An ATA Search for a Repetition of the Wow Signal

Abstract

The Allen Telescope Array was used to search for signals with characteristics similar to the “Wow” signal, the best candidate for an extraterrestrial radio signal found during Ohio State University’s (OSU’s) seven-year 21 cm 10-kHz channel sky survey for signals possibly due to extraterrestrial intelligence. While previous follow-up searches have reported null results, our observations covered a 5 deg2 field of view that extends well beyond the locus of all consistent directions of arrival (DOAs) of the original signal, and covered a 10 MHz bandwidth four times wider than the widest prior follow-up observations, using 12.8 kHz channels approximating OSU’s 10 kHz resolution. Approximately 100 hours of data were accumulated, considerably more time than any previous follow-up campaigns. We used interferometric imaging with an angular resolution of approximately 007 and automated feature-finding to search for point-like features mimicking a Wow repetition, obtaining single-channel sensitivity of ∼1.2 Jy for one minute averages. This allows identification of the DOA of a very brief repetition, with strong discrimination from radio interference, and eliminates the usual constraint that the signal must persist for long periods of time (around one hour) before the true DOA can be verified (because interfering signals from the horizon sometimes masquerade as coming from the look direction). No point-like features significantly exceeding the noise were found inside the full width at half maximum of the OSU fields of view, although one 26σ point-like feature was detected during one 10 second integration about 1/3° away.

SETI in 2020

“…Signal field. This work, by Harp et al (2020), scanned the entire field consistent with the original signal, and included a 10 MHz bandwidth and ∼100 hours of observation, the longest follow-up yet performed. Since the Wow!…”

“…Gray's application here is to the Wow! Signal (and indeed this motivated Harp et al (2020) above) but more generally is that similar "one-off" signals should be prioritized for re-observation.…”

Could the "Wow" signal have originated from a stochastic repeating beacon?

“…Despite numerous attempts to replicate the detection of Wow (Gray 1994;Gray & Marvel 2001;Gray & Ellingsen 2002;Harp et al 2020), the signal has not been observed again. The single-beam detection and lack of any repetition (especially with greater sensitivity, longer observations and broader spectral coverage), ostensibly places considerable pressure on the credibility of the Wow signal 1 .…”

“…A strictly periodic repeater might be expected if the source behaved akin to a lighthouse, perhaps as a continuous source rotating across the sky or programmed to emit only periodically in our direction. Gray & Ellingsen (2002) and Harp et al (2020) excluded strictly periodic repeaters with periods below 40 hours and longer timescales become increasingly improbable to fortuitously allow the Wow signal being detected in the first place. To date, there has been no investigation of a non-periodic, stochastic repeater though.…”

Intermittent signals and planetary days in SETI

“…For example, nine META candidate positions were re-observed for 5-10 minutes each (Lazio, Tarter & Backus 2002), and 226 candidate positions from SETI@home and the SERENDIP project at Arecibo were re-observed (Korpela, Cobb, Werthimer & Lebofsky 2004) for approximately 13 s each (Korpela, E., private communication with Gray). The Ohio State 'Wow' candidate signal (Kraus 1994) is a rare exception, with over 100 hours of follow-up observing time (Harp et al 2020, Gray & Ellingsen 2002, Gray & Marvel 2001, Gray 1994.…”