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hadronic models of blazar emission constitute an interesting alternative to the more popular leptonic ones. using the bl lac object mrk 421 as a characteristic example, we present two distinct ways of modeling the spectral energy distribution of blazars in the hadronic context, and we discuss the predictions of each variant on the spectral shape, the multi-wavelength variability, the cosmic-ray flux, and the high-energy neutrino emission. focusing on the latter, we then present an application of the hadronic model to individual bl lacs that were recently suggested to be the counterparts of some of the icecube neutrinos. | consequences of proton acceleration in blazar jets |
among the registered extremely high energy cosmic rays (ehecr, e>10^{20} ev) an event with the highest to date energy of e=3.2\cdot10^{20} ev was detected by the fly's eye experiment (fe event) in 1991. with the use of the back-tracking method for the calculation of the ehecr trajectories in galactic and extragalactic magnetic fields, we show that the galaxies ugc 03574 and ugc 03394 are the most promising candidates among the nearby extragalactic sources for the cases of iron and c-n-o group primary nucleus respectively. the most likely accelerating mechanisms are the newly-born millisecond pulsars, magnetar flares and tidal disruption events in these galaxies. | search for the astrophysical sources of the fly's eye event with the highest to date cosmic ray energy e=3.2\\cdot10^{20} ev |
it has been indicated that low-luminosity active galactic nuclei (llagns) are accelerating high-energy cosmic-ray (cr) protons in their radiatively inefficient accretion flows (riafs). if this is the case, sagittarius a* (sgr a*) should also be generating cr protons, because sgr a* is a llagn. based on this scenario, we calculate a production rate of cr protons in sgr a* and their diffusion in the central molecular zone (cmz) around sgr a*. the cr protons diffusing in the cmz create gamma-rays through pp interaction. we show that the gamma-ray luminosity and spectrum are consistent with observations if sgr a* was active in the past. | diffuse gamma-ray emission from the galactic center and implications of its past activities |
in this paper, we study the efficiency of particle acceleration in the magnetospheres of stellar mass black holes. for this purpose, we consider the linearized set of the euler equation, continuity equation and poisson equation, respectively. after introducing the varying relativistic centrifugal force, we show that the charge separation undergoes the parametric instability, leading to generation of centrifugally-excited langmuir waves. it is shown that these waves, via the langmuir collapse damp by means of the landau damping, as a result, energy transfers to particles accelerating them to energies of the order of 1016 ev. | new mechanism of acceleration of particles by stellar black holes |
using diffusive shock acceleration (dsa) simulations, we have calculated the acceleration of cosmic-ray electrons and the ensuing radio synchrotron emission at weak spherical shocks that are expected to form in the outskirts of galaxy clusters. we demonstrate that, at decelerating spherical shocks, the volume integrated spectra of both electrons and radiation deviate from the test-particle power-laws predicted for constant planar shocks, because the shock compression ratio and the flux of injected electrons decrease in time. if the postshock magnetic field strength is about 5 microgauss, at the shock age of around 50-100 myr, the volume-integrated radio spectrum steepens gradually with the spectral index from αinj to αinj+0.5 over 0.1-10 ghz, where αinj is the injection index at the shock position expected from the dsa theory. we suggest that such gradual steepening could explain the curved radio spectra of some radio relics found in galaxy clusters. | radio spectra from shock accelerated electrons in the cluster outskirts |
massive clusters, particularly merging clusters with multiple superposed subhalos, are powerful cosmic telescopes, capable of magnifying high-z galaxies, thus providing a probe of the high-z universe. in addition, merging clusters are excellent laboratories to investigate how the particles that produce cluster-scale diffuse radio emission are accelerated.we present chandra and jvla observations of the hst frontier cluster macs j0717.5+3745. macs j0717.5+3745 is the largest known cosmic lens,making it a promising target to search for lensed radio and x-ray sources. with the high-resolution 1.0-6.5 ghz jvla imaging, we find a total of 8 lensed sources with amplification factors larger than 2. two of these lensed sources are also detected in the chandra images. the majority of the lensed sources are likely star forming galaxies with star formation rates of 10-20 msun/year. our observations indicate that deep radio imaging of galaxy clusters, in combination with optical and lensing data, can be used to study the faint radio source population which would otherwise only be possible with the the square kilometre array.our radio images also show the presence of a peculiar 700 kpc elongated diffuse radio source in the cluster. chandra detects hot gas with a temperature of ~20 kev at the location of the radio source. this suggests that the radio emission traces a large shock-heated region in the cluster, where fossil particles from a tailed radio galaxy have been re-accelerated. | jvla and chandra observations of the hst frontier cluster macs j0717.5+3745 |
there are for the galaxies of frii type (like cygnus a) studied a number of hydrodynamic and kinetic processes to transport of magnetized plasma with cosmic rays, and a stratification process of rg-lobe because of ep-cosmic rays. we found that the jet and bow shock in radio galaxies are supported by the processes of ep-cosmic rays (acceleration, radiation), and the effects of changes in viscosity inside the cocoon. cosmic rays are working inside the "jet head" into the cocoon stratification: to the light caviton (with high kinematic viscosity) and to the heavy shock cover (with high magnetic viscosity). the post-jet-vortex is injected by diffusion of e-rays through the area of "jet head" mhd-turbulized, and it is flowing a caviton around. alternatively, the bow shock accompanied super sound turbulent waves and flows with p-rays. | on the p-cosmic rays as mediators of viscous forces that create shock and vortex structures in the radio galaxies |
x-ray binaries are one of the long-standing candidates as the source of galactic cosmic rays and neutrinos. the compact object in a binary system can be the site for cosmic-ray acceleration, while interactions of cosmic rays can happen in the jet of the compact object, the wind, or the companion star's atmosphere, which produce high-energy neutrinos. i will talk about a comprehensive study of tev-scale neutrinos from high-mass and low-mass x-ray binaries conducted by icecube using muon data. in the absence of significant correlation, we place upper limits on the neutrino fluxes from these sources and provide a comparison with theoretical predictions. finally, i will present the detectability of x-ray binaries in icecube-gen2. | results from an icecube search for high-energy neutrino emission from x-ray binaries |
while supernova remnants are promising candidates for cosmic ray production, they must produce on average 1050 ergs of energetic particles to sufficiently account for the galactic cosmic ray protons below 3 pev. moreover, supernova remnants that show direct observational evidence for proton accelerations to high energies are rare, and it is also unclear under which circumstances remnants efficiently produce such particles. kes 17 is a supernova remnant that shows evidence of high energy particle accelerations. in this project, we analyze its gamma-ray and x-ray spectra, with the goal of measuring the total energy of its cosmic ray population, spatial variations in the properties of the thermal x-ray emitting plasma, and constraining any non-thermal x-ray emission. this will help us determine the conditions under which remnants efficiently accelerate cosmic rays and if these remnants accelerate enough high-energy particles to account for the galactic population of cosmic rays. | the cosmic ray production of mixed morphology supernova remnant kes 17 |
galaxy clusters are expected to be reservoirs of cosmic rays accelerated by structure formation processes, galaxies, and active galactic nuclei (agn). the detection of diffuse synchrotron radio emission in several clusters confirms the presence of cosmic-ray electrons and magnetic fields permeating the intra-cluster medium (icm). while there is no direct proof for proton acceleration yet, gamma rays can prove it as cosmic-ray protons can yield high-energy (he) gamma-ray emission through neutral pion decay. additionally, some of the galaxies hosted in clusters could be detected in gamma rays individually, if harbouring agn, or via their summed output, e.g., in the case of star-forming galaxies. finally, about 80% of the mass of clusters is in the form of dark matter, and therefore they are considered prime targets for indirect dark matter searches… | ksp: clusters of galaxies |
since their discovery in 2010, the fermi bubbles have raised a lot of questions such as: what are they? how old are they? how much energy is involved? observations from radio to uv to x-ray have been addressed some of these questions, giving us a new window on energy injection at the galactic center, the growth rate of the bubble structures, the acceleration of cosmic rays, and the energy density of the photon field and magnetic field. i will provide an overview of what has been learned and what mysteries remain. | overview of the fermi bubbles |
dark matter is usually considered responsible for the flat rotation curves observed at the outer radii of spiral galaxies. since the existence of dark matter has not been indisputably detected by experiments, magnetic field is sometimes proposed to be substitute for dark matter in explaining the shape of rotation curves of spiral galaxies. magnetic field that interacts with cosmic rays generate pressure, which in turn accelerates gas flow/dynamics and affects the speed of gas rotation. some other studies discuss the possibilities that the flat or even increased rotation curves at the outer radii may be attributed both to dark matter and the galactic magnetic fields. in this work, we examined 16 rotation curve data of dwarf spiral galaxies in the spitzer photometry and accurate rotation curves (sparc) catalog obtained by spitzer in 3.6 µm. we find that the shape of the rotation curves of the dwarf spiral galaxies cannot be explained by the contribution of magnetic field alone, due to stability issues. however, adding some contribution of magnetic field to the dark matter component explains the rotation curves at the large radii better, compared to dark matter without magnetic field. we therefore determined the maximum contribution of the magnetic field for the 16 dwarf spiral galaxies. | on the maximum contribution of magnetic field to the rotation curves of dwarf spiral galaxies |
shock waves with low sonic mach number (ms) are induced by mergers and/or flow motions in the hot tenuous plasmas of the intracluster medium (icm). high-energy cosmic ray (cr) protons are expected to be accelerated at quasi-parallel shocks via diffusive shock acceleration (dsa), while proton acceleration is suppressed at quasi-perpendicular shocks. a key element of dsa is the so-called injection process, which energizes thermal protons to the suprathermal energies sufficient to diffuse across the shock. we first present a study of cr injection and early acceleration at weak quasi-parallel shocks using particle-in-cell (pic) simulations. we then propose an analytic model for the quantitative measures of cr proton acceleration in icm shocks in the test-particle regime. the model suggests that the acceleration efficiency of cr protons ranges ~ 0.001 - 0.02 in supercritical shocks with ms ~ 2.25 - 5, and the acceleration would be negligible in subcritical shocks with ms < ~2.25. we then estimate the emissions of gamma-rays and neutrinos from galaxy clusters. the predicted gamma-ray flux is below the upper limit set by fermi-lat. the neutrino flux towards clusters like the coma cluster would be about ~ 1% of that of atmospheric neutrinos at ~ 100 gev. we discuss the implication of our results. | proton acceleration in intracluster shocks and gamma ray and neutrino emissions from galaxy clusters |
radio relics, mpc-long arc-like structures in the outskirts of galaxy clusters, are believed to arise from relativistic electrons emitting synchrotron radiation in the cluster magnetic field. these features often coincide with shock fronts seen in x-ray observations of the intracluster medium which are produced by mergers. for some time, the prevailing theory has been that the electron population which produces the radio relic is accelerated from the thermal pool by diffusive shock acceleration. however, cluster merger shocks are relatively weak, and it is not clear how the aforementioned mechanism could be efficient enough. an alternative proposal is that the shock reaccelerates a pre-existing population of mildly relativistic electrons. as a potential source for thispopulation, we propose that cosmic-ray electrons contained within agn-blown bubbles are transported to larger radii and spread out across a large azimuthal distance by motions within the cluster gas. to test this hypothesis, we perform mhd simulations of agn feedback using the arepo code within clusters with two different types of gas motions, sloshing and merger-driven turbulence. we show that in each case the gas motions are able to produce distributions of cosmic rays which are plausible sources for radio relics by subsequent reacceleration by shocks. | seeding radio relics by turbulent transport of agn bubble material |
galactic outflows play an important role in galactic evolution. despite their importance, a detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. in an effort to gain more insight into the nature of these flows, we perform global three-dimensional magneto-hydrodynamical simulations of an isolated starbursting galaxy. we focus on the dynamical role of cosmic rays injected by supernovae, and specifically on the impact of the streaming and anisotropic diffusion of cosmic rays along the magnetic fields. we find that these microphysical effects can have a significant effect on the wind launching and mass loading factors depending on the details of the plasma physics. cosmic rays stream away from the densest regions near the galactic disk along partially ordered magnetic fields and, in the process, accelerate more tenuous gas away from the galaxy. for cosmic ray acceleration efficiencies broadly consistent with the observational constraints, cosmic rays are likely to have a notable impact on the wind launching. | global mhd simulations of cosmic ray driven galactic winds |
