LOFAR discovers largest carbon atoms outside our Milky Way

The starburst galaxy M82, the size of the carbon atoms and the observed spectral line

Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA) 

Click here for hi-res image

An international team of astronomers under the guidance of graduate student Leah Morabito of Leiden Observatory has for the first time discovered the largest carbon atoms outside our Milky Way with the LOFAR radio telescope. In the future astronomers will be able to measure how cold and dense the gas around these atoms is that influences star formation and the evolution of a galaxy. The results are published in the journal Astrophysical Journal Letters on 28 October.  

"Carbon atoms are about half a million times smaller than the average thickness of a human hair, but they can be a billion times larger in the cold and sparse gas. The outermost electron is then orbiting the nucleus at a much larger distance," explains first author Morabito. The outermost electron can be captured by an atom that is missing an electron. A spectral line will then be visible in the light spectrum. All spectral lines form the chemical fingerprint of an atom such as carbon.

 

Astronomers predicted in the 70’s that the carbon spectral line would be detectable outside our galaxy. This first observation took 40 years to be made. The line is hard to detect because it is too faint when the gas that is surrounding the atoms is too warm or too dense. The cold, sparse gas is present in starburst galaxies - galaxies in which stars form at a high rate. For this reason the carbon spectral line is easier to detect in galaxies of this type.

 

Most radio telescopes observe at frequencies at which the carbon line can not be detected. Other telescopes are not sensitive enough to detect the spectral lines of the carbon atoms at low frequencies. The LOFAR radio telescope, that stretches from the northeast of the Netherlands across Europe, is perfect for these kind of observations because of its frequency range and sensitivity. Co-author Raymond Oonk from Leiden Observatory en ASTRON: "LOFAR is an unique telescope. This telescope opens up a new window on the universe."

 

The carbon atoms are present in the heart of the starburst galaxy M82, where 10 times more stars are being born in the same period as in our Milky Way. The cold and sparse gas in this area impacts star formation, and the evolution of M82. "Since the co-discovery of the hydrogen 21-cm line by Dutch, American and Australian astronomers, we have been looking for a way to determine additional properties of the cold gas such as its temperature and density. It is fantastic that we now have found a way thanks to this carbon line. We can now collect more and better observations, and compare them to predictions from theoretical models," says co-author Huub Röttgering (Leiden Observatory).

 

Article:

Discovery of Carbon Radio Recombination Lines in M82, Leah K. Morabito et al., Astrophysical Journal Letters, 28 oktober 2014. Arxiv: http://arxiv.org/pdf/1410.1544v1.pdf

Source:  ASTRON - Netherlands Institute for Radio Astronomy

 

Super-telescope LOFAR finds its first pulsars

On the left of the image the central LOFAR antennas. On the right the peaked signals of the two discovered pulsars. Credit: LOFAR Pulsar Working Group 

The radio telescope LOFAR has discovered two new pulsars - fast-spinning neutron stars, remnants of massive supernova explosions. Two of these weak but quickly flashing radio sources were spotted for the first time during the ‘warm-up' for the LOFAR all-sky survey. The results are described in the PhD thesis that astronomer Thijs Coenen will defend November 20 at the University of Amsterdam.

 

The International LOFAR Telescope (ILT), designed and built by ASTRON, is a radio telescope centered in the Netherlands and spread across Europe. The telescope consists of a network of thousands of individual dipole antennas, connected over a fast network to a central supercomputer. The high sensitivity of this software telescope means it is extraordinarily suited for pulsar research. 

 

The international team of astronomers looking for new pulsars with LOFAR is led by Jason Hessels, from ASTRON and the University of Amsterdam, and Ben Stappers, from the University Manchester. The discovery highlighted by Coenen's PhD research showcases the pulsar capabilities of LOFAR, and hints at new possibilities with its successor, the Square Kilometre Array (SKA). Hessels says: "SKA will take LOFAR technology one step further, and these discoveries show we can expect to detect a large fraction of the pulsars in our Galaxy with SKA."

 

Pulsars act as cosmic lighthouses, emitting radio beams that sweep the Galaxy. Their signals allow scientists to study the behaviour of gravity and matter in circumstances so extreme that they cannot be reproduced on Earth, not even in the most advanced facility. Pulsars are important because of this - they are true cosmic laboratories. So far, about 2,000 pulsars have been identified, but astronomers think there must be about 50,000 active pulsars in our Galaxy. 

 

Using computing resources provided by the European Grid Infrastructure, Coenen and the team needed only a month to search through a set of 2010-2013 LOFAR images that would have occupied a single computer for more than a century. Coenen says: "Analysing all that data was a huge challenge, but then to find two new pulsars with this powerful telescope was very special." 

 

These first results show how LOFAR, with its flexible configuration, can produce more than a 1,000 images per second of a large part of the sky. That means the pulsar survey will be the most sensitive ever in this radio regime. 

 

Joeri van Leeuwen, Coenen's PhD co-supervisor, concludes: "With these first tests so successfully wrapped up, the hunt for new pulsars is on." 

 

 

More information

 

Science contacts (CET time):
Thijs Coenen MSc.
E-mail: t.coenen@uva.nl
Tel: +31 6 42346856

 

Dr. Joeri van Leeuwen
E-mail: leeuwen@astron.nl
Tel: +31 6 26154552

 

Dr. Jason Hessels
E-mail: hessels@astron.nl
Tel: +31 6 10260062

 

PhD thesis:
Searching for Pulsars with LOFAR, Thijs Coenen MSc.,
Public defence: 20 November 2013 at 10am in the Agnietenkapel, Amsterdam.
Supervisor: Prof. dr. M.B.M. van der Klis
Co-supervisor: Dr. A.G.J. van Leeuwen
Co-supervisor: Dr. J.W.T. Hessels

 

Pulsar Working Group:
A. Alexov, A. Bilous, R. Breton, T. Coenen, H. Falcke, J.M Griessmeier, T. Hassall, J. Hessels, A. Karastergiou, E. Keane, V. Kondratiev, M. Kramer,  M. Kuniyoshi, J. van Leeuwen, A. Noutsos, M. Serylak, M. Pilia, C. Sobey, B. Stappers, S. ter Veen, J. Verbiest, P. Weltevrede, K. Zagkouris.

