LOFAR
Encyclopedia
LOFAR is the Low Frequency Array for radio astronomy
, built by the Netherlands
astronomical foundation ASTRON
and operated by ASTRON's radio observatory.
LOFAR will be the largest connected radio telescope
ever built, using a new concept based on a vast array of omni-directional antennas. The project is based on an interferometric array of radio telescopes using about 20,000 small antennas and at least 48 larger stations. 40 of these stations are distributed across the Netherlands, five stations in Germany
, and one each in Great Britain
, France
and Sweden
. Further stations may also be built in other European countries. The total effective collecting area is up to approximately 300,000 square meter, depending on frequency and antenna configuration. The data processing is performed by a Blue Gene/P supercomputer
situated in the Netherlands at the University of Groningen
.
LOFAR was conceived as an innovative effort to force a breakthrough in sensitivity for astronomical observations at radio-frequencies below 250 MHz. Astronomical radio interferometers usually consist either of arrays of parabolic dishes
(e.g. the One-Mile Telescope
), arrays of one-dimensional antennas (e.g. the Molonglo Observatory Synthesis Telescope
) or two-dimensional arrays of omnidirectional antenna
s (e.g. Antony Hewish
' Interplanetary Scintillation Array
).
LOFAR combines aspects of many of these earlier telescopes—in particular it uses omni-directional dipole antennas as a phased array
using the aperture synthesis
technique developed in the 1950s. Like the earlier Cambridge Low Frequency Synthesis Telescope
(CLFST) low-frequency radio telescope, the design of LOFAR has concentrated on the use of large numbers of relatively cheap antennas without any moving parts, concentrated in stations, with the mapping performed using aperture synthesis software. The direction of observation ("beam") is chosen electronically by phase delays between the antennas. LOFAR can observe in several directions simultaneously which allows a multi-user operation.
The electric signals from the LOFAR antennas are digitised, transported to a central digital processor, and combined in software in order to map the sky. The cost is dominated by the cost of electronics and will follow Moore's law
, becoming cheaper with time and allowing increasingly large telescopes to be built. So LOFAR is a "software telescope". The antennas are simple enough but there are a lot of them — about 20,000 in the full LOFAR design. To make radio pictures of the sky with adequate sharpness, these antennas are to be arranged in clusters (stations) that are spread out over an area of ultimately more than 1000 km in diameter. The 40 stations in the Netherlands reach baselines of about 100 km. 30 stations are presently in operation. In Germany five stations are operating: Bonn/Effelsberg, Garching/Unterweilenbach, Tautenburg, Potsdam/Bornim and Jülich. The Effelsberg
station is operating since November 2007, the German stations in Garching/Unterweilenbach, Tautenburg and Bornim/Potsdam since 2010, and the Jülich station since 2011. One station each is completed in Great Britain (Chilbolton
) and in France (Nançay
); the Swedish station (Onsala
) is under construction. Data transport requirements are in the range of several gigabit
s per second per station and the processing power needed is tens of TeraFLOPS.
and greater sensitivity than previous surveys, such as the 7C and 8C
surveys, and surveys by the Very Large Array
(VLA) and Giant Meterwave Radio Telescope (GMRT).
LOFAR is the most sensitive radio observatory at its low observing frequencies, until the next generation of large array radio telescope, the Square Kilometre Array (SKA
), comes online around 2020.
The sensitivities and spatial resolutions attainable with LOFAR will make possible several fundamental new studies of the Universe as well as facilitating unique practical investigations of the Earth's environment.
In the following list the term
indicates the redshift
of the radio sources seen by LOFAR.
signals. In addition this key science project will make a deep survey for radio pulsars at low radio frequencies, and will hope to detect giant radio bursts from rotating neutron stars in distant galaxies.
s (HECRs and UHECRs) at energies between
eV. Both the sites and processes for accelerating particles are unknown. Possible candidate sources of these HECRs are shocks in radio lobes of powerful radio galaxies, intergalactic shocks created during the epoch of galaxy formation, so-called Hyper-novae, Gamma-ray bursts, or decay products of super-massive particles from topological defects, left over from phase transitions in the early Universe. The primary observable is the intense radio pulse that is produced when a primary CR hits the atmosphere and produces an Extensive Air Shower (EAS). An EAS is aligned along the direction of motion of the primary particle, and a substantial part of its component consists of electron-positron pairs which emit radio emission in the terrestrial magnetosphere (e.g., geo-synchrotron emission).
