The first image above (Credit: NASA/Swift/Mary Pat Hrybyk-Keith and John Jones) shows an artist's impression of a Gamma-ray Burst (GRB), the most energetic explosion in the Universe since the Big Bang. In a recent paper published in Nature Physics (06 April 2014), Prof. Bing Zhang and I made a theoretical breakthrough in understanding the radiation mechanism of GRB prompt emission. We showed that, when the magnetic field strength B in the emitting region decreases in time, the fast-cooling synchrotron spectrum is in fact in a non-steady state and becomes significantly harder than the "standard" one, thus becoming well consistent with the observed low-energy index of GRB prompt spectra. In the first column (model [a]) of the second figure above, we first reproduced the standard spectrum assuming a constant value of B. We then showed in the numerical models [b] - [d] that the fast-cooling spectrum gets indeed harder when the B value in the region decreases in time. For details, see http://www.nature.com/nphys/journal/v10/n5/abs/nphys2932.html.
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