 

Astronomy symposium in Amsterdam: 'Latest Results from the Neutron-Star Laboratory'

The photo above shows an artist impression of a neutron star, its axis and rotation.  Click here for high res image

From 6-10 May, astronomers from all over the world join in Amsterdam for a symposium about neutron stars. In debate centre Felix Meritis, they will discuss the most recent results of the research about neutron stars, collapsed cores of giant stars that have exploded as supernovas. Because of their extreme compact matter, neutron stars are excellent laboratories to explore extreme phenomena in space. 

Neutron stars exist of matter with the highest densities in the Universe: make the radius of a neutron star smaller and it becomes a black hole. The strongest magnetic fields in the Universe can also be found in and around neutron stars and fast spinning neutron stars are the best cosmic clocks. 

The reason for the meeting is the first scientific harvest of the LOFAR radio telescope, designed and built by ASTRON and built mainly in the Netherlands, and the latest status of observations of gravity waves using a group of fast spinning neutron stars. These measurements will test the gravity theory of Einstein and deliver a wealth of astronomical data.The astronomers will also discuss new important discoveries about giant magnetic fieldsin and around neutron stars, as well as the discovery of mysterious, short but powerful radio flashes from the Universe, that are thought to be connected to neutron stars. 

In the meeting, the retirement of prof. dr. Wim Hermsen, influential SRON-scientist, will also be commemmorated. Some of the distiguished guests are scientists from theUSA, among whom prof. dr. Jim Lattimer, expert in the nature of matter in neutron stars; prof. dr. Duncan Lorimer, who was the first to discover the mysterious radio flashes, and prof. dr. Andrea Lommenwho wants toresearch gravity waves by measuring arrival times of the lighthouse-like pulses of radio light. 

Another guest will be prof. dr. Alice Harding, who won the prestigious Rossi award last year for her research about pulsating neutron stars. Premier European scientists such as prof. Elena Amato and prof. Marie-Helene Grondindiscuss the influence of magnetic fields of neutron stars on the surrounding matter. Dutch speakers are, among others, dr. Jason Hessels (ASTRON) and prof. dr. Wim Hermsen (SRON). They will shed light on the results of the LOFAR telescope and ESA space telescopes INTEGRAL and XMM-Newton.

 

Date & location

 
The symposium 'Latest Results from the Neutron-Star Laboratory' takes place from 6-10 May in the debate centre Felix Meritis in Amsterdam. The meeting is organised by SRON Netherlands Institute for Space Research, Astronomical Institute Anton Pannekoek of the University of Amsterdam and ASTRON Netherlands Institute for Radio Astronomy. The website of the meeting is www.sron.nl/ns2013.

More information

 
For more information, please contact Peter Jonker (SRON), chair of the scientific organisating committee, tel. 088-777 5877, email: P.Jonker@sron.nl, or with SRON spokesman Frans Stravers, tel. 06-52679395.

 

Source: ASTRON  - Netherlands Institute for Radio Astronomy

LOFAR discovers new giant galaxy in all-sky survey

GRGs - UGC 09555

A team of astronomers led by ASTRON astronomer Dr. George Heald has discovered a previously unknown gigantic radio galaxy, using initial images from a new, ongoing all-sky radio survey. The galaxy was found using the powerful International LOFAR Telescope (ILT), built and designed by ASTRON. The team is currently performing LOFAR's first all-sky imaging survey, the Multi-frequency Snapshot Sky Survey (MSSS). While browsing the first set of MSSS images, Dr. Heald identified a new source the size of the full moon projected on the sky. The radio emission is associated with material ejected from one member of an interacting galaxy triplet system tens to hundreds of millions of years ago. The physical extent of the material is much larger than the galaxy system itself, extending millions of light years across intergalactic space. The MSSS survey is still ongoing, and is poised to discover many new sources like this one. 

The new galaxy is a member of a class of objects called Giant Radio Galaxies (GRGs). GRGs are a type of radio galaxy with extremely large physical size, suggesting that they are either very powerful or very old. LOFAR is an effective tool to find new GRGs like this one because of its extreme sensitivity to such large objects, combined with its operation at low frequencies that are well suited to observing old sources. 

The center of the new GRG is associated with one member of a galaxy triplet known as UGC 09555. The central galaxy is located at a redshift of z=0.054536, or 750 million light years from Earth. The central radio source was previously known and has a flat radio spectrum, typical of giant radio galaxies. 

LOFAR's MSSS survey is a concerted effort to image the entire northern sky at very low radio frequencies, between 30 and 160 MHz (wavelengths from 2m to 10m). The primary aim of the survey is to perform an initial shallow scan of the sky, in order to create an all-sky model that will support the calibration of much deeper observations. It is comparable in sensitivity and angular resolution to previous surveys with ‘classical' radio telescopes like the Very Large Array (VLA) in the USA, ASTRON's Westerbork Synthesis Radio Telescope (WSRT), and the Giant Metrewave Radio Telescope (GMRT) in India. MSSS is unique in that it operates at substantially lower frequencies, and is therefore poised to uncover new sources that were missed by previous surveys. Its broad bandwidth coverage is also novel in all-sky radio surveys, and will be used to provide additional information about the detected objects. 

The international team of astronomers that is performing the MSSS survey is made up of about fifty members from various institutes, mostly in the Netherlands, Germany, the UK, Poland, France and Italy.

 

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For more information please contact:
 

Femke Boekhorst, PR & Communication. 
E-mail: boekhorst@astron.nl 
Phone: +31 521 595 204

Dr. George Heald, astronomer. 
E-mail: heald@astron.nl 
Phone: +31 521 595 100

Caption to the image: Overlay of the new GRG (blue-white colors) on an optical image from the Digitized Sky survey. The inset shows the central galaxy triplet (image from Sloan Digital Sky Survey). The image is about 2 Mpc across. 

