The Discovery of 2.93 Hour Periodic Intensity Dips from X1323-619

Abstract

A 30 hr duration Exosat observation of the low-mass X-ray binary X1323-619 is reported. The 1-8 keV light curve obtained with the medium-energy (ME) instrument shows irregular intensity dips that recur every 2.93 hr as well as type 1 X-ray bursts. The intensity declines to about 50 percent of its unaffected value during the 50-minute duration dips. The dip and burst-free ME spectrum is similar to that of other X-ray burst sources, being fitted by a power-law model with energy index 0.5. Considerable low-energy absorption is also required. Spectral changes observed during dipping intervals are consistent with absorption by material with a wide range of abundances. From an analysis of the burst properties, the distance of X1323-619 is constrained to be between 10 and 20 kpc.