4U 1624-49

M. G. Watson, R. Willingale, and A. R. King, University of Leicester; J. E. Grindlay, Center for Astrophysics; and J. Halpern, Columbia Astrophysics Laboratory, report: "Observation of this object with the EXOSAT Observatory during Mar. 25-27 has shown the presence of intensity dips in its 2-10-keV x-ray light curve that recur with a period of 21 +/- 2 hr, presumably the binary period of this system. The dip pattern in each cycle lasts from 6 to 8 hr and has a complex and variable structure, making a more accurate period determination difficult. 4U 1624-49 is the seventh x-ray source to have shown such periodic intensity dips (IAUC 4039, 4044); the periods of the other six objects are all below 8 hr."