ROSAT observations of the black hole candidate V404 Cygni in quiescence

Details ROSAT observations of the black hole candidate V404 Cygni in quiescence ROSAT observations of the black hole candidate V404 Cygni in quiescence

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...429l..25w&link_type=abstract

The Astrophysical Journal, vol. 429, no. 1, pt. 2, p. L25-L28

Astronomy and Astrophysics

Astronomy

43

Accretion Disks, Black Holes (Astronomy), Stellar Luminosity, Stellar Mass Accretion, X Ray Absorption, X Ray Astronomy, X Ray Binaries, Black Body Radiation, Rosat Mission

Scientific paper

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.

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