Chandra Observations of the Nucleus of M33

TL;DR

This paper reports Chandra X-ray observations confirming the ultra-luminous X-ray source in M33's nucleus, analyzing its spectral properties, steadiness, and possible microquasar nature, with implications for understanding such sources in nearby galaxies.

Contribution

First high-resolution confirmation that the luminous X-ray source is within M33's nucleus, with spectral analysis supporting a microquasar-like nature.

Findings

X-ray source is within M33 nucleus with high confidence

Spectrum fits a disc blackbody model with specific temperature and radius

Source flux is steady with minimal variability and high luminosity

Abstract

The nearby galaxy M33 hosts the most luminous steady X-ray source in the Local Group. The high spatial resolution of Chandra allows us to confirm that this ultra-luminous X-ray source is within the nucleus and rule out at the 4.6 sigma level a previously proposed possible counterpart located 1" away. The X-ray spectrum is well fitted by a disc blackbody with kT=1.18+-0.02 keV and R cos(theta)^(0.5}=57+-3 km, consistent with earlier results from ASCA and BeppoSAX. The source flux is steady between 1 and 1e4 s (<3% rms variability, 0.5-10 keV) with a 0.5-10 keV luminosity of 1.5e39 erg/s. The X-ray properties and an association with a radio source are reminiscent of the galactic microquasar GRS 1915+105.