The Physical Parameters of the Micro-quasar S26 in the Sculptor Group Galaxy NGC 7793

TL;DR

This study analyzes the micro-quasar S26 in NGC 7793 using integral field spectroscopy, estimating shock properties, age, and jet energy, and suggests the central object is likely a black hole with a collimated jet.

Contribution

It provides detailed physical parameters of S26, including shock velocities, age, and jet energy flux, using radiative shock diagnostics and integral field spectra.

Findings

S26 is entering its radiative phase with partially-radiative shocks.

Jet velocity is approximately 330 km/s, bubble expansion is 132 km/s.

The structure's age is about 410,000 years, with a jet energy flux of (4-10)×10^{40} erg/s.

Abstract

NGC 7793 - S26 is an extended source (350 pc $\times$ 185 pc) previously studied in the radio, optical and x-ray domains. It has been identified as a micro-quasar which has inflated a super bubble. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to analyse spectra between 3600--7000 \AA. This allowed us to derive fluxes and line ratios for selected nebular lines. Applying radiative shock model diagnostics, we estimate shock velocities, densities, radiative ages and pressures across the object. We show that S26 is just entering its radiative phase, and that the northern and western regions are dominated by partially-radiative shocks due to a lower density ISM in these directions. We determine a velocity of expansion along the jet of 330 km s$^{-1}$, and a velocity of expansion of the bubble in the minor axis direction of 132 km s$^{-1}$. We determine the age of the structure to be $4.1\times10^5$ yr, and the jet energy flux to be $ (4-10)\times10^{40}$ erg s$^{-1}$ The jet appears to be collimated within $\sim0.25$ deg, and to undergo very little precession. If the relativistic $\beta \sim 1/3$, then some 4 M$_{\odot}$ of relativistic matter has already been processed through the jet. We conclude that the central object in S26 is probably a Black Hole with a mass typical of the ultra-luminous X-ray source population which is currently consuming a fairly massive companion through Roche Lobe accretion.