ASCAObservation of MS 1603.6+2600 (=UW Coronae Borealis): A Dipping Low‐Mass X‐Ray Binary in the Outer Halo?

MS 1603.6+2600 is a high-latitude X-ray binary with a 111 min orbital period,thought to be either an unusual cataclysmic variable or an unusual low-massX-ray binary. In an ASCA observation in 1997 August, we find a burst, whoselight curve suggests a Type I (thermonuclear flash) origin. We also find anorbital X-ray modulation in MS 1603.6+2600, which is likely to be periodicdips, presumably due to azimuthal structure in the accretion disk. Both areconsistent with this system being a normal low-mass X-ray binary harboring aneutron star, but at a great distance. We tentatively suggest that MS1603.6+2600 is located in the outer halo of the Milky Way, perhaps associatedwith the globular cluster Palomar 14, 11 degrees away from MS 1603.6+2600 onthe sky at an estimated distance of 73.8 kpc.Comment: 12 pages including 4 figures; ApJ, in pres