TRANSIENT EXTREMELY SOFT X-RAY EMISSION FROM THE UNUSUALLY BRIGHT CATACLYSMIC VARIABLE IN THE GLOBULAR CLUSTER M3: A NEW CV X-RAY LUMINOSITY RECORD?

We observed the accreting white dwarf (WD) 1E1339.8+2837 (1E1339) in the globular cluster M3 in 2003 November, 2004 May, and 2005 January, using the Chandra ACIS-S detector. The source was observed in 1992 to possess traits of a supersoft X-ray source (SSS), with a 0.1-2.4 keV luminosity as large as 2 x 1035 erg s-1, after which time the source's luminosity fell by roughly two orders of magnitude, adopting a hard X-ray spectrum more typical of cataclysmic variables (CVs). Our observations confirm 1E1339's hard CV-like spectrum, with photon index Γ = 1.3 ± 0.2. We found 1E1339 to be highly variable, with a 0.5-10 keV luminosity ranging from (1.4 ± 0.3) x 1034 erg s-1 to 8.5+4.9-4.6 x 1032 erg s-1, with 1E1339's maximum luminosity being perhaps the highest yet recorded for hard X-ray emission from a WD. In 2005 January, 1E1339 displayed substantial low-energy emission below ∼0.3 keV. Although current Chandra responses cannot properly model this emission, its bolometric luminosity appears comparable to or greater than that of the hard spectral component. This raises the possibility that the supersoft X-ray emission seen from 1E1339 in 1992 may have shifted to the far-UV.