The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Tsvi Piran - One of the best experts on this subject based on the ideXlab platform.
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Detectability of neutron star merger Afterglows
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Ore Gottlieb, Ehud Nakar, Tsvi PiranAbstract:VLBI and JVLA observations revealed that GW170817 involved a narrow jet ($ \theta_j \approx 4^\circ $) that dominated the Afterglow peak at our viewing angle, $ \theta_{\rm obs} \approx 20^\circ $. This implies that at the time of the Afterglow peak, the observed signal behaved like an Afterglow of a top-hat jet seen at $ \theta_{\rm obs} \gg \theta_j $, and it can be modeled by analytic expressions that describe such jets. We use a set of numerical simulations to calibrate these analytic relations and obtain generic equations for the peak time and flux of such an Afterglow as seen from various observing angles. Using the calibrated equations and the estimated parameters of GW170817, we estimate the detectability of Afterglows from future double neutron star mergers during the Advanced LIGO/Virgo observation run O3. GW170817 took place at a relatively low-density environment. Afterglows of similar events will be detectable only at small viewing angles, $ \theta_{\rm obs} \lesssim 20^\circ $, and only $\sim 20\% $ of the GW detections of these events will be accompanied by a detectable Afterglow. At higher densities, more typical to sGRB sites, up to $ 70\% $ of the GW detections are expected to be followed by a detectable Afterglow, typically at $ \theta_{\rm obs} \sim 30^\circ $. We also provide the latest time one should expect an Afterglow detection. We find that for typical parameters, if the jet emission had not been detected within about a year after the merger, it is unlikely to be ever detected.
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Linear and circular polarization in GRB Afterglows
Proceedings of Swift: 10 Years of Discovery — PoS(SWIFT 10), 2015Co-Authors: Lara Nava, Ehud Nakar, Tsvi PiranAbstract:A certain degree of linear polarization has been measured in several GRB Afterglows. More surprisingly, circular polarization has been recently measured in GRB121024A. For synchrotron emission, the polarization level depends on: (i) the local magnetic field orientation (ii) the geometry of the emitting region with respect to the line of sight and (iii) the electron pitch-angle distribution. For this reason, polarization measurements are a valuable tool to probe Afterglow micro-physics. We present numerical estimates of linear and circular polarization for different configurations (i.e., magnetic fields, geometries and pitch-angle distributions). For each different scenario, we study the conditions for reaching the maximum and minimum linear and circular polarization and provide their values. We discuss the implication of our results to the micro-physics of GRB Afterglows in view of recent polarization measurements.
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high energy Afterglow emission from gamma ray bursts
2013Co-Authors: Ramesh Narayan, Tsvi Piran, Yizhong Fan, Daming WeiAbstract:We calculate the very high energy (sub-GeV to TeV) inverse Compton emission of GRB Afterglows. We argue that this emission provides a powerful test of the currently accepted Afterglow model. We focus on two processes: synchrotron self-Compton (SSC) emission within the Afterglow blast wave, and external inverse Compton (EIC) emission which occurs when flare photons (produced by an internal process) pass through the blast wave. We show that if our current interpretations of the Swift XRT data are correct, there should be a canonical high energy Afterglow emission light curve. Our predictions can be tested with high energy observatories such as GLAST, Whipple, H.E.S.S. and MAGIC. Under favorable conditions we expect Afterglow detections in all these detectors.
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high energy Afterglow emission from gamma ray bursts
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: Ramesh Narayan, Tsvi Piran, Yizhong Fan, Daming WeiAbstract:We calculate the very high-energy (sub-GeV to TeV) inverse Compton emission of GRB Afterglows. We argue that this emission provides a powerful test of the currently accepted Afterglow model. We focus on two processes: synchrotron self-Compton emission within the Afterglow blast wave, and external inverse Compton emission which occurs when flare photons (produced by an internal process) pass through the blast wave. We show that if our current interpretations of the Swift X-ray telescope (XRT) data are correct, there should be a canonical high-energy Afterglow emission light curve. Our predictions can be tested with high-energy observatories such as GLAST, Whipple, HESS and MAGIC. Under favourable conditions we expect Afterglow detections in all these detectors.