K hot solar corona is superimposed by intense radio bursts that are associated with phenomena of the solar activity, like flares
and coronal mass ejections (CMEs)
. Solar radio radiation in the LOFAR frequency range is emitted in the middle and upper corona. So LOFAR is an ideal instrument for studies of the launch of CMEs heading towards interplanetary space. LOFAR's imaging capabilities will yield information on whether such a CME might hit the Earth. This makes LOFAR is a valuable instrument for space weather
studies.
Solar observations with LOFAR will include routine monitoring of the solar activity as the root of Space Weather. Furthermore, LOFAR's flexibility enables rapid responses to solar radio bursts with follow-up observations. Solar flares produce energetic electrons that not only lead to the emission of non-thermal solar radio radiation. The electrons also emit X-rays and heat the ambient plasma. So joint observation campaigns with other ground- and space-based instruments, e.g. RHESSI
, Hinode
, the Solar Dynamics Observatory (SDO)
, or the Solar Orbiter
provide insights into this fundamental astrophysical process.
- the Netherlands Institute for Radio Astronomy. At the same time, scientific interest in a low-frequency radio telescope began to emerge at ASTRON and at the Dutch Universities. A feasibility study was carried out and international partners sought during 1999. In 2000 the Netherlands LOFAR Steering Committee was set up by the ASTRON Board with representatives from all interested Dutch university departments and ASTRON.
In November 2003 the Dutch Government allocated 52 million euro
to fund the infrastructure of LOFAR under the Bsik programme. In accordance with Bsik guidelines, LOFAR was funded as a multidisciplinary sensor array that will facilitate research in geophysics
, computer sciences
and agriculture
as well as astronomy
.
In December 2003 LOFAR's Initial Test Station (ITS) became operational; this was an important milestone in the LOFAR development. The ITS system consists of 60 inverse V-shaped dipoles; each dipole is connected to a low-noise amplifier
(LNA), which provides enough amplification of the incoming signals to transport them over a 110 m long coaxial cable to the receiver unit (RCU).
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On April 26, 2005, an IBM
Blue Gene/L supercomputer was installed at the University of Groningen
's math center, for LOFAR's data processing
. At that time it was the second most powerful supercomputer in Europe
, after the MareNostrum
in Barcelona
.
In August/September 2006 the first LOFAR station (Core Station CS001, aka. CS1 52°54′32"N 6°52′8"E) has been put in the field using pre-production hardware. A total of 96 dual-dipole antennas (the equivalent of a full LOFAR station) are grouped in four clusters, the central cluster with 48 dipoles and other three clusters with 16 dipoles each. Each cluster is about 100 m in size. The clusters are distributed over an area of ~500 m in diameter.
In November 2007 the first international LOFAR station (DE601) next to the Effelsberg
100 m radio telescope became the first operational station. The first fully complete station, (CS302) on the edge of the LOFAR core, was delivered in May 2009, with a total of 40 Dutch stations scheduled for completion in 2011. By mid 2011, 30 stations in the Netherlands, five stations in Germany (Effelsberg, Tautenburg, Unterweilenbach, Bornim/Potsdam, and Jülich), one in the UK (Chilbolton) and one in France (Nançay) were operational.
LOFAR was officially opened on 12 June 2010 by Queen Beatrix of the Netherlands.
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
, built by the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
astronomical foundation ASTRON
ASTRON
ASTRON is the Netherlands Foundation for Research in Astronomy. ASTRON is an abbreviation of the Dutch Stichting ASTRonomisch Onderzoek in Nederland. This translates to NFRA in English, which is sometimes used to refer to ASTRON in English texts. Its main offices are in Dwingeloo at the site of the...
and operated by ASTRON's radio observatory.
