2002ApJ...578..935J

We present the results of deep X-ray and γ-ray observations of the Geminga pulsar obtained in the final years of the ASCA and CGRO missions and an upper limit from RXTE. A phase-connected ephemeris from the γ-rays is derived that spans the years 1973-2000 after allowing for a minor glitch in frequency of Δf/f=6.2x10^–10 in late 1996. ASCA observations of the hard X-ray pulse profile in 1994 and 1999 confirm this glitch. An improved characterization of the hard X-ray pulse profile and spectrum from the long ASCA observation of 1999 confirms that there is a nonthermal X-ray component that is distinct from the γ-ray spectrum as measured by EGRET. It can be parameterized as a power law of photon index Γ=1.72±0.10 with a flux of 2.62x10^–13 ergs.cm^–2.s^–1 in the 0.7-5 keV band and pulsed fraction 0.54±0.05, similar to (but more precise than) values measured previously. An extrapolation of this spectrum into the energy band observed by the RXTE PCA is consistent with the nondetection of pulsed emission from Geminga with that instrument. These results are interpreted in the context of outer-gap models, and motivations for future X-ray observations of Geminga are given.