共查询到20条相似文献，搜索用时 31 毫秒
1.
Supernova remnants (SNRs) are one of the most energetic astrophysical events and are thought to be the dominant source of Galactic cosmic rays (CRs). A recent report on observations from the Fermi satellite has shown a signature of pion decay in the gamma-ray spectra of SNRs. This provides strong evidence that high-energy protons are accelerated in SNRs. The actual gamma-ray emission from pion decay should depend on the diffusion of CRs in the interstellar medium. In order to quantitatively analyse the diffusion of high-energy CRs from acceleration sites, we have performed test particle numerical simulations of CR protons using a three-dimensional magnetohydrodynamics (MHD) simulation of an interstellar medium swept-up by a blast wave. We analyse the diffusion of CRs at a length scale of order a few pc in our simulated SNR, and find the diffusion of CRs is precisely described by a Bohm diffusion, which is required for efficient acceleration at least for particles with energies above 30 TeV for a realistic interstellar medium. Although we find the possibility of a superdiffusive process (travel distance ∝ t0.75) in our simulations, its effect on CR diffusion at the length scale of the turbulence in the SNR is limited. 相似文献
2.
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties
of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical
constraints for the total supernova (SN) explosion energy E
sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s
SN is a type Ia SN we determine for any given explosion energy E
sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes
it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E
sn=1051 erg the expected energy flux of TeV γ-rays varies from 2×10−11 to 10−13 erg/(cm2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π
0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO
and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc. 相似文献
3.
We investigated the acceleration of solar cosmic rays (SCRs) by the shock waves produced by coronal mass ejections. We performed detailed numerical calculations of the SCR spectra produced during the shock propagation in the solar corona in terms of a model based on the diffusive transport equation using a realistic set of physical parameters for the corona. The resulting SCR energy spectrum N(ε) ∝ ε?γ exp [? (ε/εmax)α] is shown to include a power-law portion with an index γ?2 that ends with an exponential tail with α ? 2.5 ? β, where β is the spectral index of the background Alfvén turbulence. The maximum SCR energy lies within the range εmax = 1–300 MeV, depending on the shock velocity. Because of the steep spectrum of the SCRs, their backreaction on the shock structure is negligible. The decrease in the Alfvén Mach number of the shock due to the increase in the Alfvén velocity with heliocentric distance r causes the efficient SCR acceleration to terminate when the shock reaches a distance of r = 2–3R⊙. Since the diffusive SCR propagation in this case is faster than the shock expansion, SCR particles intensively escape from the shock vicinity. A comparison of the calculated SCR fluxes expected near the Earth’s orbit with available experimental data indicates that the theory satisfactorily explains all of the main observed features. 相似文献
4.
For the case of Tycho’s supernova remnant (SNR) we present the relation between the blast wave and contact discontinuity radii
calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii
are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is so close
to the shock radius that it can only be explained by efficient CR acceleration which in turn makes the medium more compressible.
Together with the recently determined new value E
sn=1.2×1051 erg of the SN explosion energy this also confirms our previous conclusion that a TeV γ-ray flux of (2–5)×10−13 erg/(cm2 s) is to be expected from Tycho’s SNR. Chandra measurements and the HEGRA upper limit of the TeV γ-ray flux together limit the source distance d to 3.3≤d≤4 kpc. 相似文献
5.
The solar cosmic ray (SCR) acceleration by the shocks driven by coronal mass ejections is studied by taking into account the generation of Alfvén waves by accelerated particles. Detailed numerical calculations of the SCR spectra produced during the shock propagation through the solar corona have been performed within a quasi-linear approach with a realistic set of coronal parameters. The resultant SCR energy spectrum is shown to include a power-law part N ∝ ?-γ with an index γ = 1.7–3.5 that ends with an exponential tail. The maximum SCR energy lies within the range ? max = 0.01–10 GeV, depending on the shock velocity V S = 750–2500 km s?1. The decrease of the shock Alfvénic Mach number due to the increase Alfvén velocity with heliocentric distance r leads to the end of the efficient SCR acceleration when the shock size reaches R S ≈ 4R ⊙. In this case, the diffusive SCR propagation begins to exceed the shock velocity; as a result, SCRs escape intensively from the shock vicinity. The self-consistent generation of Alfvén waves by accelerated particles is accompanied by a steepening of the particle spectrum and an increase of their maximum energy. Comparison of the calculated SCR fluxes expected near the Earth’s orbit with the available experimental data shows that the theory explains the main observed features. 相似文献
6.
Supernova remnants (SNRs) are among the most important targets for γ-ray observatories. Being prominent non-thermal sources, they are very likely responsible for the acceleration of the bulk of Galactic cosmic rays (CRs). To firmly establish the SNR paradigm for the origin of cosmic rays, it should be confirmed that protons are indeed accelerated in, and released from, SNRs with the appropriate flux and spectrum. This can be done by detailed theoretical models which account for microphysics of acceleration and various radiation processes of hadrons and leptons. The current generation of Cherenkov telescopes has insufficient sensitivity to constrain theoretical models. A new facility, the Cherenkov Telescope Array (CTA), will have superior capabilities and may finally resolve this long standing issue of high-energy astrophysics. We want to assess the capabilities of CTA to reveal the physics of various types of SNRs in the initial 2000 years of their evolution. During this time, the efficiency to accelerate cosmic rays is highest. We perform time-dependent simulations of the hydrodynamics, the magnetic fields, the cosmic-ray acceleration, and the non-thermal emission for type Ia, Ic and IIP SNRs. We calculate the CTA response to the γ-ray emission from these SNRs for various ages and distances, and we perform a realistic analysis of the simulated data. We derive distance limits for the detectability and resolvability of these SNR types at several ages. We test the ability of CTA to reconstruct their morphological and spectral parameters as a function of their distance. Finally, we estimate how well CTA data will constrain the theoretical models. 相似文献
7.
From the little we know of the physical conditions in γ-ray bursters, it seems that they are potentially effective in the acceleration of high-energy cosmic rays (CRs), especially if the bursters are at cosmological distances. We find that, with the observed statistics and fluxes of γ-ray bursts, cosmological bursters may be an important source of cosmic rays in two regions of the observed spectrum: (1) At the very-high-energy end (E > 1019 eV), where CRs must be of extragalactic origin. (2) Around and above the spectral feature that has been described as a bump and/or a knee, which occurs around 1015 eV. The occasional bursters that occur inside the Galaxy — about once in a few hundred thousand years if burst emission is isotropic; more often, if it is beamed — could maintain the density of galactic cosmic rays at the observed level in this range. These two energy ranges might correspond to two typical CR energy scales characteristic of bursters: one pertinent to CR acceleration due to interaction of a magnetized-fireball front with an ambient medium; the other to acceleration in the fireball itself (e.g. shock acceleration). 相似文献
8.
《New Astronomy》2002,7(6):317-336
Based on the “cannonball model” for gamma-ray bursts of Dar and De Rújula, it is proposed that masses of baryonic plasma (“cannonballs”), ejected in bipolar supernova explosions in our Galaxy are the sources of hadronic Galactic cosmic rays (CRs) at all energies. The propagation of the cannonballs in the Galactic disk and halo is studied. Two mechanisms for the acceleration of the observed CRs are proposed. The first is based on ultrarelativistic shocks in the interstellar medium and could accelerate the bulk of CRs up to the “knee” energy of 4×1015 eV. The second operates with second-order Fermi acceleration within the cannonball. If the total initial energy of the ejected plasmoids in a SN explosion is 1053 erg or higher, this second mechanism may explain the CR spectrum above the knee up to the highest observed energies. It is shown that together with plausible assumptions about CR propagation in the Galactic confinement volume, the observed spectral indices of the CR spectrum can be theoretically understood to first order. The model allows a natural understanding of various basic CR observations like the absence of the Greisen–Zatsepin cutoff, the anisotropy of arrival directions as function of energy and the small Galactocentric gradient of the CR density. 相似文献
9.
Dingrong Xiong Haojing Zhang Xiong Zhang Yonggang Zheng Wenguang Liu Lisheng Mao Bangrong Huang Ting Kang Yongjuan Cha Fei Guo 《Astrophysics and Space Science》2013,343(1):345-360
Using γ-ray data detected by Fermi Large Area Telescope (LAT) and multi-wave band data for 40 TeV active galactic nuclei (AGNs), we have studied the correlations between flux densities (F R, F IR, F O, F X and F γ ) in the radio, infrared, optical, X-ray and γ-ray wave bands. Our results are the following: (1) For TeV HSP BL Lacertae objects (THBLs), there are strong correlations between F γ and F R and between F γ and F IR in all states (average/high/low); (2) The TeV radio galaxies (TRGs) deviate from the area occupied by THBLs; (3) The TeV flat-spectrum radio quasars (TFSRQs) have much stronger γ-ray emission than THBLs; (4) For THBLs, there are weak correlations between F γ and F X in all states as well as between F γ and F O in both average and high states, and a strong correlation between F γ and F O in the low state; (5) For THBLs, there are strong correlations between F O and F R in both low and average states as well as between F O and F IR in all states and between F IR and F R in all states, but no strong correlations among other bands are found. From these results, we suggest that for THBLs, the synchrotron self-Compton radiation (SSC) is the main mechanism of high energy γ-ray emission and the inverse Compton scattering of circum-nuclear dust is likely to be a important complementary mechanism. Compared with THBLs, TRGs and TFSRQs may have a different origin of high energy γ-ray. 相似文献
10.
P. E. Shtykovskiy A. A. Lutovinov M. R. Gilfanov R. A. Sunyaev 《Astronomy Letters》2005,31(4):258-262
We obtained constraints on the luminosity of the central source in SNR 1987 A using XMM-Newton and INTEGRAL data. XMM-Newton yields an upper limit on the SNR luminosity in the 2–10 keV energy band, LX ? 5 × 1034 erg s?1. Since the optical depth of the envelope is still large in the XMM-Newton energy band, this constraint carries no useful information about the luminosity of the central source. The optical depth is expected to be small in the hard (20–200 keV) X-ray band of the IBIS telescope aboard the INTEGRAL observatory. We detected no statistically significant emission from SNR 1987 A in the INTEGRAL data and obtained an upper limit of LX ? 1.1 × 1036 erg s?1 on the luminosity of the central source in the 20–60 keV band. We also obtained an upper limit on the mass of radioactive 44Ti, M(44Ti) ? 10?3M⊙. 相似文献
11.
The determination of the origin of cosmic rays with observed energies in excess of 1017 eV that exceed the expected energies of cosmic rays accelerated by supernova remnants in the galaxy is a pressing problem in modern astrophysics. Hypernova remnants are one of the possible galactic sources of cosmic rays with energies of up to 1019 eV. Hypernovae constitute a class of extremely powerful supernova explosions, whose supposed progenitors are massive Wolf-Rayet stars. We analyze the special aspects of acceleration of cosmic rays in hypernova remnants that expand in wind bubbles of Wolf-Rayet progenitor stars. We show that these cosmic rays may attain maximum energies of 1018 eV even with a relatively conservative choice of acceleration parameters and account for tens of percent of the total cosmic ray flux observed in the vicinity of the earth in the energy range of 1016–1018 eV if the galactic hypernova explosion rate in the modern epoch reaches ? S ～ 10?4 year?1. 相似文献
12.
The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma-rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma-ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non-thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of
13.
E.A. Dorfi 《Astrophysics and Space Science》2000,272(1-3):227-238
Supernova Remnants (SNRs) are the most likely sources of the galactic cosmic rays up to energies of about 1015 eV/nuc. The large scale shock waves of SNRs are almost ideal sites to accelerate particles up to these highly non-thermal
energies by a first order Fermi mechanism which operates through scattering of the particles at magnetic irregularities. In
order to get an estimate on the total amount of the explosion energy E
SNconverted into high energy particles the evolution of a SNR has to be followed up to the final merging with the interstellar
medium. This can only be done by numerical simulations since the non-linear modifications of the shock wave due to particle
acceleration as well as radiative cooling processes at later SNR stages have to be considered in such investigations. Based
on a large sample of numerical evolution calculations performed for different ambient densities n
ext, SN explosion energies, magnetic fields etc. we discuss the final ‘yields’ of cosmic rays at the final SNR stage where the
Mach number of the shock waves drops below 2. At these times the cosmic rays start to diffuse out of the remnant. In the range
of external densities of10-2 ≤ n
ext/[cm-3] ≤ 30 we find a the total acceleration efficiency of about 0.15 E
SN with an increase up to 0.24 E
SN at maximum for an external density of n
ext = 10 cm-3. Since for the larger ambient densities radiative cooling can reduce significantly the total thermal energy content of the
remnant dissipation of Alfvén waves can provide an important heating mechanism for the gas at these later stages. From the
collisions of the cosmic rays with the thermal plasma neutral pions are generated which decay subsequently into observable
γ-rays above 100 MeV. Hence, we calculate these γ-ray luminosities of SNRs and compare them with current upper limits of ground
based γ-raytelescopes. The development of dense shells due to cooling of the thermal plasma increases the γ-ray luminosities
and e.g. an external density of n
ext = 10 cm-3 with E
SN = 1051 erg can lead to a γ-ray flux above 10-6 ph cm-2 s-1 for a remnant located at a distance of 1 kpc.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The possibility of cosmic-ray (CR) acceleration to energies above 109 GeV per nucleus in extended Galactic OB associations is analyzed. A two-stage acceleration mechanism is justified: at the first stage, the acceleration by separate shock fronts from spatially and temporally correlated supernovae explosions takes place, and, at the second stage, the Fermi acceleration by supersonic turbulence in an extended, strongly perturbed region near the OB association takes place. We calculate the CR energy spectrum, the change in CR chemical composition with energy, and the energy dependence of the mean logarithm of atomic mass, ?lnA?, for the accelerated particles. The calculated values are compared with those observed near the break in the energy spectrum. We estimate the turbulence parameters, which allow the observed features of the energy spectrum and the CR enrichment with heavy elements to be explained. 相似文献
15.
The discovery of a terrestrial planet orbiting Proxima Centauri has led to a lot of papers discussing the possible conditions on this planet. Since the main factors determining space weather in the Solar System are the solar wind and cosmic rays (CRs), it seems important to understand what the parameters of the stellar wind, Galactic and stellar CRs near exoplanets are. Based on the available data, we present our estimates of the stellar wind velocity and density, the possible CR fluxes and fluences near Proxima b. We have found that there are virtually no Galactic CRs near the orbit of Proxima b up to particle energies ~1 TeV due to their modulation by the stellar wind. Nevertheless, more powerful and frequent flares on Proxima Centauri than those on the Sun can accelerate particles to maximum energies ~3150αβ GeV (α, β < 1). Therefore, the intensity of stellar CRs in the astrosphere may turn out to be comparable to the intensity of low-energy CRs in the heliosphere. 相似文献
16.
17.
T. W. Jones 《Journal of Astrophysics and Astronomy》2011,32(4):427-435
I review some basic properties of diffusive shock acceleration (DSA) in the context of young supernova remnants (SNRs). I
also point out some key differences with cosmological, cluster-related shocks. DSA seems to be very efficient in strong, young
SNR shocks. Provided the magnetic fields exceed some hundreds of μGauss (possibly amplified by CR related dynamics), these shocks can accelerate cosmic ray hadrons to PeV energies in the time
available to them. Electron energies, limited by radiative losses, are likely limited to the TeV range. Injection of fresh
particles at these shocks is poorly understood, but hadrons are much more easily injected than the more highly magnetized
electrons. That seems supported by observational data, as well. So, while CR protons in young SNRs may play very major roles
in the SNR evolution, the CR electron populations have minimal such impact, despite their observational importance. 相似文献
18.
Long TeV γ-ray campaigns have been carried out to study the spectrum, variability and duty cycle of the BL Lac object Markarian 421. These campaigns have given some evidence of the presence of protons in the jet: (i) Its spectral energy distribution which shows two main peaks; one at low energies (∼1 keV) and the other at high energies (hundreds of GeV), has been described by using synchrotron proton blazar model. (ii) The study of the variability at GeV γ-rays and X-rays has indicated no significant correlation. (iii) TeV γ-ray detections without activity in X-rays, called “orphan flares” have been observed in this object.Recently, The Telescope Array Collaboration reported the arrival of 72 ultra-high-energy cosmic rays with some of them possibly related to the direction of Markarian 421. The IceCube Collaboration reported the detection of 37 extraterrestrial neutrinos in the TeV–PeV energy range collected during three consecutive years. In particular, no neutrino track events were associated with this source. In this paper, we consider the proton–photon interactions to correlate the TeV γ-ray fluxes reported by long campaigns with the neutrino and ultra-high-energy cosmic ray observations around this blazar. Considering the results reported by The IceCube and Telescope Array Collaborations, we found that only from ∼25% to 70% of TeV fluxes described with a power law function with exponential cutoff can come from the proton–photon interactions. 相似文献
19.
J. Fang L. Zhang J. F. Zhang Y. Y. Tang H. Yu 《Monthly notices of the Royal Astronomical Society》2009,392(2):925-929
Non-thermal X-rays and very high energy (VHE) γ-rays have been detected from the supernova remnant (SNR) RX J1713.7−3946, and the recent observations with the Suzaku satellite clearly reveal a spectral cut-off in the X-ray spectrum, which directly relates to the cut-off of the energy spectrum of the parent electrons. However, whether the origin of the VHE γ-rays from the SNR is hadronic or leptonic is still in debate. We studied the multi-band non-thermal emission from RX J1713.7−3946 based on a semi-analytical approach towards the non-linear shock acceleration process by including the contribution of the accelerated electrons to the non-thermal radiation. The results show that the multi-band observations on RX J1713.7−3946 can be well explained in the model with appropriate parameters, and the TeV γ-rays have hadronic origin, i.e. they are produced via proton–proton interactions as the relativistic protons accelerated by the shock collide with the ambient matter. 相似文献
20.
Using data from ground-based observations of cosmic rays (CRs) on the worldwide network of stations and spacecraft, we have investigated the proton spectra and the CR anisotropy during the ground level enhancements of CRs on May 17, 2012 (GLE71) and January 6, 2014 (GLE72) occurred in solar cycle 24 by the spectrographic global survey method. We provide the CR rigidity spectra and the relative changes in the intensity of CRs with a rigidity of 2 GV in the solar–ecliptic geocentric coordinate system in specific periods of these events. We show that the proton acceleration during GLE71 and GLE72 occurred up to rigidities R ~ 2.3?2.5 GV, while the differential rigidity spectra of solar CRs are described neither by a power nor by an exponential function of particle rigidity. At the times of the events considered the Earth was in a loop-like structure of the interplanetary magnetic field. 相似文献