X - ray Timing Observations of PSR J 1930 + 1852 in the Crab - like SNR G 54 . 1 + 0 . 3

We present new X-ray timing and spectral observations of PSR J1930+1852, the young energetic pulsar at the center of the non-thermal supernova remnant G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer (RXTE ) and Chandra X-ray observatories we have derived an updated timing ephemeris of the 136 ms pulsar spanning 6 years. During this interval, however, the period evolution shows significant variability from the best fit constant spin-down rate of Ṗ = 7.5112(6)×10 s s, suggesting strong timing noise and/or glitch activity. The X-ray emission is highly pulsed (71± 5% modulation) and is characterized by an asymmetric, broad profile (∼ 70% duty cycle) which is nearly twice the radio width. The spectrum of the pulsed emission is well fitted with an absorbed power law of photon index Γ = 1.2 ± 0.2; this is marginally harder than that of the unpulsed component. The total 2 − 10 keV flux of the pulsar is 1.7 × 10 erg cm s. These results confirm PSR J1930+1852 as a typical Crablike pulsar. Subject headings: ISM: individual (G54.1+0.3)—ISM: jets and outflows—radiation mechanisms: non-thermal—stars:neutron (PSR J1930+1852)— supernova remnants— X-rays: ISM Laboratory of Particle Astrophysics, Institute of High Energy Physics, CAS, Beijing 100039, P.R. China; [email protected]; [email protected] Astronomy Department, University of Massachusetts, Amherst, MA 01003; [email protected] Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027; [email protected]