EDP Sciences
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Volume 415, Number 2, February IV 2004
Page(s) 443 - 450
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20034626

A&A 415, 443-450 (2004)
DOI: 10.1051/0004-6361:20034626

Reconsidering the origin of the X-ray emission lines in GRB 011211

F. Tavecchio1, G. Ghisellini1 and D. Lazzati2

1  INAF-Osserv. Astron. di Brera, via Bianchi 46, 23807 Merate, Italy
2  Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK

(Received 14 May 2003 / Accepted 29 September 2003)

We reanalyze the XMM-Newton data of GRB 011211 showing that the spectral features, interpreted by Reeves et al. (2002, 2003) as due to thermal emission from a collisionally ionized plasma, can be also reproduced by a reflection model (with ionization parameter $\xi\sim 10^2$). We discuss the implications of this interpretation, estimating the total mass required in the simplified case of a funnel geometry. We conclude that a moderate clumping of the reprocessing material (corresponding to a filling factor of the order of $f\sim 10^{-3}$) is required. Finally we show that, if this interpretation is correct, a bright quasi-thermal component is expected in the optical-UV band (containing about $90\%$ of the luminosity of the illuminating continuum), whose presence can be used to test the reflection model.

Key words: gamma rays: bursts -- line: formation -- radiation mechanisms: general

Offprint request: F. Tavecchio, tavecchio@merate.mi.astro.it

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