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

We report on the first firm detection of pulsed -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 dis- tribution is 5:4 and the lightcurve is similar to the lightcurves found earlier between 0.7 and 700 keV: a single broad asym- metric pulse reaching its maximum 0.38 0.03 in phase af- ter 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). Analysis in narrower energy windows shows that the single broad pulse is significantly detected up to 10 MeV. Above 10 MeV we do detect marginally significant (2:1) modulation with an indication for the broad pulse. However, imaging anal- ysis shows the presence of a strong 5.6 source at the position of the pulsar. To investigate this further, we have also analysed contemporaneous CGRO EGRET data (> 30 MeV) collected over a nearly 4 year period. In the 30-100 MeV energy window, adjacent to the COMPTEL 10-30 MeV range, a 4:4 source can be attributed to PSR B1509-58. Timing analysis in this en- ergy window yields an insignificant signal of 1:1, but with a shape somewhat similar to that of the COMPTEL 10-30 MeV lightcurve. Combining the two pulse-phase distributions results in a suggestive double-peaked pulsed signal above the back- ground level estimated in the spatial analyses, with one broad peak near phase 0.38 (aligned with the pulse observed at lower energies) and a second narrower peak near phase 0.85, which is absent for energies below 10 MeV. The modulation significance is, however, only 2:3 and needs confirmation. 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