Journal Article

PUBDB-2023-07081

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The Formation of Hard Very High Energy Spectra from Gamma-ray Burst Afterglows via Two-zone Synchrotron Self-Compton Emission

Khangulyan, D. (Corresponding author) ; Taylor, A. M.DESY* ; Aharonian, F.

2023
Institute of Physics Publ. London

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Please use a persistent id in citations: doi:10.3847/1538-4357/acc24e  doi:10.3204/PUBDB-2023-07081

Report No.: arXiv:2301.08578

Abstract: Electron Compton scattering of target photons into the gamma-ray energy band (inverse Compton scattering; IC) is commonly expected to dominate the very high energy (VHE) spectra in gamma-ray bursts (GRBs) especially during the afterglow phase. For sufficiently large center-of-mass energies in these collisions, the effect of the electron recoil starts reducing the scattering cross-section (the Klein–Nishina regime). The IC spectra generated in the Klein–Nishina regime is softer and has a smaller flux level compared to the synchrotron spectra produced by the same electrons. The detection of afterglow emission from nearby GRB190829A in the VHE domain with H.E.S.S. has revealed an unexpected feature: the slope of the VHE spectrum matches well the slope of the X-ray spectra, despite expectations that, for the IC production process, the impact of the Klein–Nishina effect should be strong. The multi-wavelength spectral energy distribution appears to be inconsistent with predictions of one-zone synchrotron–self-Compton models. We study the possible impact of two-zone configuration on the properties of IC emission when the magnetic field strength differs considerably between the two zones. Synchrotron photons from the strong magnetic field zone provide the dominant target for cooling of the electrons in the weak magnetic field zone, which results in a formation of hard electron distribution and consequently of a hard IC emission. We show that the two-zone model can provide a good description of the Swift's X-ray Telescope and VHE H.E.S.S. data.

Keyword(s): gamma ray: burst ; magnetic field: low ; electron: recoil ; magnetic field: high ; Compton scattering: inverse ; gamma ray: energy ; VHE ; synchrotron ; slope ; photon ; formation ; HESS ; X-ray ; spectral ; field strength ; flux ; energy spectrum ; scattering ; Non-thermal radiation sources ; Gamma-ray transient sources ; Gamma-ray bursts ; Gamma-ray astronomy ; Particle astrophysics ; X-ray sources

Note: 13 pages, 7 figures, ApJ submitted

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Contributing Institute(s):

1. Theoretische Astroteilchenphysik (Z_THAT)

Research Program(s):

1. 613 - Matter and Radiation from the Universe (POF4-613) (POF4-613)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2023

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