Misure di temperatura di rumore con diversi materiali, sulla copertura del Gregoriano di SRT

Lo scopo di questo lavoro è quello di valutare l’incremento della temperatura di rumore nei ricevitori banda K (18 - 26 GHz) e banda C (5.5 – 7.7 GHz), posizionati, rispettivamente, nel fuoco gregoriano e nella Beam waveguide del Sardinia Radio Telescope (SRT), in seguito all’inserimento di una nuova protezione come copertura della Vertex room. La necessità di tale studio è dovuta alle criticità presentate dall’attuale materiale usato come protezione della stanza del fuoco gregoriano del radio telescopio. Il materiale di base attualmente in uso è lo Styrodur 3035CS, un polistirene espanso estruso che ha un bassissima attenuazione, come dimostrato dal suo notevole utilizzo nelle finestre dei diversi ricevitori sviluppati in questi anni all’INAF, ma con l’inconveniente di peggiorare le sue prestazioni col tempo a causa dei danni procurati dagli agenti atmosferici (quali raggi UV, pioggia, ghiaccio). Al fine di ridurre l’usura dello Styrodur, abbiamo testato l’utilizzo di diversi elementi protettivi superficiali come vernici, prodotti idrorepellenti e teli di Goretex e polietilene, stimando l’effetto di queste protezioni sulla temperatura di rumore del sistema. Per tale verifica è stata misurata la variazione della temperatura di sistema Tsys del radiotelescopio al variare del tipo di protezione utilizzato

FPGA-based digital back-ends for the Sardinia Radio Telescope

The Sardinia Radio Telescope (SRT), located in San Basilio, about 35 km north of Cagliari, is the largest (64-m diameter) radio telescope in Italy. It is a general-purpose, fully-steerable radio telescope designed to operate in the 300 MHz - 116 GHz frequency range, which allows it to perform a wide variety of scientific studies. The advanced electronic digital platforms that are installed at SRT play a key role, in particular those based on FPGAs (Field Programmable Gate Array), both because of their processing capability and their reconfigurability. In this paper, we present an overview of the digital back-ends available at SRT, as well as the ones under development; it is important to underline that, for all of them, FPGAs are the beating heart

Towards coordinated site monitoring and common strategies for mitigation of Radio Frequency Interference at the Italian radio telescopes

We present a project to implement a national common strategy for the mitigation of the steadily deteriorating Radio Frequency Interference (RFI) situation at the Italian radio telescopes. The project involves the Medicina, Noto, and Sardinia dish antennas and comprised the definition of a coordinated plan for site monitoring as well as the implementation of state-of-the-art hardware and software tools for RFI mitigation. Coordinated monitoring of frequency bands up to 40 GHz has been performed by means of continuous observations and dedicated measurement campaigns with fixed stations and mobile laboratories. Measurements were executed on the frequency bands allocated to the radio astronomy and space research service for shared or exclusive use and on the wider ones employed by the current and under-development receivers at the telescopes. Results of the monitoring campaigns provide a reference scenario useful to evaluate the evolution of the interference situation at the telescopes sites and a case series to test and improve the hardware and software tools we conceived to counteract radio frequency interference. We developed a multi-purpose digital backend for high spectral and time resolution observations over large bandwidths. Observational results demonstrate that the spectrometer robustness and sensitivity enable the efficient detection and analysis of interfering signals in radio astronomical data. A prototype off-line software tool for interference detection and flagging has been also implemented. This package is capable to handle the huge amount of data delivered by the most modern instrumentation on board of the Italian radio telecsopes, like dense focal plane arrays, and its modularity easen the integration of new algorithms and the re-usability in different contexts or telescopes.Comment: 39 pages, 10 Figures and 7 Tables. INAF Technical Report n. 149 (2022). http://hdl.handle.net/20.500.12386/3208

A real-time FFT-KLT implementation for SETI research at the Sardinia Radio Telescope

