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Issue A&A
Volume 398, Number 3, February II 2003
Page(s) 919 - 925
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021724



A&A 398, 919-925 (2003)
DOI: 10.1051/0004-6361:20021724

Gamma photometric redshifts for long gamma-ray bursts

Z. Bagoly1, I. Csabai2, A. Mészáros3, P. Mészáros4, I. Horváth5, L. G. Balázs6 and R. Vavrek7

1  Laboratory for Information Technology, Eötvös University, 1117 Budapest, Pázmány P. s. 1./A, Hungary
    e-mail: bagoly@ludens.elte.hu
2  Dept. of Physics for Complex Systems, Eötvös University, 1117 Budapest, Pázmány P. s. 1./A, Hungary
    e-mail: csabai@ludens.elte.hu
3  Astronomical Institute of the Charles University, V Holesovickách 2, 180 00 Prague 8, Czech Republic
    e-mail: meszaros@mbox.cesnet.cz
4  Dept. of Astronomy & Astrophysics, Pennsylvania State University, 525 Davey Lab., University Park, PA 16802, USA
    e-mail: nnp@astro.psu.edu
5  Dept. of Physics, Bolyai Military University, 1456 Budapest, POB 12, Hungary
    e-mail: hoi@bjkmf.hu
6  Konkoly Observatory, 1505 Budapest, POB 67, Hungary
    e-mail: balazs@ogyalla.konkoly.hu
7  Max-Planck-Institut für Astronomie, 69117 Heidelberg, 17 Königstuhl, Germany
    e-mail: vavrek@mpia-hd.mpg.de

(Received 28 June 2002 / Accepted 18 November 2002 )

Abstract
It is known that the soft tail of the gamma-ray bursts' spectra show excesses from the exact power-law dependence. In this article we show that this departure can be detected in the peak flux ratios of different BATSE DISCSC energy channels. This effect allows to estimate the redshift of the bright long gamma-ray bursts in the BATSE Catalog. A verification of these redshifts is obtained for the 8 GRB which have both BATSE DISCSC data and measured optical spectroscopic redshifts. There is good correlation between the measured and estimated redshifts, and the average error is $\Delta z \approx 0.33$. The method is similar to the photometric redshift estimation of galaxies in the optical range, hence it can be called as "gamma photometric redshift estimation". The estimated redshifts for the long bright gamma-ray bursts are up to $z \simeq 4$. For the the faint long bursts - which should be up to $z \simeq 20$ - the redshifts cannot be determined unambiguously with this method.


Key words: cosmology: large-scale structure of Universe -- gamma-rays: bursts

Offprint request: Z. Bagoly, bagoly@ludens.elte.hu

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