The X-ray Spectra of Black Hole X-ray Novae in Quiescence as Measured by Chandra

Details The X-ray Spectra of Black Hole X-ray Novae in Quiescence as Measured by Chandra The X-ray Spectra of Black Hole X-ray Novae in Quiescence as Measured by Chandra

2001-11-07

arxiv.org/abs/astro-ph/0111134v2

Astronomy and Astrophysics

Astrophysics

9 pages, 6 figures, accepted for publication in ApJ

Scientific paper

10.1086/339501

We present Chandra observations of black hole X-ray novae V404 Cyg, A0620-00, GRO J1655-40 and XTE J1550-564 in quiescence. Their quiescent spectra can be well fitted by a power-law model with slope $\alpha \sim 2$. While a coronal (Raymond-Smith) model is also a statistically acceptable representation of the spectra, the best fit temperatures of these models is $\sim 5$ times higher than that seen in active stellar coronae. These four spectra of quiescent X-ray novae are all consistent with that expected for accretion via an advection-dominated accretion flow (ADAF) and inconsistent with that expected from a stellar corona. This evidence for continued accretion in quiescence further strengthens the case for the existence of event horizons in black holes. Both A0620-00 and GRO J1655-40 were fainter than in previous observations, while V404 Cyg was more luminous and varied by a factor of 2 in a few ksec. A reanalysis of the X-ray data for XTE J1550-564 shows that (like V404 Cyg and A0620-00) its luminosity exceeds the maximum prediction of the coronal model by a large factor. The 0.3-7 keV luminosity of the four sources studied ranges from $\sim 10^{30}-10^{33}$ erg/s.

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