The observable effect of a photospheric component on GRB's prompt emission spectrum: Peak energy clustering and flat spectra above the thermal peak

Asaf Pe'er, Peter Mészáros, Martin J. Rees

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations

Abstract

A thermal radiative component is likely to accompany the first stages of the prompt emission of Gamma-ray bursts (GRB's) and X-ray flashes (XRF's). We study the properties of plasmas containing a low energy thermal photon component at comoving temperature θ ≡ kT ′ / mec2 ∼ 10-5 - 10-2 interacting with an energetic electron component. We show that, for scattering optical depths larger than a few, balance between Compton and inverse-Compton scattering leads to the accumulation of electrons at values of γβ ∼ 0.1 - 0.3. For optical depths larger than ∼ 100 and characteristic GRB bulk Lorentz factors of ∼ 100 this leads to a peak in the observed photon spectrum at 0.1 - 1 MeV, very weakly dependent on the values of the free parameters. For a wide range of the optical depths 0.03 ≲ τγe ≲ 100 and comparable energy densities in the thermal and the leptonic component, a nearly flat energy spectrum (vFv ∝ v0) above the thermal peak at ≈ 10 - 100 keV and below 10 - 100 MeV is obtained, regardless of the details of the dissipation mechanism or the strength of the magnetic field. In particular, these results are applicable to the internal shock model of GRB, as well as to slow dissipation models, e.g. as might be expected from reconnection, if the dissipation occurs at a sub-photospheric radii. We conclude that dissipation near the thermal photosphere can naturally explain (a) clustering of the peak energy at sub-MeV energies at early times; (b) steep slopes observed at low energies; and (c) a flat spectrum above 10 keV at late times. Our model thus provides an alternative scenario to the optically thin synchrotron - SSC model.

Original languageEnglish
Title of host publicationGAMMA-RAY BURSTS IN THE SWIFT ERA
Subtitle of host publicationSixteenth Maryland Astrophysics Conference
Pages181-184
Number of pages4
DOIs
StatePublished - 19 May 2006
Externally publishedYes
EventGAMMA-RAY BURSTS IN THE SWIFT ERA: 16th Maryland Astrophysics Conference - Washington, D.C., United States
Duration: 29 Nov 20052 Dec 2005

Publication series

NameAIP Conference Proceedings
Volume836
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Conference

ConferenceGAMMA-RAY BURSTS IN THE SWIFT ERA: 16th Maryland Astrophysics Conference
Country/TerritoryUnited States
CityWashington, D.C.
Period29/11/052/12/05

Keywords

  • Gamma rays: bursts
  • Gamma rays: theory
  • Plasmas
  • Radiation mechanisms: nonthermal

Fingerprint

Dive into the research topics of 'The observable effect of a photospheric component on GRB's prompt emission spectrum: Peak energy clustering and flat spectra above the thermal peak'. Together they form a unique fingerprint.

Cite this