On the Wide-Band and Broadband Radio Technosignature Searches with Breakthrough Listen

Abstract: 

The search for extraterrestrial intelligence (ETI) at radio frequencies has largely been focused on continuous-wave narrowband signals. We demonstrate that different classes of wide-band and broadband pulsed beacons are energetically efficient compared to narrowband beacons over longer operational timescales. Searching for these unconventional signals enables us to constrain the existence of ETIs in proverbial multi-dimensional parameter space. These signal classes include wide-band periodic pulses akin to several powerful Earth-based air-traffic radars, 24 different types of wide-band signals with embedded modulations, and three different types of broadband signals with artificial dispersions. To scour for these 28 unique classes of signals, we have developed state-of-the-art search pipelines; leveraging advances made in the convolution/deep neural network classifiers and high-performance GPUs. We report on the first extensive survey for some of these signals towards 1883 stars in the solar neighborhood and in around half a million stars at the Galactic Center; utilizing around 250 hours of deep observations across 4 to 8 GHz using the Robert C. Byrd Green Bank Telescope as a part of the Breakthrough Listen program (Gajjar et al. 2021, 2022). Due to the absence of any signal-of-interest from our survey, we place a constraint on the existence of broadband beacons: < 1 in 1000 stars in the solar neighborhood (or in the spiral arm) and < 1 in half a million stars at the Galactic Center with broadband signal transmitter power densities of > 10^5 W/Hz and > 10^7 W/Hz, respectively. One of the major challenges in searching for these unconventional classes of signals from single dishes is the large number of false positives arising due to radio frequency interference. We will discuss how we are utilizing long-baselines of two widely-separated international LOw Frequency ARray (LOFAR) stations and band-limited spectral imaging of interferometers, such as the Giant Meterwave Radio Telescope (GMRT), to curb these challenges.