The Sardinia Radio Telescope (SRT) has just started its first observational program (Early Science Program) and the first scientific results are already coming in. Among the various projects submitted to the competitive call last December, which were granted observation time, there is one in particular dedicated to monitoring binary systems identified in X-rays: systems composed of a compact source (a neutron star or a black hole) that accretes matter from the companion star.
On the left, the light curve of GRS 1915+105 obtained from the Swift satellite. On the right, the map centered on the source obtained by SRT at 21.4 GHz, with a resolution of 55 arcseconds.
The project, proposed by an international team led by Elise Egron, a young French researcher from the INAF – Osservatorio Astronomico di Cagliari’s multifrequency group, aims to identify any variable or transient radio emissions coming from these systems, correlating them with observations at different frequencies acquired by various instruments worldwide, including space-based ones. Observations with SRT, particularly in the frequency range between 7 and 21 GHz, can provide important information on the state transitions of X-ray binaries and help validate current models that associate radio emissions with the presence of relativistic jets.
Last April 5th, during an observational session monitoring the GRS 1915+105 system, Egron’s group finally managed to detect strong signals emitted during a peculiar phase, which occurred after a strong flare observed with the Swift X-ray satellite. The observations were conducted thanks to a radio imaging acquisition technique entirely developed by the Cagliari multifrequency group, of which Egron is a part, led by Alberto Pellizzoni, who has years of experience in instrumentation development and particularly in state-of-the-art data analysis techniques. Thanks to these techniques and the brand-new data processing system with reprogrammable FPGA boards (SARDARA system, also developed in Cagliari), the multifrequency group was able to present the results just two days after the observations, publishing them through the fast system of the Astronomer’s Telegram (ATel #8921 of April 7, 2016).
“SRT has just started its observational activity with the Early Science Program (ESP) and is already producing excellent results,” says Ettore Carretti, head of the Sardinia Radio Telescope. “Results like the observation of X transients reported here, which show the quality of the scientific performance the telescope can provide. There are twelve projects in the ESP, and we expect more significant results like this to follow soon.”