COS-B Results on a Search for Pulsed Gamma-ray Emission from Radio Pulsars
Bignami, G. F.; Hermsen, W.; Boella, G.; D'Amico, N.; Bennett, K.; Buccheri, R.; Kanbach, G.; Lichti, G. G.; Mayer-Hasselwander, H. A.; Paul, J. A.; Scarsi, L.; Swanenburg, B. N.; Taylor, B. G.; Wills, R. D.; Bonnardeau, M.; Higdon, J. C.; Masnou, J.
Germany, Netherlands, Italy, France
Abstract
Gamma-ray data from ESA's satellite COS-B have been used in a search for pulsed gamma-ray emission from sources located in regions near the galactic plane. For this search, the radio data from a number of pulsars were used. Due to the inadequacy of the available radio pulsar parameters, which had to be derived by extrapolation from observations made in different epochs, the investigation has been based on a parameter scan around the predicted value of P. As a result of this search PSR 1822-09 has been recognised to be a possible gamma-ray emitter. The radiation from the already known gamma-ray pulsars PSR0531+21 and PSR0833-45 has been studied in detail. The two pulsars show very similar gamma-ray light curves, both exhibiting peaks of about equal intensity separated by 0.4 of the period. The pulsed fraction of the gamma rays of energy > 50 MeV is at least 78% in the case of PSR0531+21 and consistent with 100% for PSR0833-45. In the range 50 MeV to 4 GeV the differential energy spectrum of PSR0531+21 can be represented by (2.4 ± 0.4) x 10^-7 E- (2.1 ± 0.3) photon cm^-2 s^-1 GeV^-1 , while it is difficult to reconcile the energy spectrum of PSR0833-45 with a single power law over the same energy range. About one third of the total emission of PSR0833-45 lies between the pulses, while in the case of PSR0531+21 no such feature is evident.