Steady jets from radiatively efficient hard states in GRS 1915+105

TL;DR

This study reveals a strong correlation between radio and X-ray emissions in GRS 1915+105 during its hard state, suggesting either radiatively efficient accretion or jet-dominated X-ray emission, with implications for black hole accretion models.

Contribution

It provides the first detailed analysis of the radio-X-ray relationship in GRS 1915+105 during plateau states, proposing a possible universal transition in accretion efficiency for stellar-mass black holes.

Findings

Radio and X-ray emissions decay during plateau states, with radio decaying faster.

The power-law index of the radio-X-ray relationship is ~1.7, higher than in other XRBs.

Evidence suggests either radiatively efficient accretion or jet-dominated X-ray emission in GRS 1915+105.

Abstract

Recent studies of different X-ray binaries (XRBs) have shown a clear correlation between the radio and X-ray emission. We present evidence of a close relationship found between the radio and X-ray emission at different epochs for GRS1915+105, using observations from the Ryle Telescope and Rossi X-ray Timing Explorer satellite. The strongest correlation was found during the hard state (also known as the `plateau' state), where a steady AU-scale jet is known to exist. Both the radio and X-ray emission were found to decay from the start of most plateau states, with the radio emission decaying faster. An empirical relationship of $S_{\rm{radio}}\propto S_{\rm{X-ray}}^{\xi}$ was then fitted to data taken only during the plateau state, resulting in a power-law index of $\xi\sim1.7\pm0.3$, which is significantly higher than in other black hole XRBs in a similar state. An advection-flow model was then fitted to this relationship and compared to the universal XRB relationship as described by Gallo et al. (2003). We conclude that either (I) the accretion disk in this source is radiatively efficient, even during the continuous outflow of a compact jet, which could also suggest a universal turn-over from radiatively inefficient to efficient for all stellar-mass black holes at a critical mass accretion rate ($\dot{m}_{\rm{c}}\approx10^{18.5}$ g/s); or (II) the X-rays in the plateau state are dominated by emission from the base of the jet and not the accretion disk (e.g. via inverse Compton scattering from the outflow).