Tracing the Reverberation Lag in the Hard State of Black Hole X-Ray Binaries
Journal
Date Issued
2015
Author(s)
Description
The authors thank the anonymous referee for helpful comments that significantly improved the paper. The authors also thank Phil Uttley for useful and constructive comments. This work is based on observations obtained with XMM-Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. G.P. acknowledges support via the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408) and the Max Planck Society. T.M.-D. acknowledges support by the Spanish Ministerio de Economía y competitividad (MINECO) under grant AYA2013-42627. Facilities: XMM (EPIC pn) , RXTE (PCA).
Abstract
We report results obtained from a systematic analysis of X-ray lags in a sample of black hole X-ray binaries, with the aim of assessing the presence of reverberation lags and studying their evolution during outburst. We used XMM-Newton and simultaneous Rossi X-ray Timing Explorer (RXTE) observations to obtain broadband energy coverage of both the disk and the hard X-ray Comptonization components. In most cases the detection of reverberation lags is hampered by low levels of variability-power signal-to-noise ratio (typically when the source is in a soft state) and/or short exposure times. The most detailed study was possible for GX 339-4 in the hard state, which allowed us to characterize the evolution of X-ray lags as a function of luminosity in a single source. Over all the sampled frequencies (̃0.05-9 Hz), we observe the hard lags intrinsic to the power-law component, already well known from previous RXTE studies. The XMM-Newton soft X-ray response allows us to detail the disk variability. At low frequencies (long timescales) the disk component always leads the power-law component. On the other hand, a soft reverberation lag (ascribable to thermal reprocessing) is always detected at high frequencies (short timescales). The intrinsic amplitude of the reverberation lag decreases as the source luminosity and the disk fraction increase. This suggests that the distance between the X-ray source and the region of the optically thick disk where reprocessing occurs gradually decreases as GX 339-4 rises in luminosity through the hard state, possibly as a consequence of reduced disk truncation.
Volume
814
Issue
1
Start page
50
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...814...50D
Rights
open.access
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