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. Subject headings: pulsars: individual (J1819–1458) — radio continuum: stars — stars: flare, neutron — X-rays: stars