2010ApJ...717..795A

We report the XMM-Newton/EPIC detection in 2008 March of a luminous (L_X∼ 10^32–33 erg/s), variable X-ray source in the vicinity (within ∼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 T_X∼ 2x10⁶ K and ∼1.5x10⁷ K, attenuated by an absorbing column (N_H∼ 4x10²¹/cm2) that is consistent with the visual extinction measured toward V838 Mon (A_V∼ 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 ∼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 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.