The deepest optical investigation of the GRB790613 error box

We report the results of an optical study of the GRB 790613 field. GRB790613 was observed by SIGNE, KONUS and PVO and it has one of the smallest error boxes. Deep CCD images were obtained at the 6-m telescope of SAO RAS in 1994–1995. The average photometric limits (defined as Signal/Noise=4) for the central part of the error box were B≈26.2, V≈=25.8, R≈25.6. Down to V≈25.4 no blue optical counterpart was found for the whole CCD mosaic area. It can be interpreted as the absence of a single compact object of neutron star type with R=10 km and Tbb≈105 K as a possible potential source of γ-ray burst up to the distance of ≈40 pc. A few interesting objects were found nearby and inside the error box. One is a star-like object with B=23.03, B−V=0.05 and V−R=0.1. It is placed near the error box at the distance of about 30′′ from its boundary. It may be a QSO or a halo object: a white dwarf or a subdwarf. Another object is a poorly resolved double star. One of components is a red star of B=21.85 and another is seen...