Abstract
Gamma-ray bursts (GRBs) are the most violent explosion of massive stars in the universe discovered in 1967. Today, we still do not fully understand the emission mechanism of their prompt emission phase observed in gamma-ray energies. The idea of using synchrotron radiation from electrons to explain the observed GRB spectra is simple but problematic. In this study, we obtain 1,491 time-resolved spectra from the Fermi Gamma-ray Burst Monitor (Fermi GBM) and compute a novel quantity - the sharpness angle - around the spectral peaks or breaks. We compare the observed values to the values measured from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. We conclude that more than 90% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model. We found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58(+23/-18)% of the observed peak flux. Our results also show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase.
Coffee and tea will be served 20 minutes prior to the seminar.
Anyone interested is welcome to attend.