OBSERVATION OF THE CRAB PULSAR, PSR 0531+21, AT 0.2-6.0 MEV WITH THE FIGARO-II EXPERIMENT

Observations of the Crab pulsar (PSR 0531+21) in the energy range 0.2-6 MeV have been made with the balloon-borne FIGARO II experiment. The gross appearance of the light curve is characterized by the wellknown double-peak structure with a phase separation of 0.4. Our data confirm that the second pulse is the dominant feature, and the interpulse region is more luminous than in other energy ranges. Above ∼0.5 MeV, we can detect in the light curve an extra structure, with two features at a phase lag of 0.4 as the main one. Phase-resolved spectroscopy indicates that the first peak spectrum is concave upward, and the second one is concave downward, while the averaged spectrum is well represented by a single power law with slope 2.2. The good timing accuracy of FIGARO allowed us to measure a delay between gamma rays and radio waves of 300 ± 70 μS, that if produced by dispersion, implies a value of DM fitting very well the radio measurements 2 months before and after our observation.