Testing the jet quenching paradigm with an ultradeep observation of a steadily soft state black hole

TL;DR

This study uses ultradeep radio observations of a persistent soft state black hole to set strict limits on jet presence, challenging existing models of jet formation and quenching in black hole accretion states.

Contribution

It provides the most rigorous upper limit to date on jets in a soft state black hole binary, demonstrating significant jet suppression and informing models of jet production.

Findings

Jet emission is suppressed by over 2.5 orders of magnitude in the soft state.

Soft state black holes have fainter jets than active galactic nuclei in similar states.

The observed jet suppression exceeds some theoretical predictions.

Abstract

We present ultradeep radio observations with the Expanded Very Large Array of 4U 1957+11, a Galactic black hole candidate X-ray binary known to exist in a persistent soft X-ray state. We derive a stringent upper limit of 11.4 micro-Jy beam^-1 (3 sigma) at 5-7 GHz, which provides the most rigorous upper limit to date on the presence of jets in a soft state black hole X-ray binary. X-ray, UV and optical fluxes obtained within a few weeks of the radio data can be explained by thermal emission from the disk. At this X-ray luminosity, a hard state black hole X-ray binary that follows the established empirical radio--X-ray correlation would be at least 330-810 times brighter at radio frequencies, depending on the distance to 4U 1957+11. This jet quenching of > 2.5 orders of magnitude is greater than some models predict, and implies the jets are prevented from being launched altogether in the soft state. 4U 1957+11 is also more than one order of magnitude fainter than the faintest of the 'radio-quiet' population of hard state black holes. In addition, we show that on average, soft state stellar-mass BHs probably have fainter jets than most active galactic nuclei in a state equivalent to the soft state. These results have implications for the conditions required for powerful, relativistic jets to form, and provide a new empirical constraint for time- and accretion mode-dependent jet models, furthering our understanding of jet production and accretion onto BHs.