R. Margutti, E. Zaninoni, M. G. Bernardini, G. Chincarini, F. Pasotti, C. Guidorzi, L. Angelini, D. N. Burrows, M. Capalbi, P. A. Evans, N. Gehrels, J. Kennea, V. Mangano, A. Moretti, J. Nousek, J. P. Osborne, K. L. Page, M. Perri, J. Racusin, P. Romano, B. Sbarufatti, S. Stafford, M. Stamatikos
We present a comprehensive statistical analysis of Swift X-ray light-curves of Gamma-Ray Bursts (GRBs), collecting data from more than 650 GRBs discovered by Swift and other facilities. The unprecedented sample size allows us to constrain the rest-frame X-ray properties of GRBs from a statistical perspective, with particular reference to intrinsic time scales and the energetics of the different light-curve phases, with the final aim of distinguishing between competing models. Variability episodes superimposed on smooth light-curve decays are also studied and their properties constrained. Two fundamental questions drive this effort: i) Does the X-ray emission retain any kind of "memory" of the prompt gamma-ray phase? ii) Where is the dividing line between long and short GRB X-ray properties? We show that short GRBs decay faster, are less luminous and less energetic than long GRBs in the X-rays, but are interestingly characterized by very similar intrinsic absorption. We furthermore reveal the existence of a number of statistically significant relations that link the X-ray to prompt gamma-ray parameters in long GRBs; short GRBs are outliers of the majority of these 2-parameter relations. However and more importantly, we report on the existence of a universal 3-parameter scaling that links the X-ray and the gamma-ray energy to the prompt spectral peak energy of BOTH long and short GRBs: E_X,iso \propto (E_gamma,iso)^1.06/(E_pk^0.74)
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http://arxiv.org/abs/1203.1059
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