More information about MSSS can be found on the ASTRON website: http://www.astron.nl/radio-observatory/lofar-msss/lofar-msss.

Super-massive black hole inflates giant bubble

Click here for a high res image

Using a brand-new radio telescope, astronomers have produced one of the best images ever made at the lowest frequencies of giant bubbles produced by a super-massive black hole. The observations were performed at frequencies ranging from 20 to 160 MHz which are normally used for communications by airplane pilots. The picture shows what looks like a giant balloon filled with radio emitting plasma, which exceeds the size of an entire galaxy.

 Some black holes actively accrete matter. Part of this material does not fall into the black hole but is ejected in a narrow stream of particles, traveling at nearly the speed of light. When the stream slows down, it creates a tenuous balloon that can engulf the entire galaxy. Invisible to optical telescopes, the bubble is very prominent at low radio frequencies. The new International LOFAR Telescope (ILT) , designed and built by ASTRON in an international collaboration, is ideally suited to detect this low frequency emission.

 Click here for a hi-res version

"The result is of great importance", says Francesco de Gasperin, lead author of the study that will be published in the journal Astronomy & Astrophysics. "It shows the enormous potential of LOFAR, and provides compelling evidence of the close ties between black hole, host galaxy, and their surroundings. Like symbiotic species" adds de Gasperin, "a galaxy and its central black hole lead intimately connected lives, the galaxy providing matter to feed the black hole, and the black hole returning energy to the galaxy".

The image was made during the test-phase of LOFAR, and targeted the giant elliptical galaxy Messier 87, at the centre of a galaxy cluster in the constellation of Virgo. This galaxy is 2000 times more massive than our Milky Way and hosts in its centre one of the most massive black holes discovered so far, with a mass six billion times that of our Sun. Every few minutes this black hole swallows an amount of matter similar to that of the whole Earth, converting part of it into radiation and a larger part into powerful jets of ultra-fast particles, which are responsible for the observed radio emission.

"This is the first time such high-quality images are possible at these low frequencies", says professor Heino Falcke, chairman of the board of the ILT and co-author of the study. "This was a challenging observation; we did not expect to get such fantastic results so early in the commissioning phase of LOFAR."

 

 Click here for a hi-res version.

To determine the age of the bubble, the authors added radio observations at different frequencies from the Very Large Array in New Mexico (USA), and the Effelsberg 100-meter radio telescope near Bonn (Germany). The team found that this bubble is surprisingly young, just about 40 million years, which is a mere instant on cosmic time scales. The low frequency observation does not reveal any relic emission outside the well-confined bubble boundaries, this means that the bubble is not just a relic of an activity that happened long ago but is constantly refilled with fresh particles ejected by the central black hole.

 "What is particularly fascinating", says Andrea Merloni from the Max-Planck Institute of Extraterrestrial Physics in Garching, who supervised de Gasperin's doctoral work, "is that the results also provide clues on the violent matter-to-energy conversion that occurs very close to the black hole. In this case the black hole is particularly efficient in accelerating the jet, and much less effective in producing visible emission."

 Francesco de Gasperin performed the study as part of his PhD work at the Max Planck Institute for Astrophysics and at the Excellence Cluster Universe. De Gasperin is now a postdoctoral researcher at the University of Hamburg.

      

For more information, please contact:

ASTRON
Femke Boekhorst, PR & Communication
E-mail: boekhorst@astron.nl
Phone: + 31 521 595 204

Radboud University and ASTRON
Prof. Heino Falcke, Professor of Astroparticle Physics and Radio Astronomy
E-mail: h.falcke@astro.ru.nl
Phone: +31 24-36-52020

Max Planck Institute for Astrophysics
Francesco De Gasperin
E-mail: fdg@hs.uni-hamburg.de
Phone: +49 89 30000 2196 

Caption to the image:

This false colour image shows the galaxy M87. Optical light is shown in white/blue (Credits: SDSS), the radio emission in yellow/orange (LOFAR). At the centre, the radio emission has a very high surface brightness, showing where the jet powered by the supermassive black hole is located. Credits: Francesco de Gasperin, on behalf of the LOFAR collaboration.

The paper online: http://dx.doi.org/10.1051/0004-6361/201220209

  

About LOFAR

The LOFAR telescope, designed and built by ASTRON, is a revolutionary instrument able to detect radio waves with wavelengths up to 30-meter. Radio waves this long are typically generated by human activities as radio broadcasts, radar signals or satellite communications. They are also emitted by exotic objects in deep-space, such as accreting black holes, rotating neutron stars and supernovae. To detect these waves, LOFAR uses thousands of antennas spread all over Europe and combines the signals in a supercomputer located in the Netherlands. The 100 Gigabit per second of data flowing from all antennas are analyzed simultaneously and in real-time to provide the most detailed images ever done at these frequencies.

International LOFAR Telescope operations are coordinated by ASTRON, the Netherlands Institute for Radio Astronomy, on behalf of a consortium consisting of the Netherlands, Germany, France, the UK, and Sweden. Many of the technological solutions developed for LOFAR, in particular the calibration of phased-arrays as well as large-scale data transport and processing, will be highly relevant for future radio telescope projects such as the Square Kilometer Array (SKA).

Colliding galaxy cluster unravelled

Galaxy cluster Abell 2256 at 60 MHz made with LOFAR

Click here for a high res image

An international team of astronomers has used the International LOFAR Telescope from ASTRON, the Netherlands Institute for Radio Astronomy, to study the formation of the galaxy cluster Abell 2256. Abell 2256 is a cluster containing hundreds of galaxies at a distance of 800 million lightyears. ‘The structure we see in the radio images made with LOFAR provides us with information about the origin of this cluster, explains lead author dr. Reinout van Weeren (Leiden University and ASTRON). The study will be published in the scientific journal Astronomy & Astrophysics. The research involved a large team of scientists from 26 different universities and research institutes.

