We investigate the GeV emission from gamma-ray bursts (GRBs), using the results from the Energetic Gamma Ray Experimental Telescope (EGRET), and in view of the Gamma-ray Large Area Space Telescope (GLAST). Assuming that the conventional prompt and afterglow photons originate from synchrotron radiation, we compare an accompanying inverse-Compton component with EGRET measurements and upper limits on GeV fluence, taking Klein-Nishina feedback into account. We find that EGRET constraints are consistent with the theoretical framework of the synchrotron self-Compton model for both prompt and afterglow phases, and discuss constraints on microphysical parameters in both phases. Based on the inverse-Compton model and using EGRET results, we predict that GLAST would detect GRBs with GeV photons at a rate >~20 yr^{-1} from each of the prompt and afterglow phases. This rate applies to the high-energy tail of the prompt synchrotron emission and to the inverse-Compton component of the afterglow. Theory predicts that in a large fraction of the cases where synchrotron GeV prompt emission would be detected by GLAST, inverse-Compton photons should be detected as well at high energies >~10 GeV. Therefore GLAST will enable a more precise test of the high-energy emission mechanism. Finally, we show that the contribution of GRBs to the flux of the extragalactic gamma-ray background measured with EGRET is at least 0.01% and likely around 0.1%.
The discovery by the BeppoSAX satellite of X-ray afterglow emission from the gamma-ray burst which occurred on 28 February 1997 produced a revolution in our knowledge of the gamma-ray burst phenomenon. Along with the discovery of X-ray afterglows, the optical afterglows of gamma-ray bursts were discovered and the distance issue was settled, at least for long $γ$-ray bursts. The 30 year mystery of the gamma-ray burst phenomenon is now on the way to solution. Here I rewiew the observational status of the X-ray afterglow emission, its mean properties (detection rate, continuum spectra, line featu…
Observations and models of GRBs are reviewed with an emphasis on the early phase of the burst. Recent revision of the early afterglow model is described.
The optical afterglows of the gamma ray bursts can be strongly polarized, in principle up to tens of percents, if: (i) the afterglow is synchrotron radiation from an ultra-relativistic blast, (ii) the blast is beamed during the afterglow phase, i.e. the shock propagates within a narrow jet, (iii) we observe at the right time from the right viewing angle, (iv) magnetic fields parallel and perpendicular to the jet have different proper strengths.
The discovery of X-ray afterglows accompanying two short bursts from SGR 1900+14 is presented. The afterglow luminosities at the end of each observation are lower by 30-50% than their initial luminosities, and decay with power law indices p ~ 0.2-0.4. Their initial bolometric luminosities are L ~ 10^34-10^35 erg s^-1. We discuss analogies and differences between the X-ray afterglows of SGR short bursts and short gamma-ray bursts.
In order to assist in planing the search of supernova (SN) in the late time afterglow (AG) of the gamma ray burst (GRB) 011121 we use the Cannonball Model of GRBs and the observations of its afterglow in the R band in the first two days to predict its late time decline and intrinsic spectrum.
We consider possible interpretations of the recently detected X- ray afterglow from the gamma-ray burst source GRB 970228. Cosmological and Galactic models of gamma-ray bursts predict different flux and spectral evolution of X-ray afterglows. We show that models based on adiabatic expansion of relativistic forward shocks require very efficient particle energization or post-burst re-acceleration during the expansion. Cooling neutron star models predict a very distinctive spectral and flux evolution that can be tested in current X-ray data.
We present a set of seventeen Gamma-Ray Bursts (GRBs) with known redshifts and X-ray afterglow emission. We apply cosmological corrections in order to compare their fluxes normalized at a redshift of 1. Two classes of GRB can be defined using their X-ray afterglow light curves. We show that the brightest afterglows seem to decay faster than the dimer ones. We also point out evidences for a possible flux limit of the X-ray afterglow depending on the time elapsed since the burst. We try to interpret these observations in the framework of the canonical fireball model of GRB afterglow emission.
The "canonical behaviour" of the early X-ray afterglows of long-duration Gamma-Ray Bursts (GRBs) --observed by the X-Ray Telescope of the SWIFT satellite-- is precisely the one predicted by the Cannonball model of GRBs.
I will review the constraints set by X-ray measurements of afterglows on several issues of GRB, with particular regard to the fireball model, the environment, the progenitor and dark GRB.
