Transient supersoft X-ray emission from V751 Cyg during the optical low-state
Abstract
We have observed V751 Cyg with the ROSAT HRI during its recent optical low state and clearly detect it at a count rate of 0.015 cts/s. The X-ray intensity is a factor of ~20 higher than the upper limit obtained with the ROSAT PSPC during the optical high state. Spectral investigations suggest a very soft X-ray spectrum. We investigate archival IUE data of V751 Cyg and derive a distance of V751 Cyg of d~500 pc based on the extinction estimate of E(B-V)=0.25+-0.05. This implies that the X-ray emission is very luminous, on the order of 10^34-10^36 erg/s. The spectrum during the optical low-state is characterized by a very blue continuum and the presence of strong emission lines of the Balmer series and HeI. Also, HeII 4686 A is clearly detected. We establish that V751 Cyg is a transient supersoft X-ray source and speculate that other VY Scl stars may also be of similar type.
Keywords
Cite
@article{arxiv.astro-ph/9812054,
title = {Transient supersoft X-ray emission from V751 Cyg during the optical low-state},
author = {J. Greiner and G. H. Tovmassian and R. DiStefano and A. Prestwich and R. González-Riestra and L. Szentasko and C. Chavarria},
journal= {arXiv preprint arXiv:astro-ph/9812054},
year = {2007}
}
Comments
15 pages, 9 figs., accepted for Astronomy & Astrophysics; also available from http://www.obs.aip.de/~jcg/publis.html