Evidence of Contribution of Intervening Clouds to Gamma-Ray Burst's X-Ray Column Density
Abstract
The origin of excess of X-ray column density with respect to optical extinction in gamma-ray bursts (GRBs) is still a puzzle. A proposed explanation of the excess is the photoelectric absorption due to the intervening clouds along a GRB's line of sight. Here, we test this scenario by using the intervening Mg II absorption as a tracer of the neutral hydrogen column density of the intervening clouds. We identify a connection between the large X-ray column density (and large column density ratio of {log (N_{H,X}/N_{H\,\scriptsize{I}})}\sim 0.5) and large neutral hydrogen column density probed by the Mg II doublet ratio (DR). In addition, GRBs with large X-ray column density (and large ratio of {log (N_{H,X}/N_{H\,\scriptsize{I}})}\gt0) tend to have multiple saturated intervening absorbers with DR < 1.2. These results therefore indicate an additional contribution from the intervening system to the observed X-ray column density in some GRBs, although the contribution from the host galaxy alone cannot be excluded based on this study.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2013
- DOI:
- 10.1088/0004-637X/776/2/96
- arXiv:
- arXiv:1308.3931
- Bibcode:
- 2013ApJ...776...96W
- Keywords:
-
- gamma-ray burst: general;
- intergalactic medium;
- methods: statistical;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 16 pages, 5 figures, 1 table, accepted by ApJ