Gamma ray burst afterglows can be identified in single epoch observations using three or more optical filters. This method relies on color measurements to distinguish the power law spectrum of an afterglow from the curved spectra of stars. Observations in a fourth filter will further distinguish between afterglows and most galaxies up to redshifts z ~ 1. Many afterglows can also be identified with fewer filters using ultraviolet excess, infrared excess, or Lyman break techniques. By allowing faster identification of gamma ray burst afterglows, these color methods will increase the fraction of …
By integrating the relativistic hydrodynamic equations introduced by Taub we have determined the exact EQuiTemporal Surfaces (EQTSs) for the Gamma-Ray Burst (GRB) afterglows. These surfaces are compared and contrasted to the ones obtained, using approximate methods, by Panaitescu & Meszaros (1998), Sari (1998), Granot et al. (1999).
Radio observations of gamma-ray burst (GRB) afterglows provide both complementary and unique diagnostics of the afterglow physics and environment of the burst. Here we concentrate on three unique aspects of GRB energetics and environments afforded by radio and submillimeter observations: the non-relativistic evolution of the fireball, the density profile of the circumburst medium, and the study of obscured star formation in GRB host galaxies.
The discovery of multiband afterglows definitely shows that most $γ$-ray bursts are of cosmological origin. $γ$-ray bursts are found to be one of the most violent explosive phenomena in the Universe, in which astonishing ultra-relativistic motions are involved. In this article, the multiband observational characteristics of $γ$-ray bursts and their afterglows are briefly reviewed. The standard model of $γ$-ray bursts, i.e. the fireball model, is described. Emphasis is then put on the importance of the nonrelativistic phase of afterglows. The concept of deep Newtonian phase is elaborated. A gen…
Extended, fading emissions in multi-wavelength are observed following Gamma-ray bursts (GRBs). Recent broad-band observational campaigns led by the Swift Observatory reveal rich features of these GRB afterglows. Here we review the latest observational progress and discuss the theoretical implications for understanding the central engine, composition, and geometric configuration of GRB jets, as well as their interactions with the ambient medium.
This is a review article for the book "Compact Stellar X-Ray Sources", Editors W. Lewin and M. van der Klis, to be published by Cambridge University Press in 2003. It covers the phenomenology of cosmic gamma-ray bursts, the theory of their afterglows, and the observations and interpretation of their host galaxies.
A formula for off-axis emissions from the beamed afterglow of GRBs in a synchrotron model is derived. The formula is applied to an inhomogeneous circumstellar matter obeying n proportional to 1/r**2 suggested for SN1998bw/GRB980425. The slow decline rate as well as the X-ray flux similar to the observed values are obtained for appropriate choice of the parameters so that the association of GRB980425 with SN1998bw is further strengthened.
It is widely believed that multiwavelength afterglows of gamma-ray bursts (GRBs) originate from relativistic blast waves. We here show that in such blast waves, a significant fraction of the energy of shock-accelerated protons would be lost due to pion production by interactions with afterglow photons. This could lead to long-term production of $10^{16}$--$10^{18}$ eV neutrinos and sub-TeV $γ$-rays that accompany with usual afterglows, provided that the protons are accelerated to $10^{19}$ eV in the blast waves.
I review some of the highlights of the Rome Workshop on Gamma-Ray Bursts, and discuss some of the questions these results pose about the nature and origin of gamma-ray bursts.
The absorption feature detected in the prompt X-ray emission of GRB990705 has important consequences for its circum-burst environment and therefore on its afterglows. Here we investigate whether the circum-burst environment constrained by the absorption feature could be consistent with the observed H-band afterglow, which exhibits an earlier power law decay but a much faster decay about one day after the burst. Two possible geometries of the afterglow-emitting regions are suggested: 1) afterglow emission produced by the impact of the fireball on the surrounding torus, which serves as the absor…
Correlation studies of prompt and afterglow emissions from gamma-ray bursts (GRBs) between different spectral bands has been difficult to do in the past because few bursts had comprehensive and intercomparable afterglow measurements. In this paper we present a large and uniform data set for correlation analysis based on bursts detected by the Swift mission. For the first time, short and long bursts can be analyzed and compared. It is found for both classes that the optical, X-ray and gamma-ray emissions are linearly correlated, but with a large spread about the correlation line; stronger burst…
Based on the refined dynamical model proposed by us earlier for beamed $γ$-ray burst ejecta, we carry out detailed numerical procedure to study those $γ$-ray bursts with rapidly fading afterglows (i.e., $\sim t^{-2}$). It is found that optical afterglows from GRB 970228, 980326, 980519, 990123, 990510 and 991208 can be satisfactorily fitted if the $γ$-ray burst ejecta are highly collimated, with a universal initial half opening angle $θ_0 \sim 0.1$. The obvious light curve break observed in GRB 990123 is due to the relativistic-Newtonian transition of the beamed ejecta, and the rapidly fading …
When does a GRB stop and its afterglow begin? A GRB may be defined as emission by internal shocks and its afterglow as emission by an external shock, but it is necessary to distinguish them observationally. With these definitions irregularly varying emission (at any frequency) must be the GRB, but smoothly varying intensity is usually afterglow. The GRB itself and its afterglow may overlap in time and in frequency, and distinguishing them will, in general, require detailed modeling.
