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1.
We present gamma-ray burst afterglow light curves in X-ray, optical and radio bands for various distributions of accelerated electrons behind the shock. The effects of lateral expansion of the jet and of winds in typical Wolf-Rayet star on the evolution are discussed. The light curves in the radiative case decline more rapidly than those in the adiabatic case. Under the combined effect of jet expansion and wind environment, the light curves have the greatest deviation from those of the standard model. All these results refer to the relativistic phase. 相似文献
2.
Atish Kamble Kuntal Misra D. Bhattacharya Ram Sagar 《Monthly notices of the Royal Astronomical Society》2009,394(1):214-220
The afterglow of GRB 050401 presents several novel and interesting features. (i) An initially faster decay in optical band than in X-rays. (ii) A break in the X-ray light curve after ∼0.06 d with an unusual slope after the break. (iii)The X-ray afterglow does not show any spectral evolution across the break while the R -band light curve does not show any break. We have modelled the observed multiband evolution of the afterglow of GRB 050401 as originating in a two-component jet, and interpreting the break in X-ray light curve as due to lateral expansion of a narrow collimated outflow which dominates the X-ray emission. The optical emission is attributed to a wider jet component. Our model reproduces all the observed features of multiband afterglow of GRB 050401. We present optical observations of GRB 050401 using the 104-cm Sampurnanand Telescope at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. Results of the analysis of multiband data are presented and compared with GRB 030329, the first reported case of double jet. 相似文献
3.
There has been increasing evidence that at least some gamma-ray bursts (GRBs) are emission beamed. The beamed GRB-afterglow evolution has been discussed by several authors in the ultrarelativistic case. It has been shown that the dynamics of the blast wave will be significantly modified by the sideways expansion, and there may be a sharp break in the afterglow light curves under certain circumstances. However, this is only true when the fireball is still relativistic. Here we present an analytical approach to the evolution of the beamed GRB blast wave expanding in the surrounding medium (density in the non-relativistic case, our purpose is to explore whether the sideways expansion will strongly affect the blast-wave evolution as in the relativistic case. We find that the blast-wave evolution is strongly dependent on the speed of the sideways expansion. If it expands with the sound speed, then the jet angle θ increases with time as which means that the sideways expansion has little effect on the afterglow light curves, the flux for and for It is clear that the light curve of is not always steeper than that of as in the relativistic case. We also show that if the expansion speed is a constant, then the jet angle and the radius in this case the sideways expansion has the most significant effect on the blast-wave evolution, the flux independent of s , and we expect that there should be a smooth and gradual break in the light curve. 相似文献
4.
Shun-Lin Liang Zi-Gao Dai Yong-Feng Huang Tan Lu Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2003,3(6):526-534
Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30 pc within the initial solid angle of the jet. Asthe jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results showthat a break appears in the light curve of optical afterglow but it extends over a factor of ～ 80 in time rather than a factor of ～ 10 in time for the case of strong dust extinction and a factor of ～ 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event. 相似文献
5.
Owing to some refinements in the dynamics, we can follow the overall evolution of a realistic jet numerically until its bulk velocity is as small as c 103 c . We find no obvious break in the optical light curve during the relativistic phase itself . However, an obvious break does exist at the transition from the relativistic phase to the non-relativistic phase, which typically occurs at time t 106 106.5 s (i.e. 1030 d). The break is affected by many parameters, such as the electron energy fraction e , the magnetic energy fraction the initial half-opening angle 0 and the medium number density n . Increasing any of them to a large enough value will make the break disappear. Although the break itself is parameter-dependent, afterglows from jetted GRB remnants are uniformly characterized by a quick decay during the non-relativistic phase, with power-law timing index 2.1. This is quite different from that of isotropic fireballs, and may be of fundamental importance for determining the degree of beaming in -ray bursts observationally. 相似文献
6.
When the axis of a gamma-ray burst (GRB) does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction ξe, the magnetic energy fraction ξ2B, the width of ring A0 and the medium number density n. The overall light curve can be divided into three power-law stages, I.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet. 相似文献
7.
