Kavli Affiliate: Erin Kara
| First 5 Authors: Jingyi Wang, Erin Kara, Matteo Lucchini, Adam Ingram, Michiel van der Klis
| Summary:
We perform the first systematic search of all NICER archival observations of
black hole (and candidate) low-mass X-ray binaries for signatures of
reverberation. Reverberation lags result from the light travel time difference
between the direct coronal emission and the reflected disk component, and
therefore their properties are a useful probe of the disk-corona geometry. We
detect new signatures of reverberation lags in 8 sources, increasing the total
sample from 3 to 11, and study the evolution of reverberation lag properties as
the sources evolve in outbursts. We find that in all of the 9 sources with more
than 1 reverberation lag detection, the reverberation lags become longer and
dominate at lower Fourier frequencies during the hard-to-soft state transition.
This result shows that the evolution in reverberation lags is a global property
of the state transitions of black hole low-mass X-ray binaries, which is
valuable in constraining models of such state transitions. The reverberation
lag evolution suggests that the corona is the base of a jet which vertically
expands and/or gets ejected during state transition. We also discover that in
the hard state, the reverberation lags get shorter, just as the QPOs move to
higher frequencies, but then in the state transition, while the QPOs continue
to higher frequencies, the lags get longer. We discuss implications for the
coronal geometry and physical models of QPOs in light of this new finding.
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