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Articles on this Page
- 01/06/16--16:00: _AARTFAAC 12-station...
- 01/05/16--16:00: _Sander ter Veen: a ...
- 01/04/16--16:00: _The East Asian Obse...
- 01/03/16--16:00: _APERTIF-6 FrontEnds
- 01/07/16--16:00: _CSIRO - ASTRON Coll...
- 01/11/16--16:00: _SDSS versus BDSS
- 01/10/16--16:00: _RF cabling APERTIF-6
- 01/12/16--16:00: _LOFAR to extend int...
- 01/13/16--16:00: _2016 New Year's Spe...
- 01/14/16--16:00: _Motivating the Troops
- 01/17/16--16:00: _APERTIF-6 hardware ...
- 01/18/16--16:00: _SKA1_LOW precursor,...
- 01/19/16--16:00: _The Wideband Low No...
- 01/20/16--16:00: _Rick Perley hounour...
- 01/21/16--16:00: _South-Africa-Dutch ...
- 01/24/16--16:00: _Mounting the APERTI...
- 01/25/16--16:00: _Up Close & Personal...
- 01/26/16--16:00: _MFAA environmental ...
- 01/27/16--16:00: _Nowhere to Hide - R...
- 01/28/16--16:00: _Shaping the Future ...
- 01/06/16--16:00: AARTFAAC 12-station correlator commissioned
- 01/05/16--16:00: Sander ter Veen: a new 'Doctor' in the LOFAR Science Support group
- 01/04/16--16:00: The East Asian Observatory
- 01/03/16--16:00: APERTIF-6 FrontEnds
- 01/07/16--16:00: CSIRO - ASTRON Collaboration Gets in Shape
- 01/11/16--16:00: SDSS versus BDSS
- 01/10/16--16:00: RF cabling APERTIF-6
- 01/12/16--16:00: LOFAR to extend into Ireland
- 01/13/16--16:00: 2016 New Year's Speeches
- 01/14/16--16:00: Motivating the Troops
- 01/17/16--16:00: APERTIF-6 hardware in place
- 01/18/16--16:00: SKA1_LOW precursor, AAVS1 station clearing
- 01/19/16--16:00: The Wideband Low Noise Tile - The HI-line over five days
- 01/20/16--16:00: Rick Perley hounoured with Van Biesbroeck Prize
- 01/24/16--16:00: Mounting the APERTIF DCU backplane
- 01/25/16--16:00: Up Close & Personal with 3C293
- 01/26/16--16:00: MFAA environmental prototypes - going strong.
- 01/27/16--16:00: Nowhere to Hide - Radio Quiet AGN in the HDF-N
- 01/28/16--16:00: Shaping the Future in New Mexico
© www.aartfaac.orgThe AARTFAAC project has achieved a significant milestone with the demonstration of the working of the 12 station correlator.
AARTFAAC piggybacks on LOFAR observations by correlating the signals from the 576 individual dual-pol antennas on 12 LOFAR core stations. The goal is to detect transients, by creating an all-sky image every second and examining the image timeseries for transients and variability of the detected sources.
The AARTFAAC correlator is a GPU based system which processes an input data rate of ~60Gbps from upto 16 subbands from the 576 antennas of the AARTFAAC-12 array. It estimates the ~166000 instantaneous visibilities per spectral channel, per polarization, per second, in real time. The 6-station AARTFAAC correlator was already functional for half of 2015.
The correlator channelizes the subbanded dipole data, applies a bandpass correction and a phase correction to compensate for the slightly different clock cable lengths to each station, and correlates the signals. It consists of a machine with no less than 10 GPUs, capable of handling 16 subbands. A second machine that will correlate 16 more subbands has just arrived and will be installed soon. Together, they will operate 34 TFLOPS continuously, more than three times the performance of the LOFAR correlator.
Much effort was put in optimizing the GPU code and in handling the high data rates from the network interfaces: receiving 60 Gb/s of input data, buffering, and offloading the data to the GPUs in real time is not easily done by a single machine.
