COMPTEL detection of pulsed gamma-ray emission from B1509-58 up to at least 10 MeV

Abstract

We report on the first firm detection of pulsed gamma-ray emission from PSR B1509-58 in the 0.75-30 MeV energy range in CGRO COMPTEL data collected over more than 6 years. The modulation significance in the 0.75-30 MeV pulse-phase distribution is 5.4 sigma and the lightcurve is similar to the lightcurves found earlier between 0.7 and 700 keV: a single broad asymmetric pulse reaching its maximum 0.38 +/- 0.03 in phase after the radio peak, compared to the offset of 0.30 found in the CGRO BATSE soft gamma-ray data, and 0.27 +/- 0.01 for RXTE (2-16 keV), compatible with ASCA (0.7-2.2 keV). Spectral analysis based on the excess counts in the broad pulse of the lightcurve shows that extrapolation of the OSSE power-law spectral fit with index -1.68 describes our data well up to 10 MeV. Above 10 MeV the spectrum breaks abruptly. The precise location of the break/bend between 10 and 30 MeV depends on the interpretation of the structure in the lightcurve measured by COMPTEL and EGRET above 10 MeV.