LOFAR will be the largest connected radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
ever built, using a new concept based on a vast array of omni-directional antennas. The project is based on an interferometric array of radio telescopes using about 20,000 small antennas and at least 48 larger stations. 40 of these stations are distributed across the Netherlands, five stations in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, and one each in Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
and Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
. Further stations may also be built in other European countries. The total effective collecting area is up to approximately 300,000 square meter, depending on frequency and antenna configuration. The data processing is performed by a Blue Gene/P supercomputer
Supercomputer
A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...
situated in the Netherlands at the University of Groningen
University of Groningen
The University of Groningen , located in the city of Groningen, was founded in 1614. It is one of the oldest universities in the Netherlands as well as one of its largest. Since its inception more than 100,000 students have graduated...
.
Technical Information
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
(e.g. the One-Mile Telescope
One-Mile Telescope
The One-Mile Telescope at the Mullard Radio Astronomy Observatory is an array of radio telescopes designed to perform aperture synthesis interferometry.- History :The One Mile Telescope was completed by the Radio Astronomy Group of Cambridge...
), arrays of one-dimensional antennas (e.g. the Molonglo Observatory Synthesis Telescope
Molonglo Observatory Synthesis Telescope
The Molonglo Observatory Synthesis Telescope is a radio telescope operating at 843 MHz. It is operated by the School of Physics of the University of Sydney...
) or two-dimensional arrays of omnidirectional antenna
Omnidirectional antenna
In radio communication, an omnidirectional antenna is an antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often...
s (e.g. Antony Hewish
Antony Hewish
Antony Hewish FRS is a British radio astronomer who won the Nobel Prize for Physics in 1974 for his work on the development of radio aperture synthesis and its role in the discovery of pulsars...
' Interplanetary Scintillation Array
Interplanetary Scintillation Array
The Interplanetary Scintillation Array was built at the Mullard Radio Astronomy Observatory in 1967 and originally covered four acres . It was extended in 1978 to nine, and re-furbished in 1989. It operates at 81.5 MHz , and is made up of 4096 dipoles in a phased array. 14 beams can map the...
).
LOFAR combines aspects of many of these earlier telescopes—in particular it uses omni-directional dipole antennas as a phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
using the aperture synthesis
Aperture synthesis
Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection...
technique developed in the 1950s. Like the earlier Cambridge Low Frequency Synthesis Telescope
Cambridge Low Frequency Synthesis Telescope
The Cambridge Low-Frequency Synthesis Telescope is an east-west aperture synthesis radio telescope currently operating at 151 MHz. It consists of 60 tracking yagis on a 4.6 km baseline, giving 776 simultaneous baselines. These provide a resolution of 70×70 cosec arcsec2, with a sensitivity of...
(CLFST) low-frequency radio telescope, the design of LOFAR has concentrated on the use of large numbers of relatively cheap antennas without any moving parts, concentrated in stations, with the mapping performed using aperture synthesis software. The direction of observation ("beam") is chosen electronically by phase delays between the antennas. LOFAR can observe in several directions simultaneously which allows a multi-user operation.
The electric signals from the LOFAR antennas are digitised, transported to a central digital processor, and combined in software in order to map the sky. The cost is dominated by the cost of electronics and will follow Moore's law
Moore's Law
Moore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....
