Possible evidence for pulsed emission of high-energy gamma-rays by PSR B0656+14

We present here possible evidence for a seventh high-energy gamma-ray pulsar, PSR B0656+14, pulsating in gamma rays at E ≥ 50 MeV with the same 384.9 ms periodicity as in radio, using the data obtained during 1991 April to 1993 December by the Energetic Gamma-Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory. Since the pulsed flux is very low, we adapted a weighting method in our analysis of the data to detect the pulsar. With this technique, we found that the null hypothesis (viz., that it is not a pulsar) is probable only at a level of ≤ 2.6 × 10^-7. The phase-selected data corresponding to the peak seen in the events light curve reveals the existence of a high-energy gamma-ray source positionally consistent with the pulsar. We found that the phase-averaged high-energy gamma-ray pulsed flux from PSR B0656+14 is (4.1 ± 1.4) × 10^-8 photons cm^-2 s^-1 at E ≥ 100 MeV, and the exponent of the differential photon number spectrum, -2.8 ± 0.3. The pulsar appears to have an efficiency of approximately 0.001 in converting its spin-down energy-loss rate into high-energy gamma-rays at E ≥ 100 MeV.