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Astron. Astrophys. 328, L21-L24 (1997)

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Letter to the Editor

Gamma-ray bursts: towards a standard candle luminosity

J-L. Atteia

Centre d'Etude Spatiale des Rayonnements (CNRS/UPS), BP 4346, F-31028 Toulouse Cedex 4, France (e-mail: atteia@cesr.cnes.fr)

Received 7 July 1997 / Accepted 2 October 1997

Abstract

It is usual, in gamma-ray burst (GRB) studies, to compare the average properties of bright and faint GRBs, with the assumption that brightness classes reflect distance classes. When brightness is intented to reflect the distance to the sources, it is nevertheless important to use a quantity with a small intrinsic dispersion. We propose here a method to compare the intrinsic dispersion of various measures of GRB brightness. This method assumes that nearby bursters are homogeneously distributed in an Euclidean space with no density or luminosity evolution. We then use it to compare 5 measures of GRB brightness in the BATSE Catalog. Our analysis reveals that better (i.e. less dispersed) measures of brightness are obtained at low energy and that GRBs are much closer to standard candles below 100 keV than above. We suggest that a beaming of the emission above 100 keV could explain this behaviour.

Key words: Gamma-rays: bursts

Send offprint requests to: J-L. Atteia

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© European Southern Observatory (ESO) 1997

Online publication: March 26, 1998

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