Abstract
We discuss the importance of the simultaneous monitoring of binary X-ray sources in the optical and X-ray bands. Monitoring is important for investigating the processes that operate on the timescales of years, especially as regards the unpredictable events like the high/low state transitions and outbursts. The strategy discussed here can shed more light on the accretion processes since the optical and X-ray radiations are often emitted from different regions of the binary. We show some examples of the binary systems with the accreting compact objects of various kinds where the observations provided by the X-ray monitors onboard satellites (RXTE, Swift) are combined with a long, simultaneous dense series of data from various ground-based telescopes.