the galactic centre region is unique for its intense activity across the wavebands. the gamma-ray emission here extends up to the highest photon energies so far measured (beyond 10 tev) and spans the central molecular zone (cmz). the general spatial match between the gamma-ray and interstellar gas emission suggests the presence of cosmic-rays potentially reaching pev energies. where these cosmic-rays are being accelerated is still very much an open question although there are clues in the morphology and spectral properties of the gamma-ray emission. further clues will come from the latest high resolution (30 arc-sec) survey of the molecular gas from the mopra radio telescope in australia. such gas is likely the target for cosmic-ray collisions, generating gev to multi-tev gamma-ray emission detected by fermi-lat and hess respectively. this talk will review our knowledge of the high energy galactic centre region and present a status of the mopra cmz survey. it will conclude with a discussion of what we might learn by combining the new mopra cmz data with the fermi-lat and hess results. | extreme gamma rays from the galactic centre region |
we present a self-consistent model of the fermi bubbles, described as a decelerating outflow of gas and non-thermal particles produced within the galactic center region, on a o(100) myr timescale. motivated by observations, we use an outflow with velocity o(100) km/s, which is slower than velocities used in models describing the bubbles as a recent outburst (∼myr ago). we take into account cosmic ray (cr) energy losses due to pp interactions, and calculate the resulting γ-ray emission. our model can reproduce both the spatial morphology and the spectra of the bubbles, on a range of different scales. finally, we study which imprints a local outflow (or galactic wind) would leave on the cr spectrum and boron-to-carbon ratio at earth. we investigate the different types of breaks and/or inflections that can be generated in the cr spectrum, for different wind velocity profiles. both accelerating and decelerating outflows are considered. | a hadronic model of the fermi bubbles |
low-frequency radio observations recently revealed non-thermal emissionfrom the wolf-rayet bubble g2.4+1.4, proving that cosmic rays areaccelerated in it. we aim to gather data in the x-ray band in orderto better constrain the relativistic electron energy distributionand magnetic field in the bubble shell shocks, giving insight intoparticle acceleration processes and the role of single massive stars asprogenitors of galactic cosmic rays. the unprecedented detection of hardx-ray emission from a stellar bubble would constitute an observationalbreakthrough in high-energy astrophysics. we request for 55 ks ofobserving time with the xmm-epic instrument as it is the most sensitiveto detect the extended hard x-ray emission predicted to arise at thebubble shell. | relativistic particle acceleration in the wolf-rayet bubble g2.4+1.4 |
the possible gamma-ray excess in the inner galaxy and the galactic center suggested by fermi-lat observations has triggered great interest in the astro-particle physics community. among its various interpretations have been wimp dark matter annihilations, gamma-ray emission from a population of millisecond pulsars, or emission from cosmic rays injected in a sequence of burst-like events or continuously at the galactic center. accounting for the model systematics coming from the galactic diffuse emission in the inner part of our galaxy, we will present a comprehensive study of the latter possibility. a small series of outbursts, which took place approximately a million years ago, and 100s of thousands years ago and more recently can account for the observed gamma-ray signal. furthermore strong re-acceleration and rapid synchrotron cooling conditions within the inner tens of pc of the galaxy, could explain the hard spectrum of the observed gamma-ray excess. in fact, a connection to the fermi bubbles can be made. | the fermi galactic center excess as a signal from bursts of cosmic-rays |
it has been a long-standing question whether supernova remnants (snrs) can account for the acceleration of the bulk of galactic cosmic rays up to the knee in the cosmic ray spectrum. tev-selected snrs are interesting sources to probe this hypothesis and the entire h.e.s.s. phase i data set of the galactic plane, collected over the past decade, constitutes a unique archive to scan. the idea of the presented work is to systematically search for new snr candidates in the sky maps produced for the latest h.e.s.s. galactic plane survey (hgps), on the basis of their morphological shell-like appearance in the tev band. | search for new supernova remnant shells in the galactic plane with h.e.s.s. |
we will present models of the radio synchrotron emission from galactic supernova remnants (snrs) that use current models of galactic magnetic field to simulate snr emission as a function of their position in the galaxy. this work reveals a connection between snrs and their environment and a relationship between the angle of the symmetry axis of bilateral snrs and the galactic magnetic field. results from studying the impact of the so-called quasi-parallel and quasi-perpendicular cosmic ray electron acceleration scenarios will also be presented. this relationship has implications for understanding the magnetic field geometry and cosmic ray electron distribution in snrs, and possibly even a new method for determining distances to features of the galactic magnetic field as well as distances to some snrs. | bilateral symmetry in supernova remnants and the connection to the galactic magnetic field |
using a semi-analytic approach based on the thin-shell approximation, we calculate the long-term evolution of supernova remnants (snrs) while also accounting for the cosmic rays (crs) accelerated at their blast waves. our solution reproduces the results of state-of-the-art fluid simulations across the adiabatic and radiative stages for the gas-only case, and it predicts that typical cr acceleration efficiencies (≈10%) can boost snr momentum deposition by a factor of 2-3. this enhancement can become as large as an order of magnitude in environments in which the gas experiences more severe radiative losses. this result may have a crucial impact on modeling the effect of supernova feedback on star formation and galaxy evolution. | effect of cosmic rays on supernova remnant evolution |
g32.4+0.1 is a galactic supernova remnant (snr) that belongs tothe class of snrs that exhibit x-ray spectra that are dominated not bythermal emission but instead by synchrotron radiation. prominent examples of snrs in this class include sn 1006, g266.2-1.2 (vela jr.) and g347.3-0.5, and detailed studies of the synchrotron x-ray emission from these snrs hold the promise of elucidating how these sources accelerate cosmic-ray electrons to extremely relativistic energies. because only a few galactic snrs have been firmly established in the literature to belong to this class, detailed studies of each member are crucial. g32.4+0.1 — which is believed to lie at a distance exceeding 15 — is a heavily obscured object and for this reason it is one of the lesser-studied galactic snrs with synchrotron x-ray-dominated spectra.we present a new x-ray observation made with xmm-newton of this snr along with new l-band and p-band observations made with the jvla. the purposes of these observations is to facilitate a detailed spatially-resolved spectroscopic x-ray analysis of the synchrotron emission from g32.4+0.1 along with clear measurements of the integrated flux densities of the snr at these two radio frequencies and the corresponding spectral index of the snr as well. initial results will be presented and discussed. | new x-ray and radio observations of the synchrotron x-ray-dominated galactic supernova remnant g32.4+0.1 |
astrophysical shocks accelerate particles through the fermi acceleration process, which involves a charged particle repeatedly crossing the shock after being reflected by the local magnetic field and gaining momentum. eventually, the particles reach relativistic speeds and can be observed as cosmic rays. this is a self self-sustaining interaction because the presence of non-thermal particles in the shock-region causes instabilities in the magnetic field, which in turn allow the magnetic field to reflect the particles. this process has been studied extensively in the case of high-mach, low-β shocks, such as those that are found in stellar wind collisions and supernovae. however, there are astrophysical shocks, such as those that occur in colliding galaxy clusters, that are characterized by a low sonic mach number, combined with a high plasma-beta. so far, these shocks have been largely neglected, and little is known about their ability to accelerate particles. using a combined pic-mhd code, we have performed a series of numerical simulations of low-mach, high-beta shocks, to investigate the interaction between the particles and the magnetic field under such conditions. we find that even low-mach shocks are capable of accelerating charged particles. however, due to the behaviour of the magnetic field, the process tends to be relatively inefficient, reducing the effective contribution to the cosmic ray spectrum. furthermore, the interaction tends to radically change the nature of the shock itself, which indicates that further study is required to quantify the shocks’ long-term behaviour. | on the contribution of low-mach, high-beta shocks to the cosmic ray spectrum |
we propose a 560 ks observation of a2319 - a nearby, very hot, and the fifth brightest in x-rays, cluster of galaxies - to perform a comprehensive study of plasma physics. our goal is to probe (i) viscosity in the bulk gas through the density fluctuations power spectra on dissipative scales and (ii) thermal conduction parallel to the magnetic field lines through temperature variation along the cold front. bulk viscosity has been measured in only one cluster so far, while conduction along the field lines will be probed for the first time. a2319 is uniquely suited to address these problems in reasonable exposure time. we will search for k-h eddies for additional constraints on transport processes and a correlation between radio structures and x-ray fluctuations to test particle acceleration. | how do cosmic plasmas work? insights from the hottest brightest cold front and gas perturbations in a2319 |
possible acute and late risks to the central nervous system from galactic cosmic rays and solar particle events are concerns for human exploration of space. cns risks may include altered cognitive function, impaired balance and motor function, affective behavioral changes, or accelerated late neurodegeneration, all of which may affect performance and human health. experimental studies using accelerated charged particle beams simulating space radiation at doses below 1 gy provide evidence for changes in rodent cns which are persistent for up to a year. changes in spatial and recognition memory, executive function, measures of anxiety, and motor coordination in rats and mice are observed. these are accompanied by depressed neurogenesis, altered dendritic arbors and spine numbers, elevated oxidative stress, and neuroinflammation, including microglia activation. altered excitability, synaptic plasticity, and intrinsic membrane properties are observed in excitatory and inhibitory neurons in cortex accompanied by different levels of glutamate and gaba ion channels and neurotrophins such as bdnf. together these changes in animals attest to the potential for impairments in human brain activity for which little or no charged particle data are available. | space radiation: central nervous system risks |
the largest tev source, rx j0852.0-4622 (vela jr.), is one of the few supernova remnants (snrs) with well resolved shell-like morphology at very-high-energy (vhe; e>100 gev) gamma-rays. strong non-thermal emission across the electromagnetic spectrum from radio to vhe gamma-rays, young age and proximity of the remnant makes it one of the prime objects for the study of particle acceleration aiming to test the paradigm of snrs being sources of galactic cosmic rays. here we present deep h.e.s.s. observations of rx j0852.0-4622 with roughly doubled exposure comparing to previously published results. improved statistics together with new analysis techniques result in a firm determination of the cut-off in the gamma-ray spectrum and allow the spatially resolved spectroscopy studies. a smooth connection of the h.e.s.s. spectrum to the spectrum at gev energies as reported by fermi/lat provides an exciting opportunity to recover the present-time parent particle population in both leptonic and hadronic scenarios directly from the gamma-ray data alone. these new observations provide us a deeper insight and better understanding of the physical processes in snrs. | deep h.e.s.s. observations of the supernova remnant rx j0852.0-4622 |
the super trans-iron galactic element recorder (supertiger) was designed to measure significant statistics particularly for cosmic rays (crs) with charge > 30. these heaviest nuclei are some 10^3-10^5 times rarer than the lighter elements. with the longest science flight to date on a long duration balloon in 2012-13, supertiger has collected >1200 of these rare nuclei and millions of lighter cr events. after the instrument spent two winters in antarctica, we recovered it and are completing preparations for a second flight. we present results from the first flight, including the highest statistical precision measurements of cr charges from 30-40 to date. we anticipate even greater improvements with our second flight, this coming austral summer, 2017-18 from mcmurdo, antarctica. the results show enhanced numbers of elements formed in massive stars relative to solar system values, and thus give insight into the origin of galactic crs, likely in ob associations, and into the atomic processes which accelerate nuclei. | supertiger: on the cosmic ray charge frontier |
the cosmic ray dominated fermi bubbles in the milky way are produced either by a starburst or an agn. we can gain further insight into the physics of superbubble by studying similar bubbles around other galaxies. perhaps the best analog is in ngc 3079, which hosts a smaller and probably younger bubble, so offers an enormous opportunity for advancement. we propose chandra observation to study the non-thermal hard x-ray emission. with the new data, we can discriminate if cosmic rays are accelerated by individual snrs or by the bubble as a whole. also, we can determine the primary energy loss channel for cosmic rays -- inverse compton or synchrotron emission. finally, we will measure the pressures of the thermal and non-thermal components, which dictate the expansion of the system. | non-thermal x-ray emission from a 'fermi bubble' in an external galaxy |
the ubiquitous turbulence in the interstellar medium (ism) participates in astrophysical processes over a huge dynamic range of scales. understanding the turbulence properties in the multiphase, magnetized, partially ionized, and compressible ism is the fundamental step prior to the studies of the ism physics and other fields of astrophysics. i feel that a triad of analytical, numerical and observational efforts provides a winning combination to understand this complex system and solve long-standing puzzles. i have intensively studied the fundamental physics of magnetohydrodynamic (mhd) turbulence, and focused on two primary domains, dynamo and dissipation, which concern the origin of strong magnetic fields and the destination of turbulence, respectively. i further applied my theoretical studies in interpreting numerical results and observational data in various astrophysical contexts. the advanced analyses of mhd turbulence enable me to address a number of challenging astrophysical problems, e.g. the importance of magnetic fields for star formation in the early and present-day universe, new methods of measuring magnetic fields, the density distribution in the galaxy and the host galaxy of a fast radio burst, the diffusion and acceleration of cosmic rays in partially ionized ism phases. | the generation, destination, and astrophysical applications of magnetohydrodynamic turbulence |
