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

T. Shahbaz·V. S. Dhillon·T. R. Marsh·J. Casares·C. Zurita·P. A. Charles·C. A. Haswell·R. I. Hynes
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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 lightcurves are rapid flare events which typically last a few minutes. The power density spectrum of the lightcurves 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 (QPO) at ~2 mHz. In the context of the cellular-automaton we estimate the size of the quiescent advection-dominated flow (ADAF) region to be ~10^4 Schwarzschild radii, similar to that observed in other quiescent black hole X-ray transients, suggesting the same underlying physics. The similarites between the low/hard and quiescent state PDS suggest a similar origin for the optical and X-ray variability, most likely from regions at/near the ADAF.

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T. Shahbaz, V. S. Dhillon, T. R. Marsh, J. Casares, C. Zurita, P. A. Charles, C. A. Haswell, R. I. Hynes. 2005-07-21. ULTRACAM observations of the black hole X-ray transient XTE J1118+480 in quiescence. https://doi.org/10.1111/j.1365-2966.2005.09361.x

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