The 12-station AARTFAAC adds 6 more stations from the inner ring of the LOFAR core, significantly increasing the sensitivity (>2x) and resolution (~3x) of AARTFAAC. An example of things to come can be already seen in the above single subband, 1second integrated uncalibrated images of the full sky, using the output of the 12-station correlator. The image labeled A12 has been generated using uncalibrated visibilities from all 12 AARTFAAC stations, while the one labeled A6 is created using visibilities from the 6 superterp stations.
The two sources of bright emission are the familiar Cassieopia-A and Cygnus-A, lying within the band of Galactic emission. The higher brightness of the Galactic center (due South) in the A6 image shows the relatively larger number of short baselines in that array. The signal-to-noise and noise variances are indicative since the data are not calibrated.
Exciting times are ahead!
© S. ter VeenOn 26 November 2015, the Radboud University of Nijmegen offered the stage of its Aula to Sander ter Veen of the Science Support group of the Radio Observatory of ASTRON.
Sander's thesis is titled 'Searching for Fast Radio Transients with LOFAR'. A large part of the work is dedicated to the Fast Radio Transients Search (FRATS) project. The real-time pipeline that runs commensally on regular LOFAR observations to search for dispersed millisecond pulses is described.
Focus is given first to the detection of unknown objects and of bright sporadic signals from known pulsars. Then to the verification of the astrophysical origin of the signal and their location using LOFAR's third observing mode, the direct storage from individual antennas.
Furthermore, results of an innovative data analysis technique applied to the Globular Cluster M13 are presented. In here, first the signal is dedispersed coherently at multiple DM values, before the search is performed over a wide range of DM values, leading to the best low frequency observation of pulsar M13A.
The thesis also explores the possibility to observe faster transients - nanosecond radio pulses that are emitted when ultra-high-energy cosmic rays hit the Moon - and reports on the most stringent upper limit for ultra-high-energy cosmic rays above 10^22 eV.
The committee was impressed by Sander's work. We are all very proud of his achievement and very glad to have his expertise in the Science Support group!
© Rob MillenaarOn the occasion of a recent visit to the Hawaiian Big Island that came about because of family matters (what better reason to visit Hawaii than for a wedding), I remembered the days of UK/NL cooperation in advanced astronomy projects. In the 80's of the previous century this partnership came to full fruition with such wonderful projects as the Herschel and Newton optical telescopes on La Palma, and the ground breaking sub-millimetre radio telescope on top of Mauna Kea in Hawaii: the James Clerk Maxwell telescope, or JCMT as we came to call and love it. Together with Leiden University, SRON in Utrecht and Groningen, ASTRON has played an important role in the history of instrumentation development for the JCMT, and it is with that background that I paid a visit to the familiar headquarters of the institute, formerly known as the Joint Astronomy Centre, JAC in Hilo. Familiar to me because I worked there in the nineties and have come back many times since.
The first thing of note is that the centre is now called: East Asian Observatory (EAO). This reflects the fact that nowadays funding for the JCMT primarily comes from China, Taiwan, Japan and South Korea, after support from UK, Canada and The Netherlands dwindled down over recent years. This is a fortunate situation where, just in time, the future of the JCMT was secured by attracting these new custodians. The EAO has taken over the operations of the JCMT since earlier this year. The other telescope that was previously run by the centre, the infrared UKIRT telescope, already had its future secured by being adopted by the University of Arizona. The EAO will likely continue to take care of the engineering and IT support for UKIRT.
It is not just for my personal nostalgic reasons that I welcome the JCMT's new lease on life. The existing instrumentation and capabilities are first rate and keeping those alive will be a great benefit to the new user base of Asian astronomers in need of high sensitivity continuum, spectral and wide field imaging at the highest radio frequencies.
First mention deserves SCUBA-2, a large sub-millimetre camera, actually a focal plane array consisting of 5120-pixel superconducting sensors, operating at 450 and 850 microns. This is a spectacularly successful mapping machine, producing wonderful continuum images of the cold radio sky.
