An X-ray dip in the X-ray transient 4U 1630-47

An X-ray dip was observed during a 1996 Rossi X-Ray Timing Explorer observation of the recurrent X-ray transient 4U 1630-47. During the dip, the 2-60 keV X-ray flux drops by a factor of about 3, and, at the lowest point of the dip, the X-ray spectrum is considerably softer than at nondip times. We find that the 4U 1630-47 dip is best explained by absorption of the inner part of an accretion disk, while the outer part of the disk is unaffected. The spectral evolution during the dip is adequately described by the variation of a single parameter, the column density obscuring the inner disk.