Since their discovery 30 years ago , pulsars have been understood to be neutron stars ( NSs ) born rotating rapidly ( \sim 10 - 100 ms ) .
These neutron stars are thought to be created in supernova explosions involving massive stars , which give rise to expanding supernova remnants ( SNRs ) .
With over 220 Galactic SNRs known ( Green 1998 ) and over 1200 radio pulsars detected ( Camilo et al .
2000 ) , it is quite surprising that few associations between the two populations have been identified with any certainty .
Here we report the discovery of a remarkable 0.3 sec X-ray pulsar , PSR J1846 - 0258 , associated with the supernova remnant Kes 75 .
With a characteristic age of only 723 yr , consistent with the age of Kes 75 , PSR J1846 - 0258 is the youngest pulsar yet discovered and is being rapidly spun down by torques from a large magnetic dipole of strength \simeq 5 \times 10 ^ { 13 } G , just above the so-called quantum critical field .
PSR J1846 - 0258 resides in this transitional regime where the magnetic field is hypothesized to separate the regular pulsars from the so-called magnetars .
PSR J1846 - 0258 is evidently a Crab-like pulsar , however , its period , spin-down rate , spin-down conversion efficiency , are each an order-of-magnitude greater , likely the result of its extreme magnetic field .