Gamma-ray burst spectra from continuously accelerated electrons

Poutanen, J. and Stern, B. E. (2005) Gamma-ray burst spectra from continuously accelerated electrons. Il nuovo cimento C, 28 (3). pp. 443-446. ISSN 1826-9885

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We discuss here constraints on the particle acceleration models from the observed gamma-ray bursts spectra. The standard synchrotron shock model assumes that some fraction of available energy is given instantaneously to the electrons which are injected at high Lorentz factor. The emitted spectrum in that case corresponds to the spectrum of cooling electrons, Fν ∝ ν−1/2, is much too soft to account for the majority of the observed spectral slopes. We show that continuous heating of electrons over the life-time of a source is needed to produce hard observed spectra. In this model, a prominent peak develops in the electron distribution at energy which is a strong function of Thomson optical depth τT of heated electrons (pairs). At τT � 1, a typical electron Lorentz factor �γ� ∼ 1–2 and quasi-Thermal Comptonization operates. It produces spectrum peaking at a too high energy. Optical depths below 10−4 would be difficult to imagine in any physical scenario. At τT ≈ 10−4–10−2, �γ� ∼ 30–100 and synchrotron self-Compton radiation is the main emission mechanism. The synchrotron peak should be observed at 10–100 eV, while the self-absorbed low-energy tail with Fν ∝ ν2 can produce the prompt optical emission (like in the case of GRB 990123). The first Compton scattering radiation by nearly monoenergetic electrons peaks in the BATSE energy band and can be as hard as Fν ∝ ν1 reproducing the hardness of most of the observed GRB spectra. The second Compton peak should be observed in the high-energy gamma-ray band, possibly being responsible for the 10–100MeV emission detected in GRB 941017. A significant electron-positron pair production reduces the available energy per particle, moving spectral peaks to lower energies as the burst progresses.

Item Type: Article
Additional Information: Paper presented at the “4th Workshop on Gamma-Ray Burst in the Afterglow Era”, Rome, October 18-22, 2004.
Uncontrolled Keywords: γ-ray sources; γ-ray bursts
Subjects: 500 Scienze naturali e Matematica > 520 Astronomia e scienze connesse
Depositing User: Marina Spanti
Date Deposited: 16 Mar 2020 10:57
Last Modified: 16 Mar 2020 10:57

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