Long-term optical activity of the microquasar V4641 Sgr

摘要: We present an analysis of the optical activity microquasar V4641 Sgr using visual and photographic data. analyze four smaller (echo) outbursts that followed main outburst (1999). Their mean recurrence time TC is 377 days, with a trend decrease. interpret characteristic features recent (the narrow separated by long quiescence, clear in evolution their TC) as thermal instability accretion disk operating dwarf novae soft X-ray transients. argue luminosity echo too high to be explained emission disk. them due instability, which gives rise jet radiating also optical. This supports finding Uemura et al., PASJ 54, L79 (2002). The pre-outburst observations (1964–1967) reveal ongoing system. It displays low-amplitude fluctuations on timescale several weeks, independent orbital phase. In addition, larger brightening lasted for tens days occurred from level brightness higher than other years can resolved.