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Astron. Astrophys. 340, 447-456 (1998)

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On the true energy budget of GRB970508 and GRB971214

Abhas Mitra

Theoretical Physics Division, Bhabha Atomic Research Centre, Mumbai-400085, India

Received 10 June 1998 / Accepted 7 September 1998

Abstract

We emphasize the already known idea that since GRB970508 released an energy of [FORMULA] ergs in soft gamma rays alone, where [FORMULA] is the solid angle of the beam, the actual energy of the [FORMULA] fireball driving the blast wave could be considerably higher than this value, [FORMULA]. We further argue that, for reasonably large values of [FORMULA], as is probably suggested by the radio observations, the value of [FORMULA] erg, for GRB970508; where [FORMULA] is the number density of the ambient medium in units of 1 proton/cm3 and [FORMULA] is the epoch in months when the associated radio-blastwave degrades to become mildly relativistic. Thus the value of [FORMULA] for GRB970508 could be as large as [FORMULA]erg or even much higher. This idea is corroborated by GRB971214 for which the value of [FORMULA] is much higher than the corresponding value for GRB970508. It is likely that GRB971214 has a correspondingly higher value of [FORMULA]. We discuss that it is unlikely that this energy, [FORMULA]erg was liberated by the central engine by a direct electromagnetic mode. On the other hand, as conceived by several previous authors and as is suggested by supernova theories, the [FORMULA] fireball (FB) driving the blast wave is likely to be preceded by a much stronger neutrino burst: [FORMULA]. Although, the efficiency for [FORMULA] production by this latter route is usually found to be as low as [FORMULA], we point out that for very high values of neutrino energy release [FORMULA], it is possible that, the value of [FORMULA] increses substantially. By considering that, the value of [FORMULA] for such GRBs is indeed [FORMULA] erg, we envisage that the energy of the actual neutrino burst/wind could be as high as [FORMULA] erg (here we ignore likely loss of energy by gravitational energy mode).

This energy might be had from general relativistic collapse of a massive stellar core having initial gravitational mass, say, [FORMULA] to a stage having a potential well much deeper than what is present on a canonican neutron star surface. Accordingly, we predict that the new generation large neutrino telescopes may detect neutrino burst of energy [FORMULA] ergs, with neutrino energies touching [FORMULA] GeV, in coincidence with GRBs.

Key words: gamma rays: bursts – black hole physics

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© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998
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