The Mid-infrared Emitting Jet in the Black Hole V404 Cygni in Quiescence

TL;DR

This study uses multi-wavelength observations, including JWST and ALMA, to demonstrate that the mid-infrared excess in the quiescent black hole V404 Cygni originates from a persistent jet, not the accretion disk or circumbinary material.

Contribution

First direct evidence that the MIR excess in V404 Cygni during quiescence is due to a jet, confirmed by simultaneous multi-wavelength variability and spectral analysis.

Findings

MIR variability correlates with radio to X-ray emissions.

Spectral index indicates synchrotron radiation from a jet.

Jet emission persists into the quiescent state of the black hole.

Abstract

Observations of some quiescent black hole X-ray binaries have revealed an excess of mid-infrared (MIR) emission above that expected from their donor stars. In one system, V404 Cygni, this excess has been variously suggested to arise from the accretion disk, circumbinary material, or a compact relativistic jet. Here we present simultaneous James Webb Space Telescope (JWST), Atacama Large Millimeter/submillimeter Array (ALMA), and complementary multi-wavelength observations undertaken to resolve this uncertainty. We observed large-amplitude 21 $\mu$m variability on short timescales with JWST, particularly a dramatic flare which swiftly rose to $\approx2.4$ mJy, over 10 times the lowest observed MIR flux density. Similar variability was simultaneously observed from radio to X-ray wavelengths with other facilities throughout the campaign. This variability and the flat radio/mm/MIR spectral index ($\alpha = 0.04 \pm 0.01$) suggest that the MIR excess at and longward of 21 $\mu$m in V404 Cyg does not arise from the accretion disk or circumbinary material. Instead, the emission at 21 $\mu$m is dominated by synchrotron radiation from a jet which persists into quiescence. This result reinforces the ubiquity of the disk-jet connection in accreting black holes across a range of masses and accretion rates.