Observation of the VELA Pulsar, PSR 0833-45, at 0.2--6.0 MeV with the FIGARO II Experiment

Results are reported of a 7.75 hr observation of PSR 0833-45 in Vela with FIGARO II (French Italian GAmma Ray Observatory) performed during a balloon flight on November 25, 1988. Two-sigma upper limits for the pulsar flux are given in the gamma-ray energy range 0.2-6.0 MeV. The values are significantly lower than the measured flux obtained by the Riverside experiment as reported by Tumay Tumer et al. in 1984, 31 days after a large glitch in the pulsar period. The FIGARO data also show a departure from the extrapolatian below 50 MeV of the time-averaged flux measured by the COS B satellite, suggesting the existence of a break in the 'quiescent' energy spectrum for values at or obove 5-10 MeV.