* Astronomy

Title: A Radio SETI Campaign for microsec-sec Periodic Signals
Author: G. R. Harp, R. F. Ackermann, Alfredo Astorga, Jack Arbunich, Kristin Hightower, Seth Meitzner, W. C. Barott, Michael C. Nolan, D. G. Messerschmitt, Douglas A. Vakoch, Seth Shostak, J. C. Tarter

We report a novel radio autocorrelation (AC) search for extraterrestrial intelligence (SETI). For selected frequencies across the terrestrial microwave window (1-10 GHz) observations were conducted at the Allen Telescope Array to identify artificial non-sinusoidal periodic signals with radio bandwidths greater than 1 kHz, which are capable of carrying substantial messages with symbol-rates from 10-10e6 Hz. Out of 243 observations, about half (101) were directed toward sources with known continuum flux greater than 1 Jy (quasars, pulsars, supernova remnants and masers), based on the hypothesis that they might harbour heretofore undiscovered natural or artificial, repetitive, phase or frequency modulation. The rest of the targets were mostly toward exoplanet stars and similarly interesting targets from the standpoint of SETI. This campaign rules out several previously untested hypotheses relating to the number of artificially modulated "natural" sources. Since we are using a phase sensitive detector, these observations break new ground on this topic. We conclude that the maximum probability that future observations like the ones described here will reveal repetitively modulated emissions from a wide variety of sources, including quasars, supernova remnants and bright stars, is no more than 15-30 percent, depending on source type. The paper concludes by describing an approach to expanding this survey to many more targets and much greater sensitivity using archived and real-time data from interferometers all over the world.

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