Similarities and Differences in Accretion Flow Properties between GRS 1915+105 and IGR J17091-3624: a Case Study

TL;DR

This study compares the accretion flow properties of GRS 1915+105 and IGR J17091-3624 using spectro-temporal analysis, revealing similarities and differences in their variability classes and underlying mechanisms.

Contribution

It provides a detailed comparative analysis of the accretion flow dynamics in two black hole X-ray binaries, introducing a plausible accretion mechanism based on spectral and timing features.

Findings

Detection of sharp QPOs at ~7.1 Hz in GRS 1915+105

Observation of ~20 mHz QPOs in IGR J17091-3624

Spectral fitting with TCAF model supports proposed accretion mechanism

Abstract

We perform a comparative spectro-temporal analysis on the variability classes of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying accretion flow mechanism. The $\nu$, as well as C2 class Rossi X-Ray Timing Explorer observation, have been considered for analysis. We investigate the intensity variation of the source in different energy domains that correspond to different components of the accretion flow and infer the relative dominance of these flow components during the dip/flare events. We correlate the dependence of the dynamic photon index ($\Theta$) with intensities in different energy bands and comment on the transition of the source to hard/soft phases during soft dips/flares. We also report the presence of sharp QPOs at \sim7.1 Hz corresponding to both softer and harder domain in the case of $\nu$ variability class of GRS 1915+105 and discuss the possible accretion flow configuration it suggests. Sharp QPO around \sim20 mHz is observed in $\nu$ and C2 classes of IGR J17091-3624 in low and mid energy band (2.0-6.0 keV and 6.0-15.0 keV), but remains undetected in high energy (15.0-60.0 keV). The 2.5-25.0 keV background-subtracted spectra have also been fitted with TCAF along with a Compton reflection component. A plausible accretion flow mechanism in order to explain the observed variability has been proposed.