Title:	Synchrotron Radiation from NGC 470 HLX1—a Hidden Hyperluminous Accreting Neutron Star?
Authors:	Ghosh, Tanuman Sethi, Shiv Dewangan, Gulab Chand Bachetti, Matteo Rana, Vikram Misra, Ranjeev
Issue Date:	16-Mar-2026
Publisher:	The Astrophysical Journal
Citation:	The Astrophysical Journal, 2026, Vol. 1000 (1), AR No. 105
Abstract:	The origin of the large-amplitude, quasi-periodic X-ray flux variations in several classes of the Galactic microquasar GRS 1915+105 remains unresolved. We address this issue through flux-resolved, broadband (0.8–20 keV) spectral modeling and simultaneous covariance spectral analysis during two κ and two ω class observations using AstroSat/SXT and LAXPC. The lightcurves show strong, quasi-periodic oscillations involving rapid transitions between bright bursts and deep dips on timescales of a few tens of seconds. Flux-resolved spectroscopy indicates that high-flux intervals in both classes are dominated by a hot, optically thick accretion disk with steep Comptonized emission, whereas low-flux intervals correspond to a cooler or partially recessed disk and a harder coronal continuum. These transitions involve a systematic 1–2 keV drop in disk temperature and a pronounced hardening of the Comptonized component, with flux reductions of up to a factor of five. Using covariance spectra across 0.015–5 Hz, we show that the rapid coherent variability arises almost entirely from the disk, which exhibits strong energy-dependent variations, while the Comptonized component contributes minimally. The combined results suggest that radiation-pressure-driven structural changes in the disk, with a slower coronal response, produce the observed oscillations, consistent with cyclic disk evacuation and refilling in the κ and ω classes.
Description:	Open Access
URI:	http://hdl.handle.net/2289/8700
ISSN:	1538-4357
Alternative Location:	https://doi.org/10.48550/arXiv.2511.10183 http://doi.org/10.3847/1538-4357/ae4343
Copyright:	© 2026. National Astronomical Observatories, CAS and IOP Publishing Ltd
Appears in Collections:	Research Papers (A&A)

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