Anti-Correlation of the Near-Infrared and X-Ray Variations of the Microquasar GRS 1915+105 in Soft State

TL;DR

This study presents long-term near-infrared and X-ray observations of GRS 1915+105 in its soft state, revealing an anti-correlation between NIR flux and X-ray flares, linked to accretion disk dynamics and jet ejection.

Contribution

First detailed NIR monitoring of GRS 1915+105 during its soft state, demonstrating anti-correlation with X-ray activity and insights into accretion disk and jet interactions.

Findings

NIR flux drops > 1 mag during X-ray flares

NIR color reddens after soft state ends

NIR fading correlates with jet ejection events

Abstract

We report detailed, long term near-infrared (NIR) light curves of GRS 1915+105 in 2007-2008, covering its long "soft state" for the first time. From our NIR monitoring and the X-ray data of the All Sky Monitor (ASM) onboard Rossi X-ray Timing Explorer (RXTE), we discovered that the NIR flux dropped by > 1 mag during short X-ray flares with a time-scale of days. With the termination of the soft state, the H-Ks color reddened and the anti-correlation pattern was broken. The observed H-Ks color variation suggests that the dominant NIR source was an accretion disk during the soft state. The short X-ray flares during the soft state were associated with spectral hardening in X-rays and increasing radio emission indicating jet ejection. The temporal NIR fading during the X-ray flares, hence, implies a sudden decrease of the contribution of the accretion disk when the jet is ejected.