Fundamental Physics in Radio Astronomy

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Fundamental Physics in
Radio Astronomy

LOFAR, the Low Frequency Array, is a new radio telescope under construction by ASTRON in the Netherlands, operating in the largely unexplored frequency range between 30 and 240 MHz. LOFAR leads the way for a new generation of radio telescopes, like the planned Square Kilometre Array (see below), consisting of a multitude of small and cheep antennas without moving parts. The digital radio images are synthesized in supercomputer in real time. The innovative design of digital beam-forming will allow to point the telescope simultaneously at several positions on sky. In principle, the whole visible radio sky can be monitored continuously. LOFAR will consist about 36 stations in the Netherlands and at least 5 stations in Germany, each with 192 dipoles for the frequency range 30-80 MHz and 48 and 96 antennas, respectively, for the range 110-240 MHz. The first German station next to the 100-m Effelsberg radio telescope was completed in July 2009 and is performed by the MPIfR in collaboration with ASTRON. The MPIfR is member of the German Long Wavelength Consortium (GLOW).

With the new Effelsberg LOFAR station, the group plans to search for new pulsars and observe them in detail. The full European LOFAR array will give an unprecedented sensitivity which will allow us to detect hundreds of new pulsars. The group is actively involved in the LOFAR Key Science Project on Transients and Pulsars.

The group leads the international LOFAR Key Science Project on Cosmic Magnetism. At low frequencies, weak extended synchrotron emission in the Milky Way, around galaxies and in galaxy clusters should become observable. This will allow us to measure magnetic fields in intergalactic space.

SKA, the Square Kilometre Array, with a collecting area of about one square kilometer, will be about ten times more sensitive than any radio telescope today. The SKA will continuously cover most of the frequency range accessible from ground, from 70 MHz to 10 GHz (corresponding to wavelengths of 3 centimeters to 4 meters) in the first and second phases, later to be extended to 30 GHz (1 centimeter). The third major improvement is the enormously wide field of view, ranging from 200 square degrees at 70 MHz to at least 1 square degree at the highest frequency. The speed to survey a large part of the sky will hence be ten thousand to a million times faster than what is possible today.

The frequency range spanning more than two decades cannot be realized with one single antenna design, so this will be achieved with a combination three fundamentally different types of antennas that are now being investigated:

- a phased array of simple dipole antennas for the low-frequency range (70 to about 300 MHz),

- an array of several thousand parabolic dishes of 12-15 meters diameter each for the medium and high-frequency
range (about 300 MHz to 10 GHz),

- a phased array of “tiles” for the medium frequency range (about 500 - 1000 MHz) which can provide a large field of view.

Five Key Science Projects cover the most important fundamental questions to be investigated by the SKA. The group is particularly involved in:

- Testing General Relativity and detecting gravitational waves with pulsars

- Origin and evolution of cosmic magnetism.

The MPIfR coordinates the German SKA activities. M. Kramer and R. Beck are members of the SKA Science Working Group.