The Big Dipper - 4U1624-49

Abstract

We present a 6.3 hour observation of 4U1624-49 with the EXOSAT Medium Energy experiment. The X-ray light curve is dominated by a series of sharp dips in which the observed flux falls to ∼25% of the steady level on timescales of seconds. These dips are accompanied by strong variations in the spectral hardness consistent with large changes in the absorbing column density. No evidence is found for any dip periodicity, in contrast to the other four sources in which dip activity has been reported. We discuss the implications of these observations for models of low mass X-ray binaries.