Fermi/Swift GRB Symposium 2012: Polarisation and thermal emission in GRBs

The Fermi/Swift gamma-ray burst Symposium 2012 was held in Munich 7-11 May 2012.

Recent results on the prompt and afterglow emissions in gamma-ray burst were discussed at the Fermi/Swift gamma-ray burst Symposium 2012 which was held in Munich 7-11 May 2012.

Among the most important issues presented was the recent gamma-polarisation measurement with IKAROS-GAP. Significant degrees of polarisation in several bursts have now been detected. In particular, the change in polarisation angle was significantly detected. It was speculated that this is due to variation in emission patches in very narrowly collimated jets.

Another point which gained a lot of attention was on the existence of thermal components in GRB spectra. Previously the leading model for the prompt emission has been optically thin synchrotron emission. However, amounting observational evidence is showing that the photosphere in the relativistic flow is responsible for, at least a part of, the observed emission. Also recent progress in the theory and numerical simulations of relativistic jet was presented, and again thermal emission seems to be unavoidable.

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Conference website

Gamma ray spectrum of GRB110721A
Gamma-ray spectrum of GRB110721A which will soon be presented in a Fermi publication led by Magnus Axelsson. In addition to the dominant broad component, there is a bump at lower energies which is likely emission from the photosphere. The spectrum cannot be explained by synchrotron emission and thus disproves the long-held view that synchrotron emission alone can explain GRB spectra.

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