Space Debris Detection in Low Earth Orbit with the Sardinia Radio Telescope

Space debris are orbiting objects that represent a major threat for space operations. The most used countermeasure to face this threat is, by far, collision avoidance, namely the set of maneuvers that allow to avoid a collision with the space debris. Since collision avoidance is tightly related to the knowledge of the debris state (position and speed), the observation of the orbital debris is the key of the problem. In this work a bistatic radar configuration named BIRALET (BIstatic RAdar for LEO Tracking) is used to detect a set of space debris at 410 MHz, using the Sardinia Radio Telescope as the receiver antenna. The signal-to-noise ratio, the Doppler shift and the frequency spectrum for each debris are reported

Imaging of SNR IC443 and W44 with the Sardinia Radio Telescope at 1.5 GHz and 7 GHz

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 ultra high-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.Comment: 13 pages, 9 figures, accepted for publication to MNRAS on 18 May 201

Sviluppi di Ricevitori e di Componentistica per Banda 3 mm ad INAF-OA Cagliari

L'INAF-OA Cagliari (OACa) sta sviluppando un ricevitore criogenico a basso rumore basato su un mixer SSB (Single Side Band) a superconduttore SIS (Superconductor-Insulator-Superconductor) per la banda 3 mm. Il ricevitore, acquistato da IRAM, è stato fortemente modificato per essere adattato al fuoco Gregoriano di SRT (Sardinia Radio Telescope). Lo strumento è caratterizzato da una nuova criogenia a ciclo chiuso 4 K (per evitare l'uso di elio liquido in antenna), da un nuovo oscillatore locale (di tipo ALMA Banda 3) e da un nuovo sistema di controllo e di monitoraggio basato su schede Raspberry ed Arduino sviluppato ad OACa. Verranno presentati i recenti sviluppi sul ricevitore, inclusi i risultati preliminari della misura della temperatura di rumore, che raggiunge un valore pari a Trec=66 K alla frequenza di 86 GHz, nonostante la criogenia non sia ancora ottimizzata. L'INAF-OACa è coinvolto nel progetto AETHRA (Advanced European Technologies for Heterodyne Receivers for Astronomy) nel quadro del programma Radionet/Horizon2020 per il quale sta contribuendo al WP1 (Work Package 1). Lo scopo del WP1 è di sviluppare e costruire un dimostratore di un array di ricevitori a doppia polarizzazione per la banda 3 mm basato su amplificatori criogenici a basso rumore (LNA) in tecnologia a semiconduttore MMIC. Nell'ambito del WP1 l'OACa ha in carico il progetto di un OrthomodeTransducer (OMT) in guida d'onda o in tecnologia planare per la banda 72-116 GHz che sia integrabile con amplificatori MMICs ed adatto all'integrazione in un array da installare nel piano focale di un radiotelescopio. Verranno presentati i design preliminari degli OMT per AETHRA, che sono basati su prototipi sviluppati in passato da OACa

The control system of the 3 mm band SIS receiver for the Sardinia Radio Telescope

We present the control system of the 84-116 GHz (3 mm band) Superconductor-Insulator-Superconductor (SIS) heterodyne receiver to be installed at the Gregorian focus of the Sardinia Radio Telescope (SRT). The control system is based on a single-board computer from Raspberry, on microcontrollers from Arduino, and on a Python program for communication between the receiver and the SRT antenna control software, which remotely controls the backshorttuned SIS mixer, the receiver calibration system and the Local Oscillator (LO) system

Exploitation of bi-static radar architectures for LEO Space Debris surveying and tracking: The BIRALES/BlRALET project

The space debris population is continuously growing and it represents a potential issue for spacecraft. New collisions could exponentially rise the amount of debris and so the level of risk represented by these objects. The monitoring of space environment is necessary to prevent new collisions. For this reason, radar measurements are relevant, in particular to observe objects in Low Earth Orbit. Regarding the Italian contribution, there are two radars based on two different radio telescopes as receivers: the BIRALES and the BIRALET systems. We propose a detailed description of these systems, focusing on hardware and software components that permit to perform range and range rate measurement of resident space objects

Sardinia Array Demonstrator: Instrument Overview and Status

In the framework of the Square Kilometer Array (SKA) project, the Italian Institute for Astrophysics (INAF) has addressed several efforts in the design and prototyping of aperture arrays for low-frequency radio astronomical research. The Sardinia Array Demonstrator (SAD) is a national project aimed to develop know-how in this area and to test different architectural technologies and calibration algorithms. SAD consists of 128 prototypical dual-polarized Vivaldi antennas designed to operate at radio frequencies below 650 MHz. The antennas will be deployed at the Sardinia Radio Telescope’s site with a versatile approach able to provide two different array configurations: (i) all antennas grouped in one large station or (ii) spread among a core plus few satellite stations. This paper provides an overview of the SAD project from an instrumental point of view, and illustrates its status after 2 years from its start

SRT performance measurements (2018-2021)

Tests of characterization are periodically performed at SRT in order to check the status of the antenna, ensure a good functioning of the different components (e.g. active surface, receivers, backends, etc), and improve the observing performances at the different frequencies. In particular, the tests include measurements of beam shape, pointing, gain curves and focus for the different receivers (L, C, X and K-bands). We report the results of the main tests carried out after a long stop of the antenna due to the reparation of the main servo motors chillers in 2020 and compare them with those carried out during the recommissioning in 2018 (after the change of the actuators of the active surface). These results will be useful in order to compare the new status of the antenna after the upgrade of the new receivers at higher frequency (PON)

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

The Sardinia Radio Telescope . From a technological project to a radio observatory

Context. The Sardinia Radio Telescope (SRT) is the new 64 m dish operated by the Italian National Institute for Astrophysics (INAF). Its active surface, comprised of 1008 separate aluminium panels supported by electromechanical actuators, will allow us to observe at frequencies of up to 116 GHz. At the moment, three receivers, one per focal position, have been installed and tested: a 7-beam K-band receiver, a mono-feed C-band receiver, and a coaxial dual-feed L/P band receiver. The SRT was officially opened in September 2013, upon completion of its technical commissioning phase. In this paper, we provide an overview of the main science drivers for the SRT, describe the main outcomes from the scientific commissioning of the telescope, and discuss a set of observations demonstrating the scientific capabilities of the SRT. Aims: The scientific commissioning phase, carried out in the 2012-2015 period, proceeded in stages following the implementation and/or fine-tuning of advanced subsystems such as the active surface, the derotator, new releases of the acquisition software, etc. One of the main objectives of scientific commissioning was the identification of deficiencies in the instrumentation and/or in the telescope subsystems for further optimization. As a result, the overall telescope performance has been significantly improved. Methods: As part of the scientific commissioning activities, different observing modes were tested and validated, and the first astronomical observations were carried out to demonstrate the science capabilities of the SRT. In addition, we developed astronomer-oriented software tools to support future observers on site. In the following, we refer to the overall scientific commissioning and software development activities as astronomical validation. Results: The astronomical validation activities were prioritized based on technical readiness and scientific impact. The highest priority was to make the SRT available for joint observations as part of European networks. As a result, the SRT started to participate (in shared-risk mode) in European VLBI Network (EVN) and Large European Array for Pulsars (LEAP) observing sessions in early 2014. The validation of single-dish operations for the suite of SRT first light receivers and backends continued in the following year, and was concluded with the first call for shared-risk early-science observations issued at the end of 2015. As discussed in the paper, the SRT capabilities were tested (and optimized when possible) for several different observing modes: imaging, spectroscopy, pulsar timing, and transients