Two Fast Radio Burst Candidates Detected in the RATAN-600 Blind Survey

Abstract

We report the detection of two single dispersed pulses with widths of about 6.7\,ms and 15.6\,ms and flux densities of about 0.8 and 1.7\,Jy. These were found in a blind survey of two circular regions (Dec$\;=+22^{\circ}$ and $+5^{\circ}$,RA: 0--24~h) at high radio frequencies \mbox{(4400--5000\,MHz)} using four 4-channel filter radiometers (central frequencies of 4475, 4625, 4775, and 4925\,MHz) spanning a total frequency bandwidth of 600\,MHz. The survey was carried out with the Western Sector antenna of the RATAN-600 radio telescope, which had an effective area of 1200\,m$^2$ in~2017--2025. The total area of the survey was about 1500~square degrees, and each pointing of the antenna lasted one year. We consider these to be two rare, high-frequency FRB events (MJD~58614.38257 and MJD~58659.62482), detected with estimated dispersion measures of $200\pm20$ and $266\pm10$\,pc\,cm$^{-3}$ at a final signal-to-noise ratio (SNR) level of 8--9 after additional optimal filtration. After subtraction of the estimated dispersions within the Milky Way, we estimated redshifts of approximately 0.09 and 0.13, respectively, using the traditional equation: ${\rm DM}\,[{\rm pc~cm}^{-3}] = 1000\,z$ for the intergalactic medium. The estimated isotropic energies of the FRBs are equal to $10^{40}$\,erg and $2\times 10^{40}$\,erg, respectively. To effectively detect single pulses, we applied machine learning methods using a neural network trained on synthetic FRB pulse profiles.