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Articles on this Page
- 11/29/15--16:00: _A new full member o...
- 11/30/15--16:00: _Searching for pulsa...
- 12/01/15--16:00: _Open day prize winn...
- 12/02/15--16:00: _Today's colloquium:...
- 12/03/15--16:00: _Bootes field with L...
- 12/06/15--16:00: _Cool
- 12/07/15--16:00: _Neutral atomic hydr...
- 12/08/15--16:00: _LOFAR Dynamic Spect...
- 12/09/15--16:00: _Today's colloquium:...
- 12/10/15--16:00: _Sampling the Ionosp...
- 12/14/15--16:00: _ASTRON/JIVE scienti...
- 12/13/15--16:00: _UniBoard2 has arrived
- 12/15/15--16:00: _Our Commissioning t...
- 12/16/15--16:00: _Christmas High Tea
- 12/17/15--16:00: _The International L...
- 12/20/15--16:00: _APERTIF-6 first-fri...
- 12/21/15--16:00: _'Audio' meets 'Ultr...
- 12/22/15--16:00: _In memoriam Dan Har...
- 12/23/15--16:00: _Season's Greetings ...
- 12/27/15--16:00: _Happy Holidays from...
- 11/29/15--16:00: A new full member of IAA
- 11/30/15--16:00: Searching for pulsars with coherent dedispersion
- 12/01/15--16:00: Open day prize winners visit the DRT
- 12/03/15--16:00: Bootes field with LOFAR @ 150 MHz
- 12/06/15--16:00: Cool
- 12/07/15--16:00: Neutral atomic hydrogen in Hickson Compact Group 44
- 12/08/15--16:00: LOFAR Dynamic Spectrum Art
- 12/09/15--16:00: Today's colloquium: Emergent Gravity and the Dark Universe
- 12/10/15--16:00: Sampling the Ionosphere with Rigid Floating Groups (RFG)
- 12/14/15--16:00: ASTRON/JIVE scientists, looking the part
- 12/13/15--16:00: UniBoard2 has arrived
- 12/15/15--16:00: Our Commissioning team at work in LOFAR station Borowiec (PL610)
- 12/16/15--16:00: Christmas High Tea
- 12/17/15--16:00: The International LOFAR Telescope family has been extended!
- 12/20/15--16:00: APERTIF-6 first-fringe party
- 12/21/15--16:00: 'Audio' meets 'Ultra-Mega-High Hertz'
- 12/22/15--16:00: In memoriam Dan Harris 1935-2015
- 12/23/15--16:00: Season's Greetings from ASTRON
- 12/27/15--16:00: Happy Holidays from JIVE !
© JIVEAs reported in AJDI 2012-09-28, Leonid Gurvits was elected to the ranks of Corresponding Member of the International Academy of Astronautics (IAA). This status is the first step toward a full IAA membership. This year, Leonid has been elected to the distinguished level of a full Member (Academician) of the IAA. He got the diploma and IAA blue pin at the biennial meeting of the IAA which this year had taken place in Jerusalem, Israel, on 11 October.
On appropriate occasions, two of our colleagues, Mike Garrett (see AJDI 2014-10-14) and Leonid Gurvits could be seen proudly displaying their blue IAA pins with a little pictogram of constellation Ursa Major.
Citation: "Professor Leonid Gurvits is one of the world-leading experts in state-of-the-art radio astronomy experiments with space science missions and pioneering applications of the Very Long Baseline Interferometry (VLBI) technique in planetary and space science. His more than 35-year experience is marked by a number of acclaimed successes, such as the first dedicated Space VLBI missions VSOP/HALCA and RadioAstron, as well as VLBI tracking of a variety of planetary science missions."
© Cees Bassa, Ziggy Pleunis, Jason Hessels, Vlad KondratievThe dispersive effect of the ionized interstellar medium leads to frequency dependent delays in the arrival times of pulsed radio emission. As such, surveys for pulsars and fast radio bursts need to correct for this a priori unknown dispersion measure (DM) by computing many trial DM values. This is typically done through "incoherent dedispersion" where the timeseries in individual channels are shifted by a delay proportional to the trial DM. Though this approach works well at higher frequencies, at LOFAR frequencies the dispersive delay within a single channel can be large enough to smear out pulses. This greatly reduces the sensitivity to short pulses at high DMs like those of millisecond pulsars (MSPs) and fast radio bursts (FRBs).
