Prompt emission of high-energy photons from gamma ray bursts

Gupta, Nayantara; Zhang, Bing

Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/4473

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DC Field	Value	Language
dc.contributor.author	Gupta, Nayantara	-
dc.contributor.author	Zhang, Bing	-
dc.date.accessioned	2012-05-08T04:50:57Z	-
dc.date.available	2012-05-08T04:50:57Z	-
dc.date.issued	2007-09	-
dc.identifier.citation	Monthly Notices of the Royal Astronomical Society, 2007, Vol.380, p78	en
dc.identifier.issn	0035-8711	-
dc.identifier.issn	1365-2966 (Online)	-
dc.identifier.uri	http://hdl.handle.net/2289/4473	-
dc.description	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)	en
dc.description.abstract	Within the internal shock scenario, we consider different mechanisms of high-energy (>1 MeV) photon production inside a gamma ray burst (GRB) fireball and derive the expected high-energy photon spectra from individual GRBs during the prompt phase. The photon spectra of leptonic and hadronic origins are compared within different sets of parameter regimes. Our results suggest that the high-energy emission is dominated by the leptonic component if the fraction of shock energy carried by electrons is not very small (e.g. ɛe > 10-3). For very small values of ɛe, the hadronic emission component could be comparable to or even exceed the leptonic component in the GeV-TeV regime. However, in this case a much larger energy budget of the fireball is required to account for the same level of the observed sub-MeV spectrum. The fireballs are therefore extremely inefficient in radiation. For a canonical fireball bulk Lorentz factor (e.g. Γ = 400), emissions above ~10 GeV are attenuated by two-photon pair production processes. For a fireball with an even higher Lorentz factor, the cut-off energy is higher, and emissions of 10 TeV-PeV due to π0-decay can also escape from the internal shocks. The flux level is, however, too low to be detected by current TeV detectors, and these photons also suffer attenuation by external soft photons. The GLAST Large Area Telescope can detect prompt emission of bright long GRBs above 100 MeV. For short GRBs, the prompt emission can be only barely detected for nearby bright ones with relatively `long' durations (e.g. ~1 s). With the observed high-energy spectrum alone, it appears that there is no clean picture to test the leptonic versus hadronic origin of the gamma rays. Such an issue may be, however, addressed by collecting both prompt and afterglow data. A moderate-to-high radiative efficiency would suggest a leptonic origin of high-energy photons, while a GRB with an extremely low radiative efficiency but an extended high-energy emission component would be consistent with (but not a proof for) the hadronic origin.	en
dc.language.iso	en	en
dc.publisher	Royal Astronomical Society	en
dc.relation.uri	http://adsabs.harvard.edu/abs/2007MNRAS.380...78G	en
dc.relation.uri	http://arxiv.org/abs/0704.1329	en
dc.relation.uri	http://dx.doi.org/10.1111/j.1365-2966.2007.12051.x	en
dc.rights	2007 Royal Astronomical Society	en
dc.subject	gamma-rays: bursts	en
dc.title	Prompt emission of high-energy photons from gamma ray bursts	en
dc.type	Article	en
Appears in Collections:	Research Papers (A&A)

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