2007/03/31 by Asaf Pe'er, Felix Ryde, Ralph A. M. J. Wijers +2 · 6 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Cosmic Phenomena #Component (thermodynamics) #Energy flux #Flux (metallurgy) #Gamma-ray burst #Gamma-ray bursts and supernovae #Lorentz factor #Outflow #Redshift #Thermal #Thermal emission #astro-ph
paper · pdf · doi:10.1086/520534
published as Astrophys.J.664:L1,2007 · Discussion added on gamma-ray emission efficiency. Accepted for publication in Ap.J. Lett
arxiv created 2007/06/05 · openalex publication_date 2007/06/27 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
In recent years, increasing evidence has emerged for a thermal component in the γ- and X-ray spectrum of the prompt emission phase in gamma-ray bursts. The temperature and flux of the thermal component show a characteristic break in the temporal behavior after a few seconds. We show here that measurements of the temperature and flux of the thermal component at early times (before the break) allow the determination of the values of two of the least restricted fireball model parameters: the size at the base of the flow and the outflow bulk Lorentz factor. Relying on the thermal emission component only, this measurement is insensitive to the inherent uncertainties of previous estimates of the bulk motion Lorentz factor. We give specific examples of the use of this method: for GRB 970828 at redshift z = 0.9578, we show that the physical size at the base of the flow is r 0 = (2.9 ± 1.8) × 10 8 Y cm and the Lorentz factor of the flow is Γ = (305 ± 28) Y , and for GRB 990510 at z = 1.619, r 0 = (1.7 ± 1.7) × 10 8 Y cm and Γ = (384 ± 71) Y , where Y = 1 Y 0 is the ratio between the total fireball energy and the energy emitted in γ-rays.