Constraining the environment of GRB 990712 through emission line fluxes

Free access article

Issue		A&A Volume 457, Number 1, October I 2006


Page(s)		115 - 119
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20065672

A&A 457, 115-119 (2006)
DOI: 10.1051/0004-6361:20065672

Constraining the environment of GRB 990712 through emission line fluxes

A. Küpcü Yoldas¹, J. Greiner¹ and R. Perna²

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
e-mail: ayoldas@mpe.mpg.de
² JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, 440 UCB, Boulder 80309, USA

(Received 23 May 2006 / Accepted 27 June 2006 )

Abstract
Aims.The energy output in the gamma-ray burst (GRB) prompt emission and afterglow phase is expected to photoionize the surrounding medium out to large radii. Cooling of this gas produces line emission that is particularly strong in the optical, whose variability is a strong diagnostics of the gas density and geometry in the close environment of the burst.
Methods.We present the results of a spectral time-series analysis of the host galaxy of GRB 990712 observed up to ~6 years after the burst. We analyze the emission line fluxes, together with those of the previous observations of the same GRB, in search of photoionization signatures.
Results.We find that the emission line fluxes show no variation within the uncertainties up to 6 years after the burst, and we use the measured line intensities to set a limit on the density of the gas within a few parsecs of the burst location. This is the first time that emission from cooling GRB remnants is probed on time scales of years.

Key words: gamma rays: bursts -- stars: circumstellar matter

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