Determination of the Mass of IGR J17091-3624 from "Spectro-temporal" Variations during the Onset Phase of the 2011 Outburst

Abstract

The 2011 outburst of the black hole candidate IGR J17091-3624 followed the canonical track of state transitions along with the evolution of quasi-periodic oscillation (QPO) frequencies before it began exhibiting various variability classes similar to GRS 1915+105. We use this canonical evolution of spectral and temporal properties to determine the mass of IGR J17091-3624, using three different methods: photon index (Γ)-QPO frequency (ν) correlation, QPO frequency (ν)-time (day) evolution, and broadband spectral modeling based on two-component advective flow (TCAF). We provide a combined mass estimate for the source using a naive Bayes based joint likelihood approach. This gives a probable mass range of 11.8 {M}_⊙ -13.7 {M}_⊙ . Considering each individual estimate and taking the lowermost and uppermost bounds among all three methods, we get a mass range of 8.7 {M}_⊙ -15.6 {M}_⊙ with 90% confidence. We discuss the possible implications of our findings in the context of two-component accretion flow.