HST/NICMOS Observations of Fast Infrared Flickering in the Microquasar GRS 1915+105

TL;DR

This study reports rapid infrared flickering in the microquasar GRS 1915+105, indicating jet-related variability on timescales of seconds, which enhances understanding of jet formation near black holes.

Contribution

First detection of fast infrared flickering in GRS 1915+105, linking it to jet activity and providing new insights into jet formation mechanisms.

Findings

Infrared flux varies significantly during the plateau state.

Flickering occurs on timescales of 10-20 seconds, faster than previous IR variability.

IR variations exceed X-ray variations at similar timescales.

Abstract

We report infrared observations of the microquasar GRS 1915+105 using the NICMOS instrument of the Hubble Space Telescope during 9 visits in April-June 2003. During epochs of high X-ray/radio activity near the beginning and end of this period, we find that the $1.87 $\um infrared flux is generally low ($\sim 2$ mJy) and relatively steady. However, during the X-ray/radio ``plateau'' state between these epochs, we find that the infrared flux is significantly higher ($\sim 4-6$ mJy), and strongly variable. In particular, we find events with amplitudes $\sim 20-30$% occurring on timescales of $\sim 10-20$s (e-folding timescales of $\sim 30$s). These flickering timescales are several times faster than any previously-observed infrared variability in GRS 1915+105 and the IR variations exceed corresponding X-ray variations at the same ($\sim 8s$) timescale. These results suggest an entirely new type of infrared variability from this object. Based on the properties of this flickering, we conclude that it arises in the plateau-state jet outflow itself, at a distance $<2.5$ AU from the accretion disk. We discuss the implications of this work and the potential of further flickering observations for understanding jet formation around black holes.