共查询到20条相似文献，搜索用时 15 毫秒
1.
We have studied an electron-photon cascade in an isotropic photon field as one of the possible gamma-ray generation mechanisms in compact sources.A cascade in a monoenergetic photon field and in a field of the power-law spectrum is considered. Two types of interaction of cascade particles with the photon field are taken into account: the inverse Compton scattering of electrons and the photoproduction of electron-positron pairs by gamma-quanta. The cascade characteristics have been obtained by numerical solution of the kinetic equations. A quantitative and qualitative analysis is made of the main regularities of the cascade. We have established simple relations between the spectra of cascade particles and the parameters of the photon field and primary radiation. The magnetic field effect on the cascade characteristics is estimated. The results obtained are compared with the results of calculation of other investigators.In the first part of the paper we outline the method of solution and the results relating to the monoenergetic photon field. The theory of cascades in a photon field of the power-law spectrum and its application to the problem of gamma-rays in compact sources are discussed in the second part of the present paper. 相似文献
2.
The ultrahigh-energy (>20 TeV ) gamma rays emitted by active galactic nuclei can be absorbed in intergalactic space through the production of electron-positron pairs during their interaction with extragalactic background photon fields. The electrons and positrons produced by this interaction form an electromagnetic halo. We have studied the halo formation and calculated the halo radiation spectrum. The magnetic field in the halo formation region is assumed to be strong enough for the electron velocities to be isotropized. For such fields, the halo formation process can be described by the method of generations. We calculated the synchrotron and Compton backscattering radiation spectra for the total halo luminosity. We obtained the spatial distribution of the radiation for a point gamma-ray source. 相似文献
3.
Consideration is given to the motion of electrons in a photon field of the monoenergetic or power-law spectrum under the conditions when the main mechanism of energy loss is the inverse Compton scattering by field photons. This process changes the primary spectrum of electrons and converts low-energy field photons to high-energy gamma-quanta for which the electron confinement region is assumed to be optically thin. The electron and gamma-ray spectra have been obtained in a wide energy interval including the Klein-Nishina and Thomson regions. A simple qualitative dependence of the solutions found on the field parameters and the primary spectrum of electrons has been established.The electron and gamma-ray spectra have been obtained by numerically solving the kinetic equation dependent on two variables: the energy of electrons and their path (or the time of motion) in a photon field. The results dramatically differ from the solution of the steady-state kinetic equation which depends only on the electron energy and is frequently used in the given problem. 相似文献
4.
Recent studies suggest that pulsars could be strong sources of TeV muon neutrinos provided positive ions are accelerated by pulsar polar caps to PeV energies. In such a situation, muon neutrinos are produced through the Δ-resonance in interactions of pulsar-accelerated ions with its thermal radiation field. High-energy gamma-rays should also be produced simultaneously in pulsar environment as both charged and neutral pions are generated in the interactions of energetic hadrons with the ambient photon fields. Here, we estimate TeV gamma-ray flux at the Earth from a few nearby young pulsars. When compared with the observations, we find that proper consideration of the effect of polar cap geometry in flux calculation is important. Incorporating such an effect, we obtain the (revised) event rates at the Earth due to a few potential nearby pulsars. The results suggest that pulsars are unlikely to be detected by the upcoming neutrino telescopes. We also estimate TeV gamma-ray and neutrino fluxes from pulsar nebulae for the adopted model of particle acceleration. 相似文献
5.
本文认为强磁场中的逆Compton散射可能是γ射线爆的主要辐射机制.其能谱是由源区质子产生的低频光子经强磁场中非热电子的Compton散射形成的.我们利用非相对论情形(B/B_(cr)≤1,hv_i/m_ec~2≤1)下强磁场中的Compton散射微分截面,导出了上述Compton散射的辐射谱公式,由此很好地拟合了典型γ射线爆GB811016的观测能谱. 相似文献
6.
