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13-18 December 2015
International Conference Centre Geneva
Europe/Zurich timezone

Constraining emission mechanisms in gamma-ray bursts using spectral width

14 Dec 2015, 17:35
Level 2, Room 7&8 (International Conference Centre Geneva)

Level 2, Room 7&8

International Conference Centre Geneva

17 Rue de Varembé, 1211 Geneva


Magnus Axelsson


The emission processes active in the highly relativistic jets of gamma-ray bursts (GRBs) remain unknown. The spectra are usually well-fit by the Band function, an empirically motivated smoothly-broken power law, yet this gives little understanding of the underlying radiation mechanisms. In this talk we propose a new measure to describe spectra: the width of the EFE spectrum, a quantity dependent only on finding a good fit to the data. We apply this to the full sample of peak flux GRB spectra observed by CGRO/BATSE combined with the 2nd Fermi/GBM catalog. The results from the two instruments are fully consistent. We find that 78% of long GRBs and 85% of short GRBs cannot be explained by standard slow cooling synchrotron from a Maxwellian distribution of electrons, and almost half the spectra are more narrow that monoenergetic synchrotron. Conversely, photospheric emission can explain the spectra if mechanisms are invoked to give a spectrum much broader than a blackbody. We further find that the median widths of spectra from long and short GRBs are significantly different, and this is thus a new, independent distinction between the two classes. We will discuss the implications of theseresults and the constraints they place on possible emission mechanisms.

Primary author


Dr Luis Borgonovo (Stockholm University)

Presentation Materials