Unraveling the Hybrid Origins of the X-Ray Nonthermal Emission from IGR J17091-3624

We present a comprehensive study based on multiwavelength observations from the NuSTAR, NICER, Swift, Fermi, NEOWISE, and ATCA telescopes during the 2022 outburst of the black-hole X-ray binary IGR J17091-3624. Our investigation concentrates on the heartbeat-like variability in the X-ray emission, with the aim of using it as a tool to unravel the origin of the nonthermal emission during the heartbeat state. Through X-ray timing and spectral analysis, we observe that the heartbeat-like variability correlates with changes in the disk temperature, supporting the disk radiation pressure instability scenario. Moreover, in addition to a Comptonization component, our time-averaged and phase-resolved spectroscopy reveal the presence of a power-law component that varies independently from the disk component. Combined with the radio-X-ray spectral energy distribution fitting, our results suggest that the power-law component could originate from synchrotron self-Compton radiation in the jet, which requires a strong magnetic field of about B = (0.3-3.5) × 10⁶ G. Additionally, assuming that IGR J17091-3624 and GRS 1915 + 105 share the same radio-X-ray correlation coefficient during both the hard and the heartbeat states, we obtain a distance of 13.7 ± 2.3 kpc for IGR J17091-3624.