The Search for ExtraTerrestrial Intelligence (SETI) is a project whose goal is to find possible life signatures emitted (intentionally or unintentionally) by possible civilizations from other habitable planets. Historically, the narrow-band FFT approach has been used, since a quasi-monochromatic signal is the most probable signal one would use to send a message to another world, that is in the case of intentionally- transmitted signals. Nevertheless, we could receive an unintentionally-transmitted signal as well. In that case, it would most certainly not be a quasi-monochromatic signal, but would probably be similar (with a wider bandwidth, of the order of MHz) to the signals that we use for conventional communications on Earth. The Kahrunen-Loève Transform (KLT) is a powerful algorithm for such a kind of research. However, a real-time implementation of the KLT has thus far not worked due to a lack of technological resources. We describe a hardware-software infrastructure at the Sardinia Radio Telescope (SRT) that, in real-time, makes it possible to perform the KLT in parallel to the FFT

VLBI experiments with the dissemination of a common clock via coherent optical fiber link

Atomic clock synchronization plays an important role in both astronomical and geodetic Very Long Baseline Interferometry, as time and frequency standards are provided by station clocks. National metrological institutes have recently started streaming (via optical fiber links) frequency references from ultra-stable clocks based on optical line transitions in Strontium/Ytterbium laser-cooled lattices. Optical lattice clocks are already two orders of magnitude more stable than the radio station H-masers. In this talk we will describe how the Italian Qauntum Backbone (IQB) was used to carry out a series of European geodetic VLBI experiments in which the Medicina and Matera radio stations were connected to the same remote clock located at the Italian Metrological institute in Turin, via the IQB optical link. In the foreseeable future a European VLBI network of radio stations could be connected via optical fiber links to a single very high-performance clock hosted by a European Metrological institute

A real-time KLT implementation for radio-SETI applications

SETI, the Search for ExtraTerrestrial Intelligence, is the search for radio signals emitted by alien civilizations living in the Galaxy. Narrow-band FFT-based approaches have been preferred in SETI, since their computation time only grows like N*lnN, where N is the number of time samples. On the contrary, a wide-band approach based on the Kahrunen-Lo`eve Transform (KLT) algorithm would be preferable, but it would scale like N*N. In this paper, we describe a hardware-software infrastructure based on FPGA boards and GPU-based PCs that circumvents this computation-time problem allowing for a real-time KLT

SETI in Sardinia: status of scientific and technological developments

Since 2013, several staff members of the Cagliari Astronomical Observatory have been involved with SETI activities, both from a technological and a scientific perspective. One major asset related to this research area is the presence, in the territory, of one of the most modern single-dish antennas: the Sardinia Radio Telescope (SRT). In this paper, we outline all aspects of our initiatives in the framework of the Search for ExtraTerrestrial Intelligence. We describe the development of SRT instrumentation for the purpose of receiving data that could potentially contain signs of life, as well as the directions that we are investigating for studying and analyzing these data, including in an international context

SETI scientific activities in Sardinia: Search for ET, pulsars and Fast Radio Bursts

The Sardinia Radio Telescope, which was inaugurated in 2013, is getting ready to participate in the Search for ExtraTerrestrial Intelligence (SETI) observations. This involves, in collaboration with the SETI collaboration and the ``Breakthrough Listen initiative", the onsite installation of the SERENDIP VI setup for SETI observations. In parallel, a scientific team at the Cagliari Astronomical Observatory is becoming acquainted with SETI search algorithms: both standard algorithms using the Fast Fourier Transform; and more versatile algorithms using the Kahrunen-Loève Transform (KLT) as well as Wavelets. The team is also investigating the possibility to pursue, with the SERENDIP VI setup, the simultaneous search for Extraterrestrial Intelligence, pulsars and Fast Radio Bursts

Precessing jet nozzle connecting to a spinning black hole in M87

The nearby radio galaxy M87 offers a unique opportunity to explore the connections between the central supermassive black hole and relativistic jets. Previous studies of the inner region of M87 revealed a wide opening angle for the jet originating near the black hole. The Event Horizon Telescope resolved the central radio source and found an asymmetric ring structure consistent with expectations from General Relativity. With a baseline of 17 years of observations, there was a shift in the jet's transverse position, possibly arising from an eight to ten-year quasi-periodicity. However, the origin of this sideways shift remains unclear. Here we report an analysis of radio observations over 22 years that suggests a period of about 11 years in the position angle variation of the jet. We infer that we are seeing a spinning black hole that induces the Lense-Thirring precession of a misaligned accretion disk. Similar jet precession may commonly occur in other active galactic nuclei but has been challenging to detect owing to the small magnitude and long period of the variation.Comment: 41 pages, 7 figures, 7 table