To enable LOFAR to find MSPs and FRBs, we have developed software that uses "coherent dedispersion" to correct for the dispersion. Coherent dedispersion works by convolving a Nyquist sampled timeseries by the inverse of the transfer function of the interstellar medium, completely removing the effects of dispersion. Because coherent dedispersion is computationally expensive, it is mostly used when observing pulsars for which the DM is known.
Aided by the 600Tflops DRAGNET GPU cluster we now have the resources to compute coherent dispersion measure trials. Our software uses the DRAGNET GPUs to coherently dedisperse raw complex voltages to dozens of trial DMs, and subsequently channelizes, detects (converting to Stokes I) and rebits the data for each trial DM. Inspired by COBALT, we then use the 10G network of DRAGNET to transpose the trial DMs per subband to subbands per trial DM. Each of these coherent trials is then incoherently dedispersed around the coherent value and searched for period signals and single pulses.
The panel on the top left shows the smearing due to dispersion within a 24-kHz channel in the case of incoherent dedispersion and coherently dedispersed trials separated by 1 pc/cc. The latter enables us to limit the smearing to less than 0.1 ms. The bottom left panel shows the improvement of this approach over incoherent dedispersion on the sensitivity for pulsars with different spin periods. The sensitivity at high DMs is now limited by scattering.
A LOFAR survey (LC5_002) for millisecond pulsars associated with as of yet unclassified Fermi gamma-ray sources is presently ongoing and using this approach to generate coherently dedispersed DM trials. To our knowledge, this is the first time that any pulsar survey computes many coherent DM trials. The panel on the right shows the blind redetection of the test pulsar J1810+1744, a 1.66 ms pulsar in a 3.5 hour orbit at a DM of 39.66 pc cm-3. The nearest coherent dispersion measure trial was 39.50 pc cm-3.
© R&D departmentAt the recent ASTRON/JIVE/DOME/NOVA Open Day, the compute group presented the visitors with a quiz. If the processing power of a typical tablet computer is represented by one chocolate peanut, how many pieces of candy then represent the total compute power of LOFAR (i.e. COBALT and CEP)? To help them guessing, we showed a vase filled with the correct number of chocolate peanuts.
Of the XXX visitors who submitted an answer, 9 came close to the correct number (875). They were invited for a visit to ASTRON and recieving a one hour tour through the Dwingeloo Radio Telescope, and observing PSRB0329+54.
Eventually, five participants visited the telescope (each bringing a parent). The picture shows the group in the DRT control room, together with the guides.
We would like to thank Ina Doorten, Monique Sluiman, Roy van Werp, Michel Arts and Michael Sanders for helping with organising the tour.
© David BanekeFrom its very beginning, radio astronomy has shaped astronomy. Not only has it changed our view of the cosmos in the most literal way, it has also changed how astronomy is done and how it is organized. In the Dutch case, it also changed the structure of the astronomical community. In my talk I will describe several examples of how radio astronomy has provided a new impetus to Dutch astronomy at a crucial moment. This is important to understand the history of Dutch astronomy, but also to understand the role of instrumentation in modern astronomy.
© Image credits: Wendy Williams (Leiden), Reinout van Weeren (Harvard) and Huub Rottgering (Leiden), for the LOFAR survey team.This is the first sensitive, wide field, LOFAR image at 150 MHz. It contains more than 5000 radio sources in an area about 10 times the size of the full moon. The majority of the resolved sources are galaxies that contain an active massive black hole which is producing powerful jets of relativistic particles. The unresolved sources are mostly galaxies that are forming stars at very high rates.
The data reduction was performed with the Facet Calibration technique by Van Weeren et al. The LOFAR Calibration & Imaging Tiger Team (CITT) is developing this into a more automated pipeline to be used for any field.
© ASTRONLately we have been busy with a cool subject in every sense of the word, maybe except for the protective gear, which is not up to the latest fashion.
Accompanied to the ever present goal of achieving lower and lower noise figures, is the demand to be able to measure these results accurately. The usual way is to a use a well calibrated diode noise source. Although these are pretty accurate, the uncertainty of the generated noise temperature is too large.
To improve the accuracy, we utilize the known temperature of boiling liquid nitrogen as a constant for calculating noise temperature. This mirrors the conceptual foundation of the noise standards used in virtually all national standards laboratories world-wide.
Furthermore, an analysis of the dominant uncertainty contributors was made. This allows us to add error bars to our noise figure measurements. The insert in the top-right shows a comparison of the uncertainties of noise sources for a room-temperature LNA measured at 1 GHz. The bottom line clearly shows the huge improvement in uncertainty when using liquid nitrogen.
