A Phase-resolved View of "Heartbeat"-like variability in IGR J17091-3624 During the 2022 Outburst

TL;DR

This study provides a phase-resolved analysis of heartbeat-like variability in IGR J17091-3624 during its 2022 outburst, revealing disk instabilities and spectral variations that differ from similar phenomena in GRS 1915+105.

Contribution

It offers the first detailed phase-resolved spectral analysis of IGR J17091-3624's heartbeat-like variability during its 2022 outburst, highlighting differences from GRS 1915+105.

Findings

Detected a high-energy flux shortage at flare peaks with 15 sigma confidence.

Observed synchronous variations in disk temperature and flux during flares.

Found a positive correlation between disk temperature and flux, differing from GRS 1915+105.

Abstract

IGR J17091-3624, in addition to GRS 1915+105, is the only black hole X-ray binary that displays ``heartbeat"-like variability characterized by structured flares with high amplitudes. In this study, we conduct a detailed phase-resolved analysis of the recently identified ``heartbeat"-like Class X variability in IGR J17091-3624 during its 2022 outburst, utilizing data from NICER and NuSTAR observations. A shortage in the high-energy (>20 keV) X-ray flux is detected at peak phases of the soft X-ray flare at a ~15 sigma confidence level from the phase-folded light curves. Furthermore, our phase-resolved spectral analysis reveals variations in the spectral shape, particularly showing significant synchronous variations in the disk temperature and flux with the count rate. These findings imply that the flare is primarily driven by instabilities within the accretion disk, consistent with previous studies on the well-known Class rho variability in GRS 1915+105. However, we also observe a positive correlation between the disk temperature and flux over the flare cycle, which differs from a loop relation between the two parameters found in the Class rho variability. This could suggest differences in underlying physical processes between the two variability classes. Variations in the Componization component during flares are also observed: the electron temperature and covering fraction show anti-correlations with the disk flux, revealing potential interactions between the accretion disk and the corona during these flares.