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The interpretation and implication of the Afterglow of GRB 060218
Journal of Cosmology and Astroparticle Physics, 2006Co-Authors: Yizhong Fan, Tsvi PiranAbstract:The nearby GRB 060216/SN 2006aj was an extremely long, weak and very soft GRB. It was peculiar in many aspects. We show here that the x-ray, ultraviolet/optical and radio Afterglows of GRB 060218 have to be attributed to different physical processes arising from different emission regions. From the several components in this burst's Afterglow only the radio Afterglow can be interpreted in terms of the common external shock model. We infer from the radio that the blast wave's kinetic energy was ~1050 erg and the circumburst matter had a constant rather than a wind profile. The lack of a 'jet break' up to 22 days implies that the outflow was wide, θj>1. Even though the late x-ray Afterglow decays normally, it cannot result from an external shock because of its very steep spectrum. Furthermore, the implied kinetic energy would have produced far too much radio. We suggest that this x-ray Afterglow could be attributed to a continued activity of the central engine that within the collapsar scenario could arise from fall-back accretion. 'Central engine Afterglow' may be common in under-luminous GRBs where the kinetic energy of the blast wave is small and the external shock does not dominate over this component. Such under-luminous GRBs might be very common but they are rarely recorded because they can be detected only from short distances.
Robert Mochkovitch - One of the best experts on this subject based on the ideXlab platform.
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Radio Afterglows of binary neutron star mergers: a population study for current and future gravitational wave observing runs
Astron.Astrophys., 2019Co-Authors: Raphael Duque, Frederic Daigne, Robert MochkovitchAbstract:Following the historical observations of GW170817 and its multi-wavelength Afterglow, more radio Afterglows from neutron star mergers are expected in the future as counterparts to gravitational wave inspiral signals. Our aim is to describe these events using our current knowledge of the population of neutron star mergers based on gamma-ray burst science, and taking into account the sensitivities of current and future gravitational wave and radio detectors. We combined analytical models for the merger gravitational wave and radio Afterglow signals to a population model prescribing the energetics, circum-merger density and other relevant parameters of the mergers. We reported the expected distributions of observables (distance, orientation, Afterglow peak time and flux, etc.) for future events and studied how these can be used to further probe the population of binary neutron stars, their mergers and related outflows during future observing campaigns. In the case of the O3 run of the LIGO-Virgo Collaboration, the radio Afterglow of one third of gravitational-wave-detected mergers should be detectable (and detected if the source is localized thanks to the kilonova counterpart) by the Very Large Array. Furthermore, these events should have viewing angles similar to that of GW170817. These findings confirm the radio Afterglow as a powerful insight into these events, although some key Afterglow-related techniques, such as very long baseline interferometry imaging of the merger remnant, may no longer be feasible as the gravitational wave horizon increases.Key words: methods: statistical / stars: neutron / gravitational waves / γ-ray burst: individual: GRB170817A / γ-ray burst: general
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Detecting the imprint of a kilonova or supernova in short gamma-ray burst Afterglows
Astron.Astrophys., 2018Co-Authors: Nidhal Guessoum, Hannachi Zitouni, Robert MochkovitchAbstract:Short gamma-ray bursts result from mergers of two neutron stars or from collapsars, but probably at a smaller rate. In the first case, a kilonova occurs while in the second case a Type Ic supernova is expected. } {Even if future observations of kilonovae in association with gravitational wave events provide better data, detecting a kilonova during an Afterglow follow-up would remain useful for exploring the diversity of the kilonova phenomenon. As supernovae produce a weaker gravitational signal, Afterglow follow-up will be the only possible method to find one. In this work, we identify the conditions of the burst energy, external density, kilonova mass, supernova luminosity, that are necessary for the detection of a kilonova or supernova in the follow-up of short GRB Afterglows.} {We have used a simple kilonova model to obtain the peak luminosities and times as a function of mass, expansion velocity and ejected matter opacity. Afterglow light curves are computed for a uniform medium and a stellar wind, in the kilonova and supernova cases, respectively.} {We represent, using diagrams of the burst kinetic energy vs. density of the external medium, the domains where the kilonova or supernova at maximum is brighter than the Afterglow. %\LEt{Please check I have retained your intended meaning -> It's OK