the impact of galactic superwinds on their galaxies and the intergalacticmedium depends on the driving mechanism, which is controversial. twoleading candidates are thermally driven and cosmic ray-driven winds,which predict different velocity profiles. this will be reflectedin the temperature of the soft x-ray emitting gas. specifically, onecan determine whether a wind is accelerating or decelerating througha temperature gradient, since the soft x-rays come from shock-heatedmaterial. here we propose searching for this gradient around ngc 3079,a nearby, edge-on superwind galaxy where soft x-rays are detected to aheight of 20-25 kpc. | constraining the wind origin in ngc 3079 through x-ray temperature |
stellar feedback remains a key uncertain aspect in galaxy formation and evolution theories. in addition to the mechanical energy injection from fast stellar winds and supernovae of massive stars, their radiative transfer feedback (via direct and indirect/dust-processed radiation pressures and photo-ionization) has also been proposed to play a significant role in dispersing dense dusty gas and possibly in driving outflows from starburst regions. to test the relative efficiency of these two forms of the stellar feedback, we study the energetics of the tarantula nebula (30 doradus) in the large magellanic cloud. the nebula consists of various blisters of diffuse hot plasma enveloped by cool gas. based on the x-ray spectroscopy of the nebula, using a 100 ks suzaku x-ray observation, we estimate the thermal energy of the enclosed plasma, accounting for its temperature distribution and foreground absorption variation. the estimated thermal energy is far short of the expected fraction of the mechanical energy input from the central young stellar association (ngc 2070) of the nebula, according to the classic superbubble solution, indicating a substantial loss of energy via probably hot electron-dust interaction and cosmic-ray acceleration, as well as the cool shell formation. we further characterize the kinetic energy of dense dusty gas, using a recently published dust mass map and the velocity dispersion inferred from molecular and hi gases in the nebula. however, this component of the kinetic energy appears to be dominated by the turbulent and bulk motions of hii gas. the total kinetic energy of the nebula is consistent with the expected fraction of the mechanical energy input. therefore, the radiation transfer feedback does not seem to play a significant role in the expansion of 30 doradus. | feedback from starbursts: 30 dorado as a case study |
if galactic supernova remnants (snrs) are the main producer of cosmicray protons <3 pev, the average remnant must produce ~10^50 ergs ofcosmic rays. however, <10 snrs show observational evidence for cosmicray acceleration, and even fewer produce these particles with therequired energetics. while our recent analysis of snr kes 17 suggest itis producing cosmic ray protons, uncertainty about its age, surroundingdensity, and accelerated electron spectrum, prevents us from measuringthe energy of these cosmic rays. with the requested xmm observation wewill make these measurements and determine the mechanism responsible forits ``mixed morphology'' nature, a class of snrs associated with cosmicray production. | the cosmic ray production of mixed morphology supernova remnant kes 17 |
prescriptions for the electron injection into the diffusive shock acceleration process are required in many practical considerations of the cosmic-ray astrophysics, particularly in modeling of the synchrotron emission of astrophysical sources. inspired by the results of our particle-in-cell shock simulations, we assumed that the injection parameter xi = pinj/pth is the same for both, protons and electrons. we applied the blasi's semi-analytical model of the non-linear diffusive shock acceleration in order to obtain the particle spectra and the electron-to-proton ratio kep at high energies. by using the shock jump conditions which also include the electron heating, for the mach number ~100 we find that the ratio for the galactic cosmic rays is kep ~1:100 in the test particle case. | non-linear diffusive shock acceleration: a recipe for electron injection |
we calculate the spectrum of escaping cosmic rays accelerated in the shocks produced by expanding galactic superbubbles powered by supernovae producing a continuous energy outflow in star-forming galaxies. we use the generalized kompaneets equation solutions adapted to expansion in various external density profiles including exponential and power-law shapes, and assume that the escaping spectrum is dominated by the cosmic rays which have reached their maximum energy. we find that the escaping cr spectrum largely depends on the specific density profiles and power source properties, and the results are compared to and constrained by the observed diffuse cosmic ray spectrum spectrum. as a particular case we then also apply the results to the milky way's fermi bubble, and find that the fermi bubble cosmic rays could contribute a substantial fraction of the observed cosmic ray flux observed around 1017 ev. the work is supported by zaccheus daniel foundation (z. z.), alfred p. sloan foundation, national science foundation (nsf) grant no. phy-1620777 (k. m.), and national aeronautics and space administration (nasa) nnx13ah50g (p. m.). | cosmic rays escaping from galactic superbubbles and application to the fermi bubble |
vela jr. is the brightest steady source in the sky above 1 tev, and is one of the rare class of supernova remnants (snrs) whose shell morphology has been resolved in gamma-rays, with others being rx j1713.7-3946, sn 1006, hess j1731-347, rcw 86, and hess j1534-571. it is thus a remarkable laboratory where we can study the mechanisms through which snrs accelerate particles up to the highest energies, and thier role in the long-standing enigma of the origin of galactic cosmic-rays. the most plausible estimates of the age (and distance) of this remnant are based on the expansion measurements, using xmm-newton (katsuda et al. 2008) and chandra (allen et al. 2015). both of the two measurements focused on the brightest northwestern rim, providing a slow expansion of 0.42+/-0.10 arcsec/yr (this is the chandra result which is about half the value reported for an analysis of xmm-newton). if we assume that the chandra rate is representative of the remnant as a whole, then the results of a hydrodynamic analysis suggest that the age of vela jr. is between 2.4 kyr and 5.1 kyr. however, it has been unclear if such an assumption is valid, especially because the northwestern rim seems to be interacting with a massive hi gas entirely and molecular clouds partially (fukui et al. 2017). here, we report on our results of expansion measurements for the southern rim of the remnant. the first- and second-epoch observations were taken with xmm-newton on 2001-04-24 and with chandra on 2007-10-17, respectively. because the southern rim is not very sharp, we can directly compare the radial profiles from the two distinct satellites. we derived the proper motion to be 0.59+/-0.42 arcsec/yr, which is similar to that obtained in the northwestern rim. our result supports the assumption that the remnant is expanding uniformly, providing further evidence that the age of vela jr. is about a few thousand years old. | x-ray expansion of the southern rim of the vela jr. supernova remnant |
the origin of nonthermal emission observed from a variety of astrophysical objects is still a major unresolved issue in plasma astrophysics. shocks at snrs, with the help of a universal acceleration mechanism (i.e., diffusive shock acceleration; dsa), are widely believed to be the most probable acceleration sites of galactic cosmic rays (crs). the underlying assumption of dsa is that only particles with larmor radius much larger than the shock width can cross the shock and enter the acceleration process. this is especially challenging for thermal electrons due to their small larmor radii. in non-relativistic quasi-perpendicular shocks without significant proton acceleration, whether electrons can be injected into dsa by self-driven upstream turbulence is not well-addressed in the literature. in this thesis, i try to answer this question by performing large scale particle-in-cell (pic) simulations and magnetohydrodynamic-particle-in-cell (mhd-pic) simulations. 1d pic simulations show that electrons are injected into dsa through repeated cycles of shock drift acceleration (sda) and the scattering of self-driven upstream waves. multi-dimensional pic simulations show different electron acceleration efficiencies with different background magnetic field geometries. 2d out-of-plane shocks are much more efficient in electron acceleration compared to in-plane shocks and the acceleration efficiency in 3d shocks lies in between 2d in-plane and out-of-plane shocks. i demonstrate that both the pre-acceleration at the shock leading edge and the corrugations at the shock ramp affect the electron acceleration efficiency. for the second half of my thesis, i apply mhd-pic method to study electron acceleration in oblique shocks for larger transverse size and longer time scale. i develop a simple but more realistic electron injection prescription motivated by pic simulations. the mhd-pic simulations reproduce the most essential features of the shock structure and electron acceleration process. quasi-perpendicular shocks can self-regulate how many particles they can take in response to different injection fractions by creating shock corrugations, making mhd-pic model more robust for studying long term particle acceleration process without a detailed understanding of microphysics. by combing the results from both pic simulations and mhd-pic simulations, we can gain more insights into the physics of electron acceleration at different scales in astrophysical systems. | electron acceleration in non-relativistic quasi-perpendicular collisionless shocks. |
the first ground-level enhancement of the current solar cycle 25 occurred on 28 october 2021. it was observed by several space-borne and ground-based instruments, specifically neutron monitors. a moderate count-rate increase over the galactic-cosmic ray background was observed by high-altitude polar stations on the south pole and concordia stations at the antarctic plateau. most of the neutron monitors registered only a marginal increase. here, using de-trended records, employing verified by direct space-borne measurements method we derived the rigidity spectra and angular distribution of incoming solar protons for the gle #73. we employed the newly computed and parameterized neutron-monitor yield function. the rigidity spectra and anisotropy of the solar protons were obtained in their dynamical evolution throughout the event. quantification of acceleration mechanism is discussed. | spectral and anisotropy characteristics of the solar protons during ground level enhancement (gle) # 73 on 28 october 2021 derived with neutron monitor data |
star formation is the lynch pin that lies in between the scales of galaxy and planet formation. observational studies of molecular clouds, the sites of star formation, primarly use molecular line emission, providing dynamical and chemical information. two of the key parameters of astrochemical models are far-ultraviolet (fuv) flux and the cosmic ray ionization rate. we use analytic accretion histories to predict the bolometric and fuv luminosities of protostar clusters and compare different histories with observed bolometric luminosities. we find that the tapered turbulent core model best represents the observed luminosities and their dispersion. we extend the models to calculate the cosmic ray spectrum of protons accelerated in protostellar accretion shocks. we find that protostars are able to accelerate cosmic rays up to 10 gev. we predict increased ionization rates within protostellar cores and molecular clouds hosting over 100 protostars. our model is able to explain the substantial ionization rate, over 1000 times the typical, observed towards the omc-2 fir 4 protocluster. we model the impact of the protostellar fuv and cosmic rays on the astrochemistry on the natal molecular cloud. we couple the chemistry to the cosmic ray attenuation to solve the cosmic ray attenuation self-consistently. we find the inclusion of the embedded feedback signficantly changes the carbon chemistry and the co-to-h2 conversion factor. high-density, optically-thin tracers such as ammonia are noticabley affected. the inclusion of embedded protostellar feedback alters the chemistry throughout molecular clouds, coupling the physics ongoing on the smallest scales of star formation to molecular cloud scale. our results show that astrochemical modeling should account for ongoing star formation to correctly account for embedded fuv radiation and cosmic rays. | the impact of stellar feedback on astrochemistry |
high quality gamma-ray and radio observations of nearby galaxies offer an unprecedented opportunity to quantitatively study the properties of their cosmic ray populations. accounting for various interactions and energy losses, i developed a multi-component, single-zone model of the cosmic ray populations in the central molecular zones of star-forming galaxies. using observational knowledge of the interstellar medium and star formation, i successfully predicted the radio, gamma-ray, and neutrino spectra for nearby starbursts. using chi-squared tests to compare the models with observational radio and gamma-ray data, i placed constraints on magnetic field strengths, cosmic ray energy densities, and galactic wind (advection) speeds. the initial models were applied to and tested on the prototypical starburst galaxy m82. to further test the model and to explore the differences in environment between starbursts and active galactic nuclei, i studied ngc 253 and ngc 1068, both nearby giant spiral galaxies which have been detected in gamma-rays. additionally, i demonstrated that the excess gev energy gamma-ray emission in the galactic center is likely not diffuse emission from an additional population of cosmic rays accelerated in supernova remnants. lastly, i investigated cosmic ray populations in the starburst nuclei of arp 220, a nearby ultraluminous infrared galaxy which displays a high-intensity mode of star formation more common in young galaxies, and i showed that the nuclei are efficient cosmic-ray proton calorimeters. | cosmic ray interactions in starbursting galaxies |
