ULTRACAM observations of the black hole X-ray transient XTE J1118+480 in quiescence

Shahbaz, T.; Dhillon, V. S.; Marsh, T. R.; Casares, J.; Zurita, C.; Charles, P. A.; Haswell, C. A. and Hynes, R. I. (2005). ULTRACAM observations of the black hole X-ray transient XTE J1118+480 in quiescence. Monthly Notices of the Royal Astronomical Society, 362(3) pp. 975–982.

DOI: https://doi.org/10.1111/j.1365-2966.2005.09361.x

Abstract

We present high time-resolution multicolour observations of the quiescent soft X-ray transient XTE J1118+480 obtained with ULTRACAM. Superimposed on the double-humped continuum g- and i-band light curves are rapid flare events which typically last a few minutes. The power density spectrum of the light curves can be described by a broken power-law model with a break frequency at 2 mHz or a power-law model plus a broad quasi-periodic oscillation at 2 mHz. In the context of the cellular automaton we estimate the size of the quiescent advection-dominated accretion flow (ADAF) region to be 104 Schwarzschild radii, similar to that observed in other quiescent black hole X-ray transients, suggesting the same underlying physics. The similarities between the low/hard and quiescent-state power density spectrum suggest a similar origin for the optical and X-ray variability, most likely from regions at or near the ADAF.

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