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Afterglows after Swift
Comptes Rendus Physique, 2011Co-Authors: O. Godet, Robert MochkovitchAbstract:Abstract Since their discovery by the Beppo-SAX satellite in 1997, gamma-ray burst Afterglows have attracted an ever-growing interest. They have allowed redshift measurements that have confirmed that gamma-ray bursts are located at cosmological distances. Their study covers a huge range both in time (from one minute to several months after the trigger) and energy (from the GeV to radio domains). The purpose of this review is first to give a short historical account of Afterglow research and describe the main observational results with a special attention to the early Afterglow revealed by Swift . We then present the standard Afterglow model as it has been developed in the pre- Swift era and show how it is challenged by the recent Swift and Fermi results. We finally discuss different options (within the standard framework or implying a change of paradigm) that have been proposed to solve the current problems.
Ehud Nakar - One of the best experts on this subject based on the ideXlab platform.
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Detectability of neutron star merger Afterglows
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Ore Gottlieb, Ehud Nakar, Tsvi PiranAbstract:VLBI and JVLA observations revealed that GW170817 involved a narrow jet ($ \theta_j \approx 4^\circ $) that dominated the Afterglow peak at our viewing angle, $ \theta_{\rm obs} \approx 20^\circ $. This implies that at the time of the Afterglow peak, the observed signal behaved like an Afterglow of a top-hat jet seen at $ \theta_{\rm obs} \gg \theta_j $, and it can be modeled by analytic expressions that describe such jets. We use a set of numerical simulations to calibrate these analytic relations and obtain generic equations for the peak time and flux of such an Afterglow as seen from various observing angles. Using the calibrated equations and the estimated parameters of GW170817, we estimate the detectability of Afterglows from future double neutron star mergers during the Advanced LIGO/Virgo observation run O3. GW170817 took place at a relatively low-density environment. Afterglows of similar events will be detectable only at small viewing angles, $ \theta_{\rm obs} \lesssim 20^\circ $, and only $\sim 20\% $ of the GW detections of these events will be accompanied by a detectable Afterglow. At higher densities, more typical to sGRB sites, up to $ 70\% $ of the GW detections are expected to be followed by a detectable Afterglow, typically at $ \theta_{\rm obs} \sim 30^\circ $. We also provide the latest time one should expect an Afterglow detection. We find that for typical parameters, if the jet emission had not been detected within about a year after the merger, it is unlikely to be ever detected.
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Linear and circular polarization in GRB Afterglows
Proceedings of Swift: 10 Years of Discovery — PoS(SWIFT 10), 2015Co-Authors: Lara Nava, Ehud Nakar, Tsvi PiranAbstract:A certain degree of linear polarization has been measured in several GRB Afterglows. More surprisingly, circular polarization has been recently measured in GRB121024A. For synchrotron emission, the polarization level depends on: (i) the local magnetic field orientation (ii) the geometry of the emitting region with respect to the line of sight and (iii) the electron pitch-angle distribution. For this reason, polarization measurements are a valuable tool to probe Afterglow micro-physics. We present numerical estimates of linear and circular polarization for different configurations (i.e., magnetic fields, geometries and pitch-angle distributions). For each different scenario, we study the conditions for reaching the maximum and minimum linear and circular polarization and provide their values. We discuss the implication of our results to the micro-physics of GRB Afterglows in view of recent polarization measurements.
