A mysterious stellar system was identified this year, exhibiting 28 transit-like events over 87 days in Kepler data. This system is called EPIC 249706694 / HD 139139, and many proposed astrophysical transit scenarios have failed to properly explain the origin of these transits — giving the system the nickname “the random transiter”. This sounded like an excellent opportunity to search for technosignatures!
We took follow-up observations of HD 139139 at radio frequencies of 4-8 GHz, using the Breakthrough Listen instrument at the Green Bank Telescope. Three observations were made with the telescope pointed at the system and three slightly offset, which allows us to distinguish whether a detected signal is actually coming from the source of interest. Unfortunately, we did not detect any signals of SETI interest, but based on our search sensitivity, we were able to set a limit on the effective power of a potential transmitter to be about 10 TW. In comparison, the most powerful transmitter at the Arecibo Observatory can reach a power of about 20 TW!