A. Ong R. D. Bhattacharya C. E. Covault D. D. Dixon D. T. Gregorich D. S. Hanna S. Oser J. Qu bert D. A. Smith O. T. Tü mer A. D. Zych 《Astroparticle Physics》1996,5(3-4):353-365
There is considerable interest world-wide in developing large area atmospheric Cherenkov detectors for ground-based gamma-ray astronomy. This interest stems, in large part, from the fact that the gamma-ray energy region between 20 and 250 GeV is unexplored by any experiment. Atmospheric Cherenkov detectors offer a possible way to explore this region, but large photon collection areas are needed to achieve low energy thresholds. We are developing an experiment using the heliostat mirrors of a solar power plant as the primary collecting element. As part of this development, we built a detector using four heliostat mirrors, a secondary Fresnel lens, and a fast photon detection system. In November 1994, we used this detector to record atmospheric Cherenkov radiation produced by cosmic ray particles showering in the atmosphere. The detected rate of cosmic ray events was consistent with an energy threshold near 1 TeV. The data presented here represent the first detection of atmospheric Cherenkov radiation using solar heliostats viewed from a central tower. 相似文献
7.
Blazars are the only (with one or two exceptions) extragalactic objects which were detected and identified at gamma-ray energies
so far. It is suspected that most of the unidentified gamma-ray sources may be the blazars as well. Because the entire electromagnetic
spectrum of these objects is dominated by non-thermal radiation from relativistically moving jets, the effects such as the
Klein–Nishina regime in the Compton scattering may play a major role in shaping some parts of the blazar spectrum. Within
the framework of external radiation Compton model, we present how these effect influence the spectra of blazars for which
the production of gamma rays is dominated by Comptonization of external radiation. 相似文献
8.
The possible contribution of gamma-rays predicted within the universal cosmic-ray (CR) hypothesis to the energy range of CR spectrum above black-body cutoff is calculated. These gamma-rays arise from the relativistic electromagnetic cascade generated in the field of microwave background radiation (MBR). The ultra-high energy photons and electrons that initiate the cascade are produced at the decay of -mesons created in interactions of photons with the MBR. Simple analytic expression for cascade gamma-ray spectrum is obtained from the solution of kinetic equations for electrons and photons as well as for protons propagating in the MBR field. It is shown that at certain values of magnetic field and radio-wave density in the intergalactic space te flux of cascade gamma-rays may at least partly mask the black-body cutoff in the CR spectrum.Deceased, August 13, 1989. 相似文献
9.
Gamma-ray burst precursors as the remnant of the thermal radiation initially trapped in the fireball
Li-Xin Li 《Monthly notices of the Royal Astronomical Society》2007,380(2):621-636
In the standard fireball model of gamma-ray bursts (GRBs), the fireball starts with an optically thick phase. As it expands, the fireball becomes optically thin at some stage. The thermal radiation trapped in the originally opaque fireball then leaks out, producing a transient event. The appearance of the event is investigated in the framework of a homogeneous, spherically symmetric and freely expanding fireball produced instantly by an explosive process without continuous injection of mass and energy. We find that, generally, the event has a time duration shorter than that of the main burst, which is presumably produced by the internal shock after the fireball becomes optically thin. The event is separated from the main burst by a quiescent time interval, and is weaker than the main burst at least in a high-energy band. Hence, the event corresponds to a GRB precursor. The precursor event predicted by our model has a smooth and Fast Rise and Exponential Decay (FRED) shaped light curve, and a quasi-thermal spectrum. Typically, the characteristic blackbody photon energy is in the X-ray band. However, if the distortion of the blackbody spectrum by electron scattering is considered, the characteristic photon energy could be boosted to the gamma-ray band. Our model may explain a class of observed GRB precursors – those having smooth and FRED-shaped light curves and quasi-thermal spectra. 相似文献
10.
Kouichi Hirotani 《Astrophysics and Space Science》2005,297(1-4):81-91
We investigate a stationary pair production cascade in the outer magnetosphere of an isolated, spinning neutron star. The
charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory
electrons and/or positrons are accelerated by this field to radiate gamma-rays via curvature and inverse-Compton processes.
Some of such gamma-rays collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen
the electric field, which is self-consistently solved together with the energy distribution of particles and gamma-rays at
each point along the field lines. By solving the set of Maxwell and Boltzmann equations, we demonstrate that an external injection
of charged particles at nearly Goldreich-Julian rate does not quench the gap but shifts its position and that the particle
energy distribution cannot be described by a power-law. The injected particles are accelerated in the gap and escape from
it with large Lorentz factors. We show that such escaping particles migrating outside of the gap contribute significantly
to the gamma-ray luminosity for young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV observed for
the Vela pulsar can be explained by this component. We also discuss that the luminosity of the gamma-rays emitted by the escaping
particles is naturally proportional to the square root of the spin-down luminosity. 相似文献
11.
