IS GEMINGA A GLITCHING PULSAR

The recent discovery that Geminga is a pulsar has been followed by ind ications 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 congr uent-to 31 +/- 18. We propose that Geminga is a glitching pulsar with dynamical parameters similar to those of the Vela pulsar, whose interg litch behaviour is characterized by a large second derivative. With th e vortex unpinning model for glitches, if we adopt the hypothesis that the number of vortices unpinned in each glitch and the moment of iner tia of the crust superfluid involved in the interglitch response are t he same in Geminga as in Vela, we find that the expected interglitch s econd derivative in Geminga agrees with that of the COS-B ephemeris.