Maintaining the Ephemeris of the Geminga Pulsar Until GLAST

The Geminga pulsar is unique among gamma-ray pulsars in having a precise and continuous, phase-connected ephemeris from 1973 up to the present. Since the demise of the Compton Gamma-Ray Observatory in June 2000, the only practical method of maintaining Geminga's ephemeris is with X-ray observations. To extend our continuing XMM-Newton program on Geminga, we now request short observations twice per year until 2007, when GLAST and/or AGILE will resume the gamma-ray timing. The principal scientific need for a phase-connected ephemeris is to provide an absolute phase reference for ground-based observations, and to monitor glitch activity such as that which recurred in 2002.