LOFAR has made the first images of Abell 2256 in the frequency range of 20 to 60 MHz. What came as a surprise to scientists was that the cluster of galaxies was brighter and more complex than expected. Dr. van Weeren: ‘We think that galaxy clusters form by mergers and collisions of smaller clusters'. Abell 2256 is a prime example of a cluster that is currently undergoing a collision. The radio emission is produced by tiny elementary particles that move nearly at the speed of light. With LOFAR it is possible to study how these particles get accelerated to such speeds. ‘In particular, we will learn how this acceleration takes place in regions measuring more than 10 million light years across', says Dr. Gianfranco Brunetti from IRA-INAF in Bologna, Italy, who together with Prof. Marcus Brüggen from the Jacobs University in Bremen, coordinates the LOFAR work on galaxy clusters.

LOFAR was built by a large international consortium led by the Netherlands and which includes Germany, France, the United Kingdom and Sweden. One of the main goals of LOFAR is to survey the entire northern sky at low radio frequencies, with a sensitivity and resolution about 100 times better than what has been previously done. Scientists believe that this survey will discover more than 100 million objects in the distant Universe. ‘Soon we will start our systematic surveys of the sky that will lead to great discoveries', says Prof. Huub Röttgering from Leiden University and Principal Investigator of the "LOFAR Survey Key Project".


For more information, contact:

Dr. Reinout van Weeren, astronomer,
Leiden University and ASTRON
Tel.: +31 71 527 5864
E-mail: rvweeren@strw.leidenuniv.nl
Prof. Huub Röttgering, astronomer,
Leiden University
Tel.: +31 6 41522603
E-mail: rottgering@strw.leidenuniv.nl

Femke Boekhorst,
PR & Communication, ASTRON
Tel.: +31 521 595 204
E-mail: boekhorst@astron.nl

Link to the paper:
http://home.strw.leidenuniv.nl/~rvweeren/A2256_LBA_arx.pdf

LOFAR makes deeper images of Universe than ever before

Click here for a high res image

An international team led by astronomers at ASTRON and the Kapteyn Institute of the University of Groningen have used the LOFAR telescope, designed and constructed by ASTRON, to make the deepest wide-field images of the sky in the relatively unexplored part of the spectrum around 150 MHz. It reveals faint radio sources never seen before.

The results were presented at an international conference in Zadar, Croatia, last week (May 23-27, and were eagerly awaited by the astronomical community. The Zadar conference (organised by team member dr. V. Jelic, ASTRON), discussed the properties of the foregrounds that trouble our view of the distant Universe. Two projects were central at the conference: Planck observations of the Cosmic Microwave Background and (searches for) redshifted 21cm line observations of an era known as the Epoch of Reionization (EoR). This phase in the Universe is believed to have taken place in the period between about 400 and 800 million years after the Big Bang. The birth of the Universe took place about 13.8 billion years ago. During the EoR the neutral hydrogen was slowly disappearing, probably as a result of the strong 'ionizing' power of the first stars and quasars. Detecting the EoR is one of the hottest projects in astronomy today.

A group of astronomers based at ASTRON and the Kapteyn Institute of the University of Groningen, headed by Prof. Ger de Bruyn, Dr. Michiel Brentjens, Prof. Leon Koopmans and Prof. Saleem Zaroubi, is in the race to first detect these signals. They lead a team of about a dozen members, including astronomers currently working in Germany, USA, Canada and Sweden . The results presented at the conference constitute an important step on the road to detecting the elusive signals. However, there is still a long way to go along this road.

A very small part of the raw LOFAR image of the field centered on the bright quasar 3C196. It shows tens of discrete sources, the faintest having a flux density of only a few mJy at 150 MHz.The image has an angular resolution of 8 arcseconds. The image still needs to be deconvolved. The data was processed by Dr. Panos Labropoulos on the EoR-cluster at the University of Groningen. Click here for a high res image.

Most of the antenna stations of the International LOFAR Telescope have already been rolled out across the Netherlands and Europe. It has been taking data for a large number of astronomers after its official opening by Her Majesty queen Beatrix of the Netherlands last year. The LOFAR data on which the images are based, were obtained in a 6-hour synthesis on the night of 29/30 January 2011 and the evening of 1 April 2011 using 18 core stations and 7 remote stations. Signals were recorded with the High Band Antennas and covered the frequency range from 115 - 163 MHz. After initial processing on the central LOFAR cluster they were transferred and further processed on a cluster dedicated to the processing of data for the LOFAR Epoch-of-Reionization project. This cluster is also located at the Computing Centre of the University of Groningen.

Cutouts from a very small part of the giant images are shown in the associated figures. One of the fields is centered at the celestial North Pole which is special in the sense that night-time observations can be obtained all year round. The second field was centered at the bright compact quasar 3C196 in the constellation of Lynx. The images, which have a resolution of 8" are already comparable to, or even slightly better, than the best published images taken with the Giant Meter Wavelength Radio telescope (GMRT) in India. The images contain a large number (>1000) of both very bright and very faint sources, spanning a so-called dynamic range of more than 200,000:1 in brightness between sources in the 3C196 image.

This is an important record for the time being for LOFAR. The image quality, however, is still not perfect and significant improvements can be expected in the months ahead using improved knowledge of the effects of the LOFAR station beams. Continued efforts are also needed to improve the software to deal with imaging artefacts and the ionosphere. These two fields and several others will be observed for about 100 nights to conclusively detect signals from the EoR.

The results, and their implications, will soon be written up in two papers headed by Dr. Panos Labropoulos (ASTRON) and Dr. Sarod Yatawatta (ASTRON/ RuG) who lead the processing of the datasets for the 3C196 and NCP fields, respectively.


