The peculiar 2011 outburst of the black hole candidate IGR J17091-3624, a GRS 1915+105 like source?

TL;DR

This paper analyzes the 2011 outburst of IGR J17091-3624, revealing unique spectral evolution and flare-like events similar to GRS 1915+105, suggesting common physical instability mechanisms and considering the system's faintness due to distance and inclination.

Contribution

It provides the first detailed spectral evolution analysis of IGR J17091-3624's 2011 outburst and links its flare phenomena to those of GRS 1915+105, proposing new insights into its physical properties.

Findings

Spectral evolution differed from typical black hole transients.

Detected pseudo periodic flare-like events similar to GRS 1915+105.

Faintness may be due to high inclination angle, not just distance.

Abstract

We report on the long-term monitoring campaign of the black hole candidate IGR J17091-3624 performed with INTEGRAL and Swift during the peculiar outburst started on January 2011. We have studied the two month spectral evolution of the source in detail. Unlike the previous outbursts, the initial transition from the hard to the soft state in 2011 was not followed by the standard spectral evolution expected for a transient black hole binary. IGR J17091-3624 showed pseudo periodic flare-like events in the light curve, closely resembling those observed from GRS 1915+105. We find evidence that these phenomena are due to the same physical instability process ascribed to GRS 1915+105. Finally we speculate that the faintness of IGR J17091-3624 could be not only due to the high distance of the source but to the high inclination angle of the system as well.