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Register a new userX-ray afterglows and spectroscopy of Gamma-Ray Bursts
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Luigi Piro
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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.
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Observational evidence of iron absorption and emission lines in X-ray spectra of Gamma-Ray Bursts is quite compelling. I will briefly review the results, summarize different models and describe the connection with massive progenitors in star-forming regions implied by these results. This link is also supported by measurements of the X-ray absorbing gas in several GRBs, with column density consistent with that of Giant Molecular Clouds harbouring star-formation in our Galaxy, as well as by evidences gathered in other wavelengths. However, the volume density inferred by the fireball-jet model is much lower than typical of a GMC, and I will confront this with the alternative explanation of fireball expansion in a high dense medium, outlining the problems that both models have at present. Finally I will briefly summarize some results on dark GRBs, and describe the prospects of high resolution X-ray spectroscopy in getting closer to the central environment of GRB, and far in the Early Universe by using GRB as beacons to probe star and galaxy formation.
In this review we briefly summarize the recent developments in the research on Gamma-Ray Bursts, and discuss in more details the recent results derived from X-ray spectroscopy, in particular the detection of X-ray narrow features and their implication on our understanding on the origin of GRB. Finally, we outline the importance of high resolution spectroscopy in X-rays, which can provide new clues on the nature of progenitors, and a powerful probe of the early Universe and primordial galaxy formation .
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 origin of the X-ray afterglows of gamma-ray bursts has regularly been debated. We fit both the fireball-shock and millisecond-magnetar models of gamma-ray bursts to the X-ray data of GRB 130603B and 140903A. We use Bayesian model selection to answer the question of which model best explains the data. This is dependent on the maximum allowed non-rotating neutron star mass $M_{textrm{TOV}}$, which depends solely on the unknown nuclear equation of state. We show that the data for GRB140903A favours the millisecond-magnetar model for all possible equations of state, while the data for GRB130603B favours the millisecond-magnetar model if $M_{textrm{TOV}} gtrsim 2.3 M_{odot}$. If $M_{textrm{TOV}} lesssim 2.3 M_{odot}$, the data for GRB130603B supports the fireball-shock model. We discuss implications of this result in regards to the nuclear equation of state and the prospect of gravitational-wave emission from newly-born millisecond magnetars.
We report the discovery of a transient and fading hard X-ray emission in the BATSE lightcurves of a sample of short gamma-ray bursts. We have summed each of the four channel BATSE light curves of 76 short bursts to uncover the average overall temporal and spectral evolution of a possible transient signal following the prompt flux. We found an excess emission peaking ~30 s after the prompt one, detectable for ~100 s. The soft power-law spectrum and the time-evolution of this transient signal suggest that it is produced by the deceleration of a relativistic expanding source, as predicted by the afterglow model.
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