Gamma-ray bursts: towards a standard candle luminosity

TL;DR

This paper introduces a method to compare the intrinsic dispersion of different gamma-ray burst brightness measures, revealing that GRBs are closer to standard candles below 100 keV, which could be due to emission beaming.

Contribution

It proposes a new method to assess the intrinsic dispersion of GRB brightness measures and applies it to show GRBs are more standard candles at lower energies.

Findings

Lower energy brightness measures have less dispersion.

GRBs are closer to standard candles below 100 keV.

Beaming may explain energy-dependent brightness dispersion.

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.