XMM-Newton and VLT observations of the afterglow of GRB 040827

Author(s): De Luca, A; Melandri, A; Caraveo, PA; et al.

Source: ASTRONOMY & ASTROPHYSICS  Volume: 440   Issue: 1   Pages: 85-92   DOI: 10.1051/0004-6361:20052884   Published: SEP 2005

The field of the Gamma-Ray Burst GRB040827 was observed with XMM-Newton and with the ESO/VLT starting similar to 6 and similar to 12 h after the burst, respectively. A fading X-ray afterglow is clearly detected with the XMM-Newton/EPIC instrument, with a time decay t(-delta), with delta = 1.41 +/- 0.10. Its spectrum is well described by a power law (photon index Gamma = 2.3 +/- 0.1) affected by an absorption largely exceeding (by a factor similar to 5) the expected Galactic one, requiring the contribution of an intrinsic, redshifted absorber. In the optical/NIR range, the afterglow emission was observed in the K-s band as a weak source superimposed on the host galaxy, with magnitude K-s = 19.44 +/- 0.13 (12 h after the GRB, contribution from the host subtracted); in other bands the flux is dominated by the host galaxy. Coupling constraints derived from X-ray spectral fitting and from photometry of the host, we estimated a gas column density in the range (0.4-2.6) x 10(22) cm(-2) in the GRB host galaxy, likely located at a redshift 0.5 < z < 1.7. GRB040827 stands out as the best example of an X-ray afterglow with intrinsic absorption.