Change search
ReferencesLink to record
Permanent link

Direct link
Upper limits on the high-energy emission from gamma ray bursts observed by AGILE-GRID
Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Show others and affiliations
2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 547, A95- p.Article in journal (Refereed) Published
Abstract [en]

Context. The detection and the characterization of the high energy emission component from individual gamma-ray bursts (GRBs) is one of the key science objectives of the currently operating gamma-ray satellite AGILE, launched in April 2007. In its first two years of operation AGILE detected three GRBs with photons of energy larger than 30 MeV. One more GRB was detected in AGILE third operation year, while operating in spinning mode. Aims. For the 64 other GRBs localized during the period July 2007 to October 2009 in the field of view of the AGILE Gamma-Ray Imaging Detector (GRID), but not detected by this instrument, we estimate the count and flux upper limits on the GRB high energy emission in the AGILE-GRID energy band (30 MeV-3 GeV). Methods. To calculate the count upper limits, we adopted a Bayesian approach. The flux upper limits are derived using several assumptions on the high-energy spectral behavior. For 28 GRBs with available prompt spectral information, a flux upper limit and the comparison with the expected flux estimated from spectral extrapolation of the Band spectrum to the 30 MeV-3 GeV band are provided. Moreover, upper limits on the flux under the assumption of an extra power law component dominating the 30 MeV-3 GeV band are calculated for all GRBs and considering four different values for the spectral photon index. Finally, we performed a likelihood upper limit on the possible delayed emission up to 1 h after the GRB. Results. The estimated flux upper limits range between 1 x 10(-4) and similar to 2 x 10(-2) photons cm(-2) s(-1) and generally lie above the flux estimated from the extrapolation of the prompt emission in the 30 MeV-3 GeV band. A notable case is GRB 080721, where the AGILE-GRID upper limit suggests a steeper spectral index or the presence of a cut-off in the high energy part of the Band prompt spectrum. The four GRBs detected by AGILE-GRID show high-energy (30 MeV-3 GeV) to low-energy (1 keV-10 MeV) fluence ratios similar to those estimated in this paper for the 64 GRBs without GRID detection, favoring the possibility that AGILE-GRID detected only high-fluence, hard GRBs. From the flux upper limits derived in this work we put some constraint on high-energy radiation from the afterglow emission and from synchrotron self Compton emission in internal shocks.

Place, publisher, year, edition, pages
2012. Vol. 547, A95- p.
Keyword [en]
gamma-ray burst: general
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-85527DOI: 10.1051/0004-6361/201016238ISI: 000311031700095OAI: diva2:585991


Available from: 2013-01-10 Created: 2013-01-08 Last updated: 2013-01-10Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text
By organisation
The Oskar Klein Centre for Cosmo Particle Physics (OKC)
In the same journal
Astronomy and Astrophysics
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 21 hits
ReferencesLink to record
Permanent link

Direct link