Methods for detection and analysis of weak radio sources with single-dish radiotelescopes

The detection of faint radio sources (mJy/sub-mJy events) is an open issue in single-dish radio astronomy. To date, observations of undetected radio sources in singledish mode often result in a rough upper limit based on the root mean square (RMS) of the image. Using Sardinia Radio Telescope (SRT), we compare the sensitivity and robustness of three methods applied to the detection of faint radio sources: the smart quick-look method, the source extraction method (typical of high-energy astronomy), and the fit with a 2-D Gaussian. The targets of interest are the faint radio afterglow emission (due to synchrotron radiation) from gamma-ray bursts (GRBs), flashes of high-energy radiation of cosmological origin. To this aim, we developed a Python code specific for the analysis of point-like radio sources applied to the SRT C-band (6:9 GHz) observations of both undetected sources (GRB afterglows of 181201A and 190114C) and the detected Galactic binary GRS 1915+105. Our comparative analysis of the different detection methods made extensive use of simulations as a useful complement of actual radio observations. The best method for the SRT data analysis is the fit with a 2-D Gaussian, as it pushes down the sensitivity limits of singledish observations –with respect to more traditional techniques– to ~ 1:8 mJy, improving by ~ 40% compared with the initial value. This analysis shows that –especially for faint sources– an accurate knowledge of the radio background is essential.