The beaming angle (zeta) is the main uncertainty in gamma ray burst energy requirements today. We summarize predictions for the light curves of beamed bursts, and model the R band light curve of GRB 970508 to derive zeta > 30 degrees. This yields an irreducible minimum energy requirement of 3.4 times 10^{49} ergs to power the afterglow alone.
The energy requirements of gamma ray bursts have in past been poorly constrained because of three major uncertainties: The distances to bursts, the degree of burst beaming, and the efficiency of gamma ray production. The first of these has been resolved, with both indirect evidence (the distribution of bursts in flux and position) and direct evidence (redshifted absorption features in the afterglow spectrum of GRB 970508) pointing to cosmological distances. We now wish to address the second uncertainty. Afterglows allow a statistical test of beaming, described in an earlier paper. In this pape…
We present numerical simulations of Gamma-Ray Bursts arising from external shocks in the impulsive and wind models, including a weak or a strong coupling between electrons and protons plus magnetic fields, and analyze the burst features in each scenario. The dynamics of the ejecta and external medium are followed into the late stages of deceleration, in order to study the hydrodynamics of the remnant and the temporal and spectral evolution of the afterglow. A brief comparison with the optical and radio afterglows of GRB 970228 and GRB 970508 is made.
Polarimetry of Gamma-Ray Burst (GRB) afterglows in the last few years has been considered one of the most effective tool to probe the geometry, energetic, dynamics and the environment of GRBs. We report some of the most recent results and discuss their implications and future perspectives.
We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be detected in supernova searches as a function of limiting flux. Although GRB afterglows are rarer than supernovae, they are detectable at greater distances because of their higher intrinsic luminosity. Assuming that GRBs trace the cosmic star formation history and that every GRB gives rise to a bright afterglow, we find that the average detection rate of supernovae and afterglows should be comparable at limiting magnitudes brighter than K=18. The actual rate of afterglows is expected to be somewhat lower since only a fracti…
Radio afterglow studies have become an integral part of the study of gamma-ray bursts, providing complementary and sometimes unique diagnostics on GRB explosions, their progenitors, and their environments. This brief review consists of two parts. The first section is a summary of current search strategies and the main observational properties of radio afterglows. In the second section we highlight the key scientific contributions made by radio observations, either alone or as part of panchromatic studies.
We use the very simple and successful Cannonball Model (CB) of gamma ray bursts (GRBs) and their afterglows (AGs) to analyze the observations of the strongly extinct optical AG of GRB 010921 with ground-based telescopes at early times, and with the HST at later time. We show that GRB 010921 was indeed associated with a 1998bw-like supernova at the GRB's redshift.
The successful launch and operation of NASA's Swift Gamma-Ray Burst Explorer open a new era for the multi-wavelength study of the very early afterglow phase of gamma-ray bursts (GRBs). GRB early afterglow information is essential to explore the unknown physical composition of GRB jets, the link between the prompt gamma-ray emission and the afterglow emission, the GRB central engine activity, as well as the immediate GRB environment. Here I review some of the recent theoretical efforts to address these problems and describe how the latest Swift data give answers to these outstanding questions.
