Title:	The dark nature of GRB 051022 and its host galaxy
Authors:	Castro-Tirado, A.J. Bremer, M. McBreen, S. Kamble, Atish P. Bhattacharya, D. +17 Co-authors
Keywords:	gamma rays: bursts techniques: photometric techniques: spectroscopic X-rays: general cosmology: observations
Issue Date:	Nov-2007
Publisher:	EDP Sciences for ESO
Citation:	Astronomy and Astrophysics, 2007, Vol.475, p101
Abstract:	Aims.We present multiwavelength (X-ray/optical/near-infrared/millimetre) observations of GRB 051022 between 2.5 h and 1.15 yr after the event. It is the most intense gamma-ray burst ( 10-4 erg cm-2) detected by HETE-2, with the exception of the nearby GRB 030329. Methods: Optical and near infrared observations did not detect the afterglow despite a strong afterglow at X-ray wavelengths. Millimetre observations at Plateau de Bure (PdB) detected a source and a flare, confirming the association of this event with a moderately bright (R = 21.5) galaxy. Results: Spectroscopic observations of this galaxy show strong [O II], Hβ and [O III] emission lines at a redshift of 0.809. The spectral energy distribution (SED) of the galaxy implies AV (rest frame) = 1.0 and a starburst occuring 25 Myr ago, during which the star-forming-rate reached 50 Mȯ/yr. In conjunction with the spatial extent ( 1'') it suggests a very luminous (MV = - 21.8) blue compact galaxy, for which we also find Z˜ Z_ȯ. The X-ray spectrum shows evidence of considerable absorption by neutral gas with NH, X-ray = 3.47+0.48-0.47 × 1022 cm-2 (rest frame). Absorption by dust in the host galaxy at z = 0.809 certainly cannot account for the non-detection of the optical afterglow, unless the dust-to-gas ratio is quite different than that seen in our Galaxy (i.e. large dust grains). Conclusions: It is likely that the afterglow of the dark GRB 051022 was extinguished along the line of sight by an obscured, dense star forming region in a molecular cloud within the parent host galaxy. This galaxy is different from most GRB hosts being brighter than L* by a factor of 3. We have also derived a {SFR} ˜ 50 M_ȯ/yr and predict that this host galaxy will be detected at sub-mm wavelengths. Based on observations taken with the 1.0 m telescope at ARIES, with the 2.0 m telescope at Hanle, with the 1.5 m Carlos Sánchez at Observatorio del Teide, with the 1.5 m telescope at Observatorio de Sierra Nevada, with the 3.5 m Telescope at the Spanish-German Calar Alto Observatory, with the 3.5 m Telescopio Nazionale Galileo, with the 4.2 m William Herschel telescope, at the Observatorio del Roque de los Muchachos in La Palma, and with the 6.0 m Bolshoi Azimuthal Telescope at the Special Astrophysical Observatory in Zelenchukskaya.
Description:	Open Access.
URI:	http://hdl.handle.net/2289/3488
ISSN:	E-ISSN: 1432-0746 P-ISSN: 0004-6361
Alternative Location:	http://arxiv.org/abs/astro-ph/arXiv:0708.3043 http://dx.doi.org/10.1051/0004-6361:20066748 http://adsabs.harvard.edu/abs/2007A%26A...475..101C
Copyright:	2007 European Southern Observatory
Appears in Collections:	Research Papers (A&A)

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