Upper limits to low energy ν̄ e flux from GRB 990705

The detection of Gamma Ray Burst GRB 990705 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 GRB 990705. 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 ν̄e flux · cross-section, integrated over different time durations, ∫ ∫ Φν̄eσdEdt. Moreover, assuming thermal ν̄e spectra at the source, upper limits to the ν̄e flux, integrated over time duration, for different spectral temperatures, are obtained. Based on these limits and on the expectations for ν emission from collapsing astrophysical objects, the occurrence of a gravitational stellar collapse can be excluded up to a distance r ≈ 50 kpc, in the case of time coincidence with GRB 990705, and r ≈ 20 kpc, for the 24 hours preceding it.