Study of Calibration Sources at 22 and 37 GHz Frequency Bands with RT-22 CrAO RAS

Abstract

We present the measurement results for the spectral flux densities of 19 calibration sources observed with the RT-22 single-dish telescope of the Crimean Astrophysical Observatory of the Russian Academy of Sciences at 22.2 and 36.8 GHz in 2017–2020. About half of them belong to the commonly accepted secondary standards with periodically monitored flux densities at radio frequencies. The measurements were carried out to refine the calibration measurements of the RATAN-600 radio telescope at high frequencies. The specificity of RATAN-600 meridian observations requires a ‘‘grid’’ of calibration objects distributed over declinations from \(-35^{\circ}\) to \(+90^{\circ}\) instead of 1–3 conventional calibrators which are sufficient for observations at different heights with a single-dish antenna. The radio variability of the objects was estimated taking into account the literature measurements, the results were interpolated to a frequency of 30 GHz. It was found that radio variability at 22 GHz at time scales of about 20–30 years exceeds 10\(\%\) for the calibrators 4C \(+\)16.09 and 3C 309.1. We discuss a possibility of verifying the calibration sources at the RT-22 by a new method that uses a noise signal generator as an indicator of their relative flux density accuracy.