Gamma-Ray Sources Observed by Cos-B

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The pulse shape and the spectrum of PSR B0531+21 (Crab pulsar) in the low-energy gamma rays observed with FIGARO II

The FIGARO II experiment observed the Crab pulsar in the energy range 0.15-4 MeV during two transmediterranean flights, on 1990 July 9 and on 1986 July 11. A detailed analysis of the pulse profiles shows that the profile in the energy band 0.37-0.51 MeV is characterized, in addition to the main ones, by the presence in the Interpeak region of two other peaks, which could be associated with the 0.44 MeV line reported by Massaro et al. (1991). Spectral analysis confirms that the Ip spectrum, harder than those of P1 and P2, should progressively steepen with increasing energy. We conclude that the observed Crab emission can be due to the superposition of two components and that the one dominant in the Ip is associated with the pair production in the magnetosphere

OBSERVATION OF THE X-RAY PULSAR-A 0535+26 WITH THE FIGARO-II EXPERIMENT

The FIGARO II experiment observed the transient X-ray pulsar A0535+26 in the 0.15-4 MeV range, only 11.1 +/- 4 days after an expected outburst. We found evidence for periodicity at 103.2 sec close to the extrapolated value. The light-curve and the spectral shape of this low energy gamma-ray emission are presented here

OBSERVATION OF A0535+26 AT ENERGIES ABOVE 150 KEV WITH THE FIGARO-II EXPERIMENT

The transient pulsating X-ray source A0535 + 26 was observed by the FIGARO II gamma-ray experiment on 1990 July 9. The periodogram of about 6 hr of data shows only one significant signal (3.5 sigma) at the period of 103.2 s, very close to the expected one. The folded light curve is characterized by a double-peak structure and a narrow dip; It is similar to that at lower energies. The pulsed flux is (8.6 +/- 2.3) x 10(-6) photons cm-2 s-1 keV-1 in the 148-260 keV band. We also find evidence of a low-energy cutoff below 167 keV

PHASE DISTRIBUTION OF THE 0.44 MEV FEATURE IN THE CRAB PULSAR SPECTRUM

On 1990 July 9, the balloon-borne experiment FIGARO II (0.15 - 4 MeV) observed the Crab region. The light-curve of PSR 0531+212 shows, in addition to the well-known two-peak structures, evidence for extra structures at absolute radio phases 0.1, 0.3, and 0.45 around the energy 0.44 MeV. The phase-resolved spectroscopy confirms that an excess, compatible with a line-like feature, is present at these phase positions