For more information, please contact:

ASTRON:

Prof. Ger de Bruyn, senior astronomer. Phone: +31 521 595 787. E-mail: ger@astron.nl

Dr. Michiel Brentjens, support scientist. Phone: +31 521 595 781. E-mail: brentjens@astron.nl

University of Groningen:

Prof. Leon Koopmans, astronomer. Phone: + 31 50 363 6519. E-mail: Koopmans@astro.rug.nl


Captions by top image:

A tiny part of the LOFAR image of the field centered on the North Celestial Pole. It shows at least 7 discrete sources, some of them double or complex. The faintest source has a flux density of only a few mJy at 150 MHz. The image has an angular resolution of 8 arcseconds but still needs to be deconvolved. The data was processed by Dr. Sarod Yatawatta on the EoR-cluster at the University of Groningen Acknowledgements:

The data were obtained as part of the commissioning of LOFAR and the results obtained thus far are a tribute to the hard work of a large group of people, usually referred to as the LOFAR collaboration.

About LOFAR:

The International LOFAR telescope is a Pan-European collaborative project led by ASTRON Netherlands Institute for Radio Astronomy. Combining thousands of simple dipole receivers with powerful digital signal processing and high-performance computing, LOFAR can rapidly survey wide areas of the sky, looking in multiple directions simultaneously and relatively unexplored low frequencies, opening open up a new window for astronomers.

LOFAR will focus on six areas of research:

1. The Epoch of Reionisation - understanding how the first stars and black holes made the universe hot.
2. Extragalactic surveys - what is the history of star formation and black hole growth over cosmological time?
3. Transients and Pulsars - probing the extreme astrophysical environments that lead to transient bright bursts in the radio sky.
4. Cosmic rays - what is the origin of the most energetic particles in the universe?
5. Solar and space environment - mapping the structure of the solar wind, how it relates to solar bursts, and how it interacts with the Earth.
6. Cosmic Magnetism - what is the origin of the large-scale magnetic fields that pervade the universe?

See also www.astron.nl and www.lofar.org

C'est magnifique: LOFAR goes multi-national

This image shows radio sources in the wide field surrounding 3C196, which is the bright spot at the center of the image. (high resolution image)

This image hows the blow-up of 3C196 from the previous image. Made with the Dutch baselines only, the smallest detail seen in this image is 265 thousand light years across and 3C196 appears as a single source.

This image made with the Dutch and the international baselines offers an increase of 30 fold in resolution. The quasar 3C196 is seen to consist of two slightly extended components with the smallest detail in the image being 7 thousand light years.

Image credits of the above images: multi-national LOFAR commissioning teams led by Olaf Wucknitz (Argelander Institut für Astronomie, University of Bonn, Germany) and Reinout van Weeren (Leiden Observatory, University of Leiden).

For the first time, the signals from antenna stations of the giant radio telescope LOFAR in the Netherlands, France, Germany, and the United Kingdom have been simultaneously combined together in the LOFAR BlueGene/P supercomputer. This achievement makes the International LOFAR Telescope (ILT), an array with both excellent sensitivity, thanks to the 40 Dutch stations at the heart of the array, and excellent resolving power, thanks to its European dimensions out to 1000 km.

LOFAR, the Low Frequency Array, was built by ASTRON in the Netherlands. It is currently being extended to European dimensions with partners in France, Germany, Sweden, and the United Kingdom (the Swedish station awaits completion later this year). Combining the Dutch and international LOFAR signals together is an important milestone that truly unites the various stations into a new and powerful facility - the ILT.

The new capabilities now realized, are demonstrated in an amazing sequence of low-frequency images of the bright radio quasar 3C196, located in a galaxy so distant that light takes 6.9 billion years to reach the Earth. This sequence shows the huge field of view that can be uniquely captured by LOFAR and covers an area of the sky equivalent to a staggering 1000 full moons, revealing a stunning variety of objects, surrounding 3C196. Some individual celestial objects may appear rather compact when viewed with the LOFAR core in the Netherlands alone. Now, with the combined multi-national resolving power of the ILT, the structure of such distant objects can be revealed with a resolution as fine as 0.2 arcseconds, close to 1/10000 of the diameter of the full moon.

ILT Director Dr. René Vermeulen of ASTRON is delighted with the news: "Years of design and development work have led to this great achievement. We now have fantastic evidence of the full potential of this revolutionary new telescope, which is drawing great interest from the astronomical community all across Europe, and beyond. Their research interests start in the upper reaches of Earth's atmosphere, and go right out to the furthest and youngest parts of the Universe. Our first multi-national result will cement an already close international collaboration of all partners in the ILT".

For more information, please contact:

Dr. René Vermeulen, director of the International LOFAR Telescope (ILT). Tel.: +31 521 595 100. E-mail: rvermeulen@astron.nl

Femke Boekhorst, PR & Communication, ASTRON. Tel.: +31 521 595 204. E-mail: boekhorst@astron.nl


About LOFAR

The International LOFAR telescope is a Pan-European collaborative project led by ASTRON Netherlands Institute for Radio Astronomy. Combining thousands of simple dipole receivers with powerful digital signal processing and high-performance computing, LOFAR can rapidly survey wide areas of the sky, looking in multiple directions simultaneously and relatively unexplored low frequencies, opening open up a new window for astronomers.


LOFAR will focus on six areas of research:


1. The Epoch of Reionisation - understanding how the first stars and black holes made the universe hot.
2. Extragalactic surveys - what is the history of star formation and black hole growth over cosmological time?
3. Transients and Pulsars - probing the extreme astrophysical environments that lead to transient bright bursts in the radio sky.
4. Cosmic rays - what is the origin of the most energetic particles in the universe?
5. Solar and space environment - mapping the structure of the solar wind, how it relates to solar bursts, and how it interacts with the Earth.
6. Cosmic Magnetism - what is the origin of the large-scale magnetic fields that pervade the universe?

The quasar galaxy 3C 196

3C 196 is a quasar (compact radio source) in a galaxy so far away that light from it has travelled for almost half the age of the universe to reach us (at a redshift of z=0.871). The word "quasar" means "quasi-stellar object". Quasars look like single stars in visible light because the light coming from close to the central black hole is so bright that it outshines all the stars in the galaxy in which it is embedded. The quasar 3C 196 was picked for the first light image of the LOFAR Telescope to show the massive increase in image sharpness (resolution) when the international stations are added to LOFAR.

