the Sardinia Radio Telescope (SRT) went through the technical commissioning phase. The characterization involved three¯rst-light receivers, ranging in frequency between 300 MHz and 26 GHz, connected to a Total Power back-end. It also tested and employed the telescope active surface installed in the main re°ector of the antenna. The instrument status and performance proved to be in good agreement with the expectations in terms of surface panels alignment (at present 300 m rms to be improved with microwave holography), gain ($0.6 K/Jy in the given frequency range), pointing accuracy (5 arcsec at 22 GHz) and overall single-dish operational capabilities. Unresolved issues include the commissioning of the receiver centered at 350 MHz, which was compromised by several radio frequency interferences, and a lower-than-expected aperture e±ciency for the 22-GHz receiver when pointing at low elevations. Nevertheless, the SRT, at present completing its Astronomical Validation phase, is positively approaching its opening to the scienti¯c community.

Observations of supernova remnants (SNRs) are a powerful tool for investigating the later stages of stellar evolution, the properties of the ambient interstellar medium, and the physics of particle acceleration and shocks. For a fraction of SNRs, multi-wavelength coverage from radio to ultrahigh-energies has been provided, constraining their contributions to the production of Galactic cosmic rays. Although radio emission is the most common identifier of SNRs and a prime probe for refining models, high-resolution images at frequencies above 5 GHz are surprisingly lacking, even for bright and well-known SNRs such as IC443 and W44. In the frameworks of the Astronomical Validation and Early Science Program with the 64-m single-dish Sardinia Radio Telescope, we provided, for the first time, single-dish deep imaging at 7 GHz of the IC443 and W44 complexes coupled with spatially-resolved spectra in the 1.5 − 7 GHz frequency range. Our images were obtained through on-the-fly mapping techniques, providing antenna beam oversampling and resulting in accurate continuum flux density measurements. The integrated flux densities associated with IC443 are S 1.5GHz = 134 ± 4 Jy and S 7GHz = 67 ± 3 Jy. For W44, we measured total flux densities of S 1.5GHz = 214 ± 6 Jy and S 7GHz = 94 ± 4 Jy. Spectral index maps provide evidence of a wide physical parameter scatter among different SNR regions: a flat spectrum is observed from the brightest SNR regions at the shock, while steeper spectral indices (up to ∼ 0.7) are observed in fainter cooling regions, disentangling in this way different populations and spectra of radio/gamma-ray-emitting electrons in these SNRs.

We present new observations of the galaxy cluster 3C 129 obtained with the Sardinia Radio Telescope in the frequency range 6000−7200 MHz, with the aim to image the large-angular-scale emission at high-frequency of the radio sources located in this cluster of galaxies. The data were acquired using the recently-commissioned ROACH2-based backend to produce full-Stokes image cubes of an area of 1 o ×1 o centered on the radio source 3C 129. We modeled and deconvolved the telescope beam pattern from the data. We also measured the instrumental polarization beam patterns to correct the polarization images for off-axis instrumental polarization. Total intensity images at an angular resolution of 2.9 ′ were obtained for the tailed radio galaxy 3C 129 and for 13 more sources in the field, including 3C 129.1 at the galaxy cluster center. These data were used, in combination with literature data at lower frequencies, to derive the variation of the synchrotron spectrum of 3C 129 along the tail of the radio source. If the magnetic field is at the equipartition value, we showed that the lifetimes of radiating electrons result in a radiative age for 3C 129 of t syn ≃ 267 ± 26 Myrs. Assuming a linear projected length of 488 kpc for the tail, we deduced that 3C 129 is moving supersonically with a Mach number of M = v gal /c s = 1.47. Linearly polarized emission was clearly detected for both 3C 129 and 3C 129.1. The linear polarization measured for 3C 129 reaches levels as high as 70% in the faintest region of the source where the magnetic field is aligned with the direction of the tail.

The Sardinia Radio Telescope (SRT) is a 64-m, fully-steerable single-dish radio telescope that was recently commissioned both technically and scientifically with regard to the basic observing modes. In order to improve the scientific capability and cover all the requirements for an advanced single-dish radio telescope, we developed the SArdinia Roach2-based Digital Architecture for Radio Astronomy (SARDARA), a wide-band, multi-feed, general-purpose, and reconfigurable digital platform, whose preliminary setup was used in the early science program of the SRT in 2016. In this paper, we describe the backend both in terms of its scientific motivation and technical design, how it has been interfaced with the telescope environment during its development and, finally, its scientific commissioning in different observing modes with single-feed receivers.

We describe the design, construction and\ud performance of a compact orthomode transducer (OMT) for the\ud L-band receiver (1.3 GHz - 1.8 GHz) of the Sardinia Radio\ud Telescope (SRT). The complete OMT consists of a cylindrical\ud orthomode junction (OMJ), which is presented in this paper, and\ud two identical 180° hybrid power combiners in double ridged\ud waveguide, which have been proposed in a previous work. The\ud OMT operates at the cryogenic temperature of 20 K to reduce its\ud thermal noise contribution to the noise of the receiving chain.\ud Therefore, particular care has been taken in the design of the\ud OMJ to minimize its dimension and insure a good thermalization.\ud The proposed OMT has been designed and optimized by using\ud CST Microwave studio, and then manufactured, tested at room\ud temperature, and installed on the L-band receiver of SRT. The\ud measured results fully comply with the design specifications. In\ud particular, the isolation between the OMT output ports is more\ud than 40 dB, and the cross polarization is less than -35 dB for both\ud polarization channels