Bibcode
De Marco, B.; Ponti, G.; Muñoz-Darias, T.; Nandra, K.
Referencia bibliográfica
The Astrophysical Journal, Volume 814, Issue 1, article id. 50, 14 pp. (2015).
Fecha de publicación:
11
2015
Revista
Número de citas
81
Número de citas referidas
75
Descripción
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.
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