共查询到17条相似文献，搜索用时 393 毫秒
1.
If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets,their early afterglows may differ from those of GRBs,and when the ultra-relativistic outflow inter-acts with the surrounding medium,there are two shocks formed,a forward shock (FS),and a reverse shock (RS). We calculate numerically the early afterglow powered by uniform jets,Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differen-tial equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets,the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect,but in the stellar wind environment,the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets (Gaussian and power-law jets),where there are emission materials on the line of sight,the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic (in stellar wind). 相似文献
2.
Ting Yan Da-Ming Wei Yi-Zhong Fan 《天体物理学报》2007,7(6):777-788
If X-ray flashes （XRFs） and X-ray rich Gamma-ray Bursts （XRRGs） have the same origin as the Gamma-ray bursts （GRBs） but are viewed off-center from structured jets, their early afterglows may differ from those of GRBs, and when the ultra-relativistic outflow inter- acts with the surrounding medium, there are two shocks formed, a forward shock （FS）, and a reverse shock （RS）. We calculate numerically the early afterglow powered by uniform jets, Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differential equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets, the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect, but in the stellar wind environment, the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets （Gaussian and power-law jets）, where there are emission materials on the line of sight, the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic （in stellar wind）. 相似文献
3.
Da-Min Meng Hong-Yan Zhou Center for Astrophysics and Department of Astronomy Applied Physics University of Science Technology of China Hefei 《中国天文和天体物理学报》2006,6(1):25-34
We compile a sample of 11 Fanaroff-Riley type I Radio Galaxies(FR-I RGs)with multi-wavelength observations to address the dynamic behavior of jets in these objects.Optical images acquired by the Hubble Space Telescope(HST)are carefully analyzed.The method and reduction procedure are described in detail. Unresolved optical cores emerge after having properly removed starlight from the host galaxies in eight of the FR-I RGs,of which five are new identifications.Broad band spectral properties of these newly identified compact cores are compared with that previously found in FR-I RGs,as well as the low-energy-peaked BL Lac objects. The similarity between them argues for the same non-thermal synchrotron origin. Well-resolved optical jets with knotty morphologies are found in three FR-I RGs in our sample,namely 3C 15,3C 66B and B20755 37.The optical counterparts to the inner radio/X-ray jets are identified and a clear one-to-one correspondence between the optical,radio and X-ray knots is found.The structure and information on the optical jets are discussed.Physical parameters such as the knots position,flux and size are also presented.Detailed comparison between the multi-wavelength data and radiative and dynamic models of jet will be made in a forthcoming paper. 相似文献
4.
Xiao-Rong Lu 《天体物理学报》2008,8(1):50-62
It has long remained an open question as to the geometry of the broad line region （BLR） in active galactic nuclei （AGNs）. The reverberation mapping technique which measures the response of the broad emission lines to the ionizing continuum, when combined with multiwavelength continuum fitted by sophisticated accretion disks, provides a way of probing the BLR geometry. We analyze a sample of 35 AGNs, which have been monitored by the reverberation mapping campaign. In view of energy budget, the reverberation-based BH masses are found to be in agreement with those obtained by accretion disk models in two thirds of the present sample while the reverberation mapping methods underestimate the BH masses in about one third of objects, as also suggested by CoUin et al. in a recent work. We point out that there are obviously two kinds of BLR geometry, which are strongly dependent on the Eddington ratio, and separated by the value LBol/LEdd - 0.1. These results prefer a scenario of the disk and wind configuration of the BLR and identify the Eddington ratio as the physical driver regulating the wind in the BLR. 相似文献
5.
The relativistic external shock model of gamma-ray burst(GRB) afterglows has been established with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ε_e and for the magnetic field ε_B, the number density of the environment n and the index of the powerlaw distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as: the wind medium environment by letting n change with radius,the energy injection model by letting kinetic energy change with time and so on. In this paper, by assuming all four parameters(except p) change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range. 相似文献
6.
Using the generic hydrodynamic model of gamma-ray burst(GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity,failed and standard GRBs in different observational bands of FAST’s energy window.The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except those of low luminosity GRBs could be observed by a large radio telescope as long as the domains of time and frequency are appropriate. It is important to note that FAST can detect relatively weak radio afterglows at a higher frequency of 2.5 GHz for very high redshift up to z = 15 or even more. Radio afterglows of low luminosity GRBs can only be detected after the completion of the second phase of FAST. FAST is expected to significantly expand the sample of GRB radio afterglows in the near future. 相似文献
7.
Xue-Feng Wu Zi-Gao Dai Yong-Feng Huang Hai-Tao Ma Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2004,4(5):455-472
Optical and radio afterglows arising from shocks by relativistic conical ejecta running into pre-burst massive stellar winds are revisited. Under the homogeneous thin-shell approximation and a realistic treatment for the lateral expansion of jets, our results show that a notable break exists in the optical light curve in most cases we calculated in which the physical parameters are varied within reasonable ranges. For a relatively tenuous wind which cannot decelerate the relativistic jet to cause a light curve break within days, the wind termination shock due to the ram pressure of the surrounding medium occurs at a small radius, namely, a few times 1017 cm. In such a structured wind environment, the jet will pass through the wind within several hours and run into the outer uniform dense medium. The resulting optical light curve flattens with a shallower drop after the jet encounters the uniform medium, and then declines deeply, triggered by runaway lateral expansion. 相似文献
8.
