Search for activity in the centimeter band of Solar-type dwarfs with Earth-like planets on the RATAN-600 radio telescope
The paper presents the results of multi-wave radio observations of sixteen red dwarfs with Earth-like planets in the habitable zones on RATAN-600. In the passage mode, radiometers of four frequency ranges of 22, 11, 4.7 and 2.3 GHz (1.38, 2.68, 6.38, 13.3 cm) were used with a sampling step of quasi-simultaneous registration of about $\sim 18$ Hz and an exposure duration (the time of passage of the instrument's directivity pattern) of 1.5 -- 15 s. Observations were carried out from 3 to 27 times in April-May 2018, while radio emission was not detected. Upper limits were established for its intensity in flares with a duration of 0.05 -- 10 s at the level of 80 -- 800 mJy (corresponding to a luminosity of $10^{23} - 10^{29}$ erg/s) and in a steady state with a luminosity of $10^{22} - 10^{27}$ erg/s. During the observations, 11 anomalous flux outlier at the level of 100 mJy were registered, which apparently have an atmospheric (thunderstorms, airplanes) origin. Assuming an artificial origin of the sought radio emission (transmission from inhabited planets), the upper limits of the power of hypothetical transmitters were $2\times 10^9 - 10^{15}$ W, interestingly that the lower boundary of this interval close to the power of terrestrial planetary radars.