Supersoft X-ray source in the globular cluster M3 (NGC 5272)

We studied the nature of a transient supersoft X-ray source (SSS), 1E 1339. 8+2837, in the globular cluster M3 (NGC 5272) using the ASCA data and the a rchival ROSAT data. We found that 1E 1339.8+2837 was observed most of the t ime as a CV-type X-ray source and had a hard energy spectrum approximated b y a bremsstrahlung model of 5 keV. It switched to a high state only during 1991-92 at a luminosity of 10(35) erg s(-1), which is larger than that in t he low state by nearly two orders of magnitude. We confirmed the very soft energy spectrum characteristic of the SSS during the high state. Thus, 1E 1 339.8+2837 is considered to be a white-dwarf binary, making a transition be tween the SSS and the CV. We discuss a possible model of 1E 1339.8+2837, a dwarf nova including a massive white dwarf.