2013/03/31 by Z. Lucas Uhm, Bing Zhang · 197 citations
Physics and Astronomy · #Astrophysics #Astrophysics and Cosmic Phenomena #Atomic physics #Electron #Flux (metallurgy) #Gamma-ray burst #Gamma-ray bursts and supernovae #Magnetic field #Nuclear physics #Optics #Photon #Physics #Pulsars and Gravitational Waves Research #Quantum mechanics #RADIUS #Radiation #Synchrotron #Synchrotron radiation #astro-ph.HE
paper · pdf · doi:10.1038/nphys2932
published in Nature Physics 10(5), 351-356 (Nature Portfolio) · Accepted for publication in Nature Physics. This version is the original submitted version. A refereed version (with minor revision) will appear in Nature Physics
arxiv created 2014/02/27 · openalex publication_date 2014/04/05 · arxiv updated 2015/06/15 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling time scale tc is shorter than the dynamical time scale tdyn, electrons are cooled down below the minimum injection energy. It has been believed that such "fast cooling" electrons have an energy distribution dNe /dγe ∝ γe-2, and their synchrotron radiation flux density has a spectral shape Fν∝ ν-1/2. On the other hand, in a transient expanding astrophysical source, such as a gamma-ray burst (GRB), the magnetic field strength in the emission region continuously decreases with radius. Here we study such a system, and find that in a certain parameter regime, the fast cooling electrons can have a harder energy spectrum, and the standard d Ne / d γe ∝ γe-2 spectrum is achieved only in the deep fast cooling regime when tc ≪ tdyn. We apply this new physical regime to GRBs, and suggest that the GRB prompt emission spectra whose low-energy photon index α has a typical value -1 could be due to synchrotron radiation in this moderately fast cooling regime.