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The metallicity of gamma-ray burst environments from high-energy observations
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2011 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 527, A104- p.Article in journal (Refereed) Published
Abstract [en]

Gamma-ray bursts (GRBs) and their early afterglows ionise their circumburst material. Only high-energy spectroscopy therefore, allows examination of matter close to the burst itself. Soft X-ray absorption allows an estimate to be made of the total column density in metals. The detection of the X-ray afterglow can also be used to place a limit on the total gas column along the line of sight based on the Compton scattering opacity. Such a limit would enable, for the first time, the determination of lower limits on the metallicity in the circumburst environments of GRBs. In this paper, we determine the limits that can be placed on the total gas column density in the vicinities of GRBs based on Compton scattering. We simulate the effects of Compton scattering on a collimated beam of high-energy photons passing through a shell of high column-density material to determine the expected lightcurves, luminosities, and spectra. We compare these predictions to observations, and determine what limits can be placed on the total gas column density. The smearing out of pulses in the lightcurve from Compton scattering is not likely to be observable, and its absence does not place strong constraints on the Compton depth. However, the distribution of observed luminosities of bursts allows us to place statistical, model-dependent limits that are typically less than or similar to 10(25) cm(-2) for less luminous bursts, and as low as similar to 10(24) cm(-2) for the most luminous. By using the shape of the high-energy broadband spectrum, however, limits as low as similar to 5 x 10(24) cm(-2) can be placed on individual bursts, implying metallicity lower limits from X-and gamma-rays alone from 0 up to 0.01 Z/Z(circle dot). At extremely high redshifts, this limit would be at least 0.02 Z/Z(circle dot), enough to distinguish population III from non-primordial GRBs.

Place, publisher, year, edition, pages
2011. Vol. 527, A104- p.
Keyword [en]
gamma-ray burst: general, gamma-ray burst: individual: GRB 050904, early Universe, galaxies: ISM, dark ages, reionisation, first stars, stars: Population III
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-67900DOI: 10.1051/0004-6361/201016050ISI: 000287484100119OAI: diva2:472122
authorCount :2Available from: 2012-01-03 Created: 2012-01-02 Last updated: 2012-01-03Bibliographically approved

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Laursen, Peter
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