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The synchrotron spectrum of fast cooling electrons revisited

Granot, Jonathan and Piran, Tsvi and Sari, Re'em (2000) The synchrotron spectrum of fast cooling electrons revisited. In: Gamma Ray Bursts: 5th Huntsville Symposium, Huntsville, AL, 18-22 October 1999. American Institute of Physics Conference Proceedings. No.526. American Institute of Physics , Melville, NY, pp. 489-493. ISBN 1-56396-947-5 http://resolver.caltech.edu/CaltechAUTHORS:GRAaipcp00

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Abstract

We discuss the spectrum arising from synchrotron emission by fast cooling electrons when fresh electrons are continually accelerated by a strong blast wave into a power law distribution of energies. The fast cooling spectrum was so far described by four power law segments: Fnu[proportional]nu^2, nu^1/3, nu^–1/2 and nu^–p/2, divided by three break frequencies: nusa<nuc<num. This is valid for a homogeneous electron distribution. However, hot electrons are located right after the shock, while most electrons are farther down stream and have cooled. We show that this spatial distribution introduces a new break frequency, nuac, in the optically thick regime: nuac<nusa<nuc<num, and a new spectral slope: Fnu[proportional]nu^11/8 for nuac<nu<nusa, while the familiar Fnu[proportional]nu^2 is obtained only for nu<nuac. While the above ordering of the break frequencies is relevant for afterglows with typical parameters in an ISM environment, other possibilities may also be relevant for internal shocks or afterglows in dense circumstellar winds. We discuss possible applications for gamma-ray bursts (GRBs) and their afterglows, in the context of the internal-external shock model. This may explain spectral slopes steeper than 1/3 seen in the 1–10 keV range in some bursts, if nusa reaches the X-ray.


Item Type:Book Section
Additional Information:©2000 American Institute of Physics. Issue Date: September 8, 2000
Subject Keywords:gamma-ray sources (astronomical), synchrotron radiation, afterglows, plasma shock waves, cosmic ray energy spectra, stellar winds, astrophysical jets, intergalactic matter
Record Number:CaltechAUTHORS:GRAaipcp00
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:GRAaipcp00
Alternative URL:http://dx.doi.org/10.1063/1.1361587
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9544
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:01 Feb 2008
Last Modified:26 Dec 2012 09:49

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