An anomalous quiescent stellar mass black hole

Abstract

We present the results of a 40 ks Chandra observation of the quiescent stellar mass black hole GS 1354-64. A total of 266 net counts are detected at the position of this system. The resulting spectrum is found to be consistent with the spectra of previously observed quiescent black holes, i.e., a power law with a photon index of Γ 2. The inferred luminosity in the 0.5-10 keV band is found to lie in the range 0.5-6.5 × 1034 erg s -1, where the uncertainty in the distance is the dominant source of this large luminosity range. Nonetheless, this luminosity is over an order of magnitude greater than that expected from the known distribution of quiescent stellar mass black hole luminosities and makes GS 1354-64 the only known stellar mass black hole to disagree with this relation. This observation suggests the possibility of significant accretion persisting in the quiescent state. © 2011. The American Astronomical Society. All rights reserved.