Clustering in the luminosity of the afterglows of gamma-ray burst has been reported in the optical and X-ray. We investigate the possibility that a clustering in the luminosity of the afterglows of gamma-ray burst exists in near infrared (J, H, K bands). We use observations of events occurring from 1997 to the end of 2007. We correct the gamma-ray burst afterglow light curve for distance effect and time dilation, and replace all light curves to a common distance of z=1. We used only observations of signal emitted in the near infrared (in the burst frame). We observe a clustering identical to t…
We applied cosmological and absorption corrections to the X-ray and optical afterglow fluxes of a sample of Gamma-Ray Burst sources of known distance. We find a good correlation in X-rays and that the GRBs in our sample form two well defined classes. We tentatively interpret them as radiative and adiabatic afterglow behaviours in the framework of the fireball model for GRBs. We do not observe this correlation at optical wavelengths. This discrepancy with the model may be due to the absorption in the source vicinity.
We present optical and near-infrared searches for afterglow emission from the first four Swift bursts with accurate positions from the X-ray Telescope (XRT). Using telescopes at Las Campanas, Keck, and Palomar observatories we rapidly identified and followed up afterglows for three of the four bursts. The burst positions were also observed with the Very Large Array, but no radio afterglow emission was detected. The optical/NIR afterglows are fainter than about 75% of all afterglows detected to date, with GRB 050126 being the faintest, and were identified thanks to accurate and rapid positions …
While all but one Gamma-Ray Bursts observed in the X-ray band showed an X-ray afterglow, about 60 per cent of them have not been detected in the optical band. We demonstrate that in many cases this is not due to adverse observing conditions, or delay in performing the observations. We also show that the optically non-detected afterglows are not affected by particularly large Galactic absorbing columns, since its distribution is similar for both the detected and non-detected burst subclasses. We then investigate the hypothesis that the failure of detecting the optical afterglow is due to absorp…
An overview of the optical and near-IR observations of GRBs in the Afterglow Era is presented, covering the period 1997-2000. They have allowed to a better understanding of the underlying GRB physics as well as to constraint the progenitor models.
The optical afterglows of gamma-ray bursts can be used to probe the physics, geometry, and environments of gamma-ray bursts. In this article I discuss the how spectra and photometry can be used to constrain fireball parameters, describe several types of breaks that might be observed in the optical decay, and briefly review the late-time bumps and rapid variations in optical light curves.
We compute the afterglow of gamma-ray bursts produced by purely electromagnetic outflows to see if it shows characteristic signatures differing from those obtained with the standard internal/external shock model. Using a simple approach for the injection of electromagnetic energy to the forward shock we obtain the afterglow evolution both during the period of activity of the central source and after. Our method equally applies to a variable source. Afterglow light curves in the visible and X-ray bands are computed both for a uniform medium and a stellar wind environment. They are brighter at e…
We report optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB021004. Our observation revealed the existence of a short plateau phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid fading phase. This plateau phase lasted for about 2 hours from 0.024 to 0.10 d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB990123. We propose that the plateau phase can be interpreted as the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time w…
The recently discovered GRB afterglow is believed to be described reasonably well by synchrotron emission from a slowing down relativistic shell that collides with an external medium. To compare theoretical models with afterglow observations we calculate here the broad band spectrum and corresponding light curve of synchrotron radiation from a power-law distribution of electrons in an expanding relativistic shock. Both the spectrum and the light curve consist of several power-law segments. The light curve is constructed under two limiting models for the hydrodynamical evolution of the shock: f…
We present an update of our systematic analysis of all Gamma-Ray Burst (GRB) afterglow data, now published through the end of 2004, in an attempt to detect the predicted supernova light component. We fit the observed photometric light curves as the sum of an afterglow, an underlying host galaxy, and a supernova component. The latter is modeled using published UBVRI light curves of SN 1998bw as a template. The total sample of afterglows with established redshifts contains now 29 bursts (GRB 970228 - GRB 041006). For 13 of them a weak supernova excess (scaled to SN 1998bw) was found. In agreemen…
This work is part of a systematic re-analysis program of all the data of Gamma-Ray Burst (GRB) X-ray afterglows observed so far, in order to constrain the GRB models. We present here a systematic analysis of those afterglows observed by XMM-Newton between January 2000 and March 2004. This dataset includes GRB 011211 and GRB 030329. We have obtained spectra, light curves and colors for these afterglows. In this paper we focus on the continuum spectral and temporal behavior. We compare these values with the theoretical ones expected from the fireball model. We derive constraints about the burst …
Before 2004, nearly all GRB afterglow data could be understood in the context of the external shocks model. This situation has changed in the past two years, when it became clear that some afterglow components should be attributed to the activity of the central engine; i.e., the {\it central engine afterglow}. We review here the afterglow emission that is directly related to the GRB central engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in pre-{\it Swift} era, has become generally accepted now.