, becoming cheaper with time and allowing increasingly large telescopes to be built. So LOFAR is a "software telescope". The antennas are simple enough but there are a lot of them — about 20,000 in the full LOFAR design. To make radio pictures of the sky with adequate sharpness, these antennas are to be arranged in clusters (stations) that are spread out over an area of ultimately more than 1000 km in diameter. The 40 stations in the Netherlands reach baselines of about 100 km. 30 stations are presently in operation. In Germany five stations are operating: Bonn/Effelsberg, Garching/Unterweilenbach, Tautenburg, Potsdam/Bornim and Jülich. The Effelsberg
Effelsberg
The Effelsberg 100-m Radio Telescope is a radio telescope in the Ahrgebirge in Bad Münstereifel, district of Euskirchen, North Rhine-Westphalia, Germany.- Geography :...
station is operating since November 2007, the German stations in Garching/Unterweilenbach, Tautenburg and Bornim/Potsdam since 2010, and the Jülich station since 2011. One station each is completed in Great Britain (Chilbolton
Chilbolton
Chilbolton is a village and civil parish in Hampshire, England, near to Stockbridge. Its most notable feature is the Chilbolton Observatory situated on the disused RAF Chilbolton airfield...
) and in France (Nançay
Nançay
Nançay is a commune in the Cher department in central France.-Geography:The village is located south of the Sologne and north-east of Vierzon. The Rère flows southwestward through the middle of the commune.-History:...
); the Swedish station (Onsala
Onsala
Onsala is a locality situated in Kungsbacka Municipality, Halland County, Sweden, with 11,375 inhabitants in 2005. It is also the biggest peninsula in Sweden, south of Gothenburg....
) is under construction. Data transport requirements are in the range of several gigabit
Gigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
s per second per station and the processing power needed is tens of TeraFLOPS.
Sensitivity
The mission of LOFAR is to survey the Universe at radio frequencies from ~10–240 MHz with greater resolutionAngular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
and greater sensitivity than previous surveys, such as the 7C and 8C
Eighth Cambridge Survey
The 8C Survey or Rees 38 MHz survey is an astronomical catalogue of celestial radio sources as measured at 38 MHz. It was published in 1990 by the Radio Astronomy Group of the University of Cambridge. Sources are labelled 8C HHMM+DDd where HHMM is the Right Ascension in hours and...
surveys, and surveys by the Very Large Array
Very Large Array
The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...
(VLA) and Giant Meterwave Radio Telescope (GMRT).
LOFAR is the most sensitive radio observatory at its low observing frequencies, until the next generation of large array radio telescope, the Square Kilometre Array (SKA
Square Kilometre Array
The Square Kilometre Array is a radio telescope in development which will have a total collecting area of approximately one square kilometre. It will operate over a wide range of frequencies and its size will make it 50 times more sensitive than any other radio instrument...
), comes online around 2020.
Science case
In the following list the term
indicates the redshiftRedshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
of the radio sources seen by LOFAR.
- In the very distant Universe (
), LOFAR can search for the signature produced by the reionizationReionizationIn Big Bang cosmology, reionization is the process that reionized the matter in the universe after the "dark ages," and is the second of two major phase changes of gas in the universe. As the majority of baryonic matter is in the form of hydrogen, reionization usually refers to the reionization of...
of neutral hydrogenHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. This crucial phase change is predicted to occur at the epoch of the formation of the first stars and galaxies, marking the end of the so-called "dark ages". The redshiftRedshiftIn physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
at which reionization is believed to occur will shift the 21 cm line of neutral hydrogenHydrogen lineThe hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum...
at 1420.40575 MHz into the LOFAR observing window. (The frequency observed today is lower by a factor of 1/(z+1).) - In the distant "formative" Universe (
), LOFAR will detect the most distant massive galaxies and will study the processes by which the earliest structures in the Universe (galaxies, clusters and active nuclei) form and probe the intergalactic gas. - In the magnetic Universe, LOFAR will map the three-dimensional distribution of cosmic rays and global magnetic fieldMagnetic fieldA magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
in our own and nearby galaxies, in galaxy clusters and in the intergalactic medium. - The high energy Universe, LOFAR will detect the ultra high energy cosmic rays as they pierce the Earth’s atmosphere. A dedicated test station for this purpose, LOPESLOPES (telescope)The LOPES project is a cosmic ray detector array, located in Karlsruhe, Germany, and is operated in coincidence with an existing, well calibrated air shower experiment called KASCADE....
