Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of HII regions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of HII regions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities. We investigate the possibility of accelerating local thermal electrons up to relativistic energies in HII region shocks. We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes. We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the "deep south" (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength ($0.3-4$ mG), density ($1-9\times10^4$ cm$^{-3}$), and flow velocity in the shock reference frame ($33-50$ km s$^{-1}$) expected in DS. We suggest a mechanism able to accelerate thermal electrons inside HII regions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes.
The spectra of high-energy protons and nuclei accelerated by supernova remnant shocks are calculated taking into account magnetic field amplification and Alfvenic drift for different types of SNRs during their evolution. The overall energy spectrum and elemental composition of cosmic rays after propagation through the Galaxy are found.
A shock-accelerated particle flux \propto p^-s, where p is the particle momentum, follows from simple theoretical considerations of cosmic-ray acceleration at nonrelativistic shocks followed by rigidity-dependent escape into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with s ~ 2.8 provides an adequate fit to the Fermi-LAT gamma-ray emission spectra of high-latitude and molecular cloud gas when uncertainties in nuclear production models are considered. A break in the spectrum of cosmic-ray protons claimed by Neronov, Semikoz, & Taylor (PRL, 108, 051105, 2012) when fitting …
We investigate the theoretical and observational implications of the acceleration of protons and heavier nuclei in supernova remnants (SNRs). By adopting a semi-analytical technique, we study the non-linear interplay among particle acceleration, magnetic field generation and shock dynamics, outlining a self-consistent scenario for the origin of the spectrum of Galactic cosmic rays as produced in this class of sources. Moreover, the inferred chemical abundances suggest nuclei heavier than Hydrogen to be relevant not only in the shock dynamics but also in the calculation of the gamma-ray emissio…
The spectra of high-energy protons and nuclei accelerated by supernova remnant shocks are calculated taking into account magnetic field amplification and Alfvenic drift both upstream and downstream of the shock for different types of supernova remnants during their evolution. The maximum energy of accelerated particles may reach $5\cdot10^{18}$ eV for Fe ions in Type IIb SNRs. The calculated energy spectrum of cosmic rays after propagation through the Galaxy is in good agreement with the spectrum measured at the Earth.
Recently a substantial part of globular cluster population has been established as GeV gamma-ray sources by the Fermi-LAT telescope. We investigate possible production of the high energy gamma-rays by relativistic electrons injected from the population of fast rotating, magnetized White Dwarfs within the globular cluster. These electrons comptonize the radiation field within the globular cluster. We conclude that gamma-rays produced by electrons accelerated by the whole population of White Dwarfs within a specific cluster are on the level of detectability of the future Cherenkov telescope arra…
Ultra-high-energy cosmic rays (UHECRs) can be accelerated by tidal disruption events of stars by black holes. We suggest a novel mechanism for UHECR acceleration wherein white dwarfs (WDs) are tidally compressed by intermediate-mass black holes (IMBHs), leading to their ignition and subsequent explosion as a supernova. Cosmic rays accelerated by the supernova may receive an energy boost when crossing the accretion-powered jet. The rate of encounters between WDs and IMBHs can be relatively high, as the number of IMBHs may be substantially augmented once account is taken of their likely presence…
The thermal structure of the post-shock region of a young supernova remnant (SNR) is heavily affected by two main physical effects, the back-reaction of accelerated cosmic rays (CRs) and the Rayleigh-Taylor (RT) instabilities developing at the contact discontinuity between the ejecta and the shocked interstellar medium (ISM). Here, we investigate the role played by both physical mechanisms in the evolution of SNRs through detailed 3D MHD modeling. Our model describes the expansion of the remnant through a magnetized ISM, including consistently the initial ejecta clumping and the effects on sho…