We calculate the {\it afterglow} emission for Gamma-Ray Bursts (GRBs) going off in an extremely low density medium, referred to as {\it naked bursts}. Our results also apply to the case where the external medium density falls off sharply at some distance from the burst. The observed afterglow flux in this case originates at high latitudes, i.e. where the angle between the fluid velocity and the observer line of sight is greater than $Γ^{-1}$. The observed peak frequency of the spectrum for naked bursts decreases with observer time as $t^{-1}$, and the flux at the peak of the spectrum falls off…
For Gamma-Ray Bursts occurring in dense star-forming regions, the X-ray afterglow behavior minutes to days after the trigger may be dominated by the small-angle scattering of the prompt X-ray emission off dust grains. We give a simple illustrative model for the X-ray light curves at different X-ray energies, and discuss possible implications. A bump followed by a steeper decay in soft X-rays is predicted for bursts which are heavily obscured in the optical.
Electrons in shocks are efficiently energized due to the cross-shock potential, which develops because of differential deflection of electrons and ions by the magnetic field in the shock front. The electron energization is necessarily accompanied by scattering and thermalization. The mechanism is efficient in both magnetized and non-magnetized relativistic electron-ion shocks. It is proposed that the synchrotron emission from the heated electrons in a layer of strongly enhanced magnetic field is responsible for gamma ray burst afterglows.
We compiled a large sample of Swift-era photometric data on long (Type II) and short (Type I) GRB afterglows. We compare the luminosity and energetics of the different samples to each other and to the afterglows of the pre-Swift era. Here, we present the first results of these studies.
The discovery of GRBs' afterglows has allowed us to establish several facts: their distance and energy scales, the fact that they are due to explosions, that the explosions are relativistic, and that the afterglow emission mechanism is synchrotron radiation. On the other hand, recent data have shown that the fireball model is wrong when it comes to the emission mechanism of the true burst (which is unlikely to be synchrotron again) and that shocks are not external. Besides these relatively tame points, I will also discuss the less well established physics of the energy deposition mechanism, as…
GRB 991014 is one of the shortest gamma-ray bursts detected so far with the Wide Field Cameras aboard BeppoSAX, both in gamma-rays and X-rays. The duration is 9.6 sec in 2-28 keV and 3.2 sec in 40 to 700 keV (as measured between the times when 5 and 95% of the burst photons have been accumulated). We refine the InterPlanetary Network annulus of the burst, present the detection of the X-ray afterglow of GRB 991014 within this refined annulus, and discuss X-ray and gamma-ray observations of the prompt and afterglow emission. Except for the briefness of the prompt event, no other unusual aspects …
Gamma-ray bursts (GRBs) are energetic explosions that for 0.01--100 s are the brightest gamma-ray sources in the sky. Observations of the early evolution of afterglows we expected to provide clues about the nature of the bursts, but their rapid fading has hampered such studies; some recent rapid localizations of bursts have improved the situation. Here we report on an early detection of the very bright afterglow of the burst of 29 March 2003 (GRB030329). Our data show that, even early in the aferglow phase, the light curve shows unexpectedly complicated structures superimposed on the fading ba…
We present interplanetary network localization, spectral, and time history information for four short-duration, hard spectrum gamma-ray bursts, GRB000607, 001025B, 001204, and 010119. All of these events were followed up with sensitive radio and optical observations (the first and only such bursts to be followed up in the radio to date), but no detections were made, demonstrating that the short bursts do not have anomalously intense afterglows. We discuss the upper limits, and show that the lack of observable counterparts is consistent both with the hypothesis that the afterglow behavior of th…
We calculate the GeV afterglow emission expected from a few mechanisms related to GRBs and their afterglows. Given the brightness of the early X-ray afterglow emission measured by Swift/XRT, GLAST/LAT should detect the self-Compton emission from the forward-shock driven by the GRB ejecta into the circumburst medium. Novel features discovered by Swift in X-ray afterglows (plateaus and chromatic light-curve breaks) indicate the existence of a pair-enriched, relativistic outflow located behind the forward shock. Bulk and inverse-Compton upscattering of the prompt GRB emission by such outflows pro…
