Low-luminosity gamma-ray bursts as a distinct GRB population: a firmer case from multiple criteria constraints
Abstract
The intriguing observations of the Swift/Burst Alert Telescope (BAT) X-ray flash (XRF) 060218 and the BATSE-BeppoSAX gamma-ray burst GRB 980425, both with much lower luminosity and redshift compared to other observed bursts, naturally lead to the question of how these low-luminosity (LL) bursts are related to high-luminosity (HL) bursts. Incorporating the constraints from both the flux-limited samples observed with Compton Gamma-ray Observatory (CGRO)/BATSE and Swift/BAT and the redshift-known gamma-ray burst (GRB) sample, we investigate the luminosity function for both LL and HL GRBs through simulations. Our multiple criteria, including the logN - logP distributions from the flux-limited GRB sample, the redshift and luminosity distributions of the redshift-known sample and the detection ratio of HL and LL GRBs with Swift/BAT, provide a set of stringent constraints to the luminosity function. Assuming that the GRB rate follows the star formation rate (SFR), our simulations show that a simple power law (PL) or a broken power-law model of luminosity function fails to reproduce the observations and a new component is required. This component can be modelled with a broken power, which is characterized by a sharp increase in the burst number at around L < 1047 erg s-1. The lack of detection of moderate-luminosity GRBs at redshift ~0.3 indicates that this feature is not due to the observational biases. The inferred local rate, ρ0, of LL GRBs from our model is ~200 Gpc-3 yr-1 at ~1047 erg s-1, much larger than that of HL GRBs. These results imply that LL GRBs could be a separate GRB population from HL GRBs. The recent discovery of a local X-ray transient 080109/SN 2008D would strengthen our conclusion if the observed non-thermal emission has a similar origin as the prompt emission of most GRBs and XRFs.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2009
- DOI:
- 10.1111/j.1365-2966.2008.14063.x
- arXiv:
- arXiv:0801.4751
- Bibcode:
- 2009MNRAS.392...91V
- Keywords:
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- gamma-rays: bursts;
- gamma-ray: observations;
- methods: statistical;
- Astrophysics
- E-Print:
- 22 pages, 9 figures, 3 tables