Optical afterglow luminosities in the Swift epoch: confirming clustering and bimodality
Abstract
We show that gamma-ray bursts (GRBs) of known redshift and rest-frame optical extinction detected by the Swift satellite fully confirm earlier results concerning the distribution of the optical afterglow luminosity at 12h after trigger (rest-frame time). This distribution is bimodal and relatively narrow, especially for the high-luminosity branch. This is intriguing, given that Swift GRBs have, on average, a redshift larger than pre-Swift ones, and is unexpected in the common scenario explaining the GRB afterglow. We investigate if the observed distribution can be the result of selection effects affecting a unimodal parent luminosity distribution, and find that either the distribution is intrinsically bimodal, or most (60 per cent) of the bursts are absorbed by a substantial amount of grey dust. In both cases we suggest that most dark bursts should belong to the underluminous optical family.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2008
- DOI:
- 10.1111/j.1745-3933.2008.00467.x
- arXiv:
- arXiv:0801.4759
- Bibcode:
- 2008MNRAS.386L..87N
- Keywords:
-
- radiation mechanisms: non-thermal;
- dust;
- extinction;
- gamma-rays: bursts;
- Astrophysics
- E-Print:
- 5 pages 3 figures, minor revision, added reference, accepted for publication in MNRAS Letters