Cosmic rays (CRs) are thought to play a dynamically important role in several key aspects of galaxy evolution, including the structure of the interstellar medium, the formation of galactic winds, and the non-thermal pressure support of halos. We introduce a numerical model solving for the CR streaming instability and acceleration of CRs at shocks with a fluid approach in the adaptive mesh refinement code ramses. CR streaming is solved with a diffusion approach and its anisotropic nature is naturally captured. We introduce a shock finder for the ramses code that automatically detects shock disc…
The composition of the overall spectrum of cosmic rays (CRs) is studied under the assumption that ultra high energy CRs above the energy 10^{17} eV are produced at the shock created by the expanding cocoons around active galactic nuclei (AGNs). It is shown that the expected CR composition is characterised by two peaks in the energy dependence of the mean CR atomic number <A(ε)>. The first one at the energy ε\approx 10^{17} eV corresponds to the very end of the Galactic CR component, produced in supernova remnants (SNRs). It is followed by a sharp decrease of <A(ε)> within the energy interval f…
The maximum energy to which cosmic rays can be accelerated at weakly-magnetised ultra-relativistic shocks is investigated. We demonstrate that for such shocks, in which the scattering of energetic particles is mediated exclusively by ion skin-depth scale structures, as might be expected for a Weibel-mediated shock, there is an intrinsic limit on the maximum energy to which particles can be accelerated. This maximum energy is determined from the requirement that particles must be isotropised in the downstream plasma frame before the mean field transports them far downstream, and falls considera…
We investigate the role played by initial clumping of ejecta and by efficient acceleration of cosmic rays (CRs) in determining the density structure of the post-shock region of a Type Ia supernova remnant (SNR) through detailed 3D MHD modeling. Our model describes the expansion of a SNR through a magnetized interstellar medium (ISM), including the initial clumping of ejecta and the effects on shock dynamics due to back-reaction of accelerated CRs. The model predictions are compared to the observations of SN 1006. We found that the back-reaction of accelerated CRs alone cannot reproduce the obs…
We explore the possibility that the hotspot of ultrahigh energy cosmic rays (UHECR) detected by the Telescope Array (TA) from the approximate direction of M82 and the M81 group of galaxies might be the echo of UHECR emitted by Centaurus A in an earlier more powerful phase. Echoes from other starburst galaxies or groups of galaxies may contribute to the UHECR flux at the Earth. We use an illustrative Monte Carlo model of mono-energetic UHECR transport by small angle scattering to generate synthetic sky maps. The model informs a discussion of overall energetics and time and distance scales. We f…
The formation of massive stars play a crucial role in galaxies from numerous points of view. The protostar generates a strong ultraviolet radiation field that ionizes its surroundings, and it drives powerful shock waves in the neighbouring medium in the form of jets and bipolar outflows, whose structure can be partially organized by local, strong magnetic field. Such an ejection activity locally modifies the interstellar chemistry, contributing to the cycle of matter. It also significantly participates to the energetic balance of galaxies. In the latter stages of massive star formation, the pr…
Supernova remnants are believed to be a major source of cosmic-rays in the Galaxy. As their progenitors are commonly found clustered in OB associations, one has to consider the possibility of collective effects in the acceleration process. In this work we investigate the shape of the spectrum of protons accelerated inside the superbubbles blown around clusters of massive stars. To do so we embed semi-analytical models of particle acceleration and transport inside Monte-Carlo simulations of OB associations timelines. We consider regular acceleration at the shock front of supernova remnants, as …
The origin of ultra-high-energy cosmic rays (UHECRs) remains elusive. Gamma-ray bursts (GRBs) are among the best candidates able to meet the stringent energy requirements needed for particle acceleration to such high energies. If UHECRs were accelerated by the central engine of GRB 221009A, it might be possible to detect secondary photons and neutrinos as the UHECRs travel from the source to the Earth. Here we attempt to interpret some of the early publicly available data connected to this burst. If the reported early GeV-TeV detection was produced by secondary emission from UHECRs it probably…
The Pierre Auger Collaboration has provided a compelling indication for a possible correlation between the arrival directions of ultrahigh-energy cosmic rays and nearby starburst galaxies. Herein we show how the latest large-scale modeling of starburst galaxies is compatible with the cosmic rays producing the anisotropy signal being accelerated at the terminal shock of superwinds.
