We report the discovery of \gamma -ray pulsations ( \geq 0.1 GeV ) from the young radio and X-ray pulsar PSR J0205 + 6449 located in the Galactic supernova remnant 3C 58 .
Data in the \gamma -ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope ( formerly GLAST ) , while the radio rotational ephemeris used to fold \gamma -rays was obtained using both the Green Bank Telescope and the Lovell telescope at Jodrell Bank .
The light curve consists of two peaks separated by 0.49 \pm 0.01 \pm 0.01 cycles which are aligned with the X-ray peaks .
The first \gamma -ray peak trails the radio pulse by 0.08 \pm 0.01 \pm 0.01 , while its amplitude decreases with increasing energy as for the other \gamma -ray pulsars .
Spectral analysis of the pulsed \gamma -ray emission suggests a simple power law of index -2.1 \pm 0.1 \pm 0.2 with an exponential cut-off at 3.0 ^ { +1.1 } _ { -0.7 } \pm 0.4 GeV .
The first uncertainty is statistical and the second is systematic .
The integral \gamma -ray photon flux above 0.1 GeV is ( 13.7 \pm 1.4 \pm 3.0 ) \times 10 ^ { -8 } cm ^ { -2 } s ^ { -1 } , which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3 \times 10 ^ { 34 } ergs s ^ { -1 } and an efficiency \eta of 0.3 % .
Finally , we report a 95 % upper limit on the flux of 1.7 \times 10 ^ { -8 } cm ^ { -2 } s ^ { -1 } for off-pulse emission from the object .