiral is oriented in an opposite direction, the particles do not reach the force free regime, but tend to stable equilibrium locations. | centrifugal acceleration in the isotropic photon field |
in this paper, we study relativistic dynamics of charged particles corotating with prescribed trajectories, having the shape of dipolar magnetic field lines. in particular, we consider the role of the drag force caused by the photon field the forming of equilibrium positions of the charged particles. alongside a single particle approach, we also study behavior of ensemble of particles in the context of stable positions. as we have shown, the together they create surfaces where particles are at stable equilibrium positions. in this paper, we examine these shapes and study parameters they depend on. it has been found that under certain conditions, there are two distinct surfaces with stable equilibrium positions. | 3d study of centrifugal acceleration in isotropic photon fields |
with enzo simulations run on the jülich supercomputers, we have investigated the evolution of magnetic fields in the largest cosmic structures (namely galaxy clusters and filaments connecting them) with unprecedented dynamical range. these simulations revealed the full development of the small-scale dynamo in eulerian cosmological magneto-hydrodynamical simulations. the turbulent motions developed during the formation of clusters are energetic enough to foster the growth of magnetic fields by several orders of magnitude, starting from weak magnetic fields up strengths of $\sim \rm \mu g$ as observed. furthermore, shock waves are launched during cluster formation and they are able to accelerate cosmic-ray electrons, that emit in the radio wavelengths. radio observations of this emission provide information on the local magnetic field strength. we have incorporated, for the first time, the cooling of cosmic-ray electrons when modelling this emission. in this contribution, we present our advances in modelling these physical processes. here, we mostly focus on the most interesting object in our sample of galaxy clusters, which shows the complexity of magnetic fields and the potential of existing and future multi-wavelengths observations in the study of the weakly collisional plasma on $\sim$ megaparsecs scales. | a song of shocks and dynamo: numerical studies of a galaxy cluster merger in the himag project |
the process of stationary acceleration of protons by an electric field in the electromagnetic field of active galactic nuclei, including the regions of the magnetosphere of a supermassive black hole and a relativistic jet, is considered. the process of collisionless acceleration of the proton as a component of ultrahigh energy cosmic rays is assumed. it is shown that during acceleration to the maximum energy γmax the main part of the energy is achieved by a proton in the magnetosphere up to γmax (2/3) in the region of the light cylinder. further achievement of the maximum energy γmax occurs in the jet region, where, depending on the parameters of the amplitudes of the electric and magnetic fields, various acceleration regimes are possible. | acceleration of the high energy protons in an active galactic nuclei |
we give an overview of the agile γ-ray satellite scientific highlights. agile is an italian space agency (asi) mission devoted to observations in the 30mev-50gev γ-ray energy range, with simultaneous x-ray imaging in the 18-60kev band. launched in april 2007, the agile satellite has completed its tenth year of operations in orbit, and it is substantially contributing to improve our knowledge of the high-energy sky. emission from cosmic sources at energies above 100mev is intrinsically nonthermal, and the study of the wide variety of observed galactic and extragalactic γ-ray sources provides a unique opportunity to test theories of particle acceleration and radiation processes in extreme conditions. | agile results on relativistic outflows above 100mev |
a major feature of the energy spectrum of the cosmic radiation above 10$^{19}$ ev is the increasing fraction of heavy nuclei with respect to light nuclei. this fact, along with other simple assumptions, is adopted to calculate the energy spectrum of the cosmic radiation up to 2.4$\times$10$^{21}$ ev. the predicted spectrum maintains the index of 2.67 observed at lower energies which is the basic, known, empirical well-assessed feature of the physical mechanism accelerating cosmic rays in the galaxy. indeed above 10$^{19}$ ev the injection of nuclei is inhibited by some filter and this inhibition causes a staircase profile of the energy spectrum. it is argued that particle injection failure versus energy commences with protons, followed by helium and then by other heavier nuclei up to uranium. around 7.5$\times$10$^{20}$ the cosmic radiation consists solely of nuclei heavier than copper and the estimated intensity is 1.8$\times$10$^{-30}$ particles/gev s sr m$^2$. | the energy spectrum of ultraheavy nuclei above 10$^{20}$ ev |