The accretion of matter onto intermediate polar White Dwarfs (IPWDs) seems to provide attractive conditions for acceleration of particles to high energies in a strongly magnetized turbulent region at the accretion disk inner radius. We consider possible acceleration of electrons and hadrons in such region and investigate their high energy radiation processes. It is concluded that accelerated electrons loose energy mainly on synchrotron process producing non-thermal X-ray emission. On the other hand, accelerated hadrons are convected onto the WD surface and interact with dense matter. As a resu…
Supernova remnants (SNRs) have been regarded as major acceleration sites of Galactic cosmic rays. Recent X-ray studies revealed neutral Fe K$α$ line emission from dense gas in the vicinity of some SNRs, which can be best interpreted as K-shell ionization of Fe atoms in the gas by sub-relativistic particles accelerated in the SNRs. In this Letter, we propose a novel method of constraining the composition of particles accelerated in SNRs, which is currently unknown. When energetic heavy ions collide with target atoms, their strong Coulomb field can easily cause simultaneous ejection of multiple …
We study the escape of cosmic-ray protons accelerated at a supernova remnant (SNR). We are interested in their propagation in interstellar medium (ISM) after they leave the shock neighborhood where they are accelerated, but when they are still near the SNR with their energy density higher than that in the average ISM. Using Monte-Carlo simulations, we found that the cosmic-rays with energies of <~TeV excite Alfven waves around the SNR on a scale of the SNR itself if the ISM is highly ionized. Thus, even if the cosmic-rays can leave the shock, scattering by the waves prevents them from moving f…
Numerous authors have suggested that the ultra-high energy cosmic rays (UHECR) detected by the Pierre Auger Observatory and other cosmic-ray telescopes may be accelerated in the nuclei, jets or lobes of radio galaxies. Here I focus on stochastic acceleration in the lobes. I show that the requirement that they accelerate protons to the highest observed energies places constraints on the observable properties of radio lobes that are satisfied by a relatively small number of objects within the Greisen-Zat'sepin-Kuzmin (GZK) cutoff; if UHECR are protons and are accelerated within radio lobes, thei…
It is difficult to distinguish hadronic process from the leptonic one in $γ$-ray observation, which is however crucial in revealing the origin of cosmic rays. As an endeavor in the regard, we focus in this work on the complex $γ$-ray emitting region, which partially overlaps with the unidentified TeV source HESS~J1858+020 and includes supernova remnant (SNR) G35.6$-$0.4 and HII region G35.6$-$0.5. We reanalyze CO-line, HI, and Fermi-LAT GeV $γ$-ray emission data of this region. The analysis of the molecular and HI data suggests that SNR G35.6$-$0.4 and HII region G35.6$-$0.5 are located at dif…
We examine limits to the energy to which cosmic rays can be accelerated by relativistic shocks, showing that acceleration of light ions as high as 100 EeV is unlikely. The implication of our estimates is that if ultra-high energy cosmic rays are accelerated by shocks, then those shocks are probably not relativistic.
The discovery of the sources of ultra-high energy photons by High-Altitude Water Cerenkov Gamma ray Observatory and Large High Altitude Air Shower Observatory in our Galaxy has revolutionised the field of gamma ray astronomy in the last few years. These emissions are sometimes found in the vicinity of powerful pulsars or supernova remnants associated with giant molecular clouds. Inverse Compton emission by shock accelerated electrons emitted by pulsars and proton-proton interactions of shock accelerated protons emitted by supernova remnants with cold protons in molecular clouds are often ident…
The composition of Galactic Cosmic Rays (GCR) presents strong similarities to the standard (cosmic) composition, but also noticeable differences, the most important being the high isotopic ratio of Ne22/Ne20 which is about 5 times higher in GCR than in the Sun. This ratio provides key information on the GCR origin. We investigate the idea that GCR are accelerated by the forward shocks of supernova explosions, as they run through the presupernova winds of the massive stars and through the interstellar medium. We use detailed wind and core yields of rotating and non-rotating models of massive st…
Observations of large-scale radio emissions prove the existence of shock accelerated cosmic-ray electrons in galaxy clusters, while the lack of detected $γ$-rays limits the acceleration of cosmic-ray protons in galaxy clusters. This challenges our understanding of how diffusive shock acceleration works. In this work, we couple the most updated recipes for shock acceleration in the intracluster medium to state-of-the-art magneto-hydrodynamical simulations of massive galaxy clusters. Furthermore, we use passive tracer particles to follow the evolution of accelerated cosmic-rays. We show that whe…
We report the first detection of >100 MeV gamma rays associated with a behind-the-limb solar flare, which presents a unique opportunity to probe the underlying physics of high-energy flare emission and particle acceleration. On 2013 October 11 a GOES M1.5 class solar flare occurred ~ 9.9 degrees behind the solar limb as observed by STEREO-B. RHESSI observed hard X-ray emission above the limb, most likely from the flare loop-top, as the footpoints were occulted. Surprisingly, the Fermi Large Area Telescope (LAT) detected >100 MeV gamma-rays for ~30 minutes with energies up to GeV. The LAT emiss…
