Coded mask X-ray images of the Large Magellanic Cloud: hard X-ray emission from EXO 053109–6609.2

Hard X-ray (2–32 keV) imaging observations of the Large Magellanic Cloud (LMC) with the University of Birmingham coded mask X-ray telescope (SL2 XRT) have detected significant high-energy flux from EXO 053109–6609.2, a source recently discovered at soft X-ray energies with EXOSAT. We confirm the conclusion reached by Brunner that, despite earlier conclusions to the contrary, the source has a very hard spectrum. Assuming the source to be in the LMC, its luminosity in the 2–10 keV energy band is $\approx 1\times{10}^{37}\,\text{erg s}^{-1}.$ A comparison of the SL2 XRT flux with observations with other instruments shows that the source is highly variable on a time-scale of years or less. The spectral and temporal characteristics of this source are consistent with an identification as either a Be star/neutron star binary system or a background active galactic nucleus. Recent spectroscopic observations (M. Pakull and K. Beuermann, private communication) favour the former.