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 x 10(13) 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 x 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 x 10(-9) ergs cm(-2) s(-1) on the absorbed 0.3-5 keV flux of any bursts.