Cosmic-ray acceleration has been a long-standing mystery and despite more than a century of study, we still do not have a complete census of acceleration mechanisms. The collision of strong stellar winds in massive binary systems creates powerful shocks, which have been expected to produce high-energy cosmic-rays through Fermi acceleration at the shock interface. The accelerated particles should collide with stellar photons or ambient material, producing non-thermal emission observable in X-rays and gamma-rays. The supermassive binary star eta Carinae drives the strongest colliding wind shock …
Galactic cosmic rays (CR) are particles presumably accelerated in supernova remnant shocks that propagate in the interstellar medium up to the densest parts of molecular clouds, losing energy and their ionisation efficiency because of the presence of magnetic fields and collisions with molecular hydrogen. Recent observations hint at high levels of ionisation and at the presence of synchrotron emission in protostellar systems, which leads to an apparent contradiction. We want to explain the origin of these CRs accelerated within young protostars as suggested by observations. Our modelling consi…
In the solar flare observed on June 3, 2012, high energy gamma-rays and neutrons were observed. The event includes a remarkable feature of a high neutron/gamma-ratio in the secondary particles. We have examined whether this high n/$γ$-ratio can be explained by simulation. As a result of simulations using the GEANT4 program, the high n/$γ$-ratio may be reproduced for the case that helium and other heavy ions were dominantly accelerated in the flare.
Cosmic rays pervade the Galaxy and are thought to be accelerated in supernova shocks. The interaction of cosmic rays with dense interstellar matter has two important effects: 1) high energy (>1 GeV) protons produce γ-rays by π0-meson decay; 2) low energy (< 1 GeV) cosmic rays (protons and electrons) ionize the gas. We present here new observations towards a molecular cloud close to the W51C supernova remnant and associated with a recently discovered TeV γ-ray source. Our observations show that the cloud ionization degree is highly enhanced, implying a cosmic ray ionization rate ~ 10-15 s-1, i.…
Galactic cosmic rays are believed to be accelerated at supernova remnants via diffusive shock acceleration. Though this mechanism gives fairly robust predictions for the spectrum of particles accelerated at the shock, the spectrum of the cosmic rays which are eventually injected in the interstellar medium is more uncertain and depends on the details of the process of particle escape from the shock. Knowing the spectral shape of these escaping particles is of crucial importance in order to assess the validity of the supernova remnant paradigm for cosmic ray origin. Moreover, after escaping from…
The galactic cosmic rays are generally believed to be originated in supernova remnants (SNRs), produced in diffusive shock acceleration (DSA) process in supernova blast waves driven by expanding SNRs. One of the key unsettled issue in SNR origin of cosmic ray model is the maximum attainable energy by a cosmic ray particle in the supernova shock. Recently it has been suggested that an amplification of effective magnetic field strength at the shock may take place in young SNRs due to growth of magnetic waves induced by accelerated cosmic rays and as a result the maximum energy achieved by cosmic…
We report a discovery of bright blob-like enhancements of an Fe I K$α$ line in the northwest and the middle of the supernova remnant (SNR) IC 443. The distribution of the line emission is associated with molecular clouds interacting with the shock front, and is totally different from that of the plasma. The Fe I K$α$ line has a large equivalent width. The most plausible scenario for the origin of the line emission is that the MeV protons accelerated in the shell leak into the molecular clouds and ionize the Fe atoms therein. The observed Fe I K$α$ line intensity is consistent with the predicti…
Neutron star mergers (NSMs) are one of the most plausible sources of r-process elements in the universe. Therefore NSMs can also be a major source of ultra-heavy elements in cosmic rays. In this paper, we first estimate the contribution of r-process elements synthesized in NSMs to the ultra-heavy element cosmic rays (UHCRs) by calculating transport equations that take into account energy loss processes and spallations. We show that the flux of UHCRs accelerated by NSMs themselves fluctuates by many orders of magnitude on the timescale of several million years and can overwhelm UHCRs accelerate…
The understanding of the nature of ultra-high-energy cosmic rays is one of the most intriguing open questions for current and future observatories. These particles are expected to be accelerated in extragalactic sources. Because of their low flux, their detection is done indirectly observing extensive air-showers, with ground-based experiments. A review of the detection technique and the most recent results is presented with a look to the perspectives for the future.