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the Afterglows of swift era gamma ray bursts i comparing pre swift and swift era long soft type ii grb optical Afterglows
The Astrophysical Journal, 2010Co-Authors: D A Kann, Ehud Nakar, S Klose, Nathaniel R Butler, D Malesani, A C Wilson, B B Zhang, A S Pozanenko, P JakobssonAbstract:We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) Afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB Afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the Afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift Afterglows. The results of a former study, which showed that GRB Afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two Afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical Afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB Afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on Afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature Afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.
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the Afterglows of swift era gamma ray bursts ii type i grb versus type ii grb optical Afterglows
arXiv: Astrophysics, 2008Co-Authors: D A Kann, Ehud Nakar, S Klose, Bing Zhang, S Covino, Nathaniel R Butler, D Malesani, A C Wilson, L A Antonelli, G ChincariniAbstract:We use a large sample of GRB Afterglow and prompt-emission data (adding further GRB Afterglow observations in this work) to compare the optical Afterglows (or the lack thereof) of Type I GRBs with those of Type II GRBs. In comparison to the Afterglows of Type II GRBs, we find that those of Type I GRBs have a lower average luminosity and show an intrinsic spread of luminosities at least as wide. From late and deep upper limits on the optical transients, we establish limits on the maximum optical luminosity of any associated supernova, confirming older works and adding new results. We use deep upper limits on Type I GRB optical Afterglows to constrain the parameter space of possible mini-SN emission associated with a compact-object merger. Using the prompt emission data, we search for correlations between the parameters of the prompt emission and the late optical Afterglow luminosities. We find tentative correlations between the bolometric isotropic energy release and the optical Afterglow luminosity at a fixed time after trigger (positive), and between the host offset and the luminosity (negative), but no significant correlation between the isotropic energy release and the duration of the GRBs. We also discuss three anomalous GRBs, GRB 060505, GRB 060614, and GRB 060121, in the light of their optical Afterglow luminosities. (Abridged)
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the Afterglows of swift era gamma ray bursts i comparing pre swift and swift era long soft type ii grb optical Afterglows
arXiv: Astrophysics, 2007Co-Authors: D A Kann, Ehud Nakar, S Klose, Nathaniel R Butler, D Malesani, A C Wilson, B B Zhang, A S Pozanenko, P JakobssonAbstract:We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) Afterglows including GRBs up to September 2009, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB Afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host galaxy extinction. We transformed the Afterglow light curves into an extinction-corrected z=1 system and compared their luminosities with a sample of pre-Swift Afterglows. The results of a former study, which showed that GRB Afterglows clustered and exhibited a bimodal distribution in luminosity space, is weakened by the larger sample. We found that the luminosity distribution of the two Afterglow samples (Swift-era and pre-Swift) are very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical Afterglow luminosity at one day after the GRB in the z=1 system. A comparative study of the optical luminosities of GRB Afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without reveals no indication that the former are statistically significantly more luminous. (abridged)
Bing Zhang - One of the best experts on this subject based on the ideXlab platform.
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contribution of dark matter annihilation to gamma ray burst Afterglows near massive galaxy centers
arXiv: High Energy Astrophysical Phenomena, 2020Co-Authors: Baoquan Huang, Tong Liu, Feng Huang, Dabin Lin, Bing ZhangAbstract:Gamma-ray bursts (GRBs) are believed to be powered by ultrarelativistic jets. If these jets encounter and accelerate excess electrons and positrons produced by particle dark matter (DM) annihilation, the observed electromagnetic radiation would be enhanced. In this paper, we study GRB Afterglow emission with the presence of abundant DM under the weakly interacting massive particle annihilation conditions. We calculate the light curves and spectra of the GRB Afterglows with different parameters, i.e., DM density, particle DM mass, annihilation channel, and electron density of the interstellar medium. We find that the effect of DM may become noticeable in the Afterglow spectra if the circumburst has a low electron number density ($n \lesssim 0.1~\rm cm^{-3}$) and if the DM has a high number density ($\rho_\chi \gtrsim 10^3~\rm GeV~cm^{-3}$). According to the standard galaxy DM density profile, GRB Afterglows with DM contribution might occur at distances of several to tens of parsecs from the centers of massive galaxies.
