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

Free access article

Issue		A&A Volume 440, Number 1, September II 2005


Page(s)		85 - 92
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20052884

A&A 440, 85-92 (2005)
DOI: 10.1051/0004-6361:20052884

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

A. De Luca¹, A. Melandri², P. A. Caraveo¹, D. Götz¹, S. Mereghetti¹, A. Tiengo¹, L. A. Antonelli², S. Campana³, G. Chincarini³, S. Covino³, P. D'Avanzo^{3, 4}, A. Fernandez-Soto⁵, D. Fugazza³, D. Malesani⁶, L. Stella² and G. Tagliaferri³

¹ INAF - Istituto di Astrofisica spaziale e Fisica Cosmica, sez. di Milano "G. Occhialini", via Bassini 15, 20133 Milano, Italy
e-mail: deluca@mi.iasf.cnr.it
² INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone (Rome), Italy
³ INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (LC), Italy
⁴ Università degli Studi dell'Insubria, Dipartimento di Fisica e Matematica, via Valleggio 11, 22100 Como, Italy
⁵ Observatori Astrònomic, Universitat de València, 46100 València, Spain
⁶ International School for Advanced Studies (SISSA-ISAS), via Beirut 2-4, 34014 Trieste, Italy

(Received 15 February 2005 / Accepted 8 May 2005 )

Abstract
The field of the Gamma-Ray Burst GRB 040827 was observed with XMM-Newton and with the ESO/VLT starting ~6 and ~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 $\delta=1.41\pm0.10$ . Its spectrum is well described by a power law (photon index $\Gamma=2.3\pm0.1$ ) affected by an absorption largely exceeding (by a factor ~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 $K_{\rm s}$ band as a weak source superimposed on the host galaxy, with magnitude $K_{\rm s} = 19.44 \pm 0.13$ (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 $(0.4{-}2.6)\times10^{22}$ cm^-2 in the GRB host galaxy, likely located at a redshift 0.5<z<1.7. GRB 040827 stands out as the best example of an X-ray afterglow with intrinsic absorption.

Key words: gamma rays: bursts -- X-rays: general

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