Peking University, Apr. 9, 2013: Gamma-ray bursts (GRBs) are most violent explosions in the universe since the Big Bang. Despite many years of observations and theoretical modeling, the exact mechanism to produce intense gamma-rays from these events is not identified.

In a paper published in Nature Physics this week, Z. Lucas Uhm and Bing Zhang made a theoretical breakthrough in understanding GRB emission. A typical GRB spectrum peaks in the sub-MeV range. Below this peak energy, the spectral index takes a mysterious value (-1), which is too soft for a quasi-thermal emission mechanism (+0.4 to +1) and too hard for "standard" synchrotron radiation in the strong magnetic field in the emission region (-1.5). Uhm and Zhang discovered that when considering the natural effect that the GRB jet is streaming away from the central engine so that the magnetic field strength in the emission region continuously decays with time, the synchrotron radiation spectrum is modified, which in a certain parameter regime can match the observed spectrum nicely. As a result, they identify synchrotron radiation as the leading mechanism to power GRBs. The emission site is far from the GRB central engine, where large scale magnetic fields are dissipated.

Contact:

Bing Zhang (Kavli Institute for Astronomy & Astrophysics / Department of Astronomy, Peking University, China / University of Nevada Las Vegas, USA)

Tel: 1-702-895-4050

E-mail: zhang@physics.unlv.edu

Z. Lucas Uhm (Kavli Institute for Astronomy & Astrophysics, Peking University, China)

E-mail: uhm@pku.edu.cn

Link: http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2932.html

Source: Kavli Institute for Astronomy & Astrophysics