astrophysical shocks are known to accelerate particles to high relativistic velocities. this process requires the particles to repeatedly cross the shock, a process that can only occur if the particle is reflected by the local magnetic field. such particles are observed on earth as cosmic rays. this phenomenon has been studied in considerable detail for high-mach shocks, such as the shocks that occur in colliding stellar winds and supernova explosions, but remains relatively unexplored for low-mach shocks, such as the shocks of colliding clusters of galaxies. recent simulations using the particle-in-cell (pic) method have shown that, depending on the exact mach number, even low-mach shocks can accelerate charged particles to the point where they start to deviate from the thermal velocity distribution. however, the computationally intensive nature of the pic calculations makes it difficult to continue the simulations to determine whether the particles can reach relativistic speeds. we now present new simulations, using a combined pic and magnetohydrodynamics (mhd) technique. this model, which takes advantage of the computational efficiency of mhd, allows us to simulate a much larger physical volume and study the behaviour of the particles over a longer period of time in order to determine to what extent the acceleration process continues and whether these shocks are capable of contributing to the cosmic ray spectrum. | diffusive shock acceleration of cosmic rays in low-mach galaxy cluster shocks. |
recent observations found that electrons are accelerated to ∼10 gev and emit synchrotron hard x-rays in two magnetic white dwarfs (wds), also known as cataclysmic variables (cvs). in nova outbursts of wds, multi-gev gamma-rays were detected, implying that protons are accelerated to 100 gev or higher. in recent optical surveys, the wd density is found to be higher near the sun than in the galactic disk by a factor ∼2.5. the cosmic rays (crs) produced by local cvs and novae will accumulate in the local bubble for 106-107 yr. on these findings, we search for crs from historic cvs and novae in the observed cr spectra. we model the cr spectra at the heliopause as sums of galactic and local components based on observational data as much as possible. the initial galactic cr electron and proton spectra are deduced from the gamma-ray emissivity, the local electron spectrum from the hard x-ray spectra at the cvs, and the local proton spectrum from gamma-ray spectra at novae. these spectral shapes are then expressed in a simple set of polynomial functions of cr energy and regressively fitted until the high-energy (>100 gev) cr spectra near earth and the voyager-1 spectra at the heliopause are reproduced. we then extend the modeling to nuclear cr spectra and find that one spectral shape fits all local nuclear crs, and that the apparent hardening of the nuclear cr spectra is caused by the roll-down of local nuclear spectra around 100-200 gev. all local cr spectra populate a limited energy band below 100-200 gev and enhance gamma-ray emissivity below ∼10 gev. such an enhancement is observed in the inner galaxy, suggesting the cr fluxes from cvs and novae are substantially higher there. | evidence for gev cosmic rays from white dwarfs in the local cosmic ray spectra and in the gamma-ray emissivity of the inner galaxy |
we study a scenario in which the fermi bubbles are formed through a galactocentric outflow of gas and pre-accelerated cosmic-rays (cr). we take into account cr energy losses due to proton-proton interactions with the gas present in the bubbles, and calculate the associated gamma-ray emission. we find that crs diffusing and advecting within a breeze outflow result in an approximately flat surface brightness profile of the gamma-ray emission, as observed by fermi satellite. finally, we apply similar outflow profiles to larger galactocentric radii, and investigate their effects on the cr spectrum and boron-to-carbon ratio. hardenings can appear in the spectrum, even in cases with equal cr diffusion coefficients in the disk and halo [a. m. taylor, g. giacinti, cosmic rays in a galactic breeze, phys. rev. d 95 (2) (2017) 023001. arxiv:arxiv:1607.08862, doi:10.1103/physrevd.95.023001. | galactic cosmic-rays in a breeze |
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