Systematic assessment of disk truncation in the black hole X-ray binary Swift J1727.8-1613 using NICER
Abstract
The 2023/24 NICER monitoring campaign of the 7 Crab bright black hole X-ray binary Swift J1727.8-1613 covered the outburst in almost all accretion states. High-quality data are available in the high-Eddington-fraction hard-intermediate state, hard-to-soft transition, the soft state, and the poorly studied back-transition to the dim hard state, making it an ideal dataset to compare the accretion flow at vastly different accretion rates. We apply disk continuum fitting techniques to investigate the evolution of the inner disk radius throughout the outburst. Taking a temperature-dependent color-correction factor into account, we see evolution of the disk inner radius by a factor of a few comparing the hard states to the thermal/soft state. We tentatively detect an onset of disk truncation in the soft-to-hard transition, right after the source leaves the soft state. After accounting for model systematics, we find the disk to be more truncated in the high-luminosity bright hard state compared to the low-luminosity dim hard state.
Cite
@article{arxiv.2604.14693,
title = {Systematic assessment of disk truncation in the black hole X-ray binary Swift J1727.8-1613 using NICER},
author = {Ole König and James F. Steiner and Niek Bollemeijer and Riley M. T. Connors and Thomas Dauser and Michal Dovčiak and Ningyue Fan and Javier A. García and David Horn and Adam Ingram and Matteo Lucchini and Guglielmo Mastroserio and Cal Miller and Edward Nathan and Michael A. Nowak and Katja Pottschmidt and Ron Remillard and Yujia Song and Jiří Svoboda and Michiel van der Klis and Santiago Ubach and Jörn Wilms and Yuexin Zhang},
journal= {arXiv preprint arXiv:2604.14693},
year = {2026}
}
Comments
Accepted for publication in ApJ (19+5 pages, 12+7 figures)