Discovery of a 136 Millisecond Radio and X-Ray Pulsar in Supernova Remnant G54.1+0.3

We report the discovery of a pulsar with period P = 136 ms and dispersion measure 308 cm -3 pc in a deep observation of the supernova remnant (SNR) G54.1+0.3 with the Arecibo radio telescope. Timing measurements of the new pulsar, J1930+1852, reveal a characteristic age of P /2 = 2900 yr and a spin-down luminosity of = 1.2 × 10 37 ergs s -1 . We have subsequently searched archival ASCA X-ray data of this SNR and detect pulsations with a consistent period. These findings ensure that PSR J1930+1852 is the pulsar that powers the "Crab-like" SNR G54.1+0.3. Together with existing Chandra observations of the SNR, we derive an X-ray pulsed fraction (2-10 keV) of ≈27%. We also find that the cooling efficiency of the pulsar wind nebula (PWN) is intermediate between those of the Vela and Crab PWNe: L X (2-10 keV) ~ 0.002 . PSR J1930+1852 is a very weak radio source, with a period-averaged flux density at 1180 MHz of 60 μJy. For a distance of 5 kpc, its luminosity, ~1 mJy kpc 2 , is among the lowest for known young pulsars.