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Late-time detections of the X-ray Afterglow of GRB 060729 with Chandra - the latest detections ever of an X-ray Afterglow
The Astrophysical Journal, 2010Co-Authors: Dirk Grupe, Bing Zhang, Xiangyu Wang, Neil Gehrels, David N. Burrows, En-wei Liang, Gordon P. Garmire, John A. Nousek, George R. RickerAbstract:We report on 5 Chandra observations of the X-ray Afterglow of the Gamma-Ray Burst GRB 060729 performed between 2007 March and 2008 May. In all five observations the Afterglow is clearly detected. The last Chandra pointing was performed on 2008-May-04, 642 days after the burst - the latest detection of a GRB X-ray Afterglow ever. A reanalysis of the Swift XRT light curve together with the three detections by Chandra in 2007 reveals a break at about 1.0 Ms after the burst with a slight steepening of the decay slope from alpha = 1.32 to 1.61. This break coincides with a significant hardening of the X-ray spectrum, consistent with a cooling break in the wind medium scenario, in which the cooling frequency of the Afterglow crosses the X-ray band. The last two Chandra observations in 2007 December and 2008 May provide evidence for another break at about one year after the burst. If interpreted as a jet break, this late-time break implies a jet half opening angle of about 14 degrees for a wind medium. Alternatively, this final break may have a spectral origin, in which case no jet break has been observed and the half-opening angle of the jet of GRB 060729 must be larger than about 15 degrees for a wind medium. We compare the X-ray Afterglow of GRB 060729 in a wind environment with other bright X-ray Afterglows, in particular GRBs 061121 and 080319B, and discuss why the X-ray Afterglow of GRB 060729 is such an exceptionally long-lasting event.
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the Afterglows of swift era gamma ray bursts ii type i grb versus type ii grb optical Afterglows
arXiv: Astrophysics, 2008Co-Authors: D A Kann, Ehud Nakar, S Klose, Bing Zhang, S Covino, Nathaniel R Butler, D Malesani, A C Wilson, L A Antonelli, G ChincariniAbstract:We use a large sample of GRB Afterglow and prompt-emission data (adding further GRB Afterglow observations in this work) to compare the optical Afterglows (or the lack thereof) of Type I GRBs with those of Type II GRBs. In comparison to the Afterglows of Type II GRBs, we find that those of Type I GRBs have a lower average luminosity and show an intrinsic spread of luminosities at least as wide. From late and deep upper limits on the optical transients, we establish limits on the maximum optical luminosity of any associated supernova, confirming older works and adding new results. We use deep upper limits on Type I GRB optical Afterglows to constrain the parameter space of possible mini-SN emission associated with a compact-object merger. Using the prompt emission data, we search for correlations between the parameters of the prompt emission and the late optical Afterglow luminosities. We find tentative correlations between the bolometric isotropic energy release and the optical Afterglow luminosity at a fixed time after trigger (positive), and between the host offset and the luminosity (negative), but no significant correlation between the isotropic energy release and the duration of the GRBs. We also discuss three anomalous GRBs, GRB 060505, GRB 060614, and GRB 060121, in the light of their optical Afterglow luminosities. (Abridged)
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physical processes shaping gamma ray burst x ray Afterglow light curves theoretical implications from the swift x ray telescope observations
The Astrophysical Journal, 2006Co-Authors: Bing Zhang, Yizhong Fan, Jaroslaw Dyks, S Kobayashi, P Meszaros, J A Nousek, David N. Burrows, N GehrelsAbstract:With the successful launch of the Swift Gamma-Ray Burst Explorer, a rich trove of early X-ray Afterglow data has been collected by its onboard X-Ray Telescope (XRT). Some interesting features are emerging, including a distinct rapidly decaying component preceding the conventional Afterglow component in many sources, a shallow decay component before the more "normal'' decay component observed in a good fraction of GRBs, and X-ray flares in nearly half of the Afterglows. In this paper we systematically analyze the possible physical processes that shape the properties of the early X-ray Afterglow light curves and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or the X-ray flares. This provides strong evidence that the prompt emission and Afterglow emission are likely two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that very likely the forward shock keeps being refreshed for some time. This might be caused by either a long-lived central engine, or a wide distribution of the shell Lorentz factors, or else possibly the deceleration of a Poynting flux-dominated flow. X-ray flares suggest that the GRB central engine is very likely still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends to days after the burst triggers. Analyses of early X-ray Afterglow data reveal that GRBs are indeed highly relativistic events and that early Afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the Afterglow emission from an ISM environment.
