Astron. Astrophys. 334, 117–123 (1998) ASTRONOMY AND ASTROPHYSICS BV RcIc photometry of GRB 970508 optical remnant: May-August, 1997 V.V. Sokolov1, A.I. Kopylov1, S.V. Zharikov1, M. Feroci2, L. Nicastro3, and E. Palazzi3 1 Special Astrophysical Observatory of RAS, Karachai-Cherkessia, 357147 Nizhnij Arkhyz Russia (sokolov,akop,
[email protected]) 2 Istituto di Astrofisica Spaziale, CNR, Via Fosso del Cavaliere, I-00131 Roma, Italy 3 Istituto Tecnologie e Studio Radiazioni Extraterrestri CNR, Via P. Gobetti 101, I-40129 Bologna, Italy Received 2 February 1998 / Accepted 24 February 1998 Abstract. We present the results of photometric observations Thank to the fast and accurate positioning of GRBs (a few ar- of the variable optical source associated to the remnant of the cminutes) obtainable through the combined capabilities of the gamma-ray burst GRB 970508 performed at the Special As- Gamma-Ray Burst Monitor (GRBM) and Wide Field Cameras trophysical Observatory of the Russian Academy of Science (WFCs) onboard this satellite, an X-ray and optical afterglow (SAO RAS) from May to August 1997. The observations were were observed for the very first time (Costa et al. 1997b, van carried out with the standard (Johnson-Kron-Cousins) photo- Paradijs et al., 1997). metric BV RcIc system using the 1-meter and 6-meter tele- However, as was found out later, the optical data on the first scopes. The brightness of the optical source increased from GRB afterglow in the history were obtained with different in- Rc =21.19 ± 0.25 (May 9.75 UT) to Rc =19.70 ± 0.03 struments and in different photometric conditions and refer to (May 10.77 UT), whereupon it was decaying in all the four different photometric systems and bands.