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

Abstract

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 that 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 d and sometimes intervals of long-term X-ray activity. The relatively short outbursts that occurred in 1987 and 1996 exhibited different colour behaviour: the outburst in 1987 showed softening of the X-ray spectrum, whereas the outburst in 1996 showed hardening of the X-ray spectrum, as the outbursts proceeded. The outburst that started in 1977 may have lasted for up to ∼10 months, whereas the outburst that started in 1988 showed activity for up to ∼2.4 yr. Such long-term activity is reminiscent of that seen in GRS 1716-249 and in the Galactic superluminal sources GRS 1915+105 and GRO J1655-40. We refine the outburst ephemeris of 4U 1630-47 and find that the outburst recurrence timescale may have changed from ∼600 to ∼690 d between the 1984 and 1987 outbursts. If the recurrence interval of ∼690 d continues, the next outburst of 4U 1630-47 is predicted to occur in 1998 January. © 1997 RAS.