The Galactic Supersoft X-Ray Source RXJ0019+21

Abstract

We report the discovery (Beuermann et al. 1995) of a galactic supersoft X-ray source, RX J0019.8+2156, which we have identified with a 12.2mag blue star. The system shows quasi-sinusoidal variations of the optical, UV, and X-ray fluxes and systematic radial velocity variations with a period of 15.85 hours which reveals the binary nature of the source. The optical/UV continuum is characteristic of a bright accretion disk and a heated secondary with strong He II and Balmer emission lines superimposed. The Balmer lines display time-variable P Cygni type profiles indicative of a fast wind. The source is slightly reddened with E B-V ≃ 0.1, consistent with the total galactic neutral hydrogen column density at the position of RX J0019.8+2156, N H = 4x 1020 cm-2. This suggests that the object is located outside the galactic hydrogen layer. Lack of any spectral signatures of the expected F-type secondary it is likely that the distance is d > 1.5 kpc. At an adopted distance of d = 2 kpc, the system has M V = +0.4 and Lx ≃6 × 1036 ergs/s. The hot component probably is a white dwarf which accretes at a rate of ~ 10-7 M ⊙yr-1 near the limit for stable hydrogen burning. The X-ray luminosity and temperature of RX J0019.8+2156 seem to be lower compared to other supersoft sources suggesting that the system currently is in a low state between weak shell flashes. This picture is supported by the optical long-term behaviour of RX J0019.8+2156 (Greiner and Wenzel 1995).KeywordsWhite DwarfSpectral SignatureCataclysmic VariableBalmer LineFast WindThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.