SOLARNET Conference: The Many Scales of the Magnetic Sun

The SunDish project aims to map and monitor the Sun at high radio frequencies with the Italian Sardinia (64-m) and Medicina (32-m) Radio Telescopes in the K-band range (18-26 GHz), up to 100 GHz in perspective. Since the two instruments were not originally designed to observe the Sun, a new solar radio imaging system was implemented. To date we acquired more than 350 solar maps with resolutions in the 0.7-2 arcmin range, filling the observational gap in the field of chromospheric imaging at these frequencies to date.

Observations of the brightness temperature of the solar atmosphere in the radio band can map plasma processes that produce free-free emission in the local thermodynamic equilibrium and gyromagnetic phenomena, providing a probe of physical conditions in a wide range of atmospheric layers both for quiet and active regions.

As a first early science result of the project, we present the first 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. Single-dish radio imaging represents an ideal technique to perform accurately calibrated solar observations. We obtained obtained unprecedented and very precise calibrated measurements of the Quiet Sun in the K-band affected by a mean relative error of 3%.

Through systematic monitoring of the Sun, our system can provide accurate measurement of the brightness temperature of the radio-quiet Sun component; characterization of the flux density, spectral properties and long-term evolution of dynamical features (active regions, coronal holes, loop systems, streamers, and the coronal plateau); prediction of powerful flares through the detection of peculiar spectral variations in the active regions, as a valuable forecasting probe for the Space Weather hazard network.