, has been in operation since 2003. - Within our own Galaxy, LOFAR will detect flashes of low-frequency radiation from pulsars and short-lived transient eventsTransient astronomical eventA transient astronomical event, often simply called in context by astronomers a transient, is an astronomical object or phenomenon which can be observed for a short period of time...
produced by events such as stellar mergers, black hole accretion, and will search for burst from JupiterJupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
-like extrasolar planets. - Within our solar system, LOFAR will detect coronal mass ejections from the Sun and provide continuous large-scale maps of the solar windSolar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
. This crucial information about solar weather and its effect on the Earth will facilitate predictions of costly and damaging geomagnetic storms. - Within the Earth’s immediate environment, LOFAR will map irregularities in the ionosphereIonosphereThe ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
continuously, detect the ionizing effects of distant gamma ray bursts and the flashes predicted to arise from the highest energy cosmic rays, the origins of which are unclear. - By exploring a new spectral window LOFAR is likely to make unexpected "serendipitousSerendipitySerendipity means a "happy accident" or "pleasant surprise"; specifically, the accident of finding something good or useful without looking for it. The word has been voted as one of the ten English words hardest to translate in June 2004 by a British translation company. However, due to its...
" discoveries. Detection of new classes of objects and/or new astrophysical phenomena have resulted from almost all previous facilities that open new regions of the spectrum, or pushed instrumental parameters, such as sensitivity by more than an order of magnitude.
The epoch of reionization
One of the most exciting applications of LOFAR will be the search for redshifted 21 cm line emission from the Epoch of Reionization (EoR). It is currently believed that the 'dark ages', the period after recombination when the universe turned neutral, lasted until around z=20. WMAP polarization results appear to suggest that there may have been extended, or even multiple phases of reionisation, the start possibly being around z~15-20 and ending at z~6. Using LOFAR the redshift range from z=11.4 (115 MHz) to z=6 (200 MHz) can be probed.Deep extragalactic surveys
One of the most important applications of LOFAR will be to carry out large-sky surveys. Such surveys are well suited to the characteristics of LOFAR and have been designated as one of the key projects that have driven LOFAR since its inception. Such deep LOFAR surveys of the accessible sky at several frequencies will provide unique catalogues of radio sources for investigating several fundamental areas of astrophysics, including the formation of massive black holes, galaxies and clusters of galaxies. Because the LOFAR surveys will probe unexplored parameter space, it is likely that they will discover new phenomena.Transient radio phenomena and pulsars
The combination of low frequencies, omni-directional antennae, high-speed data transport and computing means that LOFAR will open a new era in the monitoring of the radio sky. It will be possible to make sensitive radio maps of the entire sky visible from The Netherlands (about 60% of the entire sky) in only one night. Transient radio phenomena, only hinted at by previous narrow-field surveys, will be discovered, rapidly localised with unprecedented accuracy, and automatically compared to data from other facilities (e.g. gamma-ray, optical, X-ray observatories). Such transient phenomena may be associated with exploding stars, black holes, flares on sun-like stars, radio bursts from exoplanets or even SETISETI
The search for extraterrestrial intelligence is the collective name for a number of activities people undertake to search for intelligent extraterrestrial life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life...
signals. In addition this key science project will make a deep survey for radio pulsars at low radio frequencies, and will hope to detect giant radio bursts from rotating neutron stars in distant galaxies.
(Ultra) high energy cosmic rays
LOFAR offers a unique possibility in particle astrophysics for studying the origin of high-energy and ultra-high-energy cosmic rayUltra-high-energy cosmic ray
In astroparticle physics, an ultra-high-energy cosmic ray or extreme-energy cosmic ray is a cosmic ray with an extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays....
