Nakar, Ehud and Ando, Shin'ichiro and Sari, Re'em (2009) Klein–Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum. Astrophysical Journal, 703 (1). pp. 675-691. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20091002-114343770
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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_ν α ν^0, instead of the classical ν^(–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.
|Additional Information:||© 2009. The American Astronomical Society. Received 2009 January 1, accepted for publication 2009 July 31 Published 2009 August 31. We thank Tsvi Piran, PawanKumar, and Orly Gnat for helpful discussions. R.S.was partially supported by ERC,ATP, and IRG grants, and a Packard Fellowships. This research was partially supported by the Israel Science Foundation (Grant No. 174/08).|
|Subject Keywords:||galaxies: active; gamma rays: bursts; pulsars: general; radiation mechanisms: non-thermal|
|Official Citation:||Klein–Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum Ehud Nakar, Shin'ichiro Ando, and Re'em Sari 2009 ApJ 703 675-691 doi: 10.1088/0004-637X/703/1/675|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||02 Oct 2009 23:28|
|Last Modified:||26 Dec 2012 11:26|
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