EDP Sciences
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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'Avanzo3, 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 )

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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© ESO 2005