ROSAT Observations of the Black Hole Candidate V404 Cygni in Quiescence
Abstract
V404 Cyg was detected with the ROSAT PSPC in a 16 ks observation 1265 days after the 1989 May outburst. This is the first unambiguous detection of a soft X-ray transient or X-ray nova black hole candidate in quiescence. The observed X-ray spectrum is extremely soft and can be described equally well by either a blackbody, power-law, or a thermal bremsstrahlung continuum. The best-fit blackbody spectrum is characterized by a temperature of 0.2 keV. A significant amount of absorption, both along the line of sight and intrinsic to the V404 Cyg system, is required to understand the observations. The 0.2-2.4 keV light curve of V404 Cyg exhibits substantial variability on timescales of less than a day. Assuming a distance of 3.5 kpc, the quiescent X-ray luminosity of V404 Cyg is 8 x 1033 ergs/s, nearly two orders of magnitude larger than the upper such as Cen X-4. The lack of a significant hard X-ray luminosity in quiescence, the presence of a large and cold neutral region in the accretion disk, and a low-mass accretion rate suggests that an accretion disk instability might account for the outburst of V404 Cyg.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1994
- DOI:
- 10.1086/187404
- Bibcode:
- 1994ApJ...429L..25W
- Keywords:
-
- Accretion Disks;
- Black Holes (Astronomy);
- Stellar Luminosity;
- Stellar Mass Accretion;
- X Ray Absorption;
- X Ray Astronomy;
- X Ray Binaries;
- Black Body Radiation;
- Rosat Mission;
- Astronomy;
- ACCRETION;
- ACCRETION DISKS;
- BLACK HOLE PHYSICS;
- STARS: BINARIES: CLOSE;
- STARS: INDIVIDUAL CONSTELLATION NAME: V404 CYGNI;
- X-RAYS: STARS