XMM Observations of an IXO in NGC 2276

TL;DR

This paper reports XMM observations of NGC 2276 revealing a highly luminous Intermediate X-ray Object with unusual spectral properties, suggesting a large black hole mass but conflicting disk temperature indications, and notes significant dimming of the galaxy's nucleus over years.

Contribution

First detailed X-ray spectral analysis of an IXO in NGC 2276 showing its high luminosity and spectral characteristics, challenging standard accretion disk models.

Findings

The IXO has a luminosity of 1.1x10^41 erg/s, making it one of the most luminous known.

The spectrum fits a multi-color disk blackbody model, indicating accretion onto a black hole.

The nuclear source has dimmed significantly over eight years.

Abstract

We present the results from a ~53 ksec XMM observation of NGC 2276. This galaxy has an unusual optical morphology with the disk of this spiral appearing to be truncated along the western edge. This XMM observation shows that the X-ray source at the western edge is a bright Intermediate X-ray Object (IXO). Its spectrum is well fit by a multi-color disk blackbody model used to fit optically thick standard accretion disks around black holes. The luminosity derived for this IXO is 1.1x10^41 erg/s in the 0.5 - 10 keV band making it one of the most luminous discovered to date. The large source luminosity implies a large mass black hole if the source is radiating at the Eddington rate. On the other hand, the inner disk temperature determined here is too high for such a massive object given the standard accretion disk model. In addition to the IXO we find that the nuclear source in this galaxy has dimmed by at least a factor of several thousand in the eight years since the ROSAT HRI observations.