Erratum: Accurate early positions for Swift GRBs: Enhancing X-ray positions with UVOT astrometry (Astronomy & Astrophysics (2007) 476 (1401-1409) DOI: 10.1051/0004-6361:20078436)

Erratum: Accurate early positions for Swift GRBs: Enhancing X-ray positions with UVOT astrometry (Astronomy & Astrophysics (2007) 476 (1401-1409) DOI: 10.1051/0004-6361:20078436

The prompt-afterglow connection in gamma-ray bursts: a comprehensive statistical analysis of Swift X-ray light curves

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 in a common rest-frame 0.3–30 keV energy band. Temporal variability episodes 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 γ-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 similar intrinsic absorption. We furthermore reveal the existence of a number of statistically significant relations that link the X-ray to prompt γ-ray parameters in long GRBs; short GRBs are outliers of the majority of these two-parameter relations. However and more importantly, we report on the existence of a universal three-parameter scaling that links the X-ray and the γ-ray energy to the prompt spectral peak energy of both long and short GRBs: EX, iso∝E[Superscript: 1.00 ± 0.06]γ, iso/E[Superscript: 0.60 ± 0.10]pk

GRB 050410 and GRB 050412: Are they really dark gamma-ray bursts?

Aims.We present a detailed analysis of the prompt and afterglow emission of GRB 050410 and GRB 050412 detected by Swift for which no optical counterpart was observed. Methods.We analysed data from the prompt emission detected by the Swift BAT and from the early phase of the afterglow obtained by the Swift narrow field instrument XRT. Results.The 15-150 keV energy distribution of the GRB 050410 prompt emission shows a peak energy at 53 -21+40 keV. The XRT light curve of this GRB decays as a power law with a slope of $\alpha=$ 1.06 $\pm$ 0.04. The spectrum is well reproduced by an absorbed power law with a spectral index $\Gamma_{\rm x}=2.4$ $\pm$ 0.4 and a low energy absorption $N_{\rm H}$ = 4 +3-2 $\times$ 1021 cm-2 which is higher than the Galactic value. The 15-150 keV prompt emission in GRB 050412 is modelled with a hard ($\Gamma$ = 0.7 $\pm$ 0.2) power law. The XRT light curve follows a broken power law with the first slope $\alpha_1$ = 0.7 $\pm$ 0.4, the break time $T_{\rm break}$ = 254 -41+79 s and the second slope $\alpha_2$ = 2.8 -0.8+0.5. The spectrum is fitted by a power law with spectral index $\Gamma_{\rm x}=1.3$ $\pm$ 0.2 which is absorbed at low energies by the Galactic column. Conclusions.The GRB 050410 afterglow light curve reveals the expected characteristics of the third component of the canonical Swift light curve. Conversely, a complex phenomenology was detected in the GRB 050412 because of the presence of the very early break. The light curve in this case can be interpreted as being the last peak of the prompt emission. The two bursts present tight upper limits for the optical emission, however, neither of them can be clearly classified as dark. For GRB 050410, the suppression of the optical afterglow could be attributed to a low density interstellar medium surrounding the burst. For GRB 050412, the evaluation of the darkness is more difficult due to the ambiguity in the extrapolation of the X-ray afterglow light curve