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Zheng, W.,Shen, R. F.,Sakamoto, T.,Beardmore, A. P.,De Pasquale, M.,Wu, X. F.,Gorosabel, J.,Urata, Y.,Sugita, S.,Zhang, B.,Pozanenko, A.,Nissinen, M.,Sahu, D. K.,Im, M.,Ukwatta, T. N.,Andreev, M.,Klun IOP Publishing 2012 The Astrophysical journal Vol.751 No.2
<P>We present a comprehensive analysis of a bright, long-duration (T-90 similar to 257 s) GRB 110205A at redshift z = 2.22. The optical prompt emission was detected by Swift/UVOT, ROTSE-IIIb, and BOOTES telescopes when the gamma-ray burst (GRB) was still radiating in the gamma-ray band, with optical light curve showing correlation with gamma-ray data. Nearly 200 s of observations were obtained simultaneously from optical, X-ray, to gamma-ray (1 eV to 5 MeV), which makes it one of the exceptional cases to study the broadband spectral energy distribution during the prompt emission phase. In particular, we clearly identify, for the first time, an interesting two-break energy spectrum, roughly consistent with the standard synchrotron emission model in the fast cooling regime. Shortly after prompt emission (similar to 1100 s), a bright (R = 14.0) optical emission hump with very steep rise (alpha similar to 5.5) was observed, which we interpret as the reverse shock (RS) emission. It is the first time that the rising phase of an RS component has been closely observed. The full optical and X-ray afterglow light curves can be interpreted within the standard reverse shock (RS) + forward shock (FS) model. In general, the high-quality prompt and afterglow data allow us to apply the standard fireball model to extract valuable information, including the radiation mechanism (synchrotron), radius of prompt emission (R-GRB similar to 3 x 10(13) cm), initial Lorentz factor of the outflow (Gamma(0) similar to 250), the composition of the ejecta (mildly magnetized), the collimation angle, and the total energy budget.</P>
Relativistic jet activity from the tidal disruption of a star by a massive black hole
Burrows, D. N.,Kennea, J. A.,Ghisellini, G.,Mangano, V.,Zhang, B.,Page, K. L.,Eracleous, M.,Romano, P.,Sakamoto, T.,Falcone, A. D.,Osborne, J. P.,Campana, S.,Beardmore, A. P.,Breeveld, A. A.,Chester, Nature Publishing Group, a division of Macmillan P 2011 Nature Vol.476 No.7361
Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.