M. De Pasquale P. Evans S. Oates M. Page S. Zane P. Schady A. Breeveld S. Holland P. Kuin M. Still P. Roming P. Ward 《Monthly notices of the Royal Astronomical Society》2009,392(1):153-169
The Swift mission has discovered an intriguing feature of gamma-ray burst (GRBs) afterglows, a phase of shallow decline of the flux in the X-ray and optical light curves. This behaviour is typically attributed to energy injection into the burst ejecta. At some point this phase ends, resulting in a break in the light curve, which is commonly interpreted as the cessation of the energy injection. In a few cases, however, while breaks in the X-ray light curve are observed, optical emission continues its slow flux decline. This behaviour suggests a more complex scenario. In this paper, we present a model that invokes a double component outflow, in which narrowly collimated ejecta are responsible for the X-ray emission while a broad outflow is responsible for the optical emission. The narrow component can produce a jet break in the X-ray light curve at relatively early times, while the optical emission does not break due to its lower degree of collimation. In our model both components are subject to energy injection for the whole duration of the follow-up observations. We apply this model to GRBs with chromatic breaks, and we show how it might change the interpretation of the GRBs canonical light curve. We also study our model from a theoretical point of view, investigating the possible configurations of frequencies and the values of GRB physical parameters allowed in our model. 相似文献
8.
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
9.
We report the first detection, with Chandra , of X-ray emission from the jet of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the bright radio and optical knot at which the jet apparently bends by approximately 70°. The Chandra observation also reveals a bright galaxy-scale atmosphere within the previously known cluster and provides a good X-ray spectrum for the bright core of 3C 346. The X-ray emission from the knot is synchrotron radiation, as seen in lower-power sources. In common with these sources, there is evidence of morphological differences between the radio/optical and X-ray structures, and the spectrum is inconsistent with a one-component continuous-injection model. We suggest that the X-ray-bright knot is associated with a strong oblique shock in a moderately relativistic, light jet, at ∼ 20° to the line of sight, and that this shock is caused by the jet interacting with the wake in the cluster medium behind the companion galaxy of 3C 346. The general jet curvature can result from pressure gradients in the cluster atmosphere. 相似文献
10.
Petar Mimica Miguel-Ángel Aloy Ewald Müller Wolfgang Brinkmann 《Astrophysics and Space Science》2004,293(1-2):165-172
We present the results of a two-dimensional relativistic hydrodynamic simulation of collisions of dense shells of matter moving within a uniform jet. The non-thermal synchrotron radiation produced by the relativistic electrons injected at shocks is computed following their temporal and spatial evolution. We test different parameterizations of the shock acceleration process and compute the corresponding X-ray light curves. A time lag between hard and soft X-ray radiation is found. The collision has an efficiency of few times 10?3 in converting kinetic energy into radiation. 相似文献
11.
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
12.
S. R. Oates M. J. Page P. Schady M. de Pasquale T. S. Koch A. A. Breeveld P. J. Brown M. M. Chester S. T. Holland E. A. Hoversten N. P. M. Kuin F. E. Marshall P. W. A. Roming M. Still D. E. Vanden Berk S. Zane J. A. Nousek 《Monthly notices of the Royal Astronomical Society》2009,395(1):490-503
We present the first statistical analysis of 27 Ultraviolet Optical Telescope (UVOT) optical/ultraviolet light curves of gamma-ray burst (GRB) afterglows. We have found, through analysis of the light curves in the observer's frame, that a significant fraction rise in the first 500 s after the GRB trigger, all light curves decay after 500 s, typically as a power law with a relatively narrow distribution of decay indices, and the brightest optical afterglows tend to decay the quickest. We find that the rise could be either produced physically by the start of the forward shock, when the jet begins to plough into the external medium, or geometrically where an off-axis observer sees a rising light curve as an increasing amount of emission enters the observers line of sight, which occurs as the jet slows. We find that at 99.8 per cent confidence, there is a correlation, in the observed frame, between the apparent magnitude of the light curves at 400 s and the rate of decay after 500 s. However, in the rest frame, a Spearman rank test shows only a weak correlation of low statistical significance between luminosity and decay rate. A correlation should be expected if the afterglows were produced by off-axis jets, suggesting that the jet is viewed from within the half-opening angle θ or within a core of a uniform energy density θc . We also produced logarithmic luminosity distributions for three rest-frame epochs. We find no evidence for bimodality in any of the distributions. Finally, we compare our sample of UVOT light curves with the X-ray Telescope (XRT) light-curve canonical model. The range in decay indices seen in UVOT light curves at any epoch is most similar to the range in decay of the shallow decay segment of the XRT canonical model. However, in the XRT canonical model, there is no indication of the rising behaviour observed in the UVOT light curves. 相似文献
13.
