Radio SETI Observations of the Interstellar Object 'Oumuamua

Abstract

Note: This is a revised version of the paper that _corrects_a_calculation_error in translating observed Jansky units to EIRP in Watts. Mistakes are labeled below. Motivated by the hypothesis that Oumuamua could conceivably be an interstellar probe, we used the Allen Telescope Array to search for radio transmissions that would indicate a non-natural origin for this object. Observations were made at radio frequencies between 1 and 10 GHz using the Array's correlator receiver with a channel bandwidth of 100 kHz. In frequency regions not corrupted by man-made interference, we find no signal flux with frequency-dependent lower limits of 0.01 Jy at 1 GHz and 0.1 Jy at 7 GHz. For a putative isotropic object, these limits correspond to transmitter powers of (was mistakenly 30 mW) 10 W and (was mistakenly 300 mW) 100 W, respectively. In frequency ranges that are heavily utilized for satellite communications, our sensitivity to weak signals is badly impinged, but we can still place an upper limit of (was mistakenly 10 W) 3 kW for a transmitter on the asteroid. For comparison and validation should a transmitter be discovered, contemporaneous measurements were made on the solar system asteroids 2017 UZ and 2017 WC with comparable sensitivities. Because they are closer to Earth, we place upper limits on transmitter power to be 0.1 and 0.001 times the limits for Oumuamua, respectively.