Next is JCMT's capability to participate in interferometry experiments. Sub-millimetre interferometry was pioneered at the JCMT using the ASTRON-built DAS backend, that combined auto and cross correlation modes. In later years I was also involved in the development of interferometry together with SMA and CSO on the mountain. It is good to see this capability still being used in successful programmes.
Receiver-wise the JCMT offers three heterodyne instruments (A band, 12 pixel B band array and D band), and the Canadian ACSIS auto-correlator has replaced our DAS a long time ago.
The photograph shows the 15 m diameter JCMT dish from the inside of the building, with its protective yet transparent membrane on the left of the frame.
When I visited the headquarters it was good to talk to so many old friends and smell the same tropical scents in the corridors that I got used to so many years ago. We wish the EAO a successful future, facilitating lots of high quality science, and continued funding to keep operating and to develop new instrumentation to remain at the forefront for a long time.
Please visit: www.eaobservatory.org
© APERTIFAt the end of October the APERTIF LNAs came in after production and testing at Variass. In November members of the APERTIF team installed these LNAs with Vivaldis in the housing and carrier produced by ITEQ.
Cabling was assembled as well and after testing members of the radio observatory installed the PAF FrontEnds of APERTIF in RT2, RT4, RT5, RT8, RT9 and RTA.
Six PAFs are installed now, the APERTIF team is doing a wonderfull job!
© FreakingNews.comSince mid 2015, the SKA1-Low CSP (Central Signal Processor) team consists of CSIRO (lead), ASTRON, the Auckland University of Technology and Curtin University. For both CSIRO in Australia and ASTRON in the Netherlands this effort is aiming towards a long term strategic collaboration which goes beyond the timelines of SKA Phase 1.
Within the digital group of ASTRON (DESP) one of our key drivers is to constantly seek ways to reduce the time to science. For this we developed:
1. a technology independent design flow which allows us to reuse code
2. generic boards that are at the edge of the technology and can be used by various applications when the need is there.
The collaboration enables us to reuse code and hardware between CSIRO and ASTRON, such that more firmware and hardware will be available for next generation instruments, in order to further reduce the time to science.
Currently the collaboration is working out very well and are we battling as one front to deliver the documentation for the delta PDR deadline at the end of January 2016. In April this year one of the design engineers of CSIRO is coming over to ASTRON for 3 months to design the hardware board together with us.
Therefore 2016 will be a very exciting year for us, with lots of challenges on both the technical and organizational front!
© astropix.nlHow do the images of an 0.4m amateur telescope in a back garden in Beilen (at 10m above sea level) compare to those of the 2.5m Sloan Deep Sky Survey telescope on a 2788m high mountain top in New Mexico?
During the first clear night in 2016, 22 integrations of 600 seconds were made through LRGB filters with a 0.4m telescope in Beilen. Those images were calibrated and combined into a colour image, which in its turn was aligned with an image made by the Sloan Digital Sky Survey, so they could easily be compared. The field contains several galaxies and a planetary nebula (PGC10427)
Beilen Digital Sky Survey: 0.4m telescope, 0.126 m2 collecting area, 10m asl, total exposure time 220 minutes
Sloan Digital Sky Survey, 2.5m telescope, 4.9m2 collecting area, 2788m asl, total exposure time 5 minutes
The most prominent difference is the better sharpness of the SDSS image, probably due to better seeing conditions at the mountain top and the better resolving power of the bigger telescope. Also the SDSS sensitivity is higher, due to the 38.9 times larger collecting area of the telescope mirror and the much darker sky background.
Still, with a bit of patience, an amateur can image very faint objects. By making even longer integrations, I've been able to reach magnitude 22.4 so far.
The full field can be seen at: http://www.astrobin.com/231418/B/
© APERTIFMany hands make light work! In december 2015 many hands of the APERTIF team went to Westerbork to install RF-cables for the hardware of six of the twelve APERTIF dishes.
