A Search for Radio Technosignatures at the Solar Gravitational Lens Targeting Alpha Centauri

Abstract

Stars provide an enormous gain for interstellar communications at their gravitational focus, perhaps as part of an interstellar network. If the Sun is part of such a network, there should be probes at the gravitational foci of nearby stars. If there are probes within the solar system connected to such a network, we might detect them by intercepting transmissions from relays at these foci. Here, we demonstrate a search across a wide bandwidth for interstellar communication relays beyond the Sun’s innermost gravitational focus at 550 au using the Green Bank Telescope (GBT) and Breakthrough Listen (BL) backend. As a first target, we searched for a relay at the focus of the Alpha Centauri AB system while correcting for the parallax due to Earth’s orbit around the Sun. We searched for radio signals directed at the inner solar system from such a source in the L and S bands. Our analysis, utilizing the turboSETI software developed by BL, did not detect any signal indicative of a non-human-made artificial origin. Further analysis excluded false negatives and signals from the nearby target HD 13908. Assuming a conservative gain of 103 in the L band and roughly 4 times that in the S band, a ∼1 m directed transmitter would be detectable by our search above 7 W at 550 au or 23 W at 1000 au in the L band, and above 2 W at 550 au or 7 W at 1000 au in the S band. Finally, we discuss the application of this method to other frequencies and targets.

A 4–8 GHz Galactic Center Search for Periodic Technosignatures

“…Our FFA searches bring novelty to radio SETI through their targeting of periodic spectral signals, a historically underexplored class of potential extraterrestrial transmissions. In contrast, traditional radio SETI programs have generally focused on the discovery of Doppler-drifting Hz-wide CW beacons (Siemion et al 2013;Harp et al 2016;Tingay et al 2016;Enriquez et al 2017;Gray & Mooley 2017;Margot et al 2018Margot et al , 2021Pinchuk et al 2019;Price et al 2020;Gajjar et al 2021;Lacki et al 2021;Traas et al 2021;Franz et al 2022;Garrett & Siemion 2023;Tusay et al 2022) and artificially dispersed broadband bursts (Gajjar et al 2021(Gajjar et al , 2022. Consequently, an equal comparison of our search sensitivity against that of past radio SETI campaigns is difficult.…”

“…In addition, such leakage signals are likely to be weaker. Hence, modern radio SETI efforts have primarily focused on wideband searches for deliberate narrowband (Δν ∼ 1 Hz) Doppler-drifting beacons from Galactic planetary systems (Siemion et al 2013;Harp et al 2016;Tingay et al 2016;Enriquez et al 2017;Gray & Mooley 2017;Margot et al 2018Margot et al , 2021Pinchuk et al 2019;Price et al 2020;Gajjar et al 2021;Lacki et al 2021;Traas et al 2021;Franz et al 2022;Garrett & Siemion 2023;Tusay et al 2022) and neighboring galaxies (Gray & Mooley 2017;Lacki et al 2021;Garrett & Siemion 2023).…”

A Green Bank Telescope Search for Narrowband Technosignatures between 1.1 and 1.9 GHz During 12 Kepler Planetary Transits

“…We attribute these signals to the Iridium satellite constellation's L-band downlink, 22 and note that these signals are bright enough to have passed turboSETI event filters in multiple GBT L-band SETI observations, even those with lower drift rate bounds. (e.g., Enriquez et al 2017;Tusay et al 2022).…”

“…This is a complementary approach to that performed by Franz et al (2022), which looked back into archival data to identify serendipitous observations during transit. We also follow the growing tradition of conducting technosignature work and obtaining novel astronomical results using a cohort-based, academic course centered research model (Margot et al 2021;Tusay et al 2022).…”