The Next Generation of Radio Astronomy

Last year, Birr was thrust to the forefront of astronomy. What may seem a quaint and unassuming town, Birr, Co. Offaly, is steeped in astronomical history and it has regained its scientific prominence with the construction of a new telescope.

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Tau.Neutrino said:

The Next Generation of Radio Astronomy

Last year, Birr was thrust to the forefront of astronomy. What may seem a quaint and unassuming town, Birr, Co. Offaly, is steeped in astronomical history and it has regained its scientific prominence with the construction of a new telescope.

more…

LOFAR was officially opened on 12 June 2010. Regular observations started in December 2012.

LOFAR stations

To make radio surveys of the sky with adequate resolution, the antennas are arranged in clusters (stations) that are spread out over an area of more than 1000 km in diameter. The LOFAR stations in the Netherlands reach baselines of about 100 km. LOFAR currently receives data from 24 core stations (in Exloo), 14 ‘remote’ stations in The Netherlands.

The locations of the international LOFAR stations are:

Germany

• Effelsberg – at the site of the Effelsberg Radio Telescope
• Unterweilenbach/Garching – run by Max Planck Institute for Astrophysics
• Tautenburg – at the site of the Thüringer Landessternwarte Tautenburg (Thuringian State Observatory)
• Potsdam-Bornim – at the site of the Astrophysikalisches Institut Potsdam
• Jülich – run by the University of Bochum, Jacobs University Bremen and Forschungszentrum Jülich
  United Kingdom
• Chilbolton – at the site of the Chilbolton Observatory
  France
• Nançay – at the site of the Nançay Radio Telescope
  Sweden
• Onsala – at the site Onsala Space Observatory
  Poland
• Baldy
• Borówiec
• Lazy
  Ireland
• Birr – at the site Birr Castle

The mission of LOFAR is to map the Universe at radio frequencies from 10–240 MHz with greater resolution and greater sensitivity than previous surveys, including the Very Large Array (VLA).

LOFAR is the most sensitive radio observatory at its low observing frequencies, until the Square Kilometre Array (SKA), comes online around 2025.

Science Case.

• In the very distant Universe (6 < z < 10), LOFAR can search for the signature produced by the reionization of neutral hydrogen.

• In the distant Universe (1.5 < z < 7), LOFAR will detect the most distant massive galaxies

• LOFAR will map the distribution of cosmic rays.

• Within the Milky Way galaxy, LOFAR will detect several hundred new pulsars, will search for short-lived transient events produced by stellar mergers or black hole accretion, and will search for burst from Jupiter-like extrasolar planets.

• Within the Solar System, LOFAR will detect coronal mass ejections from the Sun and provide continuous large-scale maps of the solar wind.

• Within the Earth’s immediate environment, LOFAR will map irregularities in the ionosphere continuously.

> LOFAR is the most sensitive radio observatory at its low observing frequencies, until the Square Kilometre Array (SKA), comes online around 2025.

Even after that, LOFAR will retain world dominance on really low frequencies of 10 to 50 MHz because the SKA is only for frequencies aboue 50 MHz.

What are the natural radio sources at such low frequencies?

Note that this is clear of AM <1.6 MHz and FM >88 MHz radio bands. But it overlaps with short wave radio and VHF TV. The ionosphere is opaque at about 9 MHz, hence the overlap with short wave radio.

“The affected frequencies at the zenith of the radio telescope are equal to fc, which has a typical maximum value of 10 MHz at the Murchison Radio Observatory in central Western Australia (lat -27, lon 116). As the elevation of the observation decreases the affected frequencies increase to a maximum of about five times fc (or around 50 MHz at MRO).

“It should be noted that the above discussion refers to a well behaved ‘quiet’ ionosphere. During certain seasons and at certain times, we find sporadic (in space and time) clouds or clumps of more highly ionised plasma forming. This is known as sporadic E (as it forms around 100 km, the altitude of the E-layer). This phenomenon can at times significantly alter affected frequencies, and of even greater significance, it can allow propagation of radio frequency interference into a radio quiet zone that one would not expect.

“Radio astronomy fields affected by this first order effect include low frequency solar and interplanetary monitors (Note that the interplanetary medium has a plasma frequency of 50 kHz at Earth orbit (1 AU)). Studies of radiation from the plasma are obviously impossible from the Earth’s surface. As these and higher frequencies (but well below fc) are suspected of being associated with the most dangerous space weather events we know (solar particle events), our inability to see them except via radiotelecopes in space is a big problem.

“Jovian decametric radiation (5 to 40 MHz) can be severely affected by ionosphere absorption.”