Hai-Tao Ma Yong-Feng Huang Zi-Gao Dai Tan Lu Department of Astronomy Nanjing University Nanjing hyf@nju.edu.cn 《中国天文和天体物理学报》2003,3(3):225-234
Observations on relativistic jets in radio galaxies, active galactic nuclei, and "microquasars" revealed that many of these outflows are cylindrical, not conical. So it is worthwhile to investigate the evolution of cylindrical jets in gamma-ray bursts. We discuss afterglows from cylindrical jets in a wind environment. Numerical results as well as analytic solutions in some special cases are presented. Our light curves are steeper compared to those in the homogeneous interstellar medium case, carefully considered by Cheng, Huang & Lu. We conclude that some afterglows, used to be interpreted as isotropic fireballs in a wind environment, can be fitted as well by cylindrical jets interacting with a wind. 相似文献
14.
15.
Elena Rossi Davide Lazzati Martin J. Rees 《Monthly notices of the Royal Astronomical Society》2002,332(4):945-950
Gamma-ray bursts are often modelled as jet-like outflows directed towards the observer; the cone angle of the jet is then commonly inferred from the time at which there is a steepening in the power-law decay of the afterglow. We consider an alternative model in which the jet has a beam pattern where the luminosity per unit solid angle (and perhaps also the initial Lorentz factor) decreases smoothly away from the axis, rather than having a well-defined cone angle within which the flow is uniform. We show that the break in the afterglow light curve then occurs at a time that depends on the viewing angle. Instead of implying a range of intrinsically different jets – some very narrow, and others with a similar power spread over a wider cone – the data on afterglow breaks could be consistent with a standardized jet, viewed from different angles. We discuss the implication of this model for the luminosity function. 相似文献
16.
Whether gamma-ray bursts are highly beamed or not is a very important question, as it has been pointed out that the beaming will lead to a sharp break in the afterglow light curves during the ultrarelativistic phase, with the breaking point determined by Γ∼1/ θ 0 , where Γ is the bulk Lorentz factor and θ 0 is the initial half opening angle of the ejecta, and such a break is claimed to be present in the light curves of some GRBs. In this paper we will examine whether all the observed breaks in GRB afterglow light curves can be explained by jet effects. Here we present a detailed calculation of the jet evolution and emission, and have obtained a simple formula of bulk Lorentz factor evolution. We show that the light curves are very smoothly steepened by jet effect, and the shape of the light curve is determined by only one parameter – , where E and n are the fireball energy and surrounding medium density, respectively. We find that for GRB 990123 and GRB 991216, the jet model can approximately fit their light curves, and the values of are about 0.17 and 0.22, respectively. On the other hand, the light curves of GRB 990510, GRB 000301c, GRB 000926 and GRB 010222 cannot be fitted by the jet model, which suggests that the breaks may be caused by some other reasons, and the jet effect should be not the unique reason. 相似文献
17.