the magnetic field may play a key role in regulating the extreme galactic center environment. we propose a chandra observation of a distinct 2'-long x-ray thread associated with a bundle of nonthermal radio filaments. this association, together with the detection of the fe 6.7-kev line emission in a suzaku spectrum, provides compelling evidence for interstellar magnetic reconnection. however, the line emission could also be due to the presence of diffuse hot plasma surrounding the thread, as indicated by existing data. this proposed deep on-axis observation will allow spatially resolved spectroscopy to critically test these scenarios and to study the underlying processes, with far-reaching implications for our understanding of plasma heating and cosmic ray acceleration in the center. | g359.55+0.16: a case of interstellar magnetic reconnection? |
understanding particle acceleration at low-mach number shocks in the intra-cluster medium is an unsolved puzzle. a small fraction of the shock energy could be channeled in the acceleration of cosmic rays, which in the presence of magnetic fields, emit synchrotron radiation and are observed as radio relics. therefore, radio relics are crucial to providing observational input to this problem and offer access to acceleration time and energy scale. we propose 190 ks deep chandra observations of a radio relic and distorted radio galaxy in abell 168 to improve our poor understanding of particle acceleration at low mach number shocks. | probing particle acceleration in abell 168 |
due to unusually quiet solar activity conditions during the previous 2009 and 2020 solar minima, record- high levels of galactic cosmic rays (gcrs) were reported. however, anomalous cosmic ray (acr) intensities did not show such extremely high levels. this discrepancy between gcr and acr intensities remains unresolved. using a 2d acceleration and transport model, we simulate the transport of gcr and acr oxygen during such atypically quiet solar minimum conditions. higher gcr intensities can be reproduced by assuming less efficient particle scattering during quiet solar minimum periods, while acr intensities are lower during very quiet solar minimum conditions. this is because of the interplay between acr acceleration, which is more efficient when more turbulence is present, and transport, which becomes increasingly inefficient when more turbulence is present. our results are in general agreement with both gcr and acr observations. | simulating gcr and acr oxygen intensities during very quiet solar minimum conditions |
the multi-facet nature of the origin of cosmic rays is such that some of the problems currently met in our path to describing available data are due to oversimplified models of cr acceleration and transport, and others to lack of knowledge of the physical processes at work in certain conditions. on the other hand, the phenomenology of cosmic rays, as arising from better observations, is getting so rich that it makes sense to try to distinguish the problems that derive from too simple views of nature and those that are challenging the very foundations of the existing paradigms. here i will briefly discuss some of these issues. | galactic cosmic rays |
to date, only a handful of shock fronts are known in merging clusters. a new one was recently reported, coincident with a well-resolved radio relic in rxcj1314-25. the peculiar shape of this shock is an interesting hydrodynamical phenomenon, possibly caused by the rapidly changing gravitational potential and the resulting pattern of gas flows. the radio relic shows branches that appear to coincide with x-ray brightness edges in the low-resolution xmm images; we may be seeing different folds of the same shock in projection. we propose to image this cluster and its network of putative shocks and map the local mach number along the main shock. comparison with the existing high-resolution radio data will provide unique constraints on the cosmic ray acceleration mechanisms. | an m-shaped shock and a multi-branch radio relic in the galaxy cluster rxcj1314-25 |
solar wind shocks and the intracluster medium comprise hot, low-density plasmas with few coulomb collisions. electrons there are not fluid and so gain and exchange energy by interaction with a variety of plasma waves. we explore two mechanisms for electron energization in such plasmas. in 2d kinetic simulations of solar wind shocks with low beta (magnetic > thermal pressure), fast-mode / oblique-whistler waves accelerate electrons in bulk via proton-scale parallel electric fields; electrons' bulk kinetic energy then converts to heat via magnetic field-aligned electrostatic wave scattering. we show and measure the heating for 2d shocks of varying magnetic obliquity and mach number, and we qualitatively map the mechanism's shock parameter regime. next, consider the intracluster medium: a high-beta plasma (thermal > magnetic pressure) in which megaparsec-scale motions promptly trigger nanoparsec-scale plasma waves, which in turn can scatter 1-100 mev cosmic ray electrons. small-scale scattering combined with large-scale motion can heat electrons, and this process is called magnetic pumping. we use 1d simulations of plasma subjected to continuous bulk compression to measure the efficiency of magnetic pumping upon cosmic ray electrons. it is speculated that magnetic pumping may help re-accelerate mev electrons to radio-emitting energies and so help explain the origin of diffuse, mhz-ghz radio halos enshrouding some clusters of galaxies. | electron energization in solar wind shocks and the intracluster medium |
dark matter does not emit light or reflect electromagnetic radiation, but its existence can be inferred from the effects of measurements such as gravity and mass. unveiling the nature of dark matter is one of the biggest mysteries of modern science. exploration of dark matter could give scientists a clearer understanding of the past and future of galaxies and the universe. chinese scientists have been engaged actively in dark matter research in recent years, and made some significant achievements in theoretical studies, numerical simulations, and experimental investigation. the dark matter particles explorer satellite (dampe) was launched by lm launch vehicle on 17th december 2015. it was constructed as a scientific satellite that has four major parts - a plastic scintillator array detector, a silicon array detector, a bgo calorimeter and a neutron detector - together comprising about 76,000 minor detectors. the main scientific purpose of dampe is to investigate dark matter particle from deep space, via high resolution observation of gamma-rays and electrons spectra, and its space distribution. it will also help scientists study the transportation and acceleration of cosmic rays in the galaxy by measuring the energy spectra of heavy ions. dampe was dubbed wukong after the monkey king character from the chinese classic legend journey to the west. "wu" means becoming aware of through the senses, and "kong" refers to the space. the figurative meaning of "wukong" is to know and comprehend the nature of the space. dampe is the most sensitive and accurate detectors designed for dark matter with the highest performance among the similar explorers. it will find the evidence that can certify the existence of dark matter. | wukong sharpens its eyes and unveils the nature of dark matter |
a new modified-gravity theory, referred to as the unified electro-gravity (ueg) theory, has been recently proposed. the theory introduces a new gravitational field in the presence of an electromagnetic field or radiation, while maintaining the conventional einstein-newtonian gravity in the external region of an electrically neutral, non-radiating body. the new ueg theory has been successfully applied to self-consistently model a spinning electron. the ueg theory, successfully applied as a substitute for the hypothetical "dark-matter" in spiral galaxies and galaxy clusters, were presented in recent aas conferences. in this paper, we would extend the ueg theory to model the observed accelerated expansion of the universe, without need for any hypothetical "dark-energy" or "dark-matter." the new ueg acceleration, produced in proportion to the cosmic background radiation-density, maybe modeled as an equivalent mass distribution over the observable universe, in addition to distribution of the conventional baryonic mass. the velocity of expansion of the current universe is found to be significantly in excess of what can be supported by the total mass (conventional baryonic, plus the new ueg equivalent-mass). it is assumed that the excess velocity would be supported by ueg acceleration due to any future star lights. in this presentation, we will focus on the ueg theory to explain the accelerated expansion in the current and recent past of the universe. as the universe expands, the equivalent mass due to the new ueg effect, enclosed in a co-moving volume, would reduce, while the enclosed baryonic mass remains constant. the reduction of the total mass would lead to an increase of the excess velocity as the universe expands, in order to conserve kinetic energy associated with the excess velocity, enforced as a requirement in the new ueg cosmology. this would result in a net acceleration of the expansion, in the current and recent past of the universe (z<1). however, in sufficient past (z>1), the normal gravitational deceleration (inward acceleration) supported by the total mass would be larger than any accelerated expansion due to the excess velocity, leading to a net deceleration of the universe's expansion for z>1. results from the ueg cosmology compare well with the standard model using the hypothetical dark-matter and dark-energy, in agreement with measurements of high-z supernovae and gamma-ray bursts. | a unified electro-gravity theory to model accelerated expansion of the universe without any dark-energy or dark-matter |
the photos of the pre-flare development observed in the spectral lines of highly ionized iron (sdo aia apparatus) indicate the energy accumulation for a flare in the corona in the pre-flare local (about 1010 cm) high temperature structure. the pre-flare structures in the corona are observed in uv spectral lines of ions fexxiv, fexxiii, fexviii several hours before big solar flares. during a flare the emission of the uv spectral lines in the corona are increased explosively. these phenomena can be used for prediction of solar cosmic rays. information obtained from the worldwide neutron monitor network and measurements on goes spacecraft demonstrates unambiguously that solar cosmic rays are generated in solar flares. these phenomena are well described by the solar flare electrodynamical model, created on the basis of the observational data and the numerical magnetohydrodynamic simulation using the initial and boundary conditions, taken from the active regions observation before the flare. it is impossible to exclude that the similar mechanism of particle acceleration is responsible for galactic cosmic rays generation. now all published mechanisms of cosmic ray generation are based on unproven assumptions. these assumptions are not confirmed by long-term observations. with the modern concept of cosmic rays, a fundamentally important question arises: can the mechanism of proton acceleration in solar flares explain the acceleration of particles of galactic cosmic rays. | diagnostics of solar flares by analyzing the spectral line emission of highly ionized iron |
the energy partitioning and magnetic field topology in radio jets from agn on galaxy cluster scales is poorly understood. we present a series of 3d mhd jet simulations with varying energy partitioning in the injected jet between kinetic and magnetic energy. specifically, we highlight the radio observational properties of these jets including radio brightness, spectral index, and polarization and compare to observed radio galaxies. these simulated radio properties are calculated from a population of cosmic ray electrons that is evolved self consistently during the simulations and include adiabatic effects, radiative losses, and shock re-acceleration. | observational signatures from kinetic and magnetic dominant agn jets |
shear flows are ubiquitously present in space and astrophysical plasmas. prominent examples include black hole accretion flows and the relativistic outflows or jets in gamma-ray bursts and active galactic nuclei (agn). fast shear flows can in principle facilitate non-thermal particle acceleration by several means. a key possibility includes a stochastic fermi-type mechanism, in which particle energization occurs as a result of elastically scattering off differentially moving (magnetic) inhomogeneities. i will review the central idea of fermi-type particle acceleration in relativistic shearing flows, highlight the expected spectral characteristics and discuss recent developments in the field. in principle, current shear scenarios provide new means beyond conventional diffusive shock acceleration by which power-law like particle distributions might be generated. when put in context, this suggests that collimated, relativistic shear flows in agn could account for the efficient in-situ acceleration of ultra-relativistic electrons required to understand extended gamma-ray emission, and be of relevance for the production of extreme cosmic rays. | energetic particle acceleration in relativistic astrophysical shear flows |
large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, pushing and redistributing material throughout the interstellar medium (ism) and galactic halo. a detailed understanding of the exact physical mechanisms responsible for these winds is lacking. non-thermal feedback from galactic cosmic rays (cr), high-energy charged particles accelerated in supernovae and young stars, can impact the efficiency in accelerating the wind. in the self-confinement model, cr stream along magnetic field lines at the alfven speed due to scattering off self-excited aflv{é}n waves. however, magneto-hydrodynamic (mhd) turbulence stirred up by stellar feedback dissipates these confining waves, allowing cr to be super aflvenic. previous simulations relying on a simplified model of transport have shown that super-alfv{é}nic streaming of crs can launch a stronger wind. we perform three-dimensional mhd simulations of a section of a galactic disk, including cr streaming dependent on the local environment, using a realistic model of turbulent dissipation of alfven waves presented in lazarian (2016). in this implementation, the cr streaming speed can be super alfv{é}nic depending on local conditions. we compare results for alfv{é}nic and locally determined streaming, and find that gas/cr distributions and instantaneous mass loading factor of the wind are different depending on the level of turbulence.lazarian, a. “damping of alfven waves by turbulence and its consequences: from cosmic-ray streaming to launching winds.” apj. vol. 833, num. 2. (2016). | role of turbulent damping in cosmic ray galactic winds |
