Megachannel Extraterrestrial Assay Candidates: No Transmissions from Intrinsically Steady Sources

摘要

We report new, more sensitive observations of nine of the 11 extrastatistical signals in the Megachannel Extraterrestrial Assay (META). These extrastatistical signals had all the expected characteristics of a transmission from an extraterrestrial transmitter, except that they did not repeat. Cordes, Lazio, & Sagan showed that this lack of repeatability could be explained by the high detection thresholds used in the reobservations of these candidates, combined with interstellar scintillation of intrinsically steady sources. We use the Cordes et al. methodology, correcting an error in the original presentation, and our new observations to rule out this scintillation hypothesis at a confidence level of at least 97.8% (for the case of an intrinsically weak source) and to a level in excess of 99% (if the source strengths are comparable to the value favored by Cordes et al.). We also demonstrate that gravitational microlensing cannot account for the initial detection of these candidate signals, nor is gravitational lensing likely to play a role in future SETI programs. We conclude that the META candidates do not reflect a large population of powerful, strong beacons.