LOW-MASS BINARY X-RAY SOURCES: MONITORING WITH VARIOUS SATELLITES

We show the importance of observing low-mass binary (LMXB) X-ray sources with the X-ray monitors onboard satellites. This enables us to study the physical processes governing the longterm activity of LMXBs. They are excellent targets for monitoring because of their strong activity. We recall that various physical processes operating in LMXBs produce specific large-amplitude variations of X-ray luminosity which can be investigated even in a single-band X-ray light curve as often provided by the monitors. We also emphasize the role of the spectral region of the X-ray monitor. Choosing the spectral region often strongly influences the profile of the observed intensity curve because different emission components may dominate in different X-ray energy ranges. We show several examples of LMXBs which undergo various types of unpredictable activity (e.g. outbursts, superorbital cycles).