© copyright reservedThis image is a slide from my presentation at ASTRON lunch talk in August, and shows one of the main scientific results from my visit to ASTRON/JIVE during the summer of 2015. The image shows a preliminary map of the total neutral atomic hydrogen (HI) in Hickson Compact Group 44 (HCG 44). HCG 44 is a group of galaxies consist of three spiral galaxies NGC 3190, NGC 3187, NGC 3185 and background galaxy, SDSS J1017.
On the left, previous observations of HCG 44 with WSRT and HIPASS from Serra et al. (2013) suggest the possibility that NGC3162 flew by the group and caused gas stripping, creating the long HI tail. Another possibility is an HI bridge between the group, the tail and NCG 3126.
KAT-7 is a 7 dish array, and a testbed for the 64-dish Meerkat. Meerkat is the South African pathfinder for the SKA. With a 1 degree field of view, and angular resolution = 4 arcmin, KAT-7 is a compact array, with low system temperature, good for measuring low surface brightness emission on large angular scales. These specifications make KAT7 ideal for investigating HI abundance in and around HCG44.
During my visit to ASTRON, I met great people, had so much fun, and learned a lot about radio astronomy. Thanks to Dr. Kelley Hess' guidance, I successfully reduced the HCG 44 data from the KAT-7 telescope and produced a cube showing HI abundance on HCG 44 compact group. Understanding the gas content and the impact of the group environment on galaxies is important for understanding their overall evolution. We detected that the tail is even more massive and more extended than the previously reported observations. We also found more large scale gas within and between the three compact group galaxies that make up HCG 44.
© AstronBecause of the ever-present possibility(*) of little problems like hardware failure, software bugs, or even human error, the LOFAR system is being monitored 24 hours a day. Sometimes we notice strange features in the inspection plots. This time Science Support asked me to find out why the HBA-ONE (Serdes Ring 01) was showing behaviour that was completely different from the much cleaner HBA-ZERO (Serdes Ring 00). It is obvious that the signal in the two messy plots is not real (although some might think of SETI).
Since I could not find a clear hardware issue in station CS026C, I asked the Duty Observer to repeat the observation, and discovered a multi-problem bug. Thanks to plots made by Richard Fallows (Inspection Plots) and Pieter Donker (Live Plots) I noticed that 25% of the HBA tiles of this station had the wrong spectral inversion setting, which mirrorred the frequency band. The second problem was an oscillating tile (T28 in HBA-ONE) that occasionally disrupted the station beam, causing the art-like structures in the beamlet inspection plots.
The spectral inversion issue has now been resolved, but tile T28 will be temporarily ignored in LOFAR observations while it is being repaired. The latter will certainly be the case by the time you read this daily image (which has taken its own good time to get posted).
(*) Editor's note: An electronic beam-forming system like LOFAR (or SKA Low) is somewhat more complex than a dish-based system, and thus has somewhat more scope for little problems like this one. Of course that is amply compensated by the advantages of multi-beaming. One just has to be vigilant, like a doting young mother.
© Erik VerlindeAt present we are witnessing a revolution in theoretical physics leading to a completely new view on space-time and gravity. Studies in string theory and black hole physics reveal a deep connection between space-time and gravity and key concepts of quantum information theory. Gravity appears as a consequence of an quantum-analogue of the first law of thermodynamics. This new view on gravity and space-time has particularly important implications for cosmology. I will argue that the positive dark energy of our universe carries an entropy density, which lead to a modification of the gravity equations compared to general relativity. At large scales there appears an additional “dark elastic force”, whose magnitude can be computed and quantitatively explains the observed phenomena currently attributed to dark matter. The main emphasis is on explaining galaxy rotation curves, but there is also good agreement with the data at cluster and cosmological scales.
© Madroon Community Consultants (MCC)The LOFAR calibration process generates "Rigid Floating Groups" (RFGs) of N instrumental phase errors, one for each LOFAR station, looking in the same direction, at the same time. Since an interferometer like LOFAR only measures phase-differences, it cannot determine absolute phases. But the N phases are highly accurate relative to each other, as demonstrated by the LOFAR image quality. The RFG has amply proved itself as a powerful constraint in calibration and modelling.
The RFG represents valuable (and unique) information for the Global Navigation Satellite Systems (GNSS). Signals from GNSS satellites are affected by the ionosphere, an undulating layer of charged particles at an altitude of 100-500km. Since the ionosphere also dominates the LOFAR instrumental effects, the RFG phases may be converted to the relative Total Electron Content (TEC) along N different lines-of-sight through the layer(s). Since any contamination by other instrumental effects will vary much more slowly, the TEC variations in position and time will be highly accurate.
