1998/12/02 by J. Greiner, Greiner, J., G. Tovmassian +15
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9812054
15 pages, 9 figs., accepted for Astronomy & Astrophysics; also available from http://www.obs.aip.de/~jcg/publis.html
arxiv created 1998/12/02 · openalex publication_date 1998/12/02 · arxiv updated 2009/12/01 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/28
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 1034-1036 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.