the parker instability impacts the evolution of galaxies and gas clouds. driven by buoyancy, it describes a feedback loop for warping magnetic fields. as the parker instability evolves, it can cause magnetic field lines to cross and reconnect, accelerating gas bubbles into or away from the disk. how these bubbles form and evolve is significant to understanding how magnetic reconnection can affect the larger galactic system. this study investigates the behavior of hot, dense gas bubbles accelerated by magnetic reconnection and heated by cosmic rays (crs). the results shed light on the effects of reconnection and the effectiveness of the code that simulates it. similar hot bubbles have been observed in the intergalactic medium. i examine the evolution of these bubbles through a combination of numerical simulations in the magnetohydrodynamic code flash and athena++ using data processing methods in python. i find evidence confirming the idea that these bubbles are formed by reconnection. i find bubble velocities over time to identify the relevant forces accelerating the bubble against gravity. the flash code does not rigorously model magnetic reconnection, but it is possible to learn about the bubble's behavior after the reconnection event. findings will inform future development of magnetohydrodynamic simulations and offer nuance to observed reconnection events. i am working to run the simulations with an improved cr package and resolution in athena++. acknowledgements: this research is generously supported by nsf grant ast 2007323, the l&s stem summer of excellence in research (laser), and the sophomore research scholarship at uw-madison. | cosmic ray and magnetically driven bubbles in galaxies |
fermi bubbles are giant gamma-ray structures extended north and south of the galactic center with characteristic sizes of the order of 10 kpc discovered by the fermi large area telescope. good correlation between radio and gamma-ray emission in the region covered by fermi bubbles implies the presence of high-energy electrons in this area. due to high energy losses it is rather problematic to transfer relativistic electrons from the galactic disk toward the fermi bubbles. therefore it is natural to assume that these electrons are accelerated in-situ. additionally this acceleration mechanism should also affect protons. in particular it may re-accelerate galactic cosmic rays produced by supernova remnants. unlike electrons, protons have huge life-times and therefore re-acceleration should not be a local effect but affect the whole galaxy. the effect may even be observed near the earth. in our model we propose that hadronic cosmic rays (cr) below the "knee" of the observed cr spectrum are produced by galactic supernova remnants distributed in the galactic disk. re-acceleration of these particles in fermi bubbles produces crs above the knee. this model provides a natural explanation of the observed cr flux, spectral indices, and matching of spectra at the knee. | fermi bubbles as sources of cosmic rays above 1 pev |
in starburst galaxies, cosmic rays accelerated by supernova interact with the interstellar medium, creating a unique gamma-ray source population. through their interactions with the medium, they undergo energy losses, and are assumed to then escape the medium according to the "leaky box" model. by considering cosmic ray injection, energy loss, secondary electron/positron creation, and escape, we model the steady state energy spectra of cosmic ray protons, electrons and positrons. for protons, our model incorporated energy losses from ionization and pion production. for electrons and positrons, we considered energy losses from ionization, bremsstrahlung radiation, synchrotron radiation, and inverse compton scattering. using the astropy package naima, these models can in turn be used to generate observables, such as the expected gamma-ray and radio emission from a starburst galaxy. the ambient gas density, escape timescale, injection spectrum power law index, and magnetic field strength are left as free parameters. these free parameters can be constrained for a particular galaxy by comparing its fermi gamma-ray and radio spectra to expected spectra generated from the steady state models. | modeling cosmic rays in starburst galaxies |
supernova remnants (snrs) are considered to be the primary source of galactic cosmic rays (crs). however, increasing evidence shows that the winds of young massive star clusters (ymcs) may also contribute substantially to cr acceleration. in this poster, we present new results analyzing 14 years of fermi gamma-ray telescope data toward 11 ymcs < 3 myr old (where supernovae have not yet occurred) in the milky way. we measure the gamma-ray luminosities from these sources, and we evaluate how efficiently their winds accelerate crs. we use these constraints to estimate the cosmic-ray density and the diffusion coefficient. these results are important inputs for cr feedback prescriptions in galaxy formation simulations. | evaluating stellar winds from young massive star clusters as cosmic-ray acceleration sites using fermi gamma-ray observations |
in this work, we present an x-ray analysis of the nearby merging double-radio-relic cluster abell 3376 (z= 0.046), observed with the suzaku xis instrument. these deep observations (∼380 ks) cover the entire double-relic region in the outskirts of the cluster. the mentioned diffuse radio structures are one of the largest arc-shaped relics known (∼mpc) and are co-spatially located with large-scale x-ray shocks (mach number m≤2-3). we confirm the presence of a prominent shock (m∼3) in the western periphery, derived from a sharp temperature drop across the shock. this is one of the strongest shocks ever detected in a merging galaxy cluster. in addition, we have preliminary indications of a shock present in the eastern outskirts. in our analysis, we are able to constrain the cosmic xray background fluctuations and limit the systematic uncertainties on the temperature in the outer regions to 20-30%. these data allow us to study the connection between shocks and radio relics as well as the particle acceleration mechanism in strong shocks. we also estimate the dynamical age of the shock front, which provides us with a better understanding of the evolution of the merging cluster. | x-ray study of the merging double-radio-relic cluster abell 3376 with suzaku |
heliosphere is a bubble occupied by the solar wind plasma and magnetic field in the local interstellar space. the motion of galactic cosmic rays (gcrs) invading into the heliosphere are strongly affected by the electromagnetic structures of the heliosphere. the statistical behavior of the gcrs near and inside the heliosphere have been conventionally studied by many authors using the diffusion convection model [e.g., moraal (2013)]. in this study we investigate the behavior of gcrs invading into the heliosphere in the level of particle trajectory. we conduct test particle simulations of gcrs by using the electromagnetic fields obtained from a global mhd simulation of the heliosphere. the mhd simulation assumes steady solar wind and interstellar wind. gcr protons are initially distributed outside the heliosphere and their motions in the steady virtual heliosphere are calculated by using the buneman-boris method. depending on their initial energy, various types of particle motions, current sheet drift, polar drift, spiral motion, shock drift, fermi-like acceleration, linear motion, resonantly scattered motion, mirror reflection by bottleneck interstellar field, are observed. we further discuss some statistics of the particles reached at the inner boundary (=50au from the sun) of the simulation domain. | properties of cosmic ray test particles in global mhd simulation of the heliosphere |
weak shocks with low sonic mach numbers are induced by mergers and/or supersonic flow motions in the hot tenuous intracluster medium (icm). high energy cosmic ray (cr) protons are expected to be accelerated at quasi-parallel shocks via diffusive shock acceleration (dsa). the key element in determining the dsa efficiency is the so-called injection process, which energizes thermal particles to suprathermal energies sufficient to diffuse across the shock transition layer. reflection of incoming particles and ensuing self-excitation of mhd/plasma waves play important roles in the particle injection to dsa. using particle-in-cell (pic) simulations and analytic modeling, we study the injection and acceleration of protons at weak shocks in high-beta plasma. we find that the proton injection at quasi-parallel shocks is effective only for supercritical shocks with the sonic mach number greater than about 2.25, and the acceleration efficiency at such shocks ranges from 0.001 to 0.01. we then quantify the cr protons produced at icm shocks in simulated galaxy clusters during the large-scale structure formation. finally, we estimate diffuse gamma-ray and neutrino emissions, resulting from inelastic collisions between cr protons and thermal protons, and evaluate the prospect of their observations. | cosmic ray proton acceleration at weak icm shocks and observational signatures |
cherenkov telescope array (cta) promises to see the high-energy universe with unprecedented sensitivity and angular resolution covering the multi-tev domain. the first part of the thesis concerns the development of a single photoelectron calibration system for the nectarcam camera. the second part aims to understand the origin of cosmic rays (crs) by performing a multiwavelength (mwl) analysis of existing data of galactic supernova remnants (snrs). finally, the third part studies cta's role in detecting snrs in search for pevatrons by simulating fluxes using gammapy. a focal plane single photoelectron (spe) calibration system has been specially designed by ijclab for the nectarcam camera of the mst telescopes. the system consists of a white painted screen, a fishtail light guide, and a flasher. the flashes mimic the cherenkov radiation and illuminate the focal plane under the screen homogeneously. then, through the xy motorization, the screen is moved across the entire focal plane of the nectarcam camera. this thesis work concerns the development of the calibration system. in particular, the design of the calibration screen was optimized, and an algorithm to scan the focal plane was written. finally, the data from the mst calibration runs were analyzed, and the results show a good performance of the calibration system. snrs are promising candidate sources for galactic crs. the charged crs can be detected indirectly by the γ- ray observations through the π0 production and consequent decay to high-energy γ-rays. in this thesis work, we study the trends in favor of lepto-hadronic scenarios and search for snrs which show signs of hadron acceleration up to the highest energies. we have performed an mwl study on nine snrs using data from different instruments different. the data were fitted with radiative models to evaluate the hadronic contribution. the fit results were analyzed using three different methods: likelihood comparison, bic criterion, and the estimation of the hadronic contribution as a function of energy bins. the results showed that all the studied snrs favor the lepto-hadronic model over a pure leptonic one. we identified four snrs, rx j1713, cassiopeia a, hess j1731, and hawc j2227, which showed important hadronic contributions up to a few tev, thus making them promising pevatron candidates. additionally, for some snrs, excess flux was observed at high energies. the last part of the thesis is dedicated to assessing cta's capability to detect snrs. this involves answering if cta can 1) improve the observations of the potential pevatron sources previously identified, 2) detect different proton cutoff energy values, and 3) identify the contribution of heavier elements to the excess flux at high-energy observed before. to do so, cta fluxes are simulated by gammapy using physically motivated models taken from the results of the mwl study performed earlier. cta has provided flux covering a wide energy range with less uncertainty compared to current instruments. for source rx j1713, a contribution of heavy elements was introduced. the result showed that by using a combination of hydrogen and nitrogenlike elements, a better fit was obtained compared to the fit using only protons. in addition to the previous simulation study, we also analyzed the results of the galactic plane survey simulated by the galactic group of cta. the study showed that cta would increase the number of detected snrs by a factor of 2. additionally, snrs covering a large distance (up to 20 kpcs), with flux as low as ∼ 10‑14 photons cm‑2s‑1 would be easily detected by cta. | cherenkov telescope array : development of a calibration system for nectarcam and study of supernova remnants as pevatron candidates |
the question if there is life on other planets has fueled a decade full of exciting discoveries in the field of exo-planet research. the number of known exoplanets has grown beyond 5,000 till today and with the launch of the james webb space telescope, we are now able to probe the atmospheres of the most nearby systems directly, allowing to search for tracers of life. however, most of the current approaches of finding life are based on a "follow-the-water" strategy. here, we present a different approach by studying the impact of galactic cosmic-rays (crs) on potentially habitable planets around sun-like stars. most of the crs that interact with the earth's atmosphere originate directly from the sun. due to their low-energy they get absorbed high in the atmosphere and contribute little to the radiation-dose we receive at the surface. contrary, the galactic cr spectrum extends to much higher energies allowing the particle-induced cascades to reach ground level and directly impact life. with the recent detection of very-high energy gamma-ray emission from recurrent novae and evidence for cr acceleration in stellar clusters the number of sources known to accelerate cosmic-rays at least up into the tev-domain has doubled to four. we use observational data of the gamma-ray emission from supernova remnants, the reoccurring nova rs ophuichi, young and massive stellar clusters and the galactic center to infer the cr-density around these sources and determine distances up too which life gets affected by the produced crs for a "twin" of our solar system. | galactic cosmic-rays and habitable planets |
we propose to observe bania's clump 2, the densest cloud on the x1 orbits, for 100ks with acis-i. the large-scale molecular clouds in the galactic plane (1 kpc from the galactic center) exhibit 6.4 kev line emission, which is currently thought more likely to originate from mev-gev electron bombardment than from x-ray reflection. we want to determine which scenario is correct. if cosmic-ray excitation, do the mev-gev electrons come from dark matter annihilation or shock/wind acceleration? if x-rays, is the irradiator sgr a* or a local source? to achieve this, we will compare chandra observations in 2018 to suzaku observations in 2010 to determine the timescale of any line flux variations. | probing mev-gev electrons in the x-ray regime using molecular cloud bania's clump2 |
the transport of cosmic rays inside their sources and through the galaxy, around sources and during their journey through intergalactic space, may be heavily affected by non-linear effects, namely by 1) bulk motions induced by cosmic ray pressure gradients and 2) generation of magnetic perturbations that in turn modify the transport of charged particles. the combination of these effects gives rise to numerous non linear phenomena that are now becoming accessible to observations. this work summarises some recent results in this field of investigation and the implications for current and future observations. | a modern approach to cosmic ray transport in the galaxy |
