EDP Sciences
Free access
Volume 418, Number 1, April IV 2004
Page(s) L5 - L8
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040108

A&A 418, L5-L8 (2004)
DOI: 10.1051/0004-6361:20040108


Neutral beam model for the anomalous $\mathsf{\gamma}$-ray emission component in GRB 941017

C. D. Dermer1 and A. Atoyan2

1  Code 7653, Naval Research Laboratory, Washington, DC 20375-5352, USA http://heseweb.nrl.navy.mil/gamma/~dermer/default.htm
2  Centre de Recherches Mathématiques, Université de Montréal, Montréal, H3C 3J7, Canada
    e-mail: atoyan@crm.umontreal.ca

(Received 6 January 2004 / Accepted 4 March 2004 )

González et al. (2003) have reported the discovery of an anomalous radiation component from $\approx$ 1-200 MeV in GRB 941017. This component varies independently of and contains $\ga$ $3\times$ the energy found in the prompt ~ 50 keV-1 MeV radiation component that is well described by the relativistic synchrotron-shock model. Acceleration of hadrons to very high energies can give rise to two additional emission components, one produced inside the GRB blast wave and one associated with an escaping beam of ultra-high energy (UHE; $\ga$ 1014 eV) neutrons, $\gamma$ rays, and neutrinos. The first component extending to ~ 100 MeV is from a pair-photon cascade induced by photomeson processes with the internal synchrotron photons coincident with the prompt radiation. The outflowing UHE neutral beam can undergo further interactions with external photons from the backscattered photon field to produce a beam of hyper-relativistic electrons that lose most of their energy during a fraction of a gyroperiod in the assumed Gauss-strength magnetic fields of the circumburst medium. The synchrotron radiation of these electrons has a spectrum with $\nu F_\nu$ index equal to  +1 that can explain the anomalous component in GRB 941017. This interpretation of the spectrum of GRB 941017 requires a high baryon load of the accelerated particles in GRB blast waves. It implies that most of the radiation associated with the anomalous component is released at $\ga$ 500 MeV, suitable for observations with GLAST, and with a comparable energy fluence in ~ 100 TeV neutrinos that could be detected with a km-scale neutrino telescope like IceCube.

Key words: gamma ray bursts -- cosmic rays -- radiation processes

Offprint request: C. D. Dermer, dermer@gamma.nrl.navy.mil

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