ASCA observation 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 minute orbital pe riod, thought to be either an unusual cataclysmic variable or an unusual lo w-mass X-ray binary. In an ASCA observation in 1997 August, we find a burst , whose light curve suggests a type I (thermonuclear flash) origin. We also find an orbital X-ray modulation in MS 1603.6+2600, which is likely to be periodic dips, presumably due to azimuthal structure in the accretion disk. Both are consistent with this system being a normal low-mass X-ray binary harboring a neutron star, but at a great distance. We tentatively suggest t hat MS 1603.6+2600 is located in the outer halo of the Milky Way, perhaps a ssociated with the globular cluster Palomar 14, 11 degrees away from MS 160 3.6+2600 on the sky at an estimated distance of 73.8 kpc.