Solar observations with single-dish INAF radio telescopes: continuum imaging in the 18-26 GHz range

TL;DR

This paper introduces a new solar radio imaging system using upgraded INAF single-dish telescopes, providing high-resolution, calibrated images of the Sun in the 18-26 GHz range, enabling advanced solar and space weather studies.

Contribution

The paper presents a novel solar imaging system with calibration and early science results, filling a frequency gap and demonstrating its potential for solar physics and space weather monitoring.

Findings

170 solar disk maps in 18-26 GHz band produced

Calibration accuracy with <3% error achieved

Catalog of active regions with spectral characterization created

Abstract

We present a new solar radio imaging system implemented through the upgrade of the large single-dish telescopes of the Italian National Institute for Astrophysics (INAF), not originally conceived for solar observations. During the development and early science phase of the project (2018-2020), we obtained about 170 maps of the entire solar disk in the 18-26 GHz band, filling the observational gap in the field of solar imaging at these frequencies. These solar images have typical resolutions in the 0.7-2 arcmin range and a brightness temperature sensitivity <10 K. Accurate calibration adopting the Supernova Remnant Cas A as a flux reference, provided typical errors <3% for the estimation of the quiet-Sun level components and for active regions flux measurements. As a first early science result of the project, we present a catalog of radio continuum solar imaging observations with Medicina 32-m and SRT 64-m radio telescopes including the multi-wavelength identification of active regions, their brightness and spectral characterization. The interpretation of the observed emission as thermal bremsstrahlung components combined with gyro-magnetic variable emission pave the way to the use of our system for long-term monitoring of the Sun. We also discuss useful outcomes both for solar physics (e.g. study of the chromospheric network dynamics) and space weather applications (e.g. flare precursors studies).