Steve Croft Andrew Siemion The Search for Cosmic Greg Hellbourg (UC Berkeley) Company: SETI on ngVLA @BerkeleySETI

Maximizing the chance “Are we alone?” of success is one of the most profound human questions. The unprecedented capabilities of next generation radio telescopes, including ngVLA, will As with searches for astrophysical allow us to probe hitherto unexplored regions of parameter space, transients, the chances of a successful placing meaningful limits on the prevalence of technological detection of ETI can be increased by civilizations in the Universe, or perhaps making one of the most searching large volumes of parameter significant discoveries in the history of science. space: • Frequency coverage • Frequency resolution How to find ET • Time resolution • Time cadence • Time duration We do not know what power, frequency, duty cycle, or antenna gain ETI might use, but these • Sensitivity examples of some of the brightest Earthbound radio transmitters provide a benchmark to 5 mins ON source compare the sensitivity of current SETI experiments. Time • Sky area (number of targets) • Signal type Finding Earth Analogs 5 mins OFF source As a fast survey instrument with high sensitivity, wide frequency coverage, and This diagram (Siemion et al. 2015) SKA1 (LOW/MID) shows the minimum detectable back-end flexibility, ngVLA will excel in SKA2

) 20 1 10 equivalent isotropic radiated power 5 mins ON source these metrics. − LOFAR Arecibo (EIRP) for an extraterrestrial 19 GBT 10 transmitter with a variety of Earthbound telescopes. ngVLA (red 5 mins OFF source * 18 line) will complement SKA1-LOW and 10 ngVLA SKA1- MID as the only facilities with

17 the capability to detect “leakage” 5 mins ON source 10 transmissions from omnidirectional extraterrestrial transmitters with 16 10

Minimum Detectable EIRP (erg s power close to the brightest 5 mins OFF source transmitters on Earth (EIRP ~ 1017 15

10 −2 −1 0 1 2 erg / s). It will also provide critical 10 10 10 10 10 Frequency (GHz) capabilities in the 10 – 100 GHz range, a region of the spectrum used by * at 15pc, in a 15-minute observation Frequency many human technologies.

One method of performing a radio SETI search (such as that used by Never Stop Searching

Breakthrough Listen at the Green Bank Telescope, in the example Tel escope st at us shown here, from Enriquez et al. 2017) consists of alternating Redi s DB Head Node

observations of a target star (the “ON” source) and one or more AONET Swi t ch s e d

comparison stars (“OFF”). Algorithms search for features that appear o N s

C B2- X e D B0- 6 t A

B2- Y u p

artificial, and that are present in the ON observations and absent in the m B1- X B0- 6 o

B1- Y C B3- X B0- 6 B3- Y OFFs, to attempt to distinguish between SETI signals of interest and 2 B0- X B0- 6 1 3 B0- Y ROACH2 A S6 Cl ust er terrestrial (human-generated) radio frequency interference (RFI). 0 6 4 B4- X 10GbE Swi t ch 5 B4- Y B6- X B0, B1 30 years ago, no planets were known B6- Y Head Node ALFA Recei ver B2, B3 B5- X B5- Y B4, B5 s

outside our solar system. We now know C B6 s

Classical SETI algorithms have typically focused on the search for D e A d o N

that our Galaxy is a target-rich e

narrow-band signals, but increased computing power and more t u p m o

environment for “cradle of life” science C sophisticated algorithms (including machine learning approaches) will ROACH2 B

enable the search for increasingly complex signals, as well as better (astrobiology and SETI). AB Cl ust er classification of RFI. SETI instruments can operate with control of the telescope (e.g. SonATA, left, Harp et al. Through both targeted and commensal observations, ngVLA data will References 2016), commensally (performing a search on a copy of the data from the primary user driving be searched for signatures of technology that can be localized to Enriquez et al. (2017) ApJ, 849, 104 the telescope; e.g. SERENDIP VI, center, Chennamangalam et al. 2017), or in either mode (e.g. particular positions on the sky. Chennamangalam et al. (2017) ApJS, 228, 21 Breakthrough Listen, right, MacMahon et al. 2018). A commensal capability for ngVLA is Harp et al. (2016) AJ, 152, 181 important to enable a continuous SETI search regardless of the primary science target being MacMahon et al. (2018) ApJ, in press observed. Siemion et al. (2015), SKA science book We gratefully acknowledge support from the Breakthrough Prize Foundation.

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