AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 52. White Dwarfs, Neutron Stars and Pulsars
Display, Tuesday, June 1, 1999, 10:00am-7:00pm, Southeast Exhibit Hall

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[52.09] An Update on Timing the Geminga Pulsar with the EGRET Gamma-Ray Telescope

J.R. Mattox (Boston Univ.), J.P. Halpern (Columbia), P.A. Caraveo (Fisica Cosmica)

A 1998 observation of the Geminga Pulsar with the EGRET gamma-ray telescope indicated a rotation phase which was inconsistent with our 1997 ephemeris (Mattox et al. 1998). The gamma-ray peaks were observed in July 1998 to arrive 0.15 +/- 0.01 of a rotation earlier than predicted by the cubic ephemeris of Mattox et al. 1998. This suggests that a glitch may have occurred for this pulsar. We will report on an EGRET observation scheduled for May 1999 which will allow us to search for a change in period derivative corresponding to this possible glitch. The rotation phase measured in 1998 is not consistent with the possible sinusoidal modulation reported by Mattox et al. 1998, and this deviation suggests that the modulation apparent in 1997 is most simply explained as timing noise. Current information is available at http://gamma.bu.edu/~mattox/geminga.html.

\noindent Mattox, Halpern, Caraveo, 1998, ApJ, 493, 891.

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