Details in the Structure of a distant Quasar

First high-resolution image from the LOFAR radio telescope array

Both, the Max-Planck-Institut für Radioastronomie (Bonn) and the Max-Planck-Institut für Astrophysik (Garching), run stations of the International LOFAR telescope (ILT), coordinated by ASTRON, the Netherlands Institute for Radio Astronomy. By connecting the German LOFAR stations with the central stations in the Netherlands, an international group of scientists led by Olaf Wucknitz from the Argelander Institute of Astronomy (AIfA) at Bonn University has now produced the first high-resolution image of a distant quasar at meter radio wavelengths. This wavelength range has not been accessible to such detailed observations before, as the telescopes have to be spaced far apart. The first image showing fine details of the quasar 3C 196 observed at wavelengths between 4 and 10 m was achieved by using just a small fraction of the final LOFAR array that will cover large parts of Europe.

After first tests of the individual antennas, the observations now bring together eight stations of the "LOw Frequency ARray" (LOFAR). Five stations in the Netherlands were connected with three stations in Germany: Effelsberg near Bonn, Tautenburg near Jena and Unterweilenbach near Munich. All antennas were targeted at the quasar 3C 196, a strong radio source at a distance of several billions of light years. "We chose this object for the first tests, because we know its structure very well from observations at shorter wavelengths", explains Olaf Wucknitz (AIfA). "The goal was not to find something new but to see the same or similar structures also at very long wavelengths to confirm that the new instrument really works. Without the German stations, we only saw a fuzzy blob, no sub-structure. Once we included the long baselines, all the details showed up."

Figure 1: Radio images of the quasar 3C 196 at 4 - 10 m wavelength (30 - 80 MHz frequency). Left: Data from LOFAR stations in the Netherlands only. The resolution is not sufficient to identify any substructure. Right: Blow-up produced with data from the German stations included. The resolution of this image is about ten times better and allows for the first time to distinguish fine details in this wavelength range. The colours are chosen to resemble what the human eye would see if it were sensitive to radiation at a wavelength ten million times larger than visible light. Image: Olaf Wucknitz, Bonn University.

Observations at wavelengths covered by LOFAR are not new. In fact, the pioneers of radio astronomy started their work in the same range. However, they were only able to produce very rough maps of the sky and to measure just the positions and intensities of objects. "We are now returning to this long neglected wavelength range", says Michael Garrett, general director of ASTRON (The Netherlands), the research institute in charge of the international LOFAR project. "But this time we are able to see much fainter objects and, even more important, to image very fine details. This offers entirely new opportunities for astrophysical research."

"The high resolution and sensitivity of LOFAR mean that we are really entering uncharted territory, and the analysis of the data was correspondingly intricate", adds Olaf Wucknitz. "We had to develop completely new techniques. Nevertheless, producing the images went surprisingly smoothly in the end. The quality of the data is stunning." The next step for Wucknitz is to use LOFAR to study so-called gravitational lenses, where the light from distant objects is distorted by large mass concentrations. High resolution is required to see the interesting structures of these objects. This research would be impossible without the international stations.

The resolution of an array of radio telescopes, i.e. the size of the smallest structures that it can resolve and distinguish, depends directly on the separation between the telescopes. The larger these baselines are relative to the observed wavelength, the better the achieved resolution. Currently the German stations provide the first long baselines of the array and improve the resolution by a factor of ten over just using the Dutch stations.

"We want to use LOFAR to search for signals from very early epochs of the Universe", says Benedetta Ciardi from the Max-Planck-Institut für Astrophysik (MPA) in Garching. "Having a completely theoretical background myself, I never had thought that I would get excited over a radio image, but this result is really fascinating."

Further improvement should come very soon with observations at slightly shorter wavelengths, which will increase the resolution by another factor of four. In addition, the imaging quality will improve significantly with more stations coming online soon. The image of quasar 3C 196 therefore is just the first but very important step.

"The image quality of the final array depends crucially on the uniformity with which large areas are covered with stations", says Anton Zensus, director at Max-Planck-Institut für Radioastronomie (MPIfR) and in charge of the VLBI research group at the institute. "The German stations are already an indispensable contribution to the international array. What we are still lacking, however, is a station in northern Germany to close the gap between our stations and the ones of our Dutch friends. This would increase the image quality a lot."

Figure 2: The three German LOFAR stations contributing to this result: Left: First German station (MPIfR, Bonn) next to the 100m radio telescope at Effelsberg; Center: Details of antennas at the station near Unterweilenbach (MPA, Garching); Right: Tautenburg station on the site of the Tautenburg Observatory (TLS) with the dome of the largest optical telescope in Germany. Another station in Bornim near Potsdam is waiting for its network connection, one near Jülich will be constructed soon. Fotos: MPIfR (J. Anderson), MPA (T. Krieg), TLS

Notes:

The International LOFAR telescope (ILT) is being primarily built by ASTRON, the Netherlands Institute for Radio Astronomy, in collaboration with a number of international partners. The LOFAR station at Effelsberg is operated by MPIfR, the one in Unterweilenbach by MPA and the Tautenburg station by Thüringer Landessternwarte. The German LOFAR partners form GLOW, the German LOng Wavelength consortium.

In its final stages, the international LOFAR array will consist of at least 36 stations in the Netherlands and eight stations in Germany, France, the United Kingdom and Sweden. Currently 22 stations are operational and more are being set up in Bornim near Potsdam (Germany), Chilbolton (UK), Onsala (Sweden) and Nançay (France). Each station consists of hundreds of dipole antennas that are connected electronically to form a huge radio telescope that will cover half of Europe. With the novel techniques introduced by LOFAR, it is no longer necessary to point the radio antennas at specific objects of interest. Instead it will be possible to observe several regions of the sky simultaneously.

The data from all LOFAR stations are transfered via powerful fibre optic cables in research networks to the computing centre in Groningen in the north of the Netherlands. There they are combined and preprocessed for the final analysis which can be performed either there or at any of the participating institutes, in this case at the Argelander-Institute for Astronomy in Bonn.

