2006/05/31 by Asaf Pe’er, Asaf Pe'er, Bing Zhang · 5 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Cosmic Phenomena #Bremsstrahlung #Electron #Emission spectrum #Field (mathematics) #Gamma-ray bursts and supernovae #Magnetic field #Spectral line #Synchrotron #Synchrotron radiation #astro-ph
paper · pdf · doi:10.1086/508681
published as Astrophys.J.653:454-461,2006 · Extended explanation on alternative emission models, the radiative efficiency and derivation of eq. 2. Minor typos and English corrections; Accepted for publication in Ap.J
arxiv created 2006/08/25 · openalex publication_date 2006/12/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Synchrotron emission is believed to be a major radiation mechanism during gamma-ray bursts' (GRBs) prompt emission phase. A significant drawback of this assumption is that the theoretical predicted spectrum, calculated within the framework of the "internal shocks" scenario using the standard assumption that the magnetic field maintains a steady value throughout the shocked region, leads to a slope F ν ∝ ν -1/2 below 100 keV, which is in contradiction to the much harder spectra observed. This is due to the electron cooling time being much shorter than the dynamical time. In order to overcome this problem, we propose here that the magnetic field created by the internal shocks decays on a length scale much shorter than the comoving width of the plasma. We show that under this assumption synchrotron radiation can reproduce the observed prompt emission spectra of the majority of the bursts. We calculate the required decay length of the magnetic field, and find it to be ~10 4 -10 5 cm (equivalent to 10 5 -10 6 skin depths), much shorter than the characteristic comoving width of the plasma, ~3 × 10 9 cm. We implement our model to the case of GRB 050820A, where a break at ≲4 keV was observed, and show that this break can be explained by synchrotron self-absorption. We discuss the consequences of the small-scale magnetic field scenario on current models of magnetic field generation in shock waves.