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physical processes shaping grb x ray Afterglow lightcurves theoretical implications from the swift xrt observations
arXiv: Astrophysics, 2005Co-Authors: Bing Zhang, Yizhong Fan, Jaroslaw Dyks, S Kobayashi, P Meszaros, D N Burrows, J A Nousek, N GehrelsAbstract:(Abridged) The Swift X-Ray Telescope (XRT) reveals some interesting features of early X-ray Afterglows, including a distinct rapidly decaying component preceding the conventional Afterglow component in many sources, a shallow decay component before the more ``normal'' decay component observed in a good fraction of GRBs (e.g. GRB 050128, GRB 050315, GRB 050319, and GRB 050401), and X-ray flares in nearly half of the Afterglows (e.g. GRB 050406, GRB 050502B, GRB 050607, and GRB 050724). In this paper, we systematically analyze the possible physical processes that shape the properties of the early X-ray Afterglow lightcurves, and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or of the X-ray flares. This provides clear evidence that the prompt emission and Afterglow emission are two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that the forward shock keeps being refreshed for some time. This might be caused either by a long-lived central engine, or by a power law distribution of the shell Lorentz factors, or else by the deceleration of a Poynting flux dominated flow. X-ray flares suggest that the GRB central engine is still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends days after the burst trigger. Analyses of early X-ray Afterglow data reveal that GRBs are indeed highly relativistic events. Early Afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the Afterglow emission from an interstellar medium (ISM) environment.
Yizhong Fan - One of the best experts on this subject based on the ideXlab platform.
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high energy Afterglow emission from gamma ray bursts
2013Co-Authors: Ramesh Narayan, Tsvi Piran, Yizhong Fan, Daming WeiAbstract:We calculate the very high energy (sub-GeV to TeV) inverse Compton emission of GRB Afterglows. We argue that this emission provides a powerful test of the currently accepted Afterglow model. We focus on two processes: synchrotron self-Compton (SSC) emission within the Afterglow blast wave, and external inverse Compton (EIC) emission which occurs when flare photons (produced by an internal process) pass through the blast wave. We show that if our current interpretations of the Swift XRT data are correct, there should be a canonical high energy Afterglow emission light curve. Our predictions can be tested with high energy observatories such as GLAST, Whipple, H.E.S.S. and MAGIC. Under favorable conditions we expect Afterglow detections in all these detectors.
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high energy Afterglow emission from gamma ray bursts
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: Ramesh Narayan, Tsvi Piran, Yizhong Fan, Daming WeiAbstract:We calculate the very high-energy (sub-GeV to TeV) inverse Compton emission of GRB Afterglows. We argue that this emission provides a powerful test of the currently accepted Afterglow model. We focus on two processes: synchrotron self-Compton emission within the Afterglow blast wave, and external inverse Compton emission which occurs when flare photons (produced by an internal process) pass through the blast wave. We show that if our current interpretations of the Swift X-ray telescope (XRT) data are correct, there should be a canonical high-energy Afterglow emission light curve. Our predictions can be tested with high-energy observatories such as GLAST, Whipple, HESS and MAGIC. Under favourable conditions we expect Afterglow detections in all these detectors.
