TECHNOLOGICAL RESEARCH AT IRA

The Institute of Radioastronomy operates two 32m dish parabolic antennas in Medicina (Bologna) and Noto (Siracusa). Both observatories are part of the EVN-VLBI (European VLBI Network) consortium and of the worldwide geodetic VLBI network. The IRA antennas are also used by national and international scientific communities in many single-dish projects to perform continuum, polarimetric and spectroscopic observations.

Since the '90, IRA has been heavily involved in the design and construction as well as in the commissioning and astronomical validation of the Sardinia Radio Telescope, that was dedicated in 2013 and is now managed by the Osservatorio Astronomico di Cagliari. The SRT opens a new era for the Italian radioastronomy, offering for the first time the possibility to operate a 3-stations national interferometer. To this aim, the scientific and technical staff of IRA is making use of its long standing expertise in VLBI by actively working to build a 5-6 stations software correlator (see next topic in this page).
Together with INRIM, the National Timekeeping service, IRA is involved in a state-of-the art project (LIFT) aimed at sharing the same fiber optics infrastructure, now used to transport eVLBI data, to exchange extremely high accurate time and frequency references.

The Institute is playing a major role in VLBI activities also in the field of design and construction of new generation back-ends like the Digital Base Band Converter, (DBBC). Since 2009 IRA is collaborating with MPI-fR at the production and distribution of DBBC back-ends and all the ancillary parts to all the EVN stations, to numerous IVS stations around the world (including the Australian network) as well as to the millimeter VLBI network and the Event Horizon Telescope project.

IRA has also been strongly involved in the Square Kilometer Array project since the realization of the various BEST demonstrators which exploited the characteristics of the Northern Cross interferometer at Medicina. Currently the Institute is involved in the Aperture Array Design Consortium for the Low-Frequency Aperture Array (LFAA) of the SKA and in particular is leader for the design and development of the receivers. Also, IRA is involved in some other Working Packages of the SKA Telescope Manager Consortium.

The IRA scientific and technical team is continuously refurbishing the antenna and the observing system components allowing the original design to be upgraded in the fields of mechanics, electronics, microwave receivers, control system and control software. During recent years, in particular, the IRA team has developed multi-feed receivers for the Italian radio telescopes and has a well established experience in the field of digital, multi-purpose, programmable back-ends and data transmission on high-capacity international networks.

The exploitation of radioastronomical observations implies the use of a vast selection of software packages, each devoted to a different phase of the astronomical observation, from commanding and controlling the several devices composing the telescope to data acquisition and recording, to end with the specialized software needed for data reduction including RFI detection/excision. The development of such specific packages for single dish observations, which are not available on a commercial basis, has become a main field of activity for the IRA staff, often in the framework of international collaborations.

THE ITALIAN VLBI NETWORK AND CORRELATOR

The Italian antennas located in Medicina, Noto and Sardinia are part of the Italian network that permits to perform VLBI observations at 1.6, 5, 9, 13 and 23 GHz with a resolution up to 0.002 arc sec. The geodetic antenna in Matera (property of the Italian Space Agency) has also participated in some experimental geodetic VLBI observations with the antennas of Medicina and Noto correlated in Bologna. The DiFX (Distributed FX - Fourier transform (F) of cross multiplied spectra(X)) software correlator was successfully installed and placed in operation in the Bologna headquarters in 2012 and it consists of 3 servers. These machines provide up to 50 TB each of storage space for the raw astronomical data coming from the antennas. They are connected through a 10 Gbit optical fiber line to the GARR and GEANT networks. In addition a 40 Gbit Infiniband connection is in place to allow fast MPI (Message Passing Interface) correlation processes for the data residing on disks which are set up in RAID (Redundant Array of Independent Disks) arrays thus allowing up to a 1 GB/sec of throughput. Thanks to this configuration the servers are capable of acting as recorders for a direct network stream of data from the antennas that are connected through optical fiber (at the moment Medicina and Noto are connected at 10 Gbit) and could be used both as storage space for postponed correlation and as raw data retrieval place for international VLBI observations like EVN or RadioAstron. A management software developed in-house (VSM - Vlbi Storage Manager) allows a quick overlook of the machines storage status and it is also used as space reservation for experiments scheduling. An example of correlation processing time with DiFX software correlator is of the order of 720 GB/hr per antenna when data recorded at 1 Gbit/s from the 3 antennas is correlated, that is approximately 2/3 of an average experiment time. At present correlation tests are carried out including the new astronomical data standard VDIF (VLBI Data Interchange Format).