With these cables the PAF FrontEnd is connected through a patch panel in the container to the DCUs, ADU and LOG. Since APERTIF-6 means six FrontEnds, six, containers, six patchpanel, hundred ninety two DCUs, fourty eight ADUs and twelve LOG systems that is a lot of cabling and a lot of connectors.
Together with, Sjouke Kuindersma, Eim Mulder, Sieds Damsta, Lute van de Bult, Martijn Brenthouwer, Lesley Goudbeek, Mark Ruiter and Raymond van den Brink it took us two days to install all RF cables.
© ASTRONThe world's biggest connected radio telescope is about to become even bigger! LOFAR (Low Frequency Array) will expand into Ireland. This is not only great news for Irish astrophysics, but also for the International LOFAR Telescope (ILT).
The plans for a LOFAR station in Ireland have been around for a while, but now it's official: a LOFAR station will be built this year in Ireland. I-LOFAR (the Ireland-LOFAR consortium) has been awarded � 1.4 Million by Science Foundation Ireland (SFI). Together with � 0.5 Million in philanthropic grants plus contributions of I-LOFAR members, it is possible to build and exploit the LOFAR station, which will be constructed on the grounds of Birr Castle, located centrally in Ireland.
Yesterday (12-01-2016), during a meeting at Birr Castle, Irish Ministers Bruton (Jobs, Enterprise and Innovation) and English (Education and Skills) announced the award for I-LOFAR, as one element of a � 30M investment by SFI in research infrastructures.
LOFAR is a world-leading facility for astronomical studies, providing for highly sensitive and detailed scrutiny of the nearby and far-away Universe. LOFAR is designed and operated on behalf of the ILT by ASTRON, the Netherlands institute for Radio Astronomy. Dr. Rene Vermeulen, Director of the ILT, is delighted with the news: "The added Irish antenna station will be an excellent enhancement, extending the ILT to a pan-European fibre-connected network spanning 2000 km. Such long distances allow exquisitely finely detailed sky imaging capability. And, at least as importantly, the Irish astronomical community will now add their expertise and effort to the "ILT family", in the pursuit of a great many cutting-edge science questions that LOFAR can answer. Topics range from the properties of the Earth's upper atmosphere, flaring of the Sun, out to the far reaches of the early Universe when the first stars and galaxies formed."
The International LOFAR Telescope is the largest connected radio telescope in the world. It is being steadily enhanced since the official opening by (then) Queen Beatrix of the Netherlands in 2010. There are currently six partner countries: of the 50 antenna stations, 38 are located in the Netherlands, 6 in Germany, 3 in Poland, and 1 each in France, Sweden, and the United Kingdom. Together, these have many thousands of receiving elements. The new Irish station will increase the distances between antenna stations, thus providing finer image details.
© ASTRONToday, at 10:30, the Directors of ASTRON and JIVE will give us their traditional New Year's Speeches in the canteen.
© Madroon Community Consultants (MCC)Yesterday, in front of a spell-bound crowd, Directors Huib-Jan van Langevelde (JIVE) and Mike Garrett (ASTRON) delivered their New Year's speeches.
Huib-Jan offered lots of good stuff about JIVE now being a prestigious European Research Infrastructure Consortium (ERIC), and how his small team continues to do wonders for the VLBI community. He also mentioned the great things that are to happen in the near future, for instance the expansion across the African continent. But, while definitely stimulating, he failed to be a tough act to follow because he had not taken the trouble to prepare any pictures for people to look at while he held forth.
Fortunately, Mike then offered much more visual stimulation, and some well-timed chuckles. He started very inclusively, paying tribute to the various supporting services like AZ and ICT, that quietly make things possible for our 4 institutes. The emphasis was very much on people things, which did not fail to generate a happy atmosphere. After briefly reviewing some highlights of major ASTRON endeavours like LOFAR, WSRT/APERTIF and SKA, he confidently looked to the future. He proudly mentioned that the Dutch Junior Minister of Education recently devoted half his speaking time to gushing about ASTRON.
