Kavli Affiliate: Erin Kara
| First 5 Authors: Ningyue Fan, James F. Steiner, Cosimo Bambi, Erin Kara, Yuexin Zhang
| Summary:
We present a spectral and timing analysis of NICER observations of the black
hole X-ray binary 4U 1630-47 from 2018 to 2024. We find relativistic reflection
features in the hard and soft intermediate states, and disk wind absorption
features in the soft intermediate state and soft state. We fit the reflection
features with relxillCP and find a stable and untruncated disk in the
intermediate states; we fit the wind features with XSTAR and find a stable,
highly ionized wind with high column density across different outbursts.
Specifically, the heartbeat state is seen in two observations in 2021 and 2023
respectively. Through the phase-resolved spectral fitting, we find the flux of
the source to be correlated with the disk parameters while no strong
correlation with the coronal parameters is observed, consistent with the
scenario given by the inner disk radiation pressure instability. A hard lag on
the time scale of 1 s and high coherence is observed near the characteristic
frequency of the heartbeat, which can be explained by the viscous propagation
of mass accretion fluctuations in the disk. The positive relationship between
the heartbeat fractional rms and energy can possibly be explained by a
disk-originated oscillation which is then magnified by the corona scattering.
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