light curves of GRB 970508 optical remnant and magnitudes of underlying host galaxy

The observations with the SAO-RAS 6-m telescope in July-August 1998 show that the GRB970508 optical remnant has varied very little since November 1997. We can conclude that we observe a proper host galaxy without the GRB optical remnant. The fitting results of the light curve of the GRB remnant plus the host galaxy until about 400 days after the primary event are reported here. The best χ 2-fits with a power law, for most of the filters used, are not acceptable. Some intrinsic variability of the GRB optical remnant fading is possible , which demands a more complex law presenting the largest multiband homogeneous data set from a single telescope. The GRB970508 OT is a second optical source related to a gamma-ray burst registered by the BeppoSAX satellite. The optical variable object was first reported by H. Bond as a possible optical counterpart of GRB970508 (Bond, 1997) and was independently found in our data (R c band, 1-m telescope) only about 0.5 day later. Observations of the GRB970508 optical remnant were continued with the 6-m telescope in the standard BV R c I c bands till Aug. 1998 (Sokolov et al., 1999). The BV R c I c magnitudes of the optical counterpart did not already change in magnitude error range during the last half-year from November 1997 to August 1998. We can conclude that we observe a pure host galaxy without the optical remnant of GRB970508. If the brightness changes within the errors , and the brighness decay of the optical remnant can still be described by a power-law relation for about a year after the burst occurence, then the flux can be determined by fitting the observed BV R c I c light curves with a two-component model, the sum of the GRB970508 optical remnant fading according to a power-law, and a constant brightness of the host galaxy: F = F o × t α + F c. To investigate the possible variability of a faint source, one should avoid any systematic shifts in the observational data due to different photometric systems in various instruments. That is why, for these fits we used the homogeneous data set from the 6-m telescope only. In Table 1 the host galaxy magnitudes and fluxes are presented for 3 cases: (1) the proper late-time BV R c I c observations in Jul.-Aug. 1998 with