We investigate the shock acceleration of particles in massive galaxy mergers or collisions, and show that cosmic rays (CRs) can be accelerated up to the second knee energy ~0.1-1 EeV and possibly beyond, with a hard spectral index Gamma ~ 2. Such CRs lose their energy via hadronuclear interactions within a dynamical timescale of the merger shock, producing gamma rays and neutrinos as a by-product. If ~ 10 % of the shock dissipated energy goes into CR acceleration, some local merging galaxies will produce gamma-ray counterparts detectable by CTA. Also, based on the concordance cosmology, where …
Ultra high energy cosmic rays (UHECRs) are expected to be accelerated in astrophysical sources and to travel through extragalactic space before hitting the Earth atmosphere. They interact both with the environment in the source and with the intergalactic photon fields they encounter, causing different processes at various scales depending on the photon energy in the nucleus rest frame. UHECR interactions are sensitive to uncertainties in the extragalactic background spectrum and in the photo-disintegration models.
After the so-called cosmic recombination, the expanding universe entered into a period of darkness since most of the matter was in a neutral state. About a billion years later, however, the intergalactic space was once again ionized. The process, known as the cosmic reionization, required the operation of mechanisms that are not well understood. Among other ionizing sources, Population III stars, mini-quasars, and X-ray emitting microquasars have been invoked. In this article we propose that primordial cosmic rays, accelerated at the termination points of the jets of the first microquasars, ma…
The radioactive decay of aluminum-26 ($^{26}$Al) is an important heating source in early planet formation. Since its discovery, there have been several mechanisms proposed to introduce $^{26}$Al into protoplanetary disks, primarily through contamination by external sources. We propose a local mechanism to enrich protostellar disks with $^{26}$Al through irradiation of the protostellar disk surface by cosmic rays accelerated in the protostellar accretion shock. We calculate the $^{26}$Al enrichment, [$^{26}$Al/$^{27}$Al], at the surface of the protostellar disk in the inner AU throughout the ev…
The Fermi-LAT telescope has unexpectedly discovered GeV gamma-ray emission from the symbiotic Nova V407 Cygni. We investigate the radiation processes due to electrons and hadrons accelerated during the explosion of this Nova. We consider a scenario in which GeV gamma-ray emission observed by Fermi is produced by the electrons with energies of a few tens of GeV in the inverse Compton scattering of stellar radiation. On the other hand, the hadrons are expected to reach larger energies, due to the lack of radiation losses during acceleration process, producing TeV gamma-rays and neutrinos. We pre…
The unexpected energy spectrum of the positron/electron ratio is interpreted astrophysically, with a possible exception of the 100-300 GeV range. The data indicate that this ratio, after a decline between $0.5-8$ GeV, rises steadily with a trend towards saturation at 200-400GeV. These observations (except for the trend) appear to be in conflict with the diffusive shock acceleration (DSA) mechanism, operating in a \emph{single} supernova remnant (SNR) shock. We argue that $e^{+}/e^{-}$ ratio can still be explained by the DSA if positrons are accelerated in a \emph{subset} of SNR shocks which: (…
The gamma-ray emission of RX J1713.7-3946, despite being extensively studied in the GeV and TeV domain, remains poorly understood. This is mostly because in this range, two competing mechanisms can efficiently produce gamma rays: the inverse Compton scattering of accelerated electrons, and interactions of accelerated protons with nuclei of the ISM. In addition to the acceleration of particles from the thermal pool, the reacceleration of pre-existing CRs is often overlooked, and shall in fact also been taken into account. Especially, because of the distance to the SNR ($\sim 1$ kpc), and the lo…
We investigate non-thermal emission from the Fermi bubbles on a hadronic model. Cosmic-ray (CR) protons are accelerated at the forward shock of the bubbles. They interact with the background gas in the Galactic halo and create $π^0$-decay gamma-rays and secondary electrons through proton-proton interaction. We follow the evolution of the CR protons and electrons by calculating their distribution functions. We find that the spectrum and the intensity profile of $π^0$-decay gamma-rays are consistent with observations. We predict that the shock front is located far ahead of the gamma-ray boundary…