recurrent novae (rne) undergo episodic eruptions in the form of thermonuclear explosions, due to the accumulation of material accreted by a white dwarf from a binary companion star. the well known rn rs ophiuchi (rs oph) underwent its latest eruption in 2021, triggering numerous follow-up observations, including with the high energy stereoscopic system, an array of iacts situated in khomas highland, namibia. h.e.s.s. observes the sky in the very-high-energy gamma-ray regime. non-thermal emission was observed coincident with the nova eruption within the first days and up to a month after the initial burst event, establishing novae as galactic transients reaching tev energies. analysis and interpretation of the data identifies time-resolved acceleration of cosmic-rays, constraining models of particle energisation. combining the data taken by h.e.s.s. with concurrent observations taken by the large area telescope (lat) on board the fermi gamma-ray space telescope, a consistent temporal and spectral profile is observed, favouring a common origin to the emission. the detection and interpretation of the non-thermal vhe emission from the rn rs oph by h.e.s.s. will be presented. | efficient cosmic-ray acceleration in the recurrent nova rs ophuichi revealed by h.e.s.s. |
the elemental composition of planetary surfaces can be determined using gamma ray and neutron spectroscopy. most planetary bodies for which nuclear spectroscopy data have been acquired are round, and simple, analytic corrections for measurement geometry can be applied; however, recent measurements of the irregular asteroid 4 vesta by dawn required more detailed corrections using a shape model (prettyman et al., science 2012). in addition, subtle artifacts of topography have been observed in low altitude measurements of lunar craters, with potential implications for polar hydrogen content (eke et al., jgr 2015). to explore shape and topography effects, we have updated the general-purpose monte carlo radiation transport code mcnpx to include a polygonal shape model (prettyman and hendricks, lpsc 2015). the shape model is fully integrated with the code’s 3d combinatorial geometry modules. a voxel-based acceleration algorithm enables fast ray-intersection calculations needed for monte carlo. as modified, mcnpx can model neutron and gamma ray transport within natural surfaces using global and/or regional shape/topography data (e.g. from photogrammetry and laser altimetry). we are using mcnpx to explore the effect of small-scale roughness, regional-, and global-topography for asteroids, comets and close-up measurements of high-relief features on larger bodies, such as the lunar surface. mcnpx can characterize basic effects on measurements by an orbiting spectrometer such as 1) the angular distribution of emitted particles, 2) shielding of galactic cosmic rays by surrounding terrain and 3) re-entrant scattering. in some cases, re-entrant scattering can be ignored, leading to a fast ray-tracing model that treats effects 1 and 2. the algorithm is applied to forward modeling and spatial deconvolution of epithermal neutron data acquired at vesta. analyses of shape/topography effects and correction strategies are presented for vesta, selected small bodies and cratered planetary surfaces. | shape and topography corrections for planetary nuclear spectroscopy |
supernova remnants (snrs) have long been hypothesized to accelerate galactic cosmic rays. the energy of accelerated protons can be measured if gamma-ray emission arises primarily from inelastic collisions with the surrounding gas through neutral pion decay. here, we constrain the accelerated particle spectrum of both electrons and protons through modeling the non-thermal emission from radio to gamma rays. we analyze the synchrotron radiation spectrum of four bright radio sources detected by the fermi gamma-ray space telescope: ic443, hb21, cygnus loop, and puppis a. wmap and planck data were used to extend the radio spectrum to millimeter wavelengths to constrain the spectrum of relativistic electrons. we detect spectral breaks for snrs: hb 21, ic443 and puppis a. this complements the possible spectral breaks previously reported for wmap data, and is consistent with spectral breaks found in the planck collaboration microwave survey of snrs. the presence of a break in the radio synchrotron spectrum for puppis a is inconsistent with leptonic models of gamma-ray emission. in cygnus loop, the lack of a break is only consistent with hadronic models. | constraining cosmic ray origins through spectral radio breaks in supernova remnants |
we make the first observation-based calculation of the energy that goes into cosmic ray protons versus cosmic ray electrons in shock acceleration during structure formation. we find a ratio of energy in cosmic ray protons to energy in cosmic ray electrons of 0.86. this value, calculated from the nonthermal x-ray component reported here from rtxe and the fermi lat upper limit for gamma-ray emission, is significantly lower than theoretical estimates that place most of the nonthermal energy in protons. our estimate is based on the detection of nonthermal x-ray emission using the 3-20 kev rxte spectrum, which shows residual emission not well modeled by a single thermal component. the statistical significance of adding a nonthermal, power-law component is 96%. the significance of adding a second thermal component is 90%. the addition of a component consisting of full cosmic x-ray background fluctuation to an isothermal model is significant with 92% confidence. the cumulative probability for the two-thermal-component model is 81% and 90% for the thermal plus power law. thus the model with nonthermal emission is the preferred description of the data. evidence of shock heating between the clusters in the spectro-imaging data of xmm, chandra, and suzaku indicates that a cosmic ray component should also be present and supports a nonthermal interpretation for the additional component. the bolometric nonthermal x-ray luminosity is 1.6 × 1044 ergs s-1, 36% of the total x-ray emission in the 0.1-100 kev band. | rxte observation of the nonthermal emission from the early stage merger in a1750 |
winds are ubiquitous in galaxies and often feature bubble structures. these wind bubbles are characterized by an external forward shock expanding in the surrounding medium and a wind termination shock separating the cool and fast wind from the hot shocked wind. while the forward shock could not be able to accelerate particles efficiently for a long time, at the wind termination shock the necessary conditions for efficient acceleration may be present. we develop a model for particle acceleration at the termination shock of such bubbles analysing the consequences of different possible engines powering the wind. we finally explore the multi-messenger potential of galactic winds in terms of escaping cosmic rays and high-energy gamma rays and neutrinos produced through hadronic interactions. | particle acceleration in galactic wind bubbles |
cosmic rays (crs) and magnetic fields are important constituents in the current universe. however, the origins of crs and magnetic fields are not yet understood. recently, it is pointed out that the first generation of crs can be accelerated in the supernova remnants of the first stars. based on this expectation, we found a new scenario in which cosmic magnetic fields are generated by resistive heating induced by streaming crs. we estimated the strength of the magnetic fields generated by this new mechanism the estimated strength is sufficient as seed magnetic fields which are further amplified by dynamo processes up to micro-gauss level, that is, the strength of galactic magnetic fields in the current universe. | magnetic field generation by resistive heating induced by streaming cosmic rays at cosmic dawn |
recent icecube results suggest that the first detection of very high energy astrophysical neutrinos have been accomplished. we consider these results at face value in a galactic origin context. an outflow emission scenario from both the fermi bubble and broader halo region are considered. we motivate that such an intensity of diffuse neutrino emission could be galactic in origin if it is produced by cosmic ray transport via a galactic outflow into the halo region. this scenario requires cosmic ray transport within the outflow/halo environment to be different to that inferred locally within the disk and that activity in the central part of the galaxy accelerates cosmic rays to trans-"knee" energies before they escape into an outflow. the presence of a large reservoir of gas in a very extended halo around the galaxy, recently inferred from x-ray observations, implies that relatively modest acceleration power of 1039 erg s-1 in pev energy cosmic rays may be sufficient to explain the observed neutrino flux. such a luminosity is compatible with that required to explain the observed intensity of cosmic rays around the "knee". | a galactic halo origin of the neutrinos detected by icecube |
x-ray diagnostics of tev (teraelectronvolt) sources continues to be an important tool to identify the nature of newly detected sources as well as to pinpoint the physics processes that are at work in these highly energetic objects. this paper gives a review of recent studies that have been performed on tev sources with h.e.s.s. and xmm-newton and also other x-ray facilities. here, we mainly focus on the galactic object types γ-ray binaries and supernova remnants (snrs). γ-ray binaries form a small class of objects whose identification and study is challenging because of the sometimes very long orbital periods that need to be established from data. particular emphasis is given to snr studies, including recently identified snrs such as hess j1731-347 and hess j1534-571, as well as a revisit of rx j1713.7-3946. | x-ray observations of galactic h.e.s.s. sources: an update |
neutron monitors (nm) have been for over sixty years powerful instruments for measuring gev-energy solar protons. in that time we have learned much about the nature of ground level enhancements (gle), the signal on the ground from these high energy ions. however, the processes that govern the acceleration of these particles has their roots close to the sun. similarly, the transport of these particles to 1 au is governed by the plasma conditions in the intervening space. as an example, the transition of a gle from a highly anisotropic event to an isotropic one may be the result of either self generated turbulence or the delayed influence of the progenitor cme shock. in fact, the question still lingers whether there is a flare component to the gle, as measured with nms. thus, particle and plasma measurements at small heliocentric distances will be critical in answering questions like these. in a related question, we know that cmes are responsible for forbush decreases (fd) that are quantified in terms of the effect on nm rates. however, several critical cme measurements can now only be performed at 1 au, while the oncoming cme still has effect on the galactic cosmic ray intensity and anisotropy at 1 au. performing the critical plasma measurements at the solar orbiter radius will certainly aid in interpreting the effects of the approaching cme and fd. in this talk i will review the discovery potential in our study of the highest energy cosmic rays and the synergistic and mutual benefits we expect to realize from correlated and coordinated solar orbiter measurements and those performed by nms. | solar orbiter measurements of the highest energy solar energetic particles-neutron monitors and solar orbiter |
galactic cosmic rays are accelerated in sources situated in the disc of the galaxy, and thereafter move along spiral trajectories, scatter on magnetic inhomogeneities, and consequently diffuse through the interstellar medium and leak away into the intergalactic medium. this process of diffusion essentially erases almost all traces of the direction to their origins. thus the expectation from the early years of cosmic-ray astrophysics was that gamma-ray astronomy would help in identifying the sources: the cosmic rays subsequent to acceleration to high energies would interact with matter in the source regions, produce neutral pions, which decay and generate gamma rays. observation of such gamma rays would point directly towards the sources of cosmic rays. this expectation of identifying the sources of cosmic rays is only partially fulfilled - gamma-ray astronomy in recent decades has been able to identify a very large number of sources in the galaxy, but it has not been possible to unequivocally identify them as the sources of cosmic rays that have been observed. in this paper we identify the amount of material that cosmic rays traverse in the source regions, as this has a direct bearing on their gamma-ray emissivity and spectra. to this end we make use of all the available data on cosmic rays, especially the recent results on the spectra and composition measured with great energy resolution and statistical significance by the alpha magnetic spectrometer aboard the international space station. the analysis shows that a significant amount of material is indeed traversed by cosmic rays in the source regions allowing these regions to function as gamma-ray sources. | cosmic-ray sources as gamma-ray sources |
galaxies and nuclei in dense environment at high redshift provide a good laboratory to investigate accelerated, most extreme evolution of galaxies. the ssa22 proto-cluster at z = 3.1 is known to have a three-dimensional 50 (comoving) mpc-scale filamentary structure, traced by lyα emitters, which makes the field a suitable target in this regard. to identify dust-obscured star-formation, a contiguous 20 arcmin2 region at the node of the cosmic structure was observed in alma band 6. in total 57 alma sources have been identified above 5σ, which makes the field one of the richest field in alma-identified (sub)millimeter galaxies. the follow-up spectroscopy confirmed about 20 sources as exact proto-cluster members so far. together with high x-ray agn fraction, our results suggest that the vigorous star formation activity and the growth of super massive black holes occurred simultaneously in the densest regions at z ∼ 3. | alma deep field in the ssa22 proto-cluster at z = 3 |
there is strong evidence from recent experiments that suggest a source of galactic cosmic rays is in superbubble regions and that particles here are accelerated through the shocks from supernova explosions. through further study of ultra-heavy cosmic-rays, those particles with a z >26, we can verify and explore the particle source and acceleration process of cosmic-rays. measuring these particles is a challenge due to their low flux and high interaction cross section, requiring extremely large detectors flown on balloons and in space. in this talk we will discuss how past and recent ultra-heavy cosmic ray measurements have shaped our understanding of the cosmic-ray source and acceleration process and what we hope to learn from future measurements. we will present results on the abundances of ultra-heavy cosmic rays in the charge range 26 <= z <= 40 from the supertiger antarctic balloon flight and compare these with previous results from ace-cris and tiger. we will also review the current status of active missions to measure ultra-heavy cosmic rays and discuss future possibilities. | current and future measurements of ultra-heavy galactic cosmic rays |
