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Are Gamma-Ray Bursts a Standard Energy Reservoir?

Li L.- X.

Acta Astronomica

2008

Vol. 58, No. 2

103--112

One of the most important discoveries in the observation of gamma-ray bursts (GRBs) is that the total energy emitted by a GRB in γ-rays has a very narrow distribution around 1051 erg, which led people to claim that GRBs are standard energy explosions. As people made the claim they have ignored the selection biases which must be important since GRB observations are strongly fluence or flux-limited. In this paper we show that, when the selection effects are considered, the intrinsic distribution of the GRB energy can be very broad. The number of faint GRBs has been significantly underestimated because of the fluence or flux limit. The bright part of the distribution has been affected by another important selection effect arising from the beaming of GRB jets, which is instrument-independent and caused by the fact that brighter GRBs tend to have smaller jet angles and hence smaller probabilities to be detected. Our finding indicates that GRBs are not a standard energy reservoir, and challenges the proposal that GRBs can be used as standard candles to probe cosmology.

Protecting Life in the Milky Way: Metals Keep the GRBs Away

Stanek K. Z., Gnedin O. Y., Beacom J. F., Gould A. P., Johnson J. A., Kollmeier J. A., Modjaz M., Pinsonneault M. H., Pogge R., Weinberg D. H.

Acta Astronomica

2006

Vol. 56, No. 4

333--345

The host galaxies of the five local, z≤0.25, long-duration gamma-ray bursts (GRBs 980425, 020903, 030329, 031203 and 060218), each of which had a well-documented associated supernova, are all faint and metal-poor compared to the population of local star-forming galaxies. We quantify this statement by using a previous analysis of star-forming galaxies (0.005iso, steeply decreases with increasing host oxygen abundance. This might further indicate that (low) metallicity plays a fundamental physical role in the GRB phenomenon, and suggesting an upper metallicity limit for "cosmological" GRBs at ≈0.15 Z_solar.