A THEORY OF MULTICOLOR BLACKBODY EMISSION FROM RELATIVISTICALLY EXPANDING PLASMAS

Journal Article · Sun May 01 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/732/1/49· OSTI ID:21574623

Pe'er, Asaf ^[1]; Ryde, Felix ^[2]

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1. Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)
2. Department of Physics, Royal Institute of Technology, AlbaNova, SE-106 91 Stockholm (Sweden)

We consider the emission of photons from the inner parts of a relativistically expanding plasma outflow, characterized by a constant Lorentz factor, {Gamma}. Photons that are injected in regions of high optical depth are advected with the flow until they escape at the photosphere. Due to multiple scattering below the photosphere, the locally emerging comoving photon distribution is thermal. However, as an observer simultaneously sees photons emitted from different angles, hence with different Doppler boosting, the observed spectrum is a multicolor blackbody. We calculate here the properties of the observed spectrum at different observed times. Due to the strong dependence of the photospheric radius on the angle to the line of sight, for parameters characterizing gamma-ray bursts (GRBs) thermal photons are seen up to tens of seconds following the termination of the inner engine. At late times, following the inner engine termination, both the number flux and energy flux of the thermal spectrum decay as F{proportional_to}t{sup -2}. At these times, the multicolor blackbody emission results in a power law at low energies (below the thermal peak), with power-law index F{sub {nu}}{proportional_to}{nu}{sup 0}. We discuss the implications and limitations of this result in the study of GRBs.

• OSTI ID: 21574623
• Journal Information: Astrophysical Journal, Vol. 732, Issue 1; Other Information: DOI: 10.1088/0004-637X/732/1/49; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMIC GAMMA BURSTS
EMISSION
MULTIPLE SCATTERING
PHOTONS
PHOTOSPHERE
PLASMA
RADIANT HEAT TRANSFER
ATMOSPHERES
BOSONS
COSMIC RADIATION
ELEMENTARY PARTICLES
ENERGY TRANSFER
HEAT TRANSFER
IONIZING RADIATIONS
MASSLESS PARTICLES
PRIMARY COSMIC RADIATION
RADIATIONS
SCATTERING
SOLAR ATMOSPHERE
STELLAR ATMOSPHERES