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Register a new userDust scattering X-ray expanding rings around gamma-ray bursts
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Scattering by dust grains in our Galaxy can produce X-ray halos, visible as expanding rings, around GRBs. This has been observed in three GRBs to date, allowing to derive accurate distances for the dust clouds as well as some constraints on the prompt GRB X-ray emission that was not directly observed. We developed a new analysis method to study dust scattering expanding rings and have applied it to all the XMM-Newton and Swift/XRT follow-up observations of GRBs.
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We investigate the effect of X-ray echo emission in gamma-ray bursts (GRBs). We find that the echo emission can provide an alternative way of understanding X-ray shallow decays and jet breaks. In particular, a shallow decay followed by a normal decay and a further rapid decay of X-ray afterglows can be together explained as being due to the echo from prompt X-ray emission scattered by dust grains in a massive wind bubble around a GRB progenitor. We also introduce an extra temporal break in the X-ray echo emission. By fitting the afterglow light curves, we can measure the locations of the massive wind bubbles, which will bring us closer to finding the mass loss rate, wind velocity, and the age of the progenitors prior to the GRB explosions.
Two new expanding X-ray rings were detected by the Swift XRT instrument during early follow-up observations of GRB 061019 and GRB 070129, increasing to 5 the number of dust scattering X-ray halos observed around GRBs. Although these two halos were particularly faint, a sensitive analysis can be performed that optimizes the method originally developed by Tiengo & Mereghetti (2006) to analyze dust scattering rings observed with XMM-Newton for the Swift satellite. In the case of GRB 061019, a known giant molecular cloud is identified as the one responsible for the scattering process, and its distance is accurately measured (d=940$pm$40 pc) through the dynamics of the expanding ring. In the second case, XRT observed both the main peak of the prompt emission of GRB 070129 and the scattering halo, but the small number of detected halo photons prevents us from distinguish between different dust models.
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 .
X-ray flashes are detected in the Wide Field Cameras on BeppoSAX in the energy range 2-25 keV as bright X-ray sources lasting of the order of minutes, but remaining undetected in the Gamma Ray Bursts Monitor on BeppoSAX. They have properties very similar to the x-ray counterparts of GRBs and account for some of the Fast X-ray Transient events seen in almost every x-ray satellite. We review their X-ray properties and show that x-ray flashes are in fact very soft, x-ray rich, untriggered gamma ray bursts, in which the peak energy in 2-10 keV x-rays could be up to a factor of 100 larger than the peak energy in the 50-300 keV gamma ray range. The frequency is ~100 per year.
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