s (HECRs and UHECRs) at energies between
eV. Both the sites and processes for accelerating particles are unknown. Possible candidate sources of these HECRs are shocks in radio lobes of powerful radio galaxies, intergalactic shocks created during the epoch of galaxy formation, so-called Hyper-novae, Gamma-ray bursts, or decay products of super-massive particles from topological defects, left over from phase transitions in the early Universe. The primary observable is the intense radio pulse that is produced when a primary CR hits the atmosphere and produces an Extensive Air Shower (EAS). An EAS is aligned along the direction of motion of the primary particle, and a substantial part of its component consists of electron-positron pairs which emit radio emission in the terrestrial magnetosphere (e.g., geo-synchrotron emission).Cosmic magnetism
LOFAR opens the window to the so far unexplored low-energy synchrotron radio waves, emitted by cosmic-ray electrons in weak magnetic fields. Very little is known about the origin and evolution of cosmic magnetic fields. The space around galaxies and between galaxies may all be magnetic, and LOFAR may be the first to detect weak radio emission from such regions. LOFAR will also measure the Faraday effect, which is the rotation of polarization plane of low-frequency radio waves, and gives another tool to detect weak magnetic fields .Solar physics and space weather
The sun is an intense radio source. The already strong thermal radiation of the K hot solar corona is superimposed by intense radio bursts that are associated with phenomena of the solar activity, like flaresSolar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
and coronal mass ejections (CMEs)
Coronal mass ejection
A coronal mass ejection is a massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space....
. Solar radio radiation in the LOFAR frequency range is emitted in the middle and upper corona. So LOFAR is an ideal instrument for studies of the launch of CMEs heading towards interplanetary space. LOFAR's imaging capabilities will yield information on whether such a CME might hit the Earth. This makes LOFAR is a valuable instrument for space weather
Space weather
Space weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...
studies.
Solar observations with LOFAR will include routine monitoring of the solar activity as the root of Space Weather. Furthermore, LOFAR's flexibility enables rapid responses to solar radio bursts with follow-up observations. Solar flares produce energetic electrons that not only lead to the emission of non-thermal solar radio radiation. The electrons also emit X-rays and heat the ambient plasma. So joint observation campaigns with other ground- and space-based instruments, e.g. RHESSI
Reuven Ramaty High Energy Solar Spectroscopic Imager
Reuven Ramaty High Energy Solar Spectroscopic Imager is the sixth mission in the line of NASA Small Explorer missions...
, Hinode
Hinode
Hinode , formerly Solar-B, is a Japan Aerospace Exploration Agency Solar mission with United States and United Kingdom collaboration. It is the follow-up to the Yohkoh mission and it was launched on the final flight of the M-V-7 rocket from Uchinoura Space Center, Japan on 22 September 2006 at...
, the Solar Dynamics Observatory (SDO)
Solar Dynamics Observatory
The Solar Dynamics Observatory is a NASA mission which will observe the Sun for over five years. Launched on February 11, 2010, the observatory is part of the Living With a Star program...
, or the Solar Orbiter
Solar Orbiter
Solar Orbiter is a planned Sun-observing satellite, under development by the European Space Agency . The main mission scenario is a launch by an Atlas V from the Kennedy Space Center in Florida in January 2017...
provide insights into this fundamental astrophysical process.
Timeline
In the early 1990s, the study of aperture array technology for radio astronomy was being actively studied by ASTRONASTRON
ASTRON is the Netherlands Foundation for Research in Astronomy. ASTRON is an abbreviation of the Dutch Stichting ASTRonomisch Onderzoek in Nederland. This translates to NFRA in English, which is sometimes used to refer to ASTRON in English texts. Its main offices are in Dwingeloo at the site of the...
- the Netherlands Institute for Radio Astronomy. At the same time, scientific interest in a low-frequency radio telescope began to emerge at ASTRON and at the Dutch Universities. A feasibility study was carried out and international partners sought during 1999. In 2000 the Netherlands LOFAR Steering Committee was set up by the ASTRON Board with representatives from all interested Dutch university departments and ASTRON.
