ASCA observation of a long-duration X-ray flare from the W UMa-type binary VW Cephei

We analyze X-ray archive data of the W UMa-type binary VW Cephei taken with ASCA on 1993 November 5-6. By analyzing the light curve, we find a long-duration flare of approximate to 7.5 hr with a peak luminosity of 1.2 x 10(30) ergs s(-1) (0.4-3.0 keV) for the assumed distance of 23.2 pc. A flux dip is detected in the light curve at the orbital phase of similar to 0.5, and it is identified as an eclipse by the secondary star. We determine the timescale of the eclipse egress to be similar to 30 minutes from a model fit to the light curve. With this timescale, we estimate that the linear size of the flaring region is approximate to 5.5 x 10(10) cm, regardless of the flare models. From the spectral analysis of the data, we find that the spectrum can be well reproduced by the variable-abundance plasma model with a combination of two different temperatures, kT = 0.64 and kT = 1.91 keV. The hotter component is considered to be associated with the flare. The results are interpreted in terms of a two-ribbon flare model, in which we also discuss the possible enhancement of element abundances.