Further Information:

Argelander-Institut für Astronomie (AIfA), Bonn.

Max-Planck-Institut für Radioastronomie. (MPIfR).

Max-Planck-Institut für Astrophysik (MPA), Garching.

German LOng Wavelength (GLOW).

Netherlands Institute for Radio Astronomy (ASTRON).

LOw Frequency ARray (LOFAR), International Web site.

LOw Frequency ARray (LOFAR), German Web site.

Earlier LOFAR Press Releases:

LOFAR maps the radio sky at Effelsberg, Press Release PRI (MPIfR) 12/2009 (4), December 17, 2009. First high-band image of the world's most modern radio telescope, taken with the Effelsberg LOFAR station.

LOFAR observes across borders, Press Release ASTRON, September 23, 2009. Astronomers have succeeded in the first joint observations between the LOFAR stations in Exloo (The Netherlands) and Effelsberg (Germany).

LOFAR picks up speed, Press Release PRI (MPIfR) 12/2007 (4), December 11, 2007. First international LOFAR station in Effelsberg starts observations.

First high quality wide field LOFAR image, Press Release ASTRON, April 25, 2007. First deep wide field image made with the first LOFAR stations in the Netherlands at a frequency of about 50 MHz.

Contact:

Dr. Olaf Wucknitz,

Argelander-Institut für Astronomie, Universität Bonn.

Phone: +49-228-73-1772

E-mail: wucknitz@astro.uni-bonn.de

Dr. James Anderson,

LOFAR Station Manager Effelsberg,

Max-Planck-Institut für Radioastronomie, Bonn.

Phone: +49-228-525-356

E-mail: anderson@mpifr-bonn.mpg.de

Dr. Norbert Junkes,

Public Outreach,

Max-Planck-Institut für Radioastronomie, Bonn.

Phone: +49-228-525-399

E-mail: njunkes@mpifr-bonn.mpg.de

Additional Eyes for Pulsar Astronomers

Figure 1: Simultaneous detection of pulses from pulsar PSR B1133+16 in four widely spaced bands, using the Effelsberg telescope at 3.5 cm wavelength, the Lovell telescope at 21 cm wavelength, and LOFAR high-band (HBAs) and low-band antennas (LBAs) at 170 cm and 430 cm wavelength, respectively. The figure shows the pulse intensity as a function of time for the four observed wavelengths. The shape of the pulsar's pulsed emission maps the spreading of magnetic field lines above the pulsar's magnetic poles. Image: Aris Karastergiou, University of Oxford

Figure 2: A part of the 96 LBA dipole antennas of the LOFAR station Effelsberg can be seen in the foreground, in close proximity to the giant 100-m radio telescope. Image : Wolfgang Reich (MPIfR)

Combination of new technology telescope with existing facilities promises new insight into extreme stars

An international team of astronomers including scientists from the Max Planck Institute for Radio Astronomy has set a new world record in wavelength coverage for observing the enigmatic radio emitting stars called pulsars. They used the new European LOFAR telescope, in combination with two of the world's largest radio telescopes, the Effelsberg telescope in Germany and the Lovell telescope in the United Kingdom. This unique combination of telescopes allowed them to simultaneously observe the radio light from six different pulsars across wavelengths from only 3.5 centimetres up to 7 meters - a factor of 200 difference. These different wavelengths of radio light are analogous to the different colours perceived by the human eye and provide an unprecedented view of how radio pulsars shine.

Pulsars are rapidly rotating neutron stars, which measure only about 20 kilometers across and yet are more massive than the Sun. They produce beams of radio light from their magnetic poles, which are observable over a wide range of wavelengths.

For the last 40 years astronomers have been studying pulsars and they are getting closer and closer to understanding the mechanism that generates these intense beams. They hypothesize that the emission seen at the different wavelengths emerges from different heights above the highly magnetized pulsar surface. Emission seen at a particular radio wavelength therefore provides a slice through the pulsar's surrounding "magnetosphere" (magnetized atmosphere). The magnetic field lines that accelerate particles spread apart as one moves further and further away from the pulsar's surface. Experimental support for this hypothesis is the observation that the pulses of some pulsars become stretched out at long wavelengths (Fig. 1). The shape of the pulsar's pulsed emission is seen to evolve quite drastically as a function of wavelength and maps the spreading of magnetic field lines above the pulsar's magnetic poles.

With any single telescope, a pulsar can only be observed in a relatively narrow range of wavelengths at any given time. By combining the traditional large Effelsberg and Lovell telescopes, observing at wavelengths of centimetres, with the next generation telescope LOFAR, observing at wavelengths of meters, the astronomers were able to observe a set of six pulsars, each simultaneously across a range of nearly 8 octaves. "For comparison, consider that we have simultaneously observed these pulsars over a range equivalent to all the tones spanned by a piano," says Jason Hessels of ASTRON Netherlands Institute for Radio Astronomy. "By simultaneously observing these pulsars at such a wide range of wavelengths, we can make many snapshots of what the pulsar's emission looks like at a range of heights above the star's magnetic poles," he adds.

Key to these observations was the use of the new LOFAR telescope, which has a collection of thousands of radio antennas in stations that are centred near Exloo, in the Netherlands, and that spread from there over distances of hundreds of kilometers into neighbouring countries, such as France, Germany, Sweden, and the United Kingdom. The data taken on all stations are brought together for data analysis via high-speed networks to a BlueGene/P supercomputer and powerful cluster computers at the University of Groningen Centre for Information Technology. LOFAR is operated as an integrated facility from the ASTRON headquarters in Dwingeloo, the Netherlands. The LOFAR telescope is currently being prepared for full-scale scientific observations, and the astronomers were excited to make such high-quality, pulsar measurements even in the testing phase.

Michael Kramer, director at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, is excited about the enormous extension in wavelength coverage provided by LOFAR, of which the first international antenna station was built next to the Effelsberg telescope in Germany. "These observations show how LOFAR complements the existing radio telescopes in Europe, like the 100-m Effelsberg telescope, in a nearly perfect way" (see Fig. 2).