We discuss the afterglow emission from a relativistic jet that is initially in the radiative regime, in which the accelerated electrons are fast-cooling. We note that such a 'semiradiative' jet decelerates faster than an adiabatic jet does. We also take into account the effect of strong inverse-Compton scattering on the cooling frequency in the synchrotron component and therefore on the light-curve decay index. We find that there are two kinds of light-curve break for the jet effect. The first is an 'adiabatic break', if the electrons become slow-cooling before the jet enters a spreading phase, and the second is a 'radiative break', which appears in the contrary case. We then show how a relativistic jet evolves dynamically and derive the overall temporal synchrotron emission in both cases, focusing on the change in the light-curve decay index around the break time. Finally, in view of our results, we rule out two cases for relativistic jets which do not account for the observed light-curve breaks in a few afterglows : (i) an adiabatic jet with strong Compton cooling ( Y >1) and with the cooling frequency ν c locating in the observed energy range; (ii) a radiative jet with a significant fraction of total energy occupied by electrons ( ε e ∼1) . 相似文献
18.
During the in-spiral stage of a compact binary, a wind bubble could be blown into the interstellar medium, if electromagnetic radiation due to the binary orbital motion is strong enough. Therefore, shortduration gamma-ray bursts(SGRBs) due to double neutron star mergers would in principle happen in a wind bubble environment, which can influence the propagation of the SGRB jet and consequent afterglow emission. By calculating the dynamics and synchrotron radiation of the jet-driven external shock, we reveal that an abrupt jump could appear in the afterglow light curves of SGRBs and the observational time of the jump is dependent on the viewing angle. This light curve jump provides an observational signature to constrain the radius of the wind bubble and thus the power of the electromagnetic radiation of the binary,by combining with gravitational wave detection. 相似文献
19.
Cygnus A was the first hyper-active galaxy discovered, and it
remains by far the closest of the ultra-luminous radio galaxies. As
such, Cygnus A has played a fundamental role in the study of virtually
all aspects of extreme activity in galaxies. We present a review of jet
theory for powering the double-lobed radio emitting structures in
powerful radio galaxies, followed by a review of observations of Cygnus
A in the radio, optical, and X-ray relevant to testing various aspects
of jet theory. Issues addressed include: jet structure from pc- to
kpc-scales, jet stability, confinement, composition, and velocity, the
double shock structure for the jet terminus and the origin of multiple
radio hotspots, the nature of the filamentary structure in the radio
lobes, and the hydrodynamic evolution of the radio lobes within a dense
cluster atmosphere, including an analysis of pressure balance between
the various gaseous components. Also discussed are relativistic
particle acceleration and loss mechanisms in Cygnus A, as well as
magnetic field strengths and geometries both within the radio source,
and in the intracluster medium. We subsequently review the
classification, cluster membership, and the emission components of the
Cygnus A galaxy. The origin of the activity is discussed.
Concentrating on the nuclear regions of the galaxy, we review the
evidence for an obscured QSO, also given the constraints on the
orientation of the radio source axis with respect to the sky plane. We
present an overview of models of central engines in AGN and observations
of Cygnus A which may be relevant to testing such models. We conclude
with a brief section concerning the question of whether Cygnus A is
representative of powerful high redshift radio galaxies.
Received October 10, 1995 相似文献
20.
The acceleration mechanisms of relativistic jets are of great importance for understanding various astrophysical phenomena such as gamma-ray bursts,active galactic nuclei and microquasars.One of the most popular scenarios is that the jets are initially Poynting-flux dominated and succumb to magnetohydrodynamic instability leading to magnetic reconnections.We suggest that the reconnection timescale and efficiency could strongly depend on the geometry of the jet,which determines the length scale on which the orientations of the field lines change.In contrast to a usuallyassumed conical jet,the acceleration of a collimated jet can be found to be more rapid and efficient(i.e.a much more highly saturated Lorentz factor can be reached)while the jets with lateral expansion show the opposite behavior.The shape of the jet could be formed due to the lateral squeezing on the jet by the stellar envelope of a collapsing massive star or the interaction of the jet with stellar winds. 相似文献