Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-12-12
Astrophys.J. 592 (2003) 1018-1024
Astronomy and Astrophysics
Astrophysics
19 pages, 5 figures. To be published in The Astrophysical Journal
Scientific paper
10.1086/375854
We have examined the complete set of X-ray afterglow observations of dark and optically bright GRBs performed by BeppoSAX until February 2001. X-ray afterglows are detected in 90% of the cases. We do not find significant differences in the X-ray spectral shape, in particular no higher X-ray absorption in GRBs without optical transient (dark GRBs) compared to GRBs with optical transient (OTGRBs). Rather, we find that the 1.6-10 keV flux of OTGRBs is on average about 5 times larger than that of the dark GRBs. A K-S test shows that this difference is significant at 99.8% probability. Under the assumption that dark and OTGRB have similar spectra, this could suggest that the first are uncaught in the optical band because they are just faint sources. In order to test this hypothesis, we have determined the optical-to-X ray flux ratios of the sample. OTGRBs show a remarkably narrow distribution of flux ratios, which corresponds to an average optical-to-x spectral index 0.794\pm 0.054. We find that, while 75% of dark GRBs have flux ratio upper limits still consistent with those of OT GRBs, the remaining 25% are 4 - 10 times weaker in optical than in X-rays. The significance of this result is equal to or higher than 2.6 sigma. If this sub-population of dark GRBs were constituted by objects assimilable to OTGRBs, they should have shown optical fluxes higher than upper limits actually found. We discuss the possible causes of their behaviour, including a possible occurrence in high density clouds or origin at very high redshift and a connection with ancient, Population III stars.
't Zand Jean in
Antonelli Lucio Angelo
Costa Edgar
de Pasquale Massimiliano
Feroci Marco
No associations
LandOfFree
A comparative study of the X-ray afterglow properties of optically bright and dark GRBs does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A comparative study of the X-ray afterglow properties of optically bright and dark GRBs, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A comparative study of the X-ray afterglow properties of optically bright and dark GRBs will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-403972