These observations have the primary goal of better understanding how pulsars pulse. However, there is also much to be learned beyond studying just the pulsar itself. "Not only do such observations give us a fantastic handle on understanding the emission of pulsars, they are also a powerful probe of the interstellar gas that is between us and the pulsar," says Ben Stappers of the University of Manchester.

"We are really excited to have the first international LOFAR station operating here in direct vicinity to the giant 100-m Effelsberg radio telescope", says Kosmas Lazaridis from MPIfR. "The combination of both, large parabolic dishes for the centimetre regime, and new digital technology for the longer wavelengths provides a wealth of new data for our pulsar research programs."

The LOFAR telescope, spanning more than 1000 kilometres in Europe, will be completed in the next year and will be the most powerful telescope on Earth for observing the Universe at the longest possible radio wavelengths visible from the Earth's surface: 1-30 meters. It is expected that this will produce a flood of exciting new scientific results.

LOFAR maps the radio sky at Effelsberg

The radio sky above Effelsberg on November 10, 2009, observed with the newly installed LOFAR high-band array. Fig. 1a (left): Software-calibrated image with high signal-to-noise ratio at a frequency of 120 MHz; Fig. 1b (right): Movie, showing the sky above Effelsberg at radio frequencies from 35 MHz to 190 MHz. Images: James Anderson, MPIfR.

Click here for the figures

Scientists at the Max Planck Institute for Radio Astronomy have made the first LOFAR "all-sky" images in the 110 to 190 MHz range using LOFAR high-band antennas at the LOFAR station in Effelsberg, Germany. LOFAR is the Low Frequency Array, designed and developed by ASTRON. These images are the first high-band, all-sky images made from any complete LOFAR station, and mark a significant milestone in the development of the LOFAR project.

The first LOFAR all-sky high-band image is shown in Figure 1. This all-sky image has North at the top and East at the left, just as a person would have seen the entire sky when lying on their back on a flat field near Effelsberg late in the afternoon on November 10, if their eyes were sensitive to radio waves. The two bright (yellow) spots are Cygnus A, a giant radio galaxy powered by a supermassive black hole near, the center of the image, and Cassiopeia A, a bright radio source created by a supernova explosion about 300 years ago, at the upper-left in the image. The plane of our Milky Way galaxy can also be seen passing by both Cassiopeia A and Cygnus A, and extending down to the bottom of the image. The North Polar Spur, a large cloud of radio emission within our own galaxy, can also be seen extending from the direction of the Galactic center in the South, toward the western horizon in this image.

"We made this image with a single 60 second "exposure" at 120 MHz using our high-band LOFAR field in Effelsberg", says James Anderson, project manager of the Effelsberg LOFAR station. "The ability to make all-sky images in just seconds is a tremendous advancement compared to existing radio telescopes which often require weeks or months to scan the entire sky." This opens up exciting possibilities to detect and study rapid transient phenomena in the universe.

LOFAR, the LOw Frequency ARray, is an advanced new radio telescope being built in many countries across Europe. Operating at relatively low radio frequencies from 10 to 240 MHz, LOFAR has essentially no moving parts to track objects in the sky --- instead digital electronics are used to combine signals from many small antennas to electronically steer observations on the sky. In certain electronic modes, the signals from all of the individual antennas can be combined to make images of the entire radio sky visible above the horizon.

LOFAR uses two different antenna designs, to observe in two different radio bands, the so-called low-band from 10 to 80 MHz, and the high-band from 110 to 240 MHz. All-sky images using the low-band antennas at Effelsberg were made in 2007 (see press release "LOFAR picks up speed" from December 11, 2007).

Following the observation for the first high-band, all-sky image, scientists at MPIfR made a series of all-sky images covering a wide frequency range using both the low-band and high-band antennas at Effelsberg. A movie of these all-sky images has been compiled (Figure 1b). The movie starts at a frequency of 35 MHz, and each subsequent frame is about 4 MHz higher in frequency, through 190 MHz. The resolution of the Effelsberg LOFAR telescope changes with frequency. At 35 MHz the resolution is about 10 degrees, at 110 MHz it is about 3.4 degrees, and at 190 MHz it is about 1.9 degrees. This change in resolution can be seen by the apparent size of the two bright sources Cygnus A and Cassiopeia A as the frequency changes.

Scientists at MPIfR and other institutions around Europe will use measurements such as these to study the large-sky structure of the interstellar matter of our Milky Way galaxy. The low frequencies observed by LOFAR are ideal for studying the low energy cosmic ray electrons in the Milky Way, which trace out magnetic field structures through synchrotron emission. Other large-scale features such as supernova remnants, star-formation regions, and even some other nearby galaxies will need similar measurements from individual LOFAR telescopes to provide accurate information on the large-scale emission in these objects. "We plan to search for radio transients using the all-sky imaging capabilities of the LOFAR telescopes", says Michael Kramer, director at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn. "The detection of rapidly variable sources using LOFAR could lead to exciting discoveries of new types of astronomical objects, similar to the discoveries of pulsars and gamma-ray bursts in the past decades."

"The low-frequency sky is now truly open in Effelsberg and we have the capability at the observatory to observe in a wide frequency range from 10 MHz to 100 GHz", says Anton Zensus, also director at MPIfR. "Thus we can cover four orders of magnitude in the electromagnetic spectrum."

***

LOFAR, the LOw Frequency ARray, was designed and developed by ASTRON (Netherlands Institute for Radio Astronomy) with 36 stations centered on Exloo in the northeast of The Netherlands. It is now an international project with stations being built in Germany, France, the UK and Sweden connected to the central data processing facilities in Groningen (NL) and the ASTRON operations center in Dwingeloo (NL). The first international LOFAR station (IS-DE1) was completed on the area of the Effelsberg radio observatory next to the 100-m radio telescope of the Max-Planck-Institut fur Radioastronomie (MPIfR).