In November 2003 the Dutch Government allocated 52 million euro
Euro
The euro is the official currency of the eurozone: 17 of the 27 member states of the European Union. It is also the currency used by the Institutions of the European Union. The eurozone consists of Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg,...
to fund the infrastructure of LOFAR under the Bsik programme. In accordance with Bsik guidelines, LOFAR was funded as a multidisciplinary sensor array that will facilitate research in geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
, computer sciences
Computer Sciences
Computer Sciences can refer to:*The general field of computer science*Computer Sciences Corporation, the Fortune 500 Information Technology company...
and agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
as well as astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
.
In December 2003 LOFAR's Initial Test Station (ITS) became operational; this was an important milestone in the LOFAR development. The ITS system consists of 60 inverse V-shaped dipoles; each dipole is connected to a low-noise amplifier
Low-noise amplifier
Low-noise amplifier is an electronic amplifier used to amplify possibly very weak signals . It is usually located very close to the detection device to reduce losses in the feedline. This active antenna arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is...
(LNA), which provides enough amplification of the incoming signals to transport them over a 110 m long coaxial cable to the receiver unit (RCU).
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
Blue Gene/L supercomputer was installed at the University of Groningen
University of Groningen
The University of Groningen , located in the city of Groningen, was founded in 1614. It is one of the oldest universities in the Netherlands as well as one of its largest. Since its inception more than 100,000 students have graduated...
's math center, for LOFAR's data processing
Data processing
Computer data processing is any process that a computer program does to enter data and summarise, analyse or otherwise convert data into usable information. The process may be automated and run on a computer. It involves recording, analysing, sorting, summarising, calculating, disseminating and...
. At that time it was the second most powerful supercomputer in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, after the MareNostrum
MareNostrum
MareNostrum is a supercomputer in the Barcelona Supercomputing Center, the second most powerful in Spain. It was presented by IBM and María Jesús San Segundo, the Spanish Minister of Education and Science...
in Barcelona
Barcelona
Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...
.
In August/September 2006 the first LOFAR station (Core Station CS001, aka. CS1 52°54′32"N 6°52′8"E) has been put in the field using pre-production hardware. A total of 96 dual-dipole antennas (the equivalent of a full LOFAR station) are grouped in four clusters, the central cluster with 48 dipoles and other three clusters with 16 dipoles each. Each cluster is about 100 m in size. The clusters are distributed over an area of ~500 m in diameter.
In November 2007 the first international LOFAR station (DE601) next to the Effelsberg
Effelsberg
The Effelsberg 100-m Radio Telescope is a radio telescope in the Ahrgebirge in Bad Münstereifel, district of Euskirchen, North Rhine-Westphalia, Germany.- Geography :...
100 m radio telescope became the first operational station. The first fully complete station, (CS302) on the edge of the LOFAR core, was delivered in May 2009, with a total of 40 Dutch stations scheduled for completion in 2011. By mid 2011, 30 stations in the Netherlands, five stations in Germany (Effelsberg, Tautenburg, Unterweilenbach, Bornim/Potsdam, and Jülich), one in the UK (Chilbolton) and one in France (Nançay) were operational.
LOFAR was officially opened on 12 June 2010 by Queen Beatrix of the Netherlands.
See also
- ASKAP: Australian Square Kilometre Array Pathfinder
- Long Wavelength Array (LWA)Long Wavelength Array (LWA)The Long Wavelength Array is a radio telescope under construction in central New Mexico. It is one of the few observatories to utilize such low frequencies, and is used to study relativistic particles, cosmic evolution, astrophysical plasma, decametric radio emissions from Jupiter-like extrasolar...
- MeerKATMeerKATMeerKAT is a radio telescope under construction in the Northern Cape of South Africa. It will be the largest and most sensitive radio telescope in the southern hemisphere until the Square Kilometer Array is completed around 2024.The telescope will be used for research into cosmic magnetism,...
: Karoo Array Telescope - Square Kilometre ArraySquare Kilometre ArrayThe Square Kilometre Array is a radio telescope in development which will have a total collecting area of approximately one square kilometre. It will operate over a wide range of frequencies and its size will make it 50 times more sensitive than any other radio instrument...