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Signs of magnetic acceleration and multizone emission in GRB 080825C
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Max-Planck-Institut für Physik, Germany.
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Department of Physics, Tokyo Metropolitan University, Japan.ORCID iD: 0000-0003-4378-8785
2016 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 458, no 2, 1728-1732 p.Article in journal (Refereed) Published
Abstract [en]

One of the major results from the study of gamma-ray bursts with the Fermi Gamma-ray Space Telescope has been the confirmation that several emission components can be present in the energy spectrum. Here, we reanalyse the spectrum of GRB 080825C using data from the Fermi-Large Area Telescope (LAT) and Gamma-ray Burst Monitor instruments. Although fairly weak, it is the first gamma-ray burst detected by the Fermi-LAT. We improve on the original analysis by using the LAT Low Energy events covering the 30–100 MeV band. We find evidence of an additional component above the main emission peak (modelled using a Band function) with a significance of 3.5σ in two out of the four time bins. The component is well fitted by a Planck function, but shows unusual behaviour: the peak energy increases in the prompt emission phase, reaching energies of several MeV. This is the first time such a trend has been seen, and implies that the origin of this component is different from those previously detected. We suggest that the two spectral components likely arise in different regions of the outflow, and that strong constraints can be achieved by assuming one of them originates from the photosphere. The most promising model appears to be that the high-energy peak is the result of photospheric emission in a Poynting flux dominated outflow where the magnetization increases with time.

Place, publisher, year, edition, pages
Oxford University Press, 2016. Vol. 458, no 2, 1728-1732 p.
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-184153DOI: 10.1093/mnras/stw432ISI: 000374569600046ScopusID: 2-s2.0-84963838545OAI: diva2:915130

QC 20160419

Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2016-06-09Bibliographically approved

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