In his turn, Mike devoted a gratifyingly large part of his time to the ASTRON/JIVE Daily Image(*). He noted that about half the people in the building had submitted at least one item to our family chronicle, and he urged everyone to go on with conveying the fun of working in Dwingeloo. He ended by disclosing his choice for best Daily Image of 2015. The handing-over of a bottle of double-malt Scotch whiskey to Aleksandar Shulevski will be the subject of an AJDI in the near future. Michiel Brentjens received an honourable mention.
(*) Of course many of the images he showed in his speech were simply lifted from the AJDI archive. This increasingly valuable resource is of course available to everyone.
© APERTIFIn this last week of the year 2015 we managed to complete APERTIF-6 hardware and most of firmware and software. All hardware is installed at RT2,4,5,8,9 and A for APERTIF-6.
This is a big step into further commissioning! A very nice milestone the APERTIF team accomplished together.
We are looking forward to finish APERTIF-12 in 2016.
*APERTIF-6 is the first part of the APERTIF project which is divided into two delivery phases. In the first phase (APERTIF-6) six dishes are implemented with the single polarized version of the APERTIF system. In the second phase (APERTIF-12) another six dished will be implemented with the APERTIF system, and all twelve dishes are upgraded to a dual polarized system.
© Pieter BenthemThe Aperture Array Verification System (AAVS1) is getting into shape, as can be seen in the picture above. It shows the ground clearings of a single, 35 meter diameter station, ready to host 256 SKALA antennas.
The centre post marks the position of the Antenna Power and Interface Unit (APIU), providing power to all antennas and transporting the RF signal (using RFoF technology) to the Central Processing Facility.
AAVS1 will verify the end-to-end signal path of the Low Frequency Aperture Array (LFAA) from antenna to the output of the station beamformer. AAVS1 shall include all the components required to receive low frequency electromagnetic signals and to correlate the beams formed. LFAA is a major system and part of the Low Telescope which will be constructed in Western Australia at the Murchison Radio Observatory (MRO) as part of the first phase of the SKA Observatory. AAVS1 will also be built at the MRO, inside the current MWA footprint.
© ASTRONTo conclude the current chapter in the development of the WLNT, a new measurement session was in order. The goal of this measurement session was to verify if the WLNT produced stable results over longer periods of time (days). But, before these measurement could take place some preparations were necessary.
The front-end of the WLNT consists of bare electronics and had to be shielded from precipitation. This was done by using one of the old radomes of THEA which in the mean time had been used to cover the sandpit in the garden of one of the ASTRON employees. To provide insight in the environmental conditions, temperature and humidity loggers were placed at multiple locations and the WLNT power consumption was monitored.
To prevent that one of the ASTRON employees should stay at the measurement site over night to perform the measurements, this task was delegated to a PC. Every 20 minutes a new measurement of the HI-line was made and in between of these measurements a much wider spectrum was captured to provide insight in the present RFI conditions.
Multiple measurement sessions have taken place and all produced satisfactory results, the WLNT functioned flawlessly throughout changing temperatures and humidities. Our longest measurement session spanned 5 days and produced a very nice view of the HI-line emissions of the Milky Way over time and frequency. Every day at around 18:00 hrs the Milky Way rises above the horizon and a bump becomes visible in the measured spectrum. This bump moves slightly up in frequency due to the doppler effect, and disappears at 12:00 hrs when the Milky Way sinks below the horizon again.
This image has been created with the data from 364 separate measurements. Each measurement consisted of 501 frequency points and each point had a bandwidth of 3 kHz and has been integrated over 2 seconds. The rise of the noise floor in the image over the 5 day span of the measurement session, is due to changes in the outside temperature. The temperature dropped by almost 10 degrees which resulted in an increase in gain of the WLNT.
© NRAOThe American Astronomical Society (AAS) has awarded its prestigious George Van Biesbroeck Prize to Dr. Rick Perley of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. The society recognized Perley for his tireless and unrelenting career-long service to the global astronomical community. The prize will be presented at the AAS meeting in January of 2017.