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The interpretation and implication of the Afterglow of GRB 060218
Journal of Cosmology and Astroparticle Physics, 2006Co-Authors: Yizhong Fan, Tsvi PiranAbstract:The nearby GRB 060216/SN 2006aj was an extremely long, weak and very soft GRB. It was peculiar in many aspects. We show here that the x-ray, ultraviolet/optical and radio Afterglows of GRB 060218 have to be attributed to different physical processes arising from different emission regions. From the several components in this burst's Afterglow only the radio Afterglow can be interpreted in terms of the common external shock model. We infer from the radio that the blast wave's kinetic energy was ~1050 erg and the circumburst matter had a constant rather than a wind profile. The lack of a 'jet break' up to 22 days implies that the outflow was wide, θj>1. Even though the late x-ray Afterglow decays normally, it cannot result from an external shock because of its very steep spectrum. Furthermore, the implied kinetic energy would have produced far too much radio. We suggest that this x-ray Afterglow could be attributed to a continued activity of the central engine that within the collapsar scenario could arise from fall-back accretion. 'Central engine Afterglow' may be common in under-luminous GRBs where the kinetic energy of the blast wave is small and the external shock does not dominate over this component. Such under-luminous GRBs might be very common but they are rarely recorded because they can be detected only from short distances.
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physical processes shaping gamma ray burst x ray Afterglow light curves theoretical implications from the swift x ray telescope observations
The Astrophysical Journal, 2006Co-Authors: Bing Zhang, Yizhong Fan, Jaroslaw Dyks, S Kobayashi, P Meszaros, J A Nousek, David N. Burrows, N GehrelsAbstract:With the successful launch of the Swift Gamma-Ray Burst Explorer, a rich trove of early X-ray Afterglow data has been collected by its onboard X-Ray Telescope (XRT). Some interesting features are emerging, including a distinct rapidly decaying component preceding the conventional Afterglow component in many sources, a shallow decay component before the more "normal'' decay component observed in a good fraction of GRBs, and X-ray flares in nearly half of the Afterglows. In this paper we systematically analyze the possible physical processes that shape the properties of the early X-ray Afterglow light curves and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or the X-ray flares. This provides strong evidence that the prompt emission and Afterglow emission are likely two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that very likely the forward shock keeps being refreshed for some time. This might be caused by either a long-lived central engine, or a wide distribution of the shell Lorentz factors, or else possibly the deceleration of a Poynting flux-dominated flow. X-ray flares suggest that the GRB central engine is very likely still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends to days after the burst triggers. Analyses of early X-ray Afterglow data reveal that GRBs are indeed highly relativistic events and that early Afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the Afterglow emission from an ISM environment.
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physical processes shaping grb x ray Afterglow lightcurves theoretical implications from the swift xrt observations
arXiv: Astrophysics, 2005Co-Authors: Bing Zhang, Yizhong Fan, Jaroslaw Dyks, S Kobayashi, P Meszaros, D N Burrows, J A Nousek, N GehrelsAbstract:(Abridged) The Swift X-Ray Telescope (XRT) reveals some interesting features of early X-ray Afterglows, including a distinct rapidly decaying component preceding the conventional Afterglow component in many sources, a shallow decay component before the more ``normal'' decay component observed in a good fraction of GRBs (e.g. GRB 050128, GRB 050315, GRB 050319, and GRB 050401), and X-ray flares in nearly half of the Afterglows (e.g. GRB 050406, GRB 050502B, GRB 050607, and GRB 050724). In this paper, we systematically analyze the possible physical processes that shape the properties of the early X-ray Afterglow lightcurves, and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or of the X-ray flares. This provides clear evidence that the prompt emission and Afterglow emission are two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that the forward shock keeps being refreshed for some time. This might be caused either by a long-lived central engine, or by a power law distribution of the shell Lorentz factors, or else by the deceleration of a Poynting flux dominated flow. X-ray flares suggest that the GRB central engine is still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends days after the burst trigger. Analyses of early X-ray Afterglow data reveal that GRBs are indeed highly relativistic events. Early Afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the Afterglow emission from an interstellar medium (ISM) environment.