We report the XMM-Newton /EPIC detection in 2008 March of a luminous ( L _ { X } \sim 10 ^ { 32 - 33 } { erg } ~ { } { s } ^ { -1 } ) , variable X-ray source in the vicinity ( within \sim 6 ^ { \prime \prime } ) 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 T _ { X } \sim 2 \times 10 ^ { 6 } K and \sim 1.5 \times 10 ^ { 7 } K , attenuated by an absorbing column ( N _ { H } \sim 4 \times 10 ^ { 21 } cm ^ { -2 } ) that is consistent with the visual extinction measured toward V838 Mon ( A _ { V } \sim 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 source spectral components appear to be marginally spatially resolved , with the spatial centroid of the hard component lying closer to ( within \sim 2 ^ { \prime \prime } of ) the position of V838 Mon than the broad-band 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 the X-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 the X-rays arose as a consequence of an interaction between V838 Mon ’ s ejecta and its early-type ( B3 V ) companion .