For the past year, ASTRON and the Dutch Aerospace Center (NLR) have collaborated in the Symbionos project, to investigate the possibilities for cross-fertilization between LOFAR calibration and GNSS (see also an earlier AJDI). Eventually, LOFAR RFGs may help to improve mobile GNSS positioning accuracy, but for the moment we concentrated on using them to augment the large-scale ionospheric models that are routinely published by the International GNSS Service (IGS). After all, RFGs contain information about the TEC distribution with a much better resolution in position (km) and time (s).
The image shows the ionospheric "footprints" of 64 simultaneous LOFAR RFGs. They sample the ionospheric TEC along the lines-of-sight from the Dutch LOFAR stations only, in the direction of 64 bright (3C) radio sources. Of course, the shape of the RFG footprints reflects the configuration of this LOFAR sub-array (50x80km).
A practical GNSS service based on using RFGs would require a dedicated array of small (5x5m) LOFAR stations with 50-100 beams pointing at 3C sources. The array should be large enough (>100x100km) for the RFG footprints to overlap significantly at the altitude of the ionosphere. Then they can be combined to solve for the parameters of a large-scale model of the TEC(x,y,z,l,m,t) as a function of viewing position (x,y,z) and direction (l,m). Such a Minimum Ionospheric Model (MIM) might even be invertable to give the 3D TEC distribution, albeit perhaps with some extra assumptions.
Symbionos team members were Hein Zelle, Ed Kuijpers, Arnoud van Kleef and Frank Wokke from NLR, Maaijke Mevius and Bas van der Tol from ASTRON, and Jan Noordam from MCC. We gratefully acknowledge the help with the observations by Menno Norden, George Heald and Luciano Cerrigone.
© Madroon Community Consultants (MCC)Normally it does not matter very much that our scientists do not always resemble the popular image that Hollywood has created for them. After all, modern scientists are not judged by their looks, but rather by their number of publications, or the size of their grants. And visiting royalty and other dignitaries have people to help them avoid embarrassing mistakes, by pointing them towards the right persons.
But things are different when we reach out to the wider public who, as our main sponsors, deserve to be approached in the correct manner. The picture shows two of our bright young things, Harro Verkouter from JIVE and Michiel Brentjens from ASTRON, giving a creditable impersonation(*) of proper scientists at our recent ASTRON/JIVE/DOME/NOVA Open Day. Undoubtedly they will go far, even if they will look quite different by then.
(*) although they could do with a little more facial hair
© JIVE / ASTRONAfter a period of nearly 3.5 years the Radionet FP7 UniBoard2 project comes to an end. The goal of the project was to create an FPGA-based generic scalable high-performance computing platform. With the production of 7 UniBoard2s this goal has been achieved.
UniBoard2 is built with Altera Arria10 20nm FPGAs (at this point still engineering samples). Given the ultimate purpose of UniBoard2, namely next generation radio-astronomical computing, a maximal IO capacity has been implemented on UniBoard2. On the front panel 24 interfaces can be constructed of 40Gbps each. On the backplane side a total of 2Tbps connectivity is available, to other UniBoard2s, ADCs or memory devices. In total the IO for a single UniBoard2 is 3Tbps. This is close to the peak aggregated traffic on all of the Amsterdam Internet Exchange connected network ports (peak of 4.2Tbps in 2015). On the backside of UniBoard2 eight DDR4 SODIMM modules are placed. The board itself is pin-compatible with the far more powerful 14nm Stratix10 devices, which will become available in early 2017.
Within the UniBoard2 project JIVE was responsible for the project lead, the correlator firmware and parts of the test firmware. ASTRON was responsible for designing and making the hardware and parts of the test firmware. The University of Bordeaux and INAF were responsible for digital receiver firmware, the University of Manchester for the pulsar binning firmware, MPG for a beam former implementation and the University of Orleans for the RFI mitigation firmware.
© Fotos: M Norden, K StuurwoldWhen all antennas are mounted and all electronics is installed, an International LOFAR station is subjected to a well-defined Station Hardware Validation Procedure, as part of the Site Acceptance Test (SAT).
The pictures show the ASTRON commissioning team in action at the newly built Polish LOFAR station Borowiec near Poznan. Henri Meulman, Menno Norden and Klaas Stuurwold verified whether all hardware was operating, including the polarization orientation of the hundreds of dipole antennas of this station.
Only some minor issues where detected. Thanks to the well-equipped team, some coax cables which did not survive piercing by an HBA ground anchor where repaired on-site.
The SAT was witnessed by Prof. Hanna Rothkaehl from the Space Research Centre, Polish