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Abstract Recently the James Webb Space Telescope performed near-infrared spectroscopic observations of the atmosphere of a potential Hycean exoplanet, K2-18 b. These spectra provided evidence of methane and carbon dioxide in its atmosphere, along with a possible line attributed to biomarker dimethyl sulfide. In this work, we present triggered narrow-band radio observations of K2-18 b conducted using the Allen Telescope Array over 3–10 GHz, in search of signs of artificially produced radio emissions (technosignatures). We do not find any spatially isolated signals in the direction of K2-18 b, establishing lower and upper limits on the equivalent isotropic radiated power (∼10¹³–10¹⁶ W) of potential extraterrestrial transmitters between 3 and 10 GHz. This study emphasizes the importance of ongoing observations to further explore K2-18 b’s potential as a candidate for the detection of technosignatures. 

ABSTRACT FRB 20220912A is a repeating Fast Radio Burst (FRB) that was discovered in Fall 2022 and remained highly active for several months. We report the detection of 35 FRBs from 541 h of follow-up observations of this source using the recently refurbished Allen Telescope Array, covering 1344 MHz of bandwidth primarily centred at 1572 MHz. All 35 FRBs were detected in the lower half of the band with non-detections in the upper half and covered fluences from 4–431 Jy-ms (median = 48.27 Jy-ms). We find consistency with previous repeater studies for a range of spectrotemporal features including: bursts with downward frequency drifting over time; a positive correlation between bandwidth and centre frequency; and a decrease in sub-burst duration over time. We report an apparent decrease in the centre frequency of observed bursts over the two months of the observing campaign (corresponding to a drop of 6.21 ± 0.76 MHz per d). We predict a cut-off fluence for FRB 20220912A of Fmax ≲ 104 Jy-ms, for this source to be consistent with the all-sky rate, and find that FRB 20220912A significantly contributed to the all-sky FRB rate at a level of a few per cent for fluences of ∼100 Jy-ms. Finally, we investigate characteristic time-scales and sub-burst periodicities and find (a) a median inter-subburst time-scale of 5.82 ± 1.16 ms in the multi-component bursts and (b) no evidence of strict periodicity even in the most evenly spaced multi-component burst in the sample. Our results demonstrate the importance of wideband observations of FRBs, and provide an important set of observational parameters against which to compare FRB progenitor and emission mechanism models. 

Caballero identified the star 2MASS 19281982-2640123 as a potential Sun-like star from which the WOW! signal could have originated. We conducted a search for artificial narrowband (2.79 Hz/1.91 Hz), drifting (±4 Hz s^−1) technosignatures from this source using the turboSETI pipeline, from 1–2 GHz, using simultaneous multi-telescope observations with both the Robert C. Byrd Green Bank Telescope and the newly refurbished Allen Telescope Array on 2022 May 21. Both telescope observations had an overlap of 580 s. While blind searches using radio telescopes have been conducted in the general field of view in which the WOW! signal was first detected, this is the first time a targeted search has been done. No technosignature candidates were detected.