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We present observations of XRF 050406, the first burst detected by Swift showing a flare in its X-ray light curve. During this flare, which peaks at t_peak ~210s after the BAT trigger, a flux variation of (delta F)/F~6 in a very short time (delta t)/t_peak<, 11 pages, 3 figures, accepted for publication in A&A; added references, corrected typos

We report on the temporal and spectral characteristics of the early X-ray emission from the Gamma Ray Bursts GRB050126 and GRB050219A as observed by Swift. The X-ray light-curves of these 2 bursts both show remarkably steep early decays (F(t)\propto t^{-3}), breaking to flatter slopes on timescales of a few hundred seconds. For GRB050126 the burst shows no evidence of spectral evolution in the 20-150 keV band, and the spectral index of the gamma-ray and X-ray afterglows are significantly different suggesting a separate origin. By contrast the BAT spectrum of GRB050219A displays significant spectral evolution, becoming softer at later times, with Gamma evolving toward the XRT photon index seen in the early X-ray afterglow phase. For both bursts, the 0.2-10 keV spectral index pre- and post-break in the X-ray decay light-curve are consistent with no spectral evolution. We suggest that the steep early decline in the X-ray decay light-curve is either the curvature tail of the prompt emission; X-ray flaring activity; or external forward shock emission from a jet with high density regions of small angular size (> Gamma^{-1}). The late slope we associate with the forward external shock., 13 pages, 12 figures, accepted for publication in Astronomy & Astrophysics

Gamma-ray burst (GRB) progenitors are observationally linked to the death of massive stars. X-ray studies of the GRB afterglows can deepen our knowledge of the ionization status and metal abundances of the matter in the GRB environment. Moreover, the presence of local matter can be inferred through its fingerprints in the X-ray spectrum, i.e. the presence of absorption higher than the Galactic value. A few studies based on BeppoSAX and XMM-Newton found evidence of higher than Galactic values for the column density in a number of GRB afterglows. Here we report on a systematic analysis of 17 GRBs observed by Swift up to April 15, 2005. We observed a large number of GRBs with an excess of column density. Our sample, together with previous determinations of the intrinsic column densities for GRBs with known redshift, provides evidence for a distribution of absorption consistent with that predicted for randomly occurring GRB within molecular clouds., Comment: Accepted for publication on A&A (5 pages and 2 figures)

GRB 040422 was detected by the INTEGRAL satellite at an angle of only 3 degrees from the Galactic plane. Analysis of the prompt emission observed with the SPI and IBIS instruments on INTEGRAL are presented. The IBIS spectrum is well fit by the Band model with a break energy of Eo=56+/-2 keV and Epeak=41+/-3 keV. The peak flux is 1.8 10^(-7) erg/cm2/s and fluence 3.4 10^(-7) erg/cm2 in the range 20-200 keV. We then present the observations of the afterglow of GRB 040422, obtained with the ISAAC and FORS 2 instruments at the VLT less than 2 hours after the burst. We report the discovery of its near-infrared afterglow, for which we give here the astrometry and photometry. No detection could have been obtained in the R and I bands, partly due to the large extinction in the Milky Way. We re-imaged the position of the afterglow two months later in the Ks band, and detected a likely bright host galaxy. We compare the magnitude of the afterglow with a those of a compilation of promptly observed counterparts of previous GRBs, and show that the afterglow of GRB 040422 lies at the very faint end of the distribution, brighter only than that of GRB 021211, singled out later and in the optical bands, and GRB 040924 after accounting for Milky Way extinction. This observation suggests that the proportion of dark GRBs can be significantly lowered by a more systematic use of 8-m class telescopes in the infrared in the very early hours after the burst., Comment: 9 pages, 7 figures, accepted in A&A