1ES1113+432: Luminous, Soft X-ray Outburst from a Nearby Cataclysmic Variable

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Session 63 -- Intrinsic and Cataclysmic Variables
Display presentation, Thursday, 9:20-4:00, Heller Lounge Room

[63.14] 1ES1113+432: Luminous, Soft X-ray Outburst from a Nearby Cataclysmic Variable

R.A. Remillard (MIT), A.D. Silber, J.F. Schachter, P. Slane (CfA)

A remarkable X-ray transient from the Einstein Slew Survey, 1ES1113+432, is identified with a nearby, short-period cataclysmic variable. The X-ray outburst reached a peak flux of 43 IPC c/s, which is an order of magnitude above the flux observed from the brightest cataclysmic variables in other X-ray surveys. The outburst spectrum is extremely "soft", with a small percentage of photons having energies greater than 1 keV. The optical counterpart (V=16.5) exhibits a strong UV component, TiO bands from an M star, and broadened Balmer emission lines; these characteristics are reminiscent of AM Her in its low state. The I-band light curves show 0.18 mag modulations at a period of 0.966 h. These are interpreted as ellipsoidal variations in the secondary star for a binary period of 1.932 h, which is near the lower boundary of the "period gap" in the histogram of orbital periods of accreting white dwarfs. Thus, 1ES1113+432 provides the rare opportunity to study a secondary star in an evolved, short-period cataclysmic variable. The flux from the secondary (assumed ~M6) implies a distance ~ 50 pc. The peak luminosity in the soft X-ray component is then estimated to be 2.6 x 10$^{32}$ erg/s, assuming isotropic emission from a blackbody with a temperature ~25 eV. Optical outbursts as bright as V~13 were found on photographs from the Harvard Plate Library, confirming the variable nature of the optical counterpart. The historical record suggests that 1ES1113+432 remains in a low accretion state most of the time.

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