Relativistic electrons in large solar flares produce gamma-ray continuum by bremsstrahlung and microwave emission by gyrosynchrotron radiation. Using observations of the 1972, August 4 flare, we evaluate in detail the electron spectrum and the physical properties (density, magnetic field, size, and temperature) of the common emitting region of these radiations. We also obtain information on energetic protons in this flare by using gamma-ray lines. From the electron spectrum, the proton-to-electron ratio, and the time dependences of the microwave emission, the 2.2 MeV line and the gamma-ray continuum, we conclude that in large solar flares relativistic electrons and energetic nuclei are accelerated by a mechanism which is different from the mechanism which accelerates 100 keV electrons in flares.Research supported by NASA Grant 21-002-316 at the University of Maryland, College Park. 相似文献
12.
We discuss the gamma-ray absorption in the inner region of the microquasar SS433. Our investigation includes several contributions to the opacity of this system. They result from the ambient fields generated by the primary star, possibly an A-type supergiant, and a very extended disk around the black hole. Besides the sharp and dramatic absorption effect that occurs every time the star crosses the emission zone, we find in the UV photon field from the extended disk an important source of absorption for very high energy gamma-rays. This results in periodic gamma-ray observational signatures. 相似文献
13.
Inverse Compton (IC) scattering by relativistic electrons produces a major component of the diffuse emission from the Galaxy.
The photon fields involved are the cosmic microwave background and the interstellar radiation field (ISRF) from stars and
dust. Calculations of the inverse Compton distribution have usually assumed a smooth ISRF, but in fact a large part of the
Galactic luminosity comes from the most luminous stars, which are rare. Therefore we expect the ISRF, and hence the inverse
Compton emission, to be clumpy at some level, which could be detectable by instruments such as GLAST. Even individual nearby
luminous stars could be detectable assuming just the normal cosmic-ray electron spectrum. We present the basic formalism required
and give possible candidate stars to be detected and make predictions for GLAST. Then we apply the formalism to the OB associations
and the Sun, showing that the IC emission produced is not negligible compared to the sensitivity of current or coming detectors.
We estimate that the gamma-ray flux from the halo around the Sun contributes to the diffuse background emission at the few
percent level. 相似文献
14.
强磁场中相对论电子的共振逆康普顿散射(RICS)是产生伽玛射线的有效机制.以前的工作曾论证,伽玛暴(GRB)的早期伽玛射线辐射可能主要由该机制产生.利用此辐射机制,伽玛暴研究中的一些困惑有可能得到较好的解释.例如,观测统计给出的"Amati关系"的起源,两段式(折断式)幂律谱的形成,特别是其中"死线问题"的解决方案,还有偏振的存在等.这里将重点讨论折断幂律谱形成问题.基于单个电子的RICS谱功率公式,导出了强磁场中大量相对论电子穿过周边低频辐射场时产生的集体RICS辐射谱(RICS谱光度)的简化解析公式,并将它应用于中子星周边几种典型的低频场(如黑体辐射场、幂律辐射场以及热轫致辐射场),以便与实际观测谱形比较.计算表明:在满足匹配条件(即近似共振条件)下,RICS辐射效率很高,其谱形普遍为两段式的幂律谱形式,与周边低频场性质无关.还论证RICS机制可能是伽玛暴、软伽玛重复暴和伽玛射线脉冲星在高能射线波段(硬X射线和伽玛射线)的一个理想的高效辐射机制. 相似文献
15.
S. V. Golenetskii E. P. Mazets R. L. Aptekar Yu. A. Guryan V. N. Ilyinskii 《Astrophysics and Space Science》1986,124(2):243-278
The emission features observed in the energy spectra of cosmic gamma-ray bursts imply the existence of two radiation components of comparable intensity. The softer component is similar to the continua of featureless bursts. The fast decrease in the intensity of this radiation with increasing photon energy is apparently due to the neutron star's magnetosphere being opaque to hard photons because of the formation of electron-positron pairs in single- (,B) and two-photon (,), processes. The hard component originates from the annihilation of electron-positron pairs, its spectrum representing a broad line with an extended power-law wing. Such a shape of the spectrum is apparently due to either thermal broadening in a source with a spatially inhomogeneous and rapidly time-varying plasma temperature, or nonthermal energy distribution of particles in their motion along the magnetic field lines. It is assumed that the sources of these components are spatially separated, the annihilation radiation escaping from the polar regions of a strongly magnetized neutron star in a collimated beam without appreciable attenuation. 相似文献
16.
