KLEIN-NISHINA EFFECTS ON OPTICALLY THIN SYNCHROTRON AND SYNCHROTRON SELF-COMPTON SPECTRUM

Journal Article · Sun Sep 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/1/675· OSTI ID:21371985

Nakar, Ehud ^[1]; Ando, Shin'ichiro; Sari, Re'em ^[2]

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1. Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel)
2. California Institute of Technology, Mail Code 130-33, Pasadena, CA 91125 (United States)

We present analytic approximations to the optically thin synchrotron and synchrotron self-Compton (SSC) spectra when Klein-Nishina (KN) effects are important and pair production and external radiation fields can be neglected. This theory is useful for analytical treatment of radiation from astrophysical sources, such as gamma-ray bursts (GRBs), active galactic nuclei, and pulsar wind nebula, where KN effects may be important. We consider a source with continuous injection of relativistic electrons with a power-law energy distribution above some typical injection energy. We find that the synchrotron-SSC spectra can be described by a broken power law, and provide analytic estimates for the break frequencies and power-law indices. In general, we show that the dependence of the KN cross section on the energy of the upscattering electron results in a hardening of the energy distribution of fast cooling electrons and therefore in a hardening of the observed synchrotron spectrum. As a result the synchrotron spectrum of fast cooling electrons, below the typical injection energy, can be as hard as F{sub n}u propor to nu{sup 0}, instead of the classical nu{sup -1/2} when KN effects are neglected. The synchrotron energy output can be dominated by electrons with energy above the typical injection energy. We solve self-consistently for the cooling frequency and find that the transition between synchrotron and SSC cooling can result in discontinuous variations of the cooling frequency and the synchrotron and SSC spectra. We demonstrate the application of our results to theory by applying them to prompt and afterglow emission models of GRBs.

• OSTI ID: 21371985
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 703; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AFTERGLOW
APPROXIMATIONS
ASTROPHYSICS
CALCULATION METHODS
COSMIC GAMMA BURSTS
COSMIC RADIATION
COSMIC RADIO SOURCES
CROSS SECTIONS
ELECTRONS
ELEMENTARY PARTICLES
ENERGY RANGE
ENERGY SPECTRA
FERMIONS
GALAXIES
GALAXY NUCLEI
IONIZING RADIATIONS
LEPTONS
NEBULAE
PHYSICS
PRIMARY COSMIC RADIATION
PULSARS
RADIATIONS
RELATIVISTIC RANGE
SPECTRA
TAIL ELECTRONS