Rick is an old friend with a longstanding relationship with ASTRON. Apart from bickering about the correct way to design a radio telescope, we have collaborated in fields as diverse as the radio flux scale and high dynamic range imaging. In addition, he is excellent company, and, together with his Peggy, a genial host to a wide range of visitors, including those from Dwingeloo.
© ASTRONThe visit to South Africa by Netherlands Prime Minister Mark Rutte included a pivotal South African-Dutch data science partnership between key institutions from both countries bringing us closer to understanding the volume of data generated by the Square Kilometre Array (SKA), was signed on Tuesday, 17 November 2015.
This signals the unlocking of the hidden secrets in the immense amount of data generated by SKA - the world's biggest radio telescope. The agreement is part of the visit to South Africa by the Prime Minister of the Netherlands, Mr Mark Rutte, and his trade delegation of 75 companies.
SKA South Africa and the University of Cape Town, through the newly established Inter-University Institute for Data Intensive Astronomy (IDIA), signed a Memorandum of Understanding (MoU) with fellow research institutions in the Netherlands, IBM, ASTRON and NWO to collaborate in a ground-breaking research project entitled Precursor Regional Science Data Centres for the SKA (SKA-RSDC).
Professor Michael Garrett, ASTRON's general and scientific director says: "The signing of this agreement is a big step - it ensures that the huge amounts of data SKA is expected to generate in South Africa can be fully exploited by Dutch users. It is part of our ambition for Europe to have a regional scientific data centre for SKA, with a central coordinating role for The Netherlands."
Alexander Brink of IBM Science Alliances: "This South African addition to the existing collaboration between IBM Research and ASTRON is a logical step towards a wider application of innovations in handling large amounts of data. Science in the areas of data and IT forms a trinity with infrastructure and the socio-economic ecosystem. Several societal themes, such as life sciences, energy and water management, need IT research. Breakthroughs resulting from this collaboration will have a direct and positive impact in these areas, in terms of innovative power."
The techniques developed can, in turn, be applied in other fields such as big data analytics, high performance computing, green computing, and visualisation analytics.
MoU signatories: Mike Garrett, representing NWO and ASTRON; Alexander Brink, representing IBM; Jasper Horrell, representing SKA-SA/NRF; and Russ Taylor, representing IDIA/UCT.
© ASTRONThe backplane of an APERTIF DCU (Down Convertor Unit) is mounted using 28 screws. Putting in all the scews of 24 DCU's is a tremendous task. To simplify this task, Jan Idserda made a special 'tool'.
In the pictures you see Anne Koster of the technical support group using it. Using this tool instead of putting in all screws manually is not only faster but is also better from a health and safety perspective.
The tool is a good example of engineering in the most literal sense: to be ingenious. It shows that high tech is not always the solution for practical problems.
© ASTRONYou may wonder why, with so many objects in the sky, astronomers very often focus on only one of them and spend a significant fraction of their time just to try to understand that single object in all detail. The reason is that in the objects we study we find, most of the time, very complex and puzzling phenomena. So in order to make sense of it all, we need different observations, often at very different wavelengths requiring different telescopes. And, of course, detailed state-of-the-art theoretical models. Doing all this is a very time consuming process and can be done for only very few objects at a time. However, the reward can be really worth the effort. Once we manage to explain what is going on in a single object, we can use it as starting point for a general description of an entire class of similar objects.
The radio galaxy 3C293 is one of these objects; it shows many interesting physical phenomena and 3C293 is not very distant so it can be studied in much detail. In the Daily Image of 24-07-2013, we already described the very fast outflow of cold gas (with a speed of more than 1000 km/s) in this galaxy, which has been one of the extremely puzzling discoveries that the broad-band of the MFFE in the WSRT allowed us to make.