New evidence that cosmic rays (hadronic component) are accelerated by supernova remnant shocks all the way from low energies to high energies, has come from recent works combining gamma-ray observations in the sub-GeV to TeV domain on the one hand, and in the submm-mm domain on the other hand. These observations concern the specific cases of supernova remnants interacting with molecular cloud complexes, that have long been suspected to be ideal laboratories to study in situ cosmic ray acceleration and diffusion. Indeed, enhanced gamma-ray emission from neutral pion decay, as well as enhanced i…
The problem of the origin of Cosmic Rays is now over a century old and while there has been substantial progress, especially in the last decade, there are still open questions. The question of "origin" is open to at least three possible interpretations depending on whether one follows the energy powering the accelerator, the matter being accelerated, or the physics of the acceleration process; these approaches are reviewed in turn. Supernova remnants remain by far the most plausible candidates as dominant sources for the bulk of the Galactic cosmic rays, but contributions from other source pop…
We construct and discuss a toy model of the population of numerous non-identical extragalactic sources of ultra-high-energy cosmic rays. In the model, cosmic-ray particles are accelerated in magnetospheres of supermassive black holes in galactic nuclei, the key parameter of acceleration being the black-hole mass. We use astrophysical data on the redshift-dependent black-hole mass function to describe the population of these cosmic-ray accelerators, from weak to powerful, and confront the model with cosmic-ray data.
Tidal disruptions are extremely powerful phenomena that have been designated as candidate sources of ultra-high-energy cosmic rays. The disruption of a star by a black hole can naturally provide protons and heavier nuclei, which can be injected and accelerated to ultra-high energies within a jet. Inside the jet, accelerated nuclei are likely to interact with a dense photon field, leading to a significant production of neutrinos and secondary particles. We model numerically the propagation and interactions of high-energy nuclei in jetted tidal disruption events in order to evaluate consistently…
The origin of Galactic cosmic-ray ions has remained an enigma for almost a century. Although it has generally been thought that they are accelerated in the shock waves associated with powerful supernova explosions-for which there have been recent claims of evidence-the mystery is far from resolved. In fact, we may be on the wrong track altogether in looking for isolated regions of cosmic-ray acceleration.
Although several theories for the origin of cosmic rays in the region between the spectral `knee' and `ankle' exist, this problem is still unsolved. A variety of observations suggest that the transition from Galactic to extragalactic sources occurs in this energy range. In this work we examine whether a Galactic wind which eventually forms a termination shock far outside the Galactic plane can contribute as a possible source to the observed flux in the region of interest. Previous work by Bustard et al. (2017) estimated that particles can be accelerated up to energies above the `knee' up to $R…
We study interactions of cosmological relics, $X$, of mass $m$ and electric charge $qe$ in the galaxy, including thermalization with the interstellar medium, diffusion through inhomogeneous magnetic fields and Fermi acceleration by supernova shock waves. We find that for $m \mathop{}_{\textstyle \sim}^{\textstyle <} 10^{10} q \; ~{\rm GeV}$, there is a large flux of accelerated $X$ in the disk today, with a momentum distribution $\propto 1/p^{2.5}$ extending to $(βp)_{max} \sim 5 \times10^4 q \; ~{\rm GeV}$. Even though acceleration in supernova shocks is efficient, ejecting $X$ from the galax…
Newly-born pulsars offer favorable sites for the injection of heavy nuclei, and for their further acceleration to ultrahigh energies. Once accelerated in the pulsar wind, nuclei have to escape from the surrounding supernova envelope. We examine this escape analytically and numerically, and discuss the pulsar source scenario in light of the latest ultrahigh energy cosmic ray (UHECR) data. Our calculations show that, at early times, when protons can be accelerated to energies E>10^20 eV, the young supernova shell tends to prevent their escape. In contrast, because of their higher charge, iron-pe…
The iron line at 6.4 keV provides a valuable spectral diagnostic in several fields of X-ray astronomy. It often results from the reprocessing of external X-rays by a neutral or low-ionized medium, but it can also be excited by impacts of low-energy cosmic rays. This paper aims to provide signatures allowing identification of radiation from low-energy cosmic rays in X-ray spectra showing the 6.4 keV line. We study in detail the production of nonthermal line and continuum X-rays by interaction of accelerated electrons and ions with a neutral ambient gas. Corresponding models are then applied to …
