Periodic Analysis of Arrival Times in Delayed Cosmic-Ray Coincidences

GL'NN and 0 S T R I K E R (1) have proposed an clTicient acceleration mechanism for cosmic rays in the vicinity of pulsars. While the theory is ditIicult to t~est directly, an observation of h ighenergy y-rays from the direction of a pulsar would give supporting evidence for it. A flux of y-rays in the l0 ~ eV energy region has been reported from the Crab Nebula, though they may not come from its central pulsar NP 0532 (*). Some observations, using the a~mosphcric (~crenkov technique, have indicated both continuous and periodic y-rays from some other pulsars (~-5), but continued observation ham z~ot confirmed these (~'~). Indee(t, CHATTERJI.~E etal. (s) have shown that for most pulsars the flux limits obtainable with the technique are greater than the total energy output, and only the Crab pulsar is likely to ~ivc detectable fluxes. It remains possible: however, that there may bc sporadic periodic emission of detectable fluxes of y-rays, and certainly there is evidence that the flux from the Crab Nebula is correlated with ~,glitcbes ,~ in NP 0532 (). I t has also been suggested (9) that under favourable conditions charged paxticles might be cham~elled to the Earth by magnetic fields and preserve their periodicity. In this case, however, any periodicity present would correspond to an earlier m~kl~own epoch, and WEEKES (~o) has pointed out that very highly monoencrgetic beams of particles would be required to preserve phase.