共查询到20条相似文献，搜索用时 812 毫秒
1.
Liebert J Reid IN Burrows A Burgasser AJ Kirkpatrick JD Gizis JE 《The Astrophysical journal》2000,534(2):L155-L158
The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrinsic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within approximately 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions. 相似文献
2.
Li-Sheng Mao 《Astrophysics and Space Science》2012,340(2):331-349
We present the Wide-field Infrared Survey Explorer (WISE) photometric data of 158 Fermi-detected BL Lacs and investigate the nature of their mid-infrared (MIR) continuum emission. In the [3.4]-[4.6]-[12] μm color–color diagram, nearly all their colors lie within the WISE Blazar strip (WBS), which is an effective diagnostic tool to separate sources dominated by non-thermal radiation from those dominated by thermal radiation. This feature indicates that their MIR emission is predominantly non-thermal. This argument is further supported by the strong radio-MIR flux correlation. We derive their MIR spectral indices and compare them with the near-infrared (NIR) spectral indices. We find that there is a prevalent steepening from MIR spectrum to NIR spectrum. The low-frequency-peaked BL Lacs (LBLs) have on average a larger MIR spectral index and a higher MIR luminosity than the high-frequency-peaked BL Lacs (HBLs), and the intermediate-frequency-peaked BL Lacs (IBLs) appear to bridge them. The MIR-γ-ray flux correlation is highly significant. A strong positive correlation is also found between the MIR and γ-ray spectral indices. The γ-ray-MIR loudness is significantly correlated with the synchrotron peak frequency. Finally we propose that the γ-rays are highly associated with the MIR emission from the jet, and the γ-ray emission is likely from the synchrotron self-Compton process for the Fermi-detected BL Lacs in our sample. 相似文献
3.
The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for
the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results
from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has
been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence
of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the
gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST
mission. 相似文献
4.
The overall dynamical evolution and radiation mechanism of γ-ray burst (GRB) jets are briefly introduced. Various interesting
topics concerning beaming in GRBs are discussed, including jet structures, orphan afterglows and cylindrical jets. The possible
connection between GRBs and neutron stars is also addressed. 相似文献
5.
W. Bednarek 《Monthly notices of the Royal Astronomical Society》2009,397(3):1420-1425
This paper focuses on neutron stars (NS) of the magnetar type inside massive binary systems. We determine the conditions under which the matter from the stellar wind can penetrate the inner magnetosphere of the magnetar. At a certain distance from the NS surface, the magnetic pressure can balance the gravitational pressure of the accreting matter, creating a very turbulent, magnetized transition region. It is suggested that this region provides good conditions for the acceleration of electrons to relativistic energies. These electrons lose energy due to the synchrotron process and inverse Compton (IC) scattering of the radiation from the nearby massive stellar companion, producing high-energy radiation from X-rays up to ∼TeV γ-rays. The primary γ-rays can be further absorbed in the stellar radiation field, developing an IC e± pair cascade. We calculate the synchrotron X-ray emission from primary electrons and secondary e± pairs and the IC γ-ray emission from the cascade process. It is shown that quasi-simultaneous observations of the TeV γ-ray binary system LSI +61 303 in the X-ray and TeV γ-ray energy ranges can be explained with such an accreting magnetar model. 相似文献
6.
Brian J. Morsony Jared C. Workman Davide Lazzati Mikhail V. Medvedev 《Monthly notices of the Royal Astronomical Society》2009,392(4):1397-1402
We consider radiation emitted by the jitter mechanism in a Blandford–McKee self-similar blastwave. We assume the magnetic field configuration throughout the whole blastwave meets the condition for the emission of jitter radiation and we compute the ensuing images, light curves and spectra. The calculations are performed for both a uniform and a wind environment. We compare our jitter results to synchrotron results. We show that jitter radiation produces slightly different spectra than synchrotron, in particular between the self-absorption and the peak frequency, where the jitter spectrum is flat, while the synchrotron spectrum grows as ν1/3 . The spectral difference is reflected in the early decay slope of the light curves. We conclude that jitter and synchrotron afterglows can be distinguished from each other with good quality observations. However, it is unlikely that the difference can explain the peculiar behaviour of several recent observations, such as flat X-ray slopes and uncorrelated optical and X-ray behaviour. 相似文献
7.
Tomonori Totani 《Astroparticle Physics》1999,11(4):2040-455
We argue that gamma-ray bursts (GRBs) may be the origin of the cosmic gamma-ray background radiation observed in the GeV range. It has theoretically been discussed that protons may carry a much larger amount of energy than electrons in GRBs, and this large energy can be radiated in the TeV range by synchrotron radiation of ultra-high-energy protons ( 1020 eV). The possible detection of GRBs above 10 TeV suggested by the Tibet and HEGRA groups also supports this idea. If this is the case, most of TeV gamma-rays from GRBs are absorbed in intergalactic fields and eventually form GeV gamma-ray background, whose flux is in good agreement with the recent observation. 相似文献
8.
