Discovery of Pulsations and a Possible Spectral Feature in the X-Ray Emission from Rotating Radio Transient J1819-1458

PSR J1819-1458 is a rotating radio transient (RRAT) source with an inferred surface dipole magnetic field strength of 5×10¹³ G and a 4.26 s spin period. We present XMM-Newton observations of the X-ray counterpart of this source, CXOU J181939.1-145804, in which we identify pulsations and a possible spectral feature. The X-ray pulsations are at the period predicted by the radio ephemeris, providing an unambiguous identification with the radio source and confirmation of its neutron star nature. The X-ray pulse has a 0.3-5 keV pulsed fraction of 34% and is aligned with the expected phase of the radio pulse. The X-ray spectrum is fit well by an absorbed blackbody with kT=0.14 keV with the addition of an absorption feature at 1 keV, with total absorbed flux of 1.5×10^-13 ergs cm^-2 s^-1 (0.3-5 keV). This absorption feature is well modeled by a Gaussian or resonant cyclotron scattering model, but its significance is dependent on the choice of continuum model. We find no evidence for any X-ray bursts or aperiodic variability on timescales of 6 ms to the duration of the observation and can place the most stringent limit to date of <=3×10^-9 ergs cm^-2 s^-1 on the absorbed 0.3-5 keV flux of any bursts.