we present evidence for jet-like x-ray-emitting features from the nearby pulsar, b2224+65, based on three epochs of chandra x-ray observations, separated by 6 years from each other. this relatively slow rotating pulsar is well known for its extreme velocity of proper motion and associated "guitar"-shaped optical nebula in the opposite direction. the main jet-like x-ray-emitting feature is extremely narrow and significantly curved near the pulsar, but further away remains amazingly straight and is directed about 62 degrees away from the nebula, the x-ray emission of which is also detected. we find the consistent proper motions of the pulsar and the feature. the substructure of the feature varies among the epochs, while its spectrum is well characterized by a power law with a photon index of 1.2, is significantly harder than that of the pulsar, and remains remarkably consistent spatially and with the time. these results can be explained most intuitively by ballistic, relativistic, and probably magnetic field-dominated jets from the pulsar, similar to those from active galactic nuclei. indeed, we also detect the extended x-ray emission from the putative counter-jet, albeit at a much fainter level and on a much smaller scale. the luminosity of these features is 7e30 erg/s in the chandra band, accounting for about 1% of the spin-down energy rate of the pulsar. because of the flat nonthermal x-ray spectrum, this fraction increases with the photon energy. the total power required to generate the jets is likely greater than 10% of the rate. much of the acceleration of the particles for the (synchrotron) x-ray emission to energies > 100 tev likely occurs within the jets, probably via magnetic field re-connection. this jet scenario and the underlying physics can be further tested by a carefully designed x-ray monitoring of the substructure and by a measurement of the radio polarization of the pulsar, as its spin axis is expected to be aligned with the jets. we speculate that the energetic jet ejection from b2224+65 may represent a common phenomenon of pulsars, young and old, and an important source of cosmic-rays. the understanding of the ejection could also shed lights into the nature of extragalactic jets. | x-ray-emitting jet-like features from the fast-moving middle-aged pulsar b2224+65 |
from 2006 to 2016 years on the board of resurs-dk1 satellite pamela and arina cosmic rays experiments was carried out. the main goal of experiments is measurement of galactic component of cosmic rays; it also registers solar particles accelerated in powerful explosive processes on the sun (solar flares) in wide energy range. the article includes the list of solar events when pamela or arina spectrometers have registered increasing of proton flux intensities for energies more than 4 mev. | solar flare activity in 2006 - 2016 according to pamela and arina spectrometers |
jupiter's radiation belts constitute a multi-component system, trapping high intensities of electrons, protons and heavier ions. we revisit measurements from galileo's heavy ion counter (hic) instrument, a high-quality dataset that extends considerably the energy range covered by galileo/epd and juno/jedi (<10 mev/n) up to ~100 mev/n, providing key complementary observations for those two instruments in the equatorial radiation belts. thanks to hic's large geometry factor and event-based measurement capabilities, the instrument clearly resolves trace ions of both heliospheric and magnetospheric origin, such as carbon, nitrogen, sodium, magnesium, iron and others, besides the much more abundant oxygen and sulfur. in this work we re-evaluate aspects of hic's calibration, particularly for the analysis of measurements obtained at the innermost, intense radiation belts of jupiter, which are currently monitored by juno. we concentrate on previously unpublished observations from galileo's last two orbits, reaching inward of amalthea's orbit, including a close flyby of this moon. we show that the structure and composition of the heavy ion belts depends strongly on energy, l-shell and pitch angle. we find that above 50 mev/n, jupiter's heavy ion radiation belts are dominated by oxygen, appearing stable and are highly structured by strong losses at the orbits of io, thebe and amalthea, a structure reminiscent of that observed in saturn's proton radiation belts. in addition, heavy ion spectra and the corresponding phase space density profiles indicate that a local source of energy exists at least inward of amalthea, accelerating oxygen above 100 mev/n and sulphur above ∼50 mev/n. between the orbits of io and amalthea, psd profiles indicate contributions from local and adiabatic acceleration for both ion species, with the former dominating at the highest energies resolved in that region (∼50 mev/n). in conclusion, unlike earth's radiation belts, where the highest energy protons or ions observed reach the terrestrial magnetosphere pre-accelerated to the mev range in the form of solar, anomalous or galactic cosmic rays, jupiter can efficiently accelerate oxygen and sulphur, which originate at at ev energies at io and its torus, by 7-8 decades in energy. | evidence for local acceleration of heavy >10 mev/n oxygen and sulphur in jupiter's innermost radiation belts |
the review is devoted to consideration of possible observational consequences of modified gravity theories, suggested for explanation of the contemporary accelerated expansion of the universe. the major attention is paid to f(r)-models. it is shown that in systems with rising energy density high frequency and large amplitude oscillations of the curvature scalar, r(t), are induced. these oscillations lead to the production of elementary particles, which may be observed in the spectra of energetic cosmic rays. in the background of such oscillating solutions gravitation repulsion between finite-size objects becomes possible. since the lagrangian is a non-linear function of curvature, equations of motion become of higher (4th) order and exhibit very rich pattern of new physical effects. in particular, the evolution of density perturbations is strongly different from that in general relativity, amplified due to both parametric resonance and anti-friction phenomena. | instabilities in modified theories of gravity |
supertiger (super trans-iron galactic element recorder) is a long-duration-balloon instrument that completed its first antarctic flight during the 2012-2013 austral summer, spending 55 days at an average float altitude of 125,000 feet. supertiger measured the relative abundances of galactic cosmic-ray (gcr) nuclei with high statistical precision and well resolved individual element peaks from 10ne to 40zr. supertiger also made exploratory measurements of the relative abundances up to 56ba. gcr measurements up to 40zr support a source acceleration model where supernovae in ob associations preferentially accelerate refractory elements that are more readily embedded in interstellar dust grains than volatiles. in addition, injection into the gcr for both refractory and volatile elements appears to follow a charge dependence consistent with their grain sputtering cross sections. although statistics are low for elements heavier than 40zr, our preliminary measurements of the 40zr to 56ba range suggest the existence of an alternative gcr source or acceleration model for these rare elements. we report progress in refining this interesting result. | analysis progress: supertiger abundances of galactic cosmic rays for the atomic number (z) interval 40 to 56 |
supernova explosions are a major driver of galaxy evolution, and cosmic rays are a major component of that driving. this `cosmic ray feedback' presents a challenging multiscale problem in galaxy simulations. the supernova explosions on small scales (< < 1pc) which accelerate cosmic rays eventually produce the background of cosmic rays streaming throughout a galactic disk. they also affect the vertical structure of a galactic disk on large scales (> 1kpc). we examine the connection of cosmic ray production by supernovae to the vertical structure of a galactic disk using galactic patch simulations in the athena + + code. we randomly place point-like injections of cosmic rays in the mid-plane of a 1kpc2 patch of a galactic disk. these injections disrupt the vertical hydrostatic equilibrium on large scales. we observe significantly different results when using random, point-like injections instead of a constant cosmic ray flux. nasa finesst grant 80nssc22k1749. | the large scale impact of localized cosmic ray injection |
spectroscopy in the uv and x-ray can address many of the key questions posited by the 2010 decadal survey and nasa's 2013 astrophysics roadmap: how baryonic matter flows into and out of galaxies over cosmic time, how accreting stars and black holes evolve, and how feedback processes impact their ambient environments and drive galaxy evolution. to address these questions, however, high spectral resolution r is required. for example, the lynx x-ray spectrometer requires r > 5,000 to measure the absorption due to hot baryonic material distributed out to the virial radius of galaxies, while luvoir baselines two spectrometers operating in the uv, lumos and pollux, with peak resolutions of 65,000 and 120,000 respectively. in addition, the ability to customize reflection gratings for use in a specific optical system has benefits for missions ranging from flagships to smallsats. this customization can take the form of an arbitrary grating pattern, in which the groove density and orientation change over the substrate, or manufacturing a grating with a unique figure/curvature. the pollux instrument baselined for luvoir, for example, requires freeform diffractive optics. the same technology would also enable a two-element x-ray spectrometer, an instrument design compatible with a smallsat yet having 10× the effective area of the chandra transmission grating spectrometers. demonstrating the ability to make customized curved gratings capable of achieving high spectral resolution is along the critical path for several proposed high-resolution spectroscopy instruments. to that end, we propose to develop a process for fabricating such gratings and to assess their critical functionality by measuring their limiting spectral resolution. we will employ electron beam lithography (ebl) to fabricate these gratings, a technique which rasters an accelerated beam of electrons to pattern photoresist. our use of this technique leverages other recent developments, including the demonstration of large-area patterning, direct-write blazing, aberration-correction through arbitrary grating patterning, and a measurement of high limiting spectral resolution on flat ebl-written gratings. we will first develop a method for patterning curved gratings using a state-of-the-art ebl tool which has variable height adjustment. in this initial phase, we will use commercially available optical lenses to minimize cost. following this process development phase, we will next produce a customized, large-format (50 mm × 50 mm) grating pattern on a precision cylindrical lens. the customized grating pattern will be designed to produce a flat, back-diffracted wavefront when illuminated by a plane wave, and a high resolution interferometer will measure the quality of the back-diffracted wavefront. such a measurement provides crucial insight into how accurately gratings can be patterned on a curved surface. we will repeat this process with a precision spherical substrate, as achieving spherical back-diffraction requires a freeform pattern. finally, we will pattern a precision asphere acquired from the next-generation x-ray optics group at goddard space flight center to demonstrate that the developed process can be applied to flight optics. the proposed program will result in the maturation of a promising grating production technique, as well as a numerical assessment of the grating performance. this work lays the groundwork for incorporating customized curved gratings in a flight instrument for future astrophysics missions. | curved customized gratings for high energy spectroscopy |
radio shocks in merging galaxy clusters exhibit cosmic-ray acceleration to extreme energies. discrepancies between the shock strengths derived from radio and x-rays may suggest that the standard model of shock acceleration may need to be re-examined. a firm conclusion here requires a sample of mergers with a small viewing angle and simple geometry, where observational biases are minimised. double radio shocks are ideal targets, but only few of them are currently known. we propose a 38 ks exploratory chandra observation of double radio shocks in a1838 that were recently discovered by lofar. no pointed x-ray observations of this cluster exist; the proposed data will allow us to characterise its temperature, morphology, and connection to the radio emission for the | chandra observation of newly discovered double radio shocks in abell1838 |
in the period from 2006 to 2016, experiments based on the use of the pamela and arina spectrometers and aimed at detecting cosmic rays were performed on board the resurs-dk1 satellite. although the main goal of these experiments was to study the galactic component of cosmic rays, the instruments in question also detected, over a broad energy range, solar particles accelerated in powerful explosive processes on the sun (solar flares). a list of solar events in which the pamela and arina spectrometers detected, in various years of their operation, an increase in the intensities of fluxes of solar protons whose energies were above 45 mev is presented among other things. | solar flare activity from 2006 to 2016 according to data from the pamela and arina spectrometers |
the origin of the micro-gauss magnetic fields in the igm of galaxy clusters is one of the outstanding problem in modern cosmology. we demonstrate that the cluster accretion shocks are naturally and inevitably generate sub-equipartition magnetic fields from scratch in a two-step process. indeed, accretion shocks accelerate cosmic rays, which further generate magnetic fields via a streaming, weibel-type plasma instability. we stress that no seed field is needed in this scenario. we develop a self-similar model of a cosmic-ray-modified foreshock and demonstrate that, in contrast to the conventional lore, the generated magnetic fields (i) are large-scale, i.e., can be of the order of the the shock curvature radius, tens of kpc or more, hence they are effectively decoupled from dissipation and hence are long-lived on the hubble time and (ii) are strong enough, i.e., of the order of a fraction of the cosmic ray pressure, to meet observational constraints. we stress that no seed field is needed in this scenario, unlike other shock-related models of the field generation (e.g., via the bell instability or the richtmeyer-meshkov vorticity instability). supported by doe grant de-fg02-07er54940 and nsf grant ast-1209665. | how did the universe get magnetized? |
in galaxy clusters, the intracluster medium (icm) is expected to host a diffuse, long-lived, and invisible population of ''fossil'' cosmic-ray electrons (cre) with 1-100 mev energies. these cre, if re-accelerated 100x in energy, can contribute to diffuse low-frequency radio synchrotron emission. we study cre scattering and energy gain due to ion cyclotron (ic) waves generated by continuously-driven compression in 1d particle-in-cell simulations. we find that pitch-angle scattering of cre by ic waves induces energy gain via magnetic pumping. in an optimal range of ic-resonant momenta, cre may gain up to ~ 10 - 30 % of their initial energy in one compress/dilate cycle with magnetic field amplification ~ 3- 6 x , assuming adiabatic decompression without further scattering and averaging over initial pitch angle. supported by nasa atp 80nssc20k0565 and nasa finesst 80nssc21k1383. | electron re-acceleration via ion cyclotron waves in the intracluster medium |