Based on the γ-ray data of 51 γ-ray-loud blazars in the third EGRET catalog and VLBI radio data at 2.29 GHz in high state.
we studied the correlations between the VLBI and γ-rayluminosities and the fluxes using the partial correlation analysis method.
The results show that there is a strong correlation between γ-ray and VLBI radio fluxes and a significant correlation between
γ-ray and VLBI radio luminosities. These results are likely to provide a possible support for self-Compton model of the γ-ray
emission in blazars. It also shows that the γ-ray radiation may come from the region within the order of 1 pc which is consistent with the results given by luminosity variation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
It is generally believed that the synchrotron radiation of electrons from the internal shock is the main radiation mechanism of the prompt GRB (gamma-ray burst) emission. However, what this model predicts can not explain observations well. In this paper, we confirm that electrons are quickly cooled due to radiation losses and also point out that the synchrotron radiation spectrum presented in previous papers is a relatively rough estimation. We get the precise synchrotron radiation spectrum of fast-cooling electrons by carrying out a numerical calculation, and thereby reasonably explain the observed distribution of low-energy spectral index (α) of long GRBs based on a unified model. In addition, we fit the correlation between α and the peak energy of the νFν spectrum (Ep). 相似文献
10.
We calculate the reverse shock (RS) synchrotron emission in the optical and the radio wavelength bands from electron–positron pair-enriched gamma-ray burst ejecta with the goal of determining the pair content of gamma-ray bursts (GRBs) using early-time observations. We take into account an extensive number of physical effects that influence radiation from the RS-heated GRB ejecta. We find that optical/infrared flux depends very weakly on the number of pairs in the ejecta, and there is no unique signature of ejecta pair enrichment if observations are confined to a single wavelength band. It may be possible to determine if the number of pairs per proton in the ejecta is ≳100 by using observations in optical and radio bands; the ratio of flux in the optical and radio at the peak of each respective RS light curve is dependent on the number of pairs per proton. We also find that over a large parameter space, RS emission is expected to be very weak; GRB 990123 seems to have been an exceptional burst in that only a very small fraction of the parameter space produces optical flashes this bright. Also, it is often the case that the optical flux from the forward shock is brighter than the RS flux at deceleration. This could be another possible reason for the paucity of prompt optical flashes with a rapidly declining light curve at early times as was seen in GRBs 990123 and 021211. Some of these results are a generalization of similar results reported in Nakar & Piran. 相似文献
11.
Markus Böttcher 《Astrophysics and Space Science》2007,309(1-4):95-104
Blazars are the most violent steady/recurrent sources of high-energy gamma-ray emission in the known Universe. They are prominent
emitters of electromagnetic radiation throughout the entire electromagnetic spectrum. The observable radiation most likely
originates in a relativistic jet oriented at a small angle with respect to the line of sight. This review starts out with
a general overview of the phenomenology of blazars, including results from a recent multiwavelength observing campaign on
3C279. Subsequently, issues of modeling broadband spectra will be discussed. Spectral information alone is not sufficient
to distinguish between competing models and to constrain essential parameters, in particular related to the primary particle
acceleration and radiation mechanisms in the jet. Short-term spectral variability information may help to break such model
degeneracies, which will require snap-shot spectral information on intraday time scales, which may soon be achievable for
many blazars even in the gamma-ray regime with the upcoming GLAST mission and current advances in Atmospheric Cherenkov Telescope
technology. In addition to pure leptonic and hadronic models of gamma-ray emission from blazars, leptonic/hadronic hybrid
models are reviewed, and the recently developed hadronic synchrotron mirror model for TeV γ-ray flares which are not accompanied by simultaneous X-ray flares (“orphan TeV flares”) is revisited.
The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
12.
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
13.
We have collected the observational data accumulated before the Swift experiment to check the possible connection of short
gamma-ray bursts (GRBs) with low-redshift galaxies. The BATSE/IPN experimental data on well-localized short GRBs and the SDSS
DR5 and PSCz catalogs of galaxies are used. The PSCz sky coverage has allowed us to search for host galaxies for a sample
of 34 short GRBs. One or more galaxies have been found in the error boxes of six bursts, but the probability of a chance coincidence
for each of them is high. No excess of nearby galaxies in the total sample has been detected. The 90% confidence limit corresponds
to the fact that no more than 7%of the short GRBs could originate in nearby galaxies of the PSCz sample. The estimated upper
limit of several percent may be considered to be valid in the volume z = 0.015–0.025. Based on the results of our search, we have estimated the lower limits for the isotropic energies E
γiso of 31 short bursts from our sample. Their values lie within the range 1.0 × 1047–2.7 × 1049 erg. The possible fraction of the flares from magnetars in our sample of short GRBs is discussed. The SDSS sky coverage is
currently insufficient to perform a similar analysis. 相似文献
14.
