IS GEMINGA A GLITCHING PULSAR

The recent discovery that Geminga is a pulsar has been followed by indications of an anomalous second derivative nu double overdot = 2.8(1.6) x 10(-25) Hz s-1 in the COS-B data, yielding a braking index n congruent-to 31 +/- 18. We propose that Geminga is a glitching pulsar with dynamical parameters similar to those of the Vela pulsar, whose interglitch behaviour is characterized by a large second derivative. With the vortex unpinning model for glitches, if we adopt the hypothesis that the number of vortices unpinned in each glitch and the moment of inertia of the crust superfluid involved in the interglitch response are the same in Geminga as in Vela, we find that the expected interglitch second derivative in Geminga agrees with that of the COS-B ephemeris.