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 13 23-619 a total of 10 type I Xray bursts and parts of 12 intensity dips were observed. During non-bursting, non-dipping intervals, the 1.0-150 keV Bepp oSAX spectrum can be modelled by a cutoff power-law with a photon index of 1.48 +/- 0.01, a cutoff energy of 44.1(-4.4)(+5.1):: keV together with a bl ackbody with kT of 1.77 +/- 0.25 keV contributing similar to 15% of the 2-1 0keV flux. Absorption equivalent to 3.88 +/- 0.16 x 10(22) atom cm(-2) is r equired. The dips repeat with a period of 2.938 +/- 0.020 hr and span 40% o f the orbital cycle. During dips the maximum reduction in 2-10 keV intensit y is similar to 65%. The spectral changes during dips are complex and canno t 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 compon ent which must be extended, plus rapid absorption of the point-source black body. One of the bursts is double and 4 of the bursts occurred during dippi ng intervals. These bursts have 2-10 keV peak count rates reduced by only 2 2% on average from those occurring outside the dips. and are not heavily ab sorbed. One explanation for this lack of absorption is that the bursts temp orarily ionize the absorbing material responsible for the dips.