Upper limits to low energy antineutrino flux from GRB990705

Abstract

The detection of Gamma Ray Burst GRB990705 on 1999, July 5.66765 UT, pointing to the Large Magellanic Clouds, suggested the search for a possible neutrino counterpart, both in coincidence with and slightly before (or after) the photon burst. We exploited such a possibility by means of the LVD neutrino telescope (National Gran Sasso Laboratory, Italy), which has the capability to study low-energy cosmic neutrinos. No evidence for any neutrino signal, over a wide range of time durations, has been found, at the occurrence of GRB990705. Due to the lack of information about both the source distance and its emission spectrum, the results of the search are expressed in terms of upper limits, at the Earth, to the antineutrino flux $\cdot$ cross-section, integrated over different time durations. Moreover, assuming thermal antineutrino spectra at the source, upper limits to the antineutrino flux, integrated over time duration, for different spectral temperatures, are obtained. Based on these limits and on the expectations for neutrino emission from collapsing astrophysical objects, the occurrence of a gravitational stellar collapse can be excluded up to a distance r approximately 50 kpc, in the case of time coincidence with GRB990705, and r approximately 20 kpc, for the 24 hours preceding it.