We show that simple kinematic arguments can give limits on the timescale and amplitude of variabilities in gamma-ray burst (GRB) afterglows, especially when the variability timescale is shorter than the observed time since the burst Δt < t. These limits help us to identify the sources of afterglow variability. The afterglows of GRB 011211 and GRB 021004 marginally violate these limits. If such violation is confirmed by the Swift satellite, a possible explanation is that (1) the compact objects that power GRB jets continue to eject an intermittent outflow for a very long timescale (> 1 day), (2…
We investigate the consequences of a continuously injecting central engine on the gamma-ray burst afterglow emission, focusing more specifically on a highly-magnetized millisecond pulsar engine. For initial pulsar parameters within a certain region of the parameter space, the afterglow lightcurves are predicted to show a distinctive achromatic bump feature, the onset and duration of which range from minutes to months, depending on the pulsar and the fireball parameters. The detection of or upper limits on such features would provide constraints on the burst progenitor and on magnetar-like cent…
If the efficiency for producing $γ$-rays is the same in short duration ($\siml 2$ s) Gamma-Ray Bursts (GRBs) as in long duration GRBs, then the average kinetic energy of short GRBs must be $\sim 20$ times less than that of long GRBs. Assuming further that the relativistic shocks in short and long duration GRBs have similar parameters, we show that the afterglows of short GRBs will be on average 10--40 times dimmer than those of long GRBs. We find that the afterglow of a typical short GRB will be below the detection limit ($\siml 10 \microJy$) of searches at radio frequencies. The afterglow wou…
Zhang and Kobayashi (2004) attempted to calculate early afterglow emission from a system of forward and reverse shocks in GRB outflows for the case of magnetized ejecta. We point out a fundamental error in the underlying dynamical model. According to the authors, energy and momentum carried by the magnetic field of the ejecta are not transfered to the forward shock. This is an incorrect assumption that invalidates the results.
We report optical observations of the short/hard burst GRB 010119 error box, one of the smallest error boxes reported to date for short/hard GRBs. Limits of R > 22.3 and I > 21.2 are imposed by observations carried out 20.31 and 20.58 hours after the gamma-ray event, respectively. They represent the most constraining limits imposed to date on the optical emission from a short/hard gamma-ray burst afterglow.
We report on the discovery of the radio afterglow from the gamma-ray burst (GRB) of 1999 May 6 (GRB 990506) using the Very Large Array (VLA). The radio afterglow was detected at early times (1.5 days), but began to fade rapidly sometime between 1 and 5 days after the burst. If we attribute the radio emission to the forward shock from an expanding fireball, then this rapid onset of the decay in the radio predicts that the corresponding optical transient began to decay between 1 and 5 minutes after the burst. This could explain why no optical transient for GRB 990506 was detected in spite of num…
Short-duration Gamma-ray bursts (GRBs) (\leq 2{\rm s}) have remained a mystery due to the lack of afterglow detection until recently. The models to interpret short GRBs invoke distinct progenitor scenarios. Here we present a generic analysis of short GRB afterglows, and calculate the optical lightcurves of short GRBs within the framework of different progenitor models. We show that all these optical afterglows are bright enough to be detected by the Ultraviolet and Optical Telescope (UVOT) on board the {\em Swift} observatory, and that different models could be distinguished with a well-monito…
We show a possible way to measure the column density of free electrons along the light path, the so-called Dispersion Measure (DM), from the early $[\sim 415 (ν/1 {\rm GHz})^{-2} ({\rm DM}/10^{5} {\rm pc} {\rm cm}^{-3}) {\rm s}]$ radio afterglows of the gamma-ray bursts. We find that the proposed Square Kilometer Array can detect bright radio afterglows around the time $\sim 10^{3}(ν/160 {\rm MHz})^{-2}$ s to measure the intergalactic DM ($\simg 6000$ pc cm$^{-3}$ at redshift $z>6$) up to $z\sim 30$, from which we can determine the reionization history of the universe and identify the missing …
The X-ray afterglows of GRB 001025A and GRB 010220 were detected by XMM-Newton with an average 0.2--10.0 keV flux of 4.4 and 3.3x10^{-14} erg cm^{-2} s^{-1} respectively; the afterglow of GRB 001025A is observed to decay. Afterglows at other wavelengths were not detected for either burst. A set of broadened soft X-ray emission lines are detected in the afterglow of GRB 001025A, at 5.0 sigma significance above a Galactic-absorbed power-law continuum. The spectra of both afterglows are significantly better fit by a variable abundance thermal plasma model than by an absorbed power-law and are con…