the active region ar12673 is appeared near the solar activity minimum and x8.2 flare on the back side of the sun is produced. the energy for the flare is stored in the magnetic field of a current sheet and released in the corona above the active area. the flare is accompanied by a stream of solar cosmic rays that arrive to the earth along the interplanetary magnetic lines with a delay equal to the time of free flight. proton acceleration occurs in the flare current sheet. a similar mechanism seems to be responsible for galactic cosmic rays generation. | the proton solar flare above active region ar12673 on the solar back side |
we present a deep low-frequency study of 3c31, a well-studied fri radio galaxy in the local universe, using the dutch low-frequency array (lofar). our radio continuum observations between 30 and 180 mhz allow us to study the population of cosmic-ray electrons (cre) down to a lorentz factor of 100. we find that in the inner jet region, within 100 kpc from the core, the radio continuum spectrum can be described by a power-law with a radio spectral index between -0.53 and -0.56, in fair agreement what is expected for first-oder fermi acceleration by strong non-relativistic shocks. we trace the radio tails out to the furthest extent ever discovered, where 3c31 spans now roughly a degree in declination on the sky, corresponding to 1 mpc spatial extent. the radio spectral index steepens considerably in the radio tails, indicative of spectral ageing of the cre. we use an advective cosmic-ray transport model to measure the advection speed and magnetic field scale heights in the radio tails. | a low-frequency radio continuum study of the fri radio galaxy 3c31 with lofar |
the gas and dust between stars in galaxies is highly turbulent and magnetized. it is now understood that magnetic fields and turbulence affect many processes of astrophysical interest including star formation, cosmic ray acceleration, and the evolution of structures in the interstellar medium. in this talk, i shall review the fundamentals of galactic turbulence, including what energy sources drive turbulence in galactic discs. i will discuss progress in the development of new techniques for comparing observational data with magnetohydrodynamic turbulence simulations. | new diagnostics for turbulence in the multiphase interstellar medium |
quantifying whether supernova remnants (snr) are the primary acceleration source of galactic cosmic rays is a significant problem. snr with a non-thermal dominated spectrum (nd-snr) accelerates particles with high efficiency. therefore, quantitative evaluation of the occurrence rate of nd-snr is essential to quantitatively evaluate snrs' contribution to galactic cosmic rays. however, we still do not know the exact occurrence rate. to solve this problem, we focused on the fact that the occurrence rate can be estimated by comparing the mass of the progenitor star to the initial mass function. we report the discovery of a csm knot inside the nd-snr rx j1713.7-3946 and the mass estimation of the progenitor as an intermediate step. this knot was considered a wolf-rayet star (wr 85), but our analysis indicated no relation to it. our xmm-newton/rgs observation reveals line emissions from n, o, ne, mg, si, and fe. we fitted the spectrum with an absorbed thermal emission model and found that the n abundance was enriched n/h=3.5±0.8 (n/h)solar, and others are about the solar abundance. these results conclude that this knot is csm ejected when the progenitor star evolved into an rsg. from the abundance ratio of n to o and comparing it to those in outer layers of rsg stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be 15-20 msun. the fact that the progenitor star is not massive (<30 msun) suggests that nd-snr is relatively universal.next, we discuss the thermal x-ray from nd-snr rx j0852.0-4622. from our imaging analysis of super cosmos, we discovered that the hα radiation correlates with synchrotron radiation and co molecular clouds of the snr. moreover, the line intensity ratio of the uv band in this region differs from that of the vela snr, which overlaps in the direction of the line of sight (kim et al., 2012). these results suggest the existence of thermal plasma of the snr. this assertion is also supported by the fact that suzaku/xis shows an excess component in the band below 1 kev, which the synchrotron radiation of the snr cannot explain. we report the results of the mass estimation of the progenitor star when this excess component is observed with xrism/resolve. | universality of non-thermal phenomena in galactic supernova remnants probed by high resolution x-ray spectroscopy |
during the formation of the large-scale structure of the universe, intracluster media (icms), which fills the volume of galaxy clusters and is composed of hot, high-beta plasma, are continuously disturbed by major and minor mergers of clumps as well as infall along filaments of the warm-hot intergalactic medium (whim). such activities induce shock waves, which are observed in radio and x-ray mostly in cluster outskirts. these shocks are collisionless, as in other astrophysical environments, and are thought to accelerate cosmic rays (crs) via diffusive shock acceleration (dsa) mechanism. here, we present the properties of shocks in icms and their roles in the generation of nonthermal particles, studied with high-resolution simulations. we also discuss the implications on the observations of diffuse radio emission from galaxy clusters, such as radio relics. | shock waves and particle acceleration in clusters of galaxies |
we present measurements of the abundances of ultra-heavy (z>29) cosmic rays made by the cris instrument on nasa's advanced composition explorer satellite. the data set corresponds to 6413 days of data collection between december 4, 1997 and may 31, 2016. the charge resolution that we obtain is excellent, exhibiting essentially complete separation of adjacent charges in the z>28 range. we detected 196 events over the charge range of z =30-40. our measured abundances show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to a mix of massive star outflow and sn ejecta with normal ism, rather than pure ism. additionally, the refractory and volatile elements have similar slopes and refractory elements are preferentially accelerated by a factor of 4. the measured abundances support a model in which 20% of cosmic ray source material is from massive star outflow and ejecta and 80% is from normal ism. our abundances show generally good agreement with the tiger and supertiger results. this research is supported by nasa under grant # nnx13ah66g. | constraints on galactic cosmic-ray origins from elemental composition measurements |
the observed appearance of the high-energy gamma-ray emission from galactic star clusters is determined by the geometry of the cluster and the distribution of the energy sources inside the cluster. a large number of massive stars with strong winds and supernova explosions lead to the formation of multidirectional plasma flows, shocks and strong magnetohydrodynamic turbulence. magnetic turbulence is the main factor which determine the maximal energies of the accelerated particles and the power of the source. here we discuss an effect of the efficient magnetic field amplification at the supernova shocks due to the cosmic-ray driven plasma instabilities on the gamma-ray and neutrino fluxes from massive star clusters. we show here that the photon flux attenuation by the e± pair production is important for this kind of sources in the photon energy range 1015 — 1016 ev. the ratio of the gamma-ray to the neutrino fluxes is a declining function of the distance to the source at 5-15 kpc and the photon flux can be several times lower than the corresponding neutrino flux from the hadron interactions. | magnetic field amplification and high-energy emission properties of compact galactic clusters |
the escape model explains the cosmic ray (cr) knee by energy-dependent cr leakage from the milky way, with an excellent fit to all existing data. we test this model calculating the trajectories of individual crs in the galactic magnetic field. we find that the cr escape time τesc(e) exhibits a knee-like structure around e/z = few × 1015 ev for small coherence lengths and strengths of the turbulent magnetic field. the resulting intensities for different groups of nuclei are consistent with the ones determined by kascade and kascade-grande, using simple power-laws as injection spectra. the transition from galactic to extragalactic crs happens in this model at low energies and is terminated below ≈ 3 × 1018 ev. the intermediate energy region up to the ankle is populated by crs accelerated in starburst galaxies. this model provides a good fit to ln(a) data, while the estimated cr dipole anisotropy is close to, or below, upper limits in the energy range 1017 - 1018 ev. the phase of the dipole is expected to change between 1 × 1017 and 3 × 1018 ev. | the escape model for galactic cosmic rays |
during the formation of galaxy clusters by accretion of matter and mergers, turbulence is driven on large ~mpc scales in the intracluster medium (icm). the turbulence then cascades from driving scales to dissipative scales and heats the plasma, (re-)accelerates cosmic-ray particles and amplifies magnetic field. in this work, we present our latest results to follow the evolution of entrosphy, i.e. the vorticity magnitude, in the icm. for this purpose, we combine high resolution cosmological simulations with our lagrangian post-processing tool crater. this approach allows us to quantify the individual source terms of enstrophy in the course of the accretion of groups onto galaxy clusters. this study of the internal dynamics of gas substructure is very relevant as turbulence is essential an driver of the multiphase condensation cascade and thus the agn feeding. part of the work presented in this talk is published in wittor et al. 2017 (mnras). | agn near and far - clues to galaxy evolution from small to large scales |
recurrent novae (rne) undergo episodic eruptions in the form of thermonuclear explosions, due to the accumulation of material accreted by a white dwarf from a binary companion star. the well known rn rs ophiuchi (rs oph) underwent its latest eruption in 2021, triggering numerous follow-up observations, including with the high energy stereoscopic system (h.e.s.s.), an array of imaging atmospheric cherenkov telescopes (iacts) situated in khomas highland, namibia. h.e.s.s. observes the sky in the very-high-energy (vhe) gamma-ray regime of ~100 gev to a few tens of tev. non-thermal emission was observed coincident with the nova eruption within the first days and up to a month after the initial burst event, establishing novae as galactic transients reaching tev energies. analysis and interpretation of the data identifies time-resolved acceleration of cosmic-rays, constraining models of particle energisation. combining the data taken by h.e.s.s. with concurrent observations taken by the large area telescope (lat) on board the fermi gamma-ray space telescope, a consistent temporal and spectral profile is observed, favouring a common origin to the emission. the detection and interpretation of the non-thermal vhe emission from the rn rs oph by h.e.s.s. will be presented. | efficient cosmic-ray acceleration in the recurrent nova rs ophuichi revealed by h.e.s.s. |
compact binary millisecond pulsars (msps) are providing new insights into sub-luminous accretion flows and pulsar winds near the light cylinder, as well as new constraints on the maximum mass that a neutron star can support. a small sub-set of these known as "transitional msps" have shown *both* accretion- and rotation-powered phenomena. i will present the recent discovery of strong flat-topped noise in the x-ray variability of two transitional msps, with characteristic "break" frequencies in the 0.9-2.8 mhz range. i will discuss how we used these frequencies to constrain the mass accretion rate and viscosity of the accretion disk, in an intriguing (intermediate/sub-luminous) regime up to 5 orders of magnitude less luminous than the actively accreting states of x-ray binaries. i will also review the 3d space distribution of nearby compact binary msps in the galactic disk, with a population of more than 50 systems (and counting). using this distribution and a simple model of electron-positron pair acceleration in the intra-binary shock, i will then quantify their contribution to the (excess of) cosmic-ray positrons measured on earth. | pulsar winds and accretion flows in compact binary msps |
the identification of galactic pevatrons (objects capable of accelerating particles up to the pev = 1015 ev range) is one of the main goals of the cherenkov telescope array consortium. this task is in tight connection with the problem of the origin of cosmic rays, since the sources of galactic cosmic rays must accelerate protons up to at least pev energies. for a long time, supernova remnants have been pointed to as probable dominant sources of galactic cosmic rays, but whether they can be pevatrons during some period of their evolution is still unclear. alternative candidates, such as stellar clusters or superbubbles, have also been proposed as potential prominent cr sources. the unprecedented spectral and angular performance of the cherenkov telescope array will help answer important open questions about the physics of pevatrons, and shed new light on the origin of cosmic rays. | the identification of cosmic-ray pevatrons with the cherenkov telescope array |
the radio luminosities at 1.4 ghz is tightly correlated with the far-infrared luminosities for various galaxy types (e.g. [16, 6, 2]) over a wide range of redshift (see e.g. [5, 1, 15, 8, 7]). the relationship is widely believed to be driven by the internal star formation activity. radio emission from these galaxies are predominantly produced from the synchrotron emission of cosmic-ray electrons accelerated in supernova shocks. the infrared emission is due to ultraviolet light from young massive stars that is absorbed and re-radiated by dust [3]. a correlation is found also in local clusters but cluster galaxies appears to have excess radio emission relative to the amount of far-infrared emission [9, 13, 11]. in this work, we measure the far-infrared-radio relationship in a massive cluster to test how this relationship changes at intermediate z between the field and a high-density cluster environment. | far-infrared-radio relation in cluster galaxies at intermediate redshift |
high-velocity clouds moving towards the disc will reach the galactic plane and will inevitably collide with the disc, producing shocks. these shocks having velocities of hundreds of kilometres per second 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. we aim to establish under which conditions these interactions lead to significant non-thermal emission, especially gamma-rays. 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. | shocked high-velocity clouds as gamma-ray emitters |
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