We show that the explosive transition of the neutron star(NS)to a quark star(QS)(a Quark Nova)in Cassiopeia A(Cas A)a few days following the supernova(SN)proper can account for several of the puzzling kinematic and nucleosynthetic features that are observed.The observed decoupling between Fe and44Ti and the lack of Fe emission within44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by relativistic QN neutrons.Our model predicts the44Ti to be more prominent to the NW of the central compact object(CCO)than in the SE and little of it along the NE-SW jets,in agreement with Nu Star observations.Other intriguing features of Cas A are addressed,such as the lack of a pulsar wind nebula and the reported few percent drop in the CCO temperature over a period of 10 yr. 相似文献
9.
It has long remained an open question as to the geometry of the broad line region (BLR) in active galactic nuclei (AGNs). The reverberation mapping technique which mea-sures the response of the broad emission lines to the ionizing continuum, when combined with multiwavelength continuum fitted by sophisticated accretion disks, provides a way of probing the BLR geometry. We analyze a sample of 35 AGNs, which have been monitored by the reverberation mapping campaign. In view of energy budget, the reverberation-based BH masses are found to be in agreement with those obtained by accretion disk models in two thirds of the present sample while the reverberation mapping methods underestimate the BH masses in about one third of objects, as also suggested by Collin et al. in a recent work. We point out that there are obviously two kinds of BLR geometry, which are strongly dependent on the Eddington ratio, and separated by the value LBol/LEdd ～ 0.1. These results prefer a scenario of the disk and wind configuration of the BLR and identify the Eddington ratio as the physical driver regulating the wind in the BLR. 相似文献
10.
Yong-Feng Huang Ye Lu Anna Yuen Lam Wong Kwong Sang Cheng 《中国天文和天体物理学报》2007,7(3):397-404
Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly. 相似文献
11.
It is widely accepted that many gamma-ray bursts (GRBs) are produced by relativistic jets. Previous studies on the beaming effects in GRBs are mainly based on the conical geometry. However, some observations of the relativistic jets in radio galaxies, active galactic nuclei, and “micro-quasars” have shown that many of these outflows are cylindrical, but not conical. In this study, we assume that the jets that produce GRBs are cylindrical, and that the circum-burst environment is dense and optically thick. In the prompt burst phase, the strong X-ray emission can sublimate the circum-burst medium to form an optically thin channel, from which the optical photons are allowed to escape. As a result, the optical afterglows can be observed only for the observers who are positioned on the axes of jets. It is shown that the observed optical afterglows usually decay very rapidly (in the form of Sv oc t^v^l1 where p is the index of electron power-law distribution), due to the joint effect of the lateral expansion of the cylindrical jet and the absorption of optical photons by the dust outside the channel. Our model provides a possible explanation for the dark gamma-ray bursts. 相似文献
12.
13.
We study the bending of jets in binary stellar systems. A compact companion accretes mass from the slow wind of the mass-losing primary star, forms an accretion disc and blows two opposite jets. These fast jets are bent by the slow wind. Disregarding the orbital motion, we find the dependence of the bending angle on the properties of the slow wind and the jets. Bending of jets is observed in planetary nebulae which are thought to be the descendants of interacting binary stars. For example, in some of these planetary nebulae, the two bubbles (lobes) which are inflated by the two opposite jets are displaced to the same side of the symmetry axis of the nebula. Similar displacements are observed in bubble pairs in the centre of some clusters and groups of galaxies. We compare the bending of jets in binary stellar systems with that in clusters of galaxies. 相似文献
14.
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
15.
F. Genet F. Daigne R. Mochkovitch 《Monthly notices of the Royal Astronomical Society》2007,381(2):732-740
We propose to explain the recent observations of gamma-ray burst early X-ray afterglows with SWIFT by the dissipation of energy in the reverse shock that crosses the ejecta as it is decelerated by the burst environment. We compute the evolution of the dissipated power and discuss the possibility that a fraction of it can be radiated in the X-ray range. We show that this reverse shock contribution behaves in a way very similar to the observed X-ray afterglows if the following two conditions are satisfied. (i) The Lorentz factor of the material which is ejected during the late stages of source activity decreases to small values Γ < 10 and (ii) a large part of the shock-dissipated energy is transferred to a small fraction (ζ≲ 10−2 ) of the electron population. We also discuss how our results may help to solve some puzzling problems raised by multiwavelength early afterglow observations such as the presence of chromatic breaks. 相似文献
16.
EnricoRamirez-Ruiz rew I.MacFadyen DavideLazzati 《Monthly notices of the Royal Astronomical Society》2002,331(1):197-202
Recent observations suggest that long-duration γ -ray bursts and their afterglows are produced by highly relativistic jets emitted in core-collapse explosions. As the jet makes its way out of the stellar mantle, a bow shock runs ahead and a strong thermal precursor is produced as the shock breaks out. Such erupting fireballs produce a very bright γ -ray precursor as they interact with the thermal break-out emission. The prompt γ -ray emission propagates ahead of the fireball before it becomes optically thin, leading to e± pair loading and radiative acceleration of the external medium. The detection of such precursors would offer the possibility of diagnosing not only the radius of the stellar progenitor and the initial Lorentz factor of the collimated fireball, but also the density of the external environment. 相似文献
17.
Yong-feng Huang Chang-yi Tan Zi-gao Dai Tan Lu 《Chinese Astronomy and Astrophysics》2002,26(4):1744-423
Afterglows from most gamma-ray bursts, such as GRBs 970228, 970508, 971214, 980329 and 980703, decay slowly and steadily. These bursts are widely believed to be due to isotropic fireballs. However, they in fact can also be well fitted by a cylindrical jet model. It is proposed that these bursts are probably generated by cylindrical jets, and not necessarily by isotropic fireballs. 相似文献