Shallow decay phase of GRB X-ray afterglows from relativistic wind bubbles
Abstract
Aims:The postburst object of a GRB is likely to be a highly magnetized, rapidly rotating compact object (e.g., a millisecond magnetar), which could produce an ultrarelativistic electron-positron-pair wind. The interaction of such a wind with an outwardly expanding fireball ejected during the burst leads to a relativistic wind bubble (RWB). We investigate the properties of RWBs and use this model to explain the shallow decay phase of the early X-ray afterglows observed by Swift.
Methods: We numerically calculate the dynamics and radiative properties of RWBs.
Results: We find that RWBs can fall into two types: forward-shock-dominated and reverse-shock-dominated bubbles. Their radiation during a period of ~102-105 s is dominated by the shocked medium and the shocked wind, respectively, based on different magnetic energy fractions of the shocked materials. For both types, the resulting light curves always have a shallow decay phase, as discovered by Swift. In addition, we provide an example fit to the X-ray afterglows of GRB 060813 and GRB 060814 and show that they could be produced by forward-shock-dominated and reverse-shock-dominated bubbles, respectively. This implies that, for some early afterglows (e.g., GRB 060814), the long-lasting reverse shock emission is strong enough to explain their shallow decay phase.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2007
- DOI:
- 10.1051/0004-6361:20077053
- arXiv:
- arXiv:0705.1108
- Bibcode:
- 2007A&A...470..119Y
- Keywords:
-
- gamma rays: burst;
- relativity;
- shock waves;
- stars: winds;
- outflows;
- Astrophysics
- E-Print:
- 5 pages, 4 figures, Accepted for Publication in A&