An X-ray study of the dipping low mass X-ray binary XB 1323-619

During a BeppoSAX observation of the low-mass X-ray binary dip source XB 1323-619 a total of 10 type I X-ray bursts and parts of 12 intensity dips were observed. During non-bursting, non-dipping intervals, the 1-150 keV BeppoSAX spectrum can be modelled by a cutoff power-law with a photon index of 1.48 +/- 0.01, a cutoff energy of 44.1 +5.1/-4.4 keV together with a blackbody with kT of 1.77 +/- 0.25 keV contributing ~15% of the 2-10 keV flux. Absorption equivalent to 3.88 +/- 0.16x10^22 H atom cm^(-2) is required. The dips repeat with a period of 2.938 +/- 0.020 hr and span 40% of the orbital cycle. During dips the maximum reduction in 2-10 keV intensity is ~65%. The spectral changes during dips are complex and cannot be modelled by a simple absorber because of the clear presence of part of the non-dip spectrum which is not absorbed. Spectral evolution in dipping can be well modelled by progressive covering of the cutoff power-law component which must be extended, plus rapid absorption of the point-source blackbody. One of the bursts is double and 4 of the bursts occurred during dipping intervals. These bursts have 2-10 keV peak count rates reduced by only 22% on average from those occurring outside the dips, and are not heavily absorbed. One explanation for this lack of absorption is that the bursts temporarily ionize the absorbing material responsible for the dips.