3XMM J185246.6+003317 as transient neutron star

We performed an X-ray timing and spectral analysis of the variable source 3XMM J185246.6+003317 to investigate its physical nature. The data from all observations of 3XMM J185246.6+003317 conducted by XMM-Newton EPIC MOS1 and MOS2 with the same instrumental setup in 2004-2009 were reprocessed to form a homogenous data set of solar barycenter corrected photon arrival times and high S/N spectra of 3XMM J185246.6+003317. A Bayesian method for the search, detection, and estimation of the parameters of a periodic signal of unknown shape was employed, as developed by Gregory & Loredo (1992, 1993). The results show that 3XMM J185246.6+003317 is a transient neutron star with the genuine spin-period of 23.11722 (23.11711-23.11727) s and its derivative of 5.3 (0.3-5.5)×10^-11 s s^-1, implying a characteristic age of 7 (6-104) kyr, if the period derivative can be ascribed to the genuine spin-down rate of the neutron star. The rotational-phase averaged X-ray spectra at the different brightness periods can be fitted with a highly absorbed blackbody model with different temperatures. The phase-folded light curves in different energy bands with high S/N ratio show a double-peaked profile; the variations depend on time and energy, indicating that radiation emerges from at least two emitting areas. The spectra at the phases corresponding to the maxima in the phase-folded light curve show different spectral parameters of absorbed blackbody radiation, i.e. the hotter one has a smaller size. The source is detected only from September 2008 to April 2009 with persistently decreasing brightness, but not before, even though it was observed by XMM. Hence, it is a transient neutron star or a binary system hosting it.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.