Complex outburst behaviour from the black - hole candidate 4 U 1630 − 47

We present data from different epochs in 1978, 1987–1991 and 1996 from the black-hole candidate 4U1630−47. For the first time we present almost complete coverage of the outbursts which started in 1987, 1988, and 1996. We find that the outburst behaviour of 4U 1630−47 is more complex than previously realized. The source shows outbursts with durations on the order of ∼100-200 days and sometimes intervals of long-term X-ray activity. The relatively short outbursts which occurred in 1987 and 1996 exhibited different colour behaviour: the outburst in 1987 showed softening of the Xray spectrum, whereas the outburst in 1996 showed hardening of the X-ray spectrum, as the outbursts proceeded. The outburst which started in 1977 may have lasted for up to∼10 months, whereas the outburst which started in 1988 showed activity for up to∼2.4 years. Such long-term activity is reminiscent of that seen in GRS1716−249 and in the galactic superluminal sources GRS 1915+105 and GROJ1655−40. We refine the outburst ephemeris of 4U 1630−47 and find that the outburst recurrence time scale may have changed from ∼600 days to ∼690 days between the 1984 and 1987 outbursts. If the recurrence interval of ∼690 days