We present the first joint NuSTAR and NICER observations of the ultra-compact X-ray binary (UCXB) 4U 0614+091. This source shows quasi-periodic flux variations on the timescale of ~days. We use reflection modeling techniques to study various components of the accretion system as the flux varies. We find that the flux of the reflected emission and the thermal components representing the disk and the compact object trend closely with the overall flux. However, the flux of the power-law component representing the illuminating X-ray corona scales in the opposite direction, increasing as the total flux decreases. During the lowest flux observation, we see evidence of accretion disk truncation from roughly 6 gravitational radii to 11.5 gravitational radii. This is potentially analogous to the truncation seen in black hole low-mass X-ray binaries, which tends to occur during the low/hard state at sufficiently low Eddington ratios.
@article{arxiv.2308.15581,
title = {Simultaneous NICER and NuSTAR Observations of the Ultra-compact X-ray Binary 4U 0614+091},
author = {David Moutard and Renee Ludlam and Javier A. García and Diego Altamirano and Douglas J. K. Buisson and Edward M. Cackett and Jérôme Chenevez and Nathalie Degenaar and Andrew C. Fabian and Jeroen Homan and Amruta Jaodand and Sean N. Pike and Aarran W. Shaw and Tod E. Strohmayer and John A. Tomsick and Benjamin M. Coughenour},
journal= {arXiv preprint arXiv:2308.15581},
year = {2023}
}
Comments
14 Pages, 6 Figures, 6 Tables, Accepted for publication in ApJ