Mapping the Contracting Corona in GS 1354-64 with Insight-HXMT and XRISM: Evolving X-ray Lags and Quenched Reflection across a Complete State Transition
Abstract
We present a comprehensive broadband spectro-temporal analysis of the dynamically confirmed Galactic black hole transient GS 1354-64 during its 2025-26 outburst, using near-simultaneous observations from Insight-HXMT and XRISM. The high spectral resolution of the XRISM-Resolve microcalorimeter, coupled with the high-cadence broadband coverage of Insight-HXMT, reveals a dramatic evolution in the inner accretion geometry. During the early hard-intermediate state, the spectrum was dominated by a hot Comptonizing corona accompanied by relativistically broadened reflection features. As the outburst progressed, the corona cooled efficiently, the photon index steepened (Gamma >~ 2.5), and the reflection signatures, including the broad Fe K-alpha emission, were quenched, yielding a featureless, disk-dominated continuum. Concurrently, Type-C quasi-periodic oscillations (QPOs) evolved from 0.25 Hz to 6.52 Hz. Cross-spectral timing analysis revealed that the broadband X-ray time lags changed from pronounced positive (hard) delays (~160 ms) at low frequencies to near zero as the source softened. However, a statistical analysis incorporating the measurement uncertainties shows that the broadband lags lack a significant monotonic correlation with the QPO frequency, photon index, or fractional rms. Instead, the scattered lag behavior suggests a competition between positive Comptonization delays and negative thermal reverberation. While the spectral softening and QPO acceleration provide strong evidence for a geometric contraction of the corona (whether interpreted via Lense-Thirring precession or the Two-Component Advective Flow (TCAF) paradigm), the broadband timing properties underscore the turbulent and inhomogeneous nature of the inner flow as the advancing Keplerian disk drives the source into the soft state.
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BibTeX
@misc{chatterjee2026mapping,
title = {{Mapping the Contracting Corona in GS 1354-64 with Insight-HXMT and XRISM: Evolving X-ray Lags and Quenched Reflection across a Complete State Transition}},
author = {Kaushik Chatterjee and Min Wei and Jie Liao and Biswaraj Palit and Santanu Mondal and Honghui Liu and Chandra B. Singh and Sandeep K. Rout and Ashutosh Tripathi and Mayukh Pahari and Guobao Zhang and Zejun Jiang and Brajesh Kumar and Wei Wang and Hsiang-Kuang Chang and Xiaowei Liu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15569},
eprint = {2610.15569},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15569},
}
RIS
TY - UNPB
TI - Mapping the Contracting Corona in GS 1354-64 with Insight-HXMT and XRISM: Evolving X-ray Lags and Quenched Reflection across a Complete State Transition
AU - Kaushik Chatterjee
AU - Min Wei
AU - Jie Liao
AU - Biswaraj Palit
AU - Santanu Mondal
AU - Honghui Liu
AU - Chandra B. Singh
AU - Sandeep K. Rout
AU - Ashutosh Tripathi
AU - Mayukh Pahari
AU - Guobao Zhang
AU - Zejun Jiang
AU - Brajesh Kumar
AU - Wei Wang
AU - Hsiang-Kuang Chang
AU - Xiaowei Liu
PY - 2026
DA - 2026/10/11
PB - arXiv
DO - 10.48550/arxiv.2610.15569
UR - https://arxiv.org/abs/2610.15569
AB - We present a comprehensive broadband spectro-temporal analysis of the dynamically confirmed Galactic black hole transient GS 1354-64 during its 2025-26 outburst, using near-simultaneous observations from Insight-HXMT and XRISM. The high spectral resolution of the XRISM-Resolve microcalorimeter, coupled with the high-cadence broadband coverage of Insight-HXMT, reveals a dramatic evolution in the inner accretion geometry. During the early hard-intermediate state, the spectrum was dominated by a hot Comptonizing corona accompanied by relativistically broadened reflection features. As the outburst progressed, the corona cooled efficiently, the photon index steepened (Gamma >~ 2.5), and the reflection signatures, including the broad Fe K-alpha emission, were quenched, yielding a featureless, disk-dominated continuum. Concurrently, Type-C quasi-periodic oscillations (QPOs) evolved from 0.25 Hz to 6.52 Hz. Cross-spectral timing analysis revealed that the broadband X-ray time lags changed from pronounced positive (hard) delays (~160 ms) at low frequencies to near zero as the source softened. However, a statistical analysis incorporating the measurement uncertainties shows that the broadband lags lack a significant monotonic correlation with the QPO frequency, photon index, or fractional rms. Instead, the scattered lag behavior suggests a competition between positive Comptonization delays and negative thermal reverberation. While the spectral softening and QPO acceleration provide strong evidence for a geometric contraction of the corona (whether interpreted via Lense-Thirring precession or the Two-Component Advective Flow (TCAF) paradigm), the broadband timing properties underscore the turbulent and inhomogeneous nature of the inner flow as the advancing Keplerian disk drives the source into the soft state.
ER -