XMM-NEWTON DETECTION OF A TRANSIENT X-RAY SOURCE IN THE VICINITY OF V838 MONOCEROTIS

We report the XMM-Newton/EPIC detection in 2008 March of a luminous (L-X similar to 10(32-33) erg s(-1)), variable X-ray source in the vicinity (within similar to 6 '') of the enigmatic star V838 Mon, which underwent a spectacular outburst in early 2002. Spectral modeling of the XMM-Newton X-ray source indicates the presence of two plasma components with characteristic temperatures of TX similar to 2 x 10(6) K and similar to 1.5 x 10(7) K, attenuated by an absorbing column (N-H similar to 4 x 10(21) cm(-2)) that is consistent with the visual extinction measured toward V838 Mon (A(V) similar to 2). No such luminous source was detected in the immediate vicinity of V838 Mon in Chandra/ACIS-S observations obtained about one year after outburst or, most recently, in 2010 January. The two XMM-Newton source spectral components appear to be marginally spatially resolved, with the spatial centroid of the hard component lying closer to (within similar to 2 '' of) the position of V838 Mon than the broadband source or the soft source component; however, if there are two sources at or near V838 Mon, the Chandra nondetections would imply that both of them are variable. An alternative is that there is a single variable source, and that the apparent spatial separation may actually be due to photon-counting statistics or is perhaps instrumental in origin. We consider constraints placed by theX-ray detection and nondetections on a stellar merger model for the 2002 V838 Mon outburst, in which the spun-up merger product drives a powerful magnetic dynamo. Alternatively, the transient behavior of the X-ray source could indicate that theX-rays arose as a consequence of an interaction between V838 Mon's ejecta and its early-type (B3V) companion.