On-axis orphan afterglows
Abstract
In many GRB inner engine models the highly relativistic GRB jets are engulfed by slower moving matter. This could result in different beaming for the prompt γ-ray emission and for the lower energy afterglow. In this case we should expect that some observer will see on-axis orphan afterglows: X-ray, optical and radio afterglows within the initial relativistic ejecta with no preceding GRB; the prompt γ-ray emission is pointing elsewhere. We show that the observations of the WFC on BeppoSAX constrain with high certainty the prompt X-ray beaming factor to be less than twice the prompt γ-ray beaming. The results of Ariel 5 are consistent with this interpretation. The RASS from ROSAT and HEAO-1 constrain the X-ray beaming factor at 400 and 20 min after the burst, respectively, to be comparable and certainly not much larger than the γ-ray beaming factor. There is no direct limit on the optical beaming. However, we show that observations of several months with existing hardware could result in a useful limit on the optical beaming factor of GRB afterglows.
- Publication:
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New Astronomy
- Pub Date:
- February 2003
- DOI:
- 10.1016/S1384-1076(02)00202-6
- arXiv:
- arXiv:astro-ph/0207400
- Bibcode:
- 2003NewA....8..141N
- Keywords:
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- Astrophysics
- E-Print:
- 19 pages 5 figures. A revised and extended version, 3 new figures added