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4.3 Superstation

1. Introduction	A significant improvement from the scientific point of view, as regards radio astronomical research, is represented by the so called "Super Station project". Using the collecting area offered by an important structure such as the "Northern Cross" radio telescope by optimizing the antenna capabilities (with particular reference to East - West arm) it will be possible to use part of it as an element of the LOFAR interferometer, but with a much larger collecting area, improving substantially the baseline sensitivity. The largest the area used for the "super station" is, the most effective the improvements in sensitivity will be. A recent study, carried out with the collaboration of the University of Torino, has highlighted the very good capabilities in terms of performances of a cylindrical-parabolic antenna, as the "Northern Cross", in a frequency range between 100 and 700 MHz. It would be necessary to replace the sensors currently installed (half-wavelength dipoles optimized at 408 MHz) with broadband antennas. Essentially the goal is to place (after an appropriate mechanical study) sensors able to operate in the high frequency range of LOFAR observation bandwidth (120-240 MHz).
2. The Core
3.Technical Details
3.1 The System
3.2 Data processing
3.3 Antennas spec.
4.Lofar at Medicina
4.1 Baseline extension
4.2 Lofar Kit
4.3 Superstation
5. Science

The reasons to pursue this goal are simple: an antenna with an effective area much larger than any other remote station could be integrated in the LOFAR network; this area could potentially be extended to the whole area of the East-West arm (about 20000 m2). This would produce a considerable improvement in terms of performances (in particular sensitivity). The technological-logistical effort, also in this case, would be very little if compared to the expected results, both for Italian researchers who would have an instrument with considerable performances, and for the consortium, that suddenly would have in only one element the same effective area of 20 standard remote stations.

Contrary to what holds for the LOFAR standard kit, the project of this upgrade would require a more demanding technological research, so an higher investment in terms of staff and hardware.

All these efforts have an estimated cost of about 1 Million of Euros. Even if it is a substantial amount of money, it is still lower than that necessary to obtain the same performances in terms of effective area with a number of LOFAR standard remote stations (20 stations = 7-8 Millions of Euros).

A further important opportunity to explore is to consider to install both the LOFAR remote station and the Super-Station. Using separately the standalone East-West arm, we expect to get a rather large beam (about 10 arcmin at 150 MHz). Such an instrument would not be able to work on standard astrophysical applications in the LOFAR frequency range by itself. On the contrary, with the installation of the LOFAR remote station too, suitably placed, a 1.5-2 Km baseline could be obtained, allowing to have a resolution of about one arcminute (at 200 MHz), suitable to carry out important astronomical researches. The total effective area would be about 22000 m2, which is 3- 4 times larger than the Synthesis Radio Telescope (Westerbork) one, with a 2 Km baseline; all this would cost about 1.3-1.8 Million of Euros.

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