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 \dot { P } = 2900 yr and spin-down luminosity \dot { E } = 1.2 \times 10 ^ { 37 } erg 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 \approx 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 } \mbox { ( 2 - -10 keV ) } \sim 0.002 \dot { E } .
PSR J1930+1852 is a very weak radio source , with period-averaged flux density at 1180 MHz of 60 \mu Jy .
For a distance of 5 kpc , its luminosity , \sim 1 mJy kpc ^ { 2 } , is among the lowest for known young pulsars .