Spectral variability of the nucleus of M33 in a Chandra-ACIS observation

Abstract

We have analyzed a 90 ksec long observation of the bright nucleus of M33 made with Chandra/ACIS. We detected low-amplitude (~sim10%) highly significant variability on timescales of ~5000 sec. We also find associated spectral variability. The two main spectral components (a power-law with \Gamma~2 and a multicolor disk -MCD- with kT~0.9-1.2 keV) vary in relative flux. The MCD temperature also increases with increasing MCD flux. The pattern of variability is reminiscent of (but not identical to) galactic black hole binaries. A ~5 M$_{\odot}$ accreting black hole may explain this source.