OSSE Observations of the Vela and Geminga Pulsars
NAVAL RESEARCH LAB WASHINGTON DC
Pagination or Media Count:
The Oriented Scintillation Spectrometer Experiment OSSE on board the Compton Gamma Ray Observatory detected the Vela Pulsar PSR B0833-45 during August-September 1991, April-May 1992, and August 1993. Observed light curves have a two-peak pulse profile similar to that observed at higher energies, although the second peak may be wider in the OSSE light curve. Pulsed emission in the first gamma-ray peak was detected with 4.6 sigma statistical significance in the 0.07-0.6 MeV band in the sum of all three observing periods. The second gamma ray peak was detected at no more than 3 sigma significance in the same band. Due to the low statistical significance of the observations, little can be said concerning longer-term temporal variability. The spectrum is hard at lower energies and, in combination with higher energy data, appears to require a break in the 20 MeV region. OSSE also observed Geminga during July 1992, December 1993, and July 1994. No significant pulsed or time averaged emission was observed on any occasion. Upper limits to the pulsed emission suggest, but do not require, a break from the extrapolation of the spectrum measured at higher energies.