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Astron. Astrophys. Suppl. Ser.
Volume 142, Number 3, March II 2000
Page(s) 443 - 445
Published online 15 March 2000
DOI: 10.1051/aas:2000163

Astron. Astrophys. Suppl. Ser. 142, 443-445

TeV gamma-ray emission from gamma-ray bursts and ultra high energy cosmic rays[*]

T. Totani

Theory Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan

Received December 1, 1999; accepted January 3, 2000


Some recent experiments detecting very high energy (VHE) gamma-rays above 10-20 TeV, independently reported VHE bursts for some bright gamma-ray bursts (GRBs), although further confirmation is necessary. If these signals are truly from GRBs, these GRBs must emit a much larger amount of energy as VHE gamma-rays than in the ordinary photon energy range of GRBs (keV-MeV). We show that such extreme phenomena can be reasonably explained by synchrotron radiation of protons accelerated to $\sim 10^{20-21}$ eV. Protons must carry a much larger amount of energy than electrons, suggesting that energy transfer from protons into electrons in shocked matter is very inefficient. The total energy of GRBs becomes as large as $~ \raisebox{-1ex}{$\stackrel{\textstyle >}{\sim}$ } ~10^{55}
(\Delta \Omega / 4 \pi)$ergs and hence a strong beaming of GRB emission is highly likely. There may also be TeV emission in afterglow phase from external shocks, and proton synchrotron in this phase gives a quantitative explanation for the famous long duration GeV emission from GRB 940217. Most TeV gamma-rays are absorbed in intergalactic space by interactions with the infrared and microwave background radiations, and finally form gamma-ray background in GeV range. This process may explain the extragalactic background radiation observed in the EGRET range. We also discuss absorption of TeV gamma-rays in the shocked region of GRBs by the $\gamma\gamma \rightarrow {\rm e}^\pm$ process, which may provide a new channel for energy transfer from protons into electrons (and positrons). This process should be important for the energetics of GRBs.

Key words: gamma-ray bursts (GRB)

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Copyright The European Southern Observatory (ESO)

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