Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA
; Univ Manchester, Jodrell Bank Observ, Macclesfield SK11 9DL, Cheshire, England
; Arecibo Observ, NAIC, Arecibo, PR 00612 USA
; Univ Massachusetts, Dept Astron, Amherst, MA 01003 USA
; Acad Sinica, Inst High Energy Phys, Lab Cosm Ray & High Energy Astrophys, Beijing 100039, Peoples R China
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 (P) over dot = 2900 yr and a spin-down luminosity of (E) over dot = 1.2 x 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 approximate to27%. 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) similar to0.002 (E) over dot. PSR J1930+1852 is a very weak radio source, with a period-averaged flux density at 1180 MHz of 60 muJy. For a distance of 5 kpc, its luminosity, similar to1 mJy kpc(2), is among the lowest for known young pulsars.