FULL-SKY SURVEY SEARCHING FOR ULTRA-NARROW-BAND ARTIFICIAL CW SIGNALS: ANALYSIS OF THE RESULTS OF PROJECT META
Guillermo A. Lemarchand
Instituto Argentino de Radioastronmia (CONICET) &
Centro de Estudios Avanzados
Universidad de Buenos Aires
C.C.8 - Sucursal 25, (1425)
Buenos Aires, Argentina
Copyright: Paul Shuch
Project META (Megachannel ExtraTerrestrial Assay), a full-sky survey for artificial narrow-band signals, has been conducted from the Harvard/Smithsonian 26 m radiotelescope at Agassiz Station and from one of the two 30 m radiotelescopes of the Instituto Argentino de Radioastronomía (IAR). The search was performed near the 1420 MHz line of neutral hydrogen, and its second harmonic, using two 8.4 x 10^6 channel Fourier spectrometers of 0.05 Hz resolution and 400 kHz of instantaneous bandwidth. The observing frequency was corrected both for motions with respect to three astronomical inertial frames, and for the effect of Earth's rotation, which provides a characteristic changing signature for narrow-band signals of extraterrestrial origin. Among the 6 x 10^13 spectral channels searched in the northern hemisphere, Horowitz and Sagan reported 37 candidates events exceeding the average threshold of 1.7 x 10^-23 W m^-2, while in the southern hemisphere among 2 x 10^13 spectral channels analyzed we found 19 events exceeding the same threshold. The strongest signals that survive culling for terrestrial interference lie in or near the Galactic Plane.
The first high resolution southern target search around 71 stars (-90 deg < dec < -10 deg), was performed, using the facilities of IAR. For this search, we have selected, "all" the stars at distances nearer than 5 pc and those stars that are falling between +0.6 and +1.0 in the (B-V) color index, with spectral class V, that are at distances nearer than 15.5 pc. Stars bluer than +0.6 have main sequence lifetimes that are too short to provide long-term environmental stability, while stars redder than +1.0 cannot presently be detected. The observations were done with the same spectrometer, tracking each star, at least for 60 minutes, at three different epochs. The third part of the program consisted in observing simultaneously identical celestial coordinates (-30 deg < dec < -10 deg) between the Harvard/Smithsonian and the IAR's radio telescopes.
Finally, we use the Cordes-Lazio-Sagan Model based in scattering theory, simulations and empirical constraints on interstellar scintillations to discuss the intermittency of radio signals from extraterrestrial intelligence. It is showed that these narrow-band non-repeating "events" found by Project META can be generated by (a) radiometer noise fluctuations, (b) a population of constant galactic sources which undergo deep fading and amplification due to interstellar scintillation, consistent with ETI transmissions and (c) real, transient signals of either terrestrial or extraterrestrial origin. The Bayesian test shows that hypothesis (b) and (c) are both highly preferred to (a), but the first two are about equally likely. Using this analysis we discuss the best observing strategies to determine the real origin of these "events".