Yu. S. Grishkan 《Astronomy Letters》2010,36(6):381-388
The birefringence of electromagnetic radiation from gamma-ray burst (GRB) afterglows due to the Lorentz violation (LV) of
spacetime has been calculated. The dependence of this effect on the radiation wavelength and redshift z in the ΛCDM model of the Universe has been established. It is shown that polarization tests for GRB afterglows can be invoked
to measure the LV parameters. LV causes oscillations in the parameters of the afterglow spectrum that can be in the ultraviolet
spectral range and will depend significantly on redshift z. This can facilitate the recording of LV for an electromagnetic field and can lower significantly the energy threshold of
its detection. 相似文献
17.
Imaging Atmospheric Cherenkov Telescopes have revealed more than 100 TeV sources along the galactic plane, around 45% of them remain unidentified. However, radio observations revealed that dense molecular clumps are associated with 67% of 18 unidentified TeV sources. In this paper, we propose that an electron–positron magnetospheric accelerator emits detectable TeV gamma-rays when a rapidly rotating black hole enters a gaseous cloud. Since the general-relativistic effect plays an essential role in this magnetospheric lepton accelerator scenario, the emissions take place in the direct vicinity of the event horizon, resulting in a point-like gamma-ray image. We demonstrate that their gamma-ray spectra have two peaks around 0.1 GeV and 0.1 TeV and that the accelerators become most luminous when the mass accretion rate becomes about 0.01% of the Eddington accretion rate. We compare the results with alternative scenarios such as the cosmic-ray hadron scenario, which predicts an extended morphology of the gamma-ray image with a single power-law photon spectrum from GeV to 100 TeV. 相似文献
18.
H. M. Butner G. H. Moriarty-Schieven M. E. Ressler M. W. Werner 《Astrophysics and Space Science》1995,231(1-2):77-80
The exotic quantum process of photon splitting has great potential to explain the softness of emission in soft gamma repeaters (SGRs) if they originate in neutron stars with surface fields above the quantum critical fieldB
cr = 4.413×1013 Gauss. Splitting becomes prolific at such field strengths: its principal effect is to degrade photon energies, initiating a cascade that softens gamma-ray spectra. Uniform field cascade calculations have demonstrated that emission could be softened to the observed SGR energies for fields exceeding about 1014 Gauss. Recently, we have determined splitting attenuation lengths and maximum energies for photon escape in neutron star environments including the effects of magnetospheric dipole field geometry. Such escape energies esc suitably approximate the peak energy of the emergent spectrum, and in this paper we present results for
esc as a function of photon emission angles for polar cap and equatorial emission regions. The escape energy is extremely insensitive to viewing perspective for equatorial emission, arguing in favour of such a site for the origin of SGR activity. 相似文献
19.
We calculate the polarization of the radiation from an optically thick accretion disk with a vertical averaged magnetic field.
The polarization arises from the scattering of light by free electrons in a magnetized disk plasma. The Faraday rotation of
the polarization plane during the propagation of a photon in a medium with a magnetic field is considered as the main effect.
We discuss various models of optically thick accretion disks with a vertical averaged magnetic field. Our main goal is to
derive simple asymptotic formulas for the polarization of radiation in the case where the Faraday rotation angle Ψ ≫ 1 at
the Thomson optical depth τ = 1. The results of our calculations allow the magnetic field strength in the region of the marginally
stable orbit near a black hole to be estimated from polarimetric observations, including X-ray observations expected in the
future. Since the polarization spectrum of the radiation strongly depends on the accretion disk model, a realistic physical
model of the accretion disk can be determined from data on the polarization of its radiation. 相似文献
20.
Suprathermal proton bremsstrahlung (SPB) of energetic protons is an important source of high-energy X-ray and gamma-ray photons
in the interstellar medium. We calculate the suprathermal bremsstrahlung radiation power and the associated energy loss rate
of the radiating protons. Also the mean photon energy from the SPB process is derived which can be used to construct a monochromatic
approximation of the radiation power. The SPB power is the starting point for the quantitative modelling of theoretical SPB
radiation spectra in cosmic sources.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献