Historical light curve of the black hole binary V4641 Sgr based on the   Moscow and Sonneberg plate archives
  We performed digital processing of a large set of photographic plates for X-ray binary system V4641 Sgr containing a black hole. A total of 277 plates were found in archives dated between 1960 and 1992. Photographic observations revealed lower level of outburst activity if to compare with CCD data after the large 1999 outburst. Only single outburst which happened in 1978 was confirmed. If archive photographic data are used along with contemporary CCD observations, the orbital period may be improved, and its value is 2.81728 +/-0.00004 day. 
E. A. Barsukova, V. P. Goranskij, P. Kroll
astro-ph.HE