PIONEER-10 SEARCH FOR GRAVITATIONAL WAVES: NO EVIDENCE FOR COHERENT RADIATION FROM GEMINGA

It has been reported1 that an observed 160-min solar oscillation may be caused by gravitational radiation from the intense γ-ray source Geminga, a source whose period according to the report is exactly one cycle per year different from the solar oscillation period. This remarkable coincidence has motivated us to look for a sinusoidal component having a period near 160min in Doppler data from the 1981 gravitational wave search with Pioneer 10. We find no such component in our most quiet data. Thus, the amplitude of a possible sinusoidal variation is no more than 3.3 × 10−14 in fractional Doppler frequency, which for the direction of Geminga translates into an upper bound of 2 × 10−14 for the polarization component of gravitational spatial strain potentially observable. This places rather stringent limits on the amount of gravitational radiation available to excite the 160-min normal mode of the Sun.