This time, though, we looked at this object in the optical and we used the Integral Field Unit OASIS on the William Herschel Telescope at La Palma. In this way, we can map the spatial extent of the ionised component of the gas outflow in this galaxy. We detected, as expected, the jet-driven outflow along the inner radio lobes. However, the most interesting result is that we could establish that the outflow extends out to many kilo-parsec from the nucleus, well beyond the visible radio jets. This suggests the outflow is not directly driven by the radio jet, but that the radio jets inflate a large cocoon-like structure around them which, in turn, drives the outflow. Such cocoons are now also seen in simulations of jet-ISM interaction and they imply that the effect of the radio jets on the interstellar medium extends over a much larger region than that of the jets themselves and that they can have a profound effect on the evolution of central regions of the host galaxy.
These results are presented in a paper by Elizabeth Mahony, Raymond Oonk, Raffaella Morganti and various other collaborators that has been published in Monthly Notices of the Royal Astronomical Society (and also available in the astro-ph archive http://arxiv.org/abs/1510.06498). We will now apply these findings to the interpretation of the growing number of galaxies where these gas outflows have been observed. With this picture in mind, we can now asses what is the role of radio jets in shaping the evolution of galaxies.
© Rob MillenaarApproaching their two-year birthday, the Mid Frequency Aperture Array (MFAA) environmental prototypes are still going strong!
Installed during an inspiring trip to the SKA Karoo site, by our ASTRON team. The prototypes are being monitored by the local MFAA team, Andre Walker and Rob Millenaar.
The picture above shows an interesting detail. It is a top view of the "continuous array with open station cover" prototype.
The aluminum Vivaldi antennas can be seen, as well as part of the supporting structure. The station cover has been peeled back, which can partly be seen at the top left. Finally, a test pcb (green area) can be seen, mounted at the bottom.
Obviously one can imagine the thermal benefits of having an open array-housing, but downsides are also to be recognised. Although the accumulation of sand and dust is clearly happening, we are glad to see this effect to be quite minimal.
© ASTRON, University of Manchester and University of GroningenFollowing on from the work of the late Seungyoup Chi (Chi et al. 2013, or see the daily image 28-06-2013), a new, ultra-sensitive wide-field VLBI survey, targeting the Hubble Deep Field North (HDF-N), has recently been conducted. It is one of the biggest VLBI projects ever undertaken by the EVN, involving some 699 different phase centres and acquiring (in the first instance) 72 hours of observing time. From the first epoch of data, eight new radio quiet AGN have been discovered, taking the total in the field to 20.
A new calibration technique was trialed on these data, termed Multi-Source Self-Calibration (MSSC). MSSC uses the combined response of many faint sources in the field, in order to acquire phase corrections. The technique allowed one more source in the field to be detected, permitted the detection of several others with uniform weighting, and greatly improves the dynamic range of all sources in the field.
This wide-field approach to phase calibration could be relevant to many other VLBI observations, in particular those that target faint sources and currently employ phase-referencing. The calibration technique makes the detection of sub-mJy sources routine, and permits us to move towards detecting microJy compact sources.
The full paper describing MSSC is now in press and can be found at: http://arxiv.org/abs/1601.04452
© ASTRONJust prior to leaving 2015, a second technical workshop on a new generation VLA was held at NRAO's Array Operations Center in Socorro, NM. Besides presenting an impressive science update, it discussed important technical aspects of what is now referred to as the ngVLA. Great thinking about its shaping up is going on. Details can be found on https://science.nrao.edu/futures/ngvla.
Going up in frequency as high as 120 GHz, it reminded me about discussions at or around SKA meetings of SKA-High and ALMA-low. The latter is a hypothetical future ALMA with much larger collecting area, but operating at lower frequencies, to observe the red-shifted molecular universe.
Of course we also visited the JVLA, here shown in its highly photogenic compact arrangement. Impressive as the picture is, being shown around by VLA staff made me feel that the amount of dedicated and professional work done by our US colleagues to achieve its present state has been at least as impressive!
Upon reflection it made me think that the great work done in ASTRON using the WSRT, e.g. to achieve its unique high dynamic range imaging and its novel polarimetric work, now finds an outstanding science future in the US. Both were made possible through outstanding engineering design and stability of the WSRT, and the mathematical tool of MeqTrees.
Actually, it looked as if a trifle over-engineering, and years of devotion, has a price but serves the future!