Radio lobes and X-ray hot spots of the extraordinary microquasar in NGC 7793

TL;DR

This paper reports the discovery and multi-wavelength analysis of a microquasar in NGC 7793, revealing a jet-powered system with radio lobes, X-ray hot spots, and an optical nebula, analogous to the Galactic microquasar SS 433.

Contribution

It provides the first detailed multi-band study of this microquasar, demonstrating jet activity and estimating its power and age, thus expanding understanding of extragalactic microquasars.

Findings

Detected large optical nebula coinciding with radio cocoon.

Identified X-ray hot spots as bow shocks from jets.

Estimated jet power of a few times 10^{40} erg/s, active for ~10^5 years.

Abstract

We have studied the newly-discovered microquasar in NGC 7793 in radio, optical and X-ray bands. This system comprises a large (250 x 120 pc) line-emitting optical nebula, detected in H-alpha and HeII 4686. The optical nebula coincides with a synchrotron-emitting radio cocoon, with a radio luminosity about 4 times that of Cas A. The central black hole appears as a hard X-ray source with a point-like, blue optical counterpart. Two prominent radio lobes are located at the extremities of the cocoon. Just ahead of the radio lobes, we found two X-ray hot spots, which we interpret as a signature of the bow shock into the interstellar medium. The X-ray hot spots, radio lobes, X-ray core and major axis of the cocoon are well aligned, proving that the system is powered by a jet. From the X-ray data, we estimate a jet power ~ a few times 10^{40} erg/s, active over a timescale ~10^{5} yrs. This extraordinary system is a long-sought analog of the Galactic microquasar SS 433.