The balloon-borne experiment FIGARO II was launched from the base of Trapani-Milo on 1990 July 9 at 0433 UT and observed the Crab pulsar for about 5 hr. The light curve of the signal from PSR 0531 + 21 folded with the radio period shows clearly the known double-peak structure. The spectrum of the second peak, the dominant structure in the hard X-rays and low-energy gamma rays, is characterized by a feature which, if interpreted as an emission line, gives the intensity of (0.86 +/- 0.33) 10(-4) photons cm-2 s-1 at the energy of 0.44 +/- 0.01 MeV at a confidence level of 99.6%. If this feature is the signature of positron annihilation close to the neutron star surface, redshifted by the intense gravitational field, it is possible to estimate the mass-to-radius ratio of the Crab neutron star and the positron production rate from one of the polar caps. The former is equal to 0.087 M. km-1 and the latter 8.2 x 10(39) e+ s-1 for a pencil beam pattern, in reasonable agreement with some heuristic estimates based on the number of energetic particles radiating the optical pulses.
Massaro, E., Matt, G., Salvati, M., Costa, E., Mandrou, P., Niel, M., et al. (1991). DETECTION OF A FEATURE AT 0.44 MEV IN THE CRAB PULSAR SPECTRUM WITH FIGARO-II - A REDSHIFTED POSITRON-ANNIHILATION LINE. THE ASTROPHYSICAL JOURNAL, 376(1), L11-L15 [10.1086/186091].
DETECTION OF A FEATURE AT 0.44 MEV IN THE CRAB PULSAR SPECTRUM WITH FIGARO-II - A REDSHIFTED POSITRON-ANNIHILATION LINE
MATT, Giorgio;
1991-01-01
Abstract
The balloon-borne experiment FIGARO II was launched from the base of Trapani-Milo on 1990 July 9 at 0433 UT and observed the Crab pulsar for about 5 hr. The light curve of the signal from PSR 0531 + 21 folded with the radio period shows clearly the known double-peak structure. The spectrum of the second peak, the dominant structure in the hard X-rays and low-energy gamma rays, is characterized by a feature which, if interpreted as an emission line, gives the intensity of (0.86 +/- 0.33) 10(-4) photons cm-2 s-1 at the energy of 0.44 +/- 0.01 MeV at a confidence level of 99.6%. If this feature is the signature of positron annihilation close to the neutron star surface, redshifted by the intense gravitational field, it is possible to estimate the mass-to-radius ratio of the Crab neutron star and the positron production rate from one of the polar caps. The former is equal to 0.087 M. km-1 and the latter 8.2 x 10(39) e+ s-1 for a pencil beam pattern, in reasonable agreement with some heuristic estimates based on the number of energetic particles radiating the optical pulses.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