We discuss the implications of the recent X-ray and TeV γ-ray observations of the PSR B1259–63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models
of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed
behaviour of the system. We develop a model in which the broad band emission from the binary system is produced in result
of collisions of GeV–TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model
the high energy γ-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton
emission produced by low-energy (≤100 MeV) electrons from the decays of secondary charged π
± mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio
emission components.
相似文献
15.
We have studied the correlations between the near-IR and the γ-ray bands using 29 observed γ-ray-loud blazars (16 BL Lac objects
and 13flat-spectrum radio quasars (FSRQs)) with near-IR and γ-ray spectralindices and fluxes. The results show that there
are very strong correlations between near-IR mean spectral index αIR and γ-ray mean spectral index αγ and between near-IR and γ-ray fluxes. Which means that γ-ray radiation from the blazars should be mainly produced by the
synchrotron self-Compton process. In addition, the γ-ray emission of BL Lac objects may be somewhat different from flat-spectrum
radio quasars.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
By now there is no doubt that the gamma-ray bursts (GRB) have a cosmological origin. This allows to regard GRB as the most
powerful known energy sources, ε∼ 1054 erg (with a total number of gamma quanta N_γ∼ 1060). A plausible mechanism of coherent synchrotron radiation (CSR) of relativistic electrons driven by a local magnetic field
is studied in this paper. We consider relativistic electrons arising in the Compton scattering of a GRB in directions close
to that of the ray from the source to a ground-based observer. The synchrotron pulses from Compton electrons located at different
points on the line between the GRB source and the observer arrive at the observation point simultaneously. This simultaneity
ensures the coherence of the detected radiation. Both molecular clouds in the host galaxy of the GRB and our own Galaxy, as
well as the Earth atmosphere are assumed to be scatterers of the GRB radiation. Signals of each scatterer reach the Earth
surface, and can be detected at radio wavelengths. We estimate the characteristics of this radiation. The comparison of GRB
data with the corresponding information on CSR pulses offers a way to determine some global characteristics of the medium
between the Earth and the GRB source. 相似文献
17.
We investigate the production of gamma-rays in the inverse Compton (IC) scattering process by leptons accelerated inside relativistic
blobs in jets of active galactic nuclei. Leptons are injected homogeneously inside the spherical blob and initiate IC e
± pair cascade in the synchrotron radiation (produced by the same population of leptons, SSC model), provided that the optical
depth for gamma-rays is larger than unity. It is shown that for likely parameters internal absorption of gamma-rays has to
be important. We suggest that new type of blazars might be discovered by the future simultaneous X-ray and γ-ray observations, showing peak emissions in the hard X-rays, and in the GeV γ-rays. Moreover, the considered scenario might be also responsible for the orphan X-ray flares recently reported from BL Lac
type active galaxies.
相似文献
18.
We fit the spectra of Cyg X-1 using two component advective flows with Keplerian accretion disks on the equatorial plane surrounded
by sub-Keplerian disks when standing shocks are present. The soft photons generated by the bremsstrahlung and synchrotron
processes in the sub-Keplerian flow, as well as the multi-colour black body emission from the Keplerian disk are Comptonized
by the thermal and non-thermal electrons. By varying Keplerian and sub-Keplerian rates we are able to reproduce the observed
soft and hard states as far as X-ray region is concerned and ‘low γ-ray intensity’ and ‘high γ-ray intensity’ states as far as the soft γ-ray region is concerned. We also find two pivotal points where the spectra intersect as is observed in Cyg X-1.
相似文献
19.
Jet models for the high-energy emission of Galactic X-ray binary sources have regained significant interest with detailed
spectral and timing studies of the X-ray emission from microquasars, the recent detection by the HESS collaboration of very-high-energy
γ-rays from the microquasar LS 5039, and the earlier suggestion of jet models for ultraluminous X-ray sources observed in many
nearby galaxies. Here we study the synchrotron and Compton signatures of time-dependent electron injection and acceleration,
and adiabatic and radiative cooling in the jets of Galactic microquasars. 相似文献
20.
It is generally believed that the complexity and variability of the light curves of gamma-ray bursts (GRBs) are caused by the internal shocks, which would occur when a rapid shell catches up a slower one and collides with it. The electrons in the shock layer are heated by the shocks and radiate via the mechanisms of synchrotron radiation and inverse Compton scattering. Based on relativistic kinematics, a relation between the photon number of the emission from the rapidly moving shock layer and the number of the photons received by an observer is derived. Then, employing the angular spreading of the internal shock emission, the curve equation and profile of a single pulse are obtained, and the shape is typically in the shape of a fast rise and exponential decline. Furthermore, by using the model of the successive collisions of multiple shells under the condition of reasonable parameters, the observed light curves are fitted with a rather good effect. Therefore, by this means, more different types of light curves of GRBs can be explained. 相似文献