THE GEMINGA PULSAR - SOFT-X-RAY VARIABILITY AND AN EUVE OBSERVATION

We observed the Geminga pulsar with the EUVE satellite, detecting puls ed emission in the Deep Survey imager. Joint spectral fits of the EUVE flux with ROSAT PSPC data are consistent with thermal plus power-law models in which the thermal component makes the dominant contribution to the soft X-ray flux seen by EWE and ROSAT. The data are consistent with blackbody emission of T=(4-6)x10(5) K over most of the surface of the star at the measured parallax distance of 160 pc. Although model atmospheres are more realistic, and can fit the data with effective te mperatures a factor of 2 lower, current data would not discriminate be tween these and blackbody models. We also find evidence for variabilit y of Geminga's soft X-ray pulse shape. Narrow dips in the light curve that were present in 1991 had largely disappeared in 1993/1994, causin g the pulsed fraction to decline from 32% to 18%. If the dips are attr ibuted to cyclotron resonance scattering by an e(+/-) plasma on closed magnetic held lines, then the process that resupplies that plasma mus t be variable.