OBSERVATIONS OF THE PULSAR PSR-1509-58 WITH THE SIGMA-TELESCOPE

The isolated pulsar PSR 1509-58 has been detected by the coded-apertur e hard X-ray/soft gamma-ray SIGMA telescope after 192 hours of observa tions in 1990-1993. The source exhibits, in the 40-300 keV energy rang e, a photon spectrum well fitted by a power law with an index -0.9 +/- 0.6, slightly harder than that of the pulsed spectrum reported by BAT SE in the same energy interval. Taking the distance to be 4.2 kpc, the isotropic source luminosity is 6 10(35) erg s-1 in the 40-300 keV ene rgy interval, or 3 % of the total pulsar rotational energy loss. This makes PSR 1509-58 by far the most efficient producer of hard X-rays am ong the few pulsars detected so far in this energy range.