ASCAObservation of a Long‐Duration X‐Ray Flare from the W UMa–Type Binary VW Cephei

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Abstract

We analyze X-ray archive data of the W UMatype binary VW Cephei taken with ASCA on 1993 November 56. By analyzing the light curve, we nd a long-duration are of B7.5 hr with a peak luminosity of 1.2 ] 1030 ergs s~1 (0.43.0 keV) for the assumed distance of 23.2 pc. A ux dip is detected in the light curve at the orbital phase of D0.5, and it is identied as an eclipse by the secondary star. We determine the timescale of the eclipse egress to be D30 minutes from a model t to the light curve. With this timescale, we estimate that the linear size of the aring region is B5.5 ] 1010 cm, regardless of the are models. From the spectral analysis of the data, we nd that the spectrum can be well reproduced by the variable-abundance plasma model with a combination of two di erent temperatures, kT \ 0.64 and kT \ 1.91 keV. The hotter component is considered to be associated with the are. The results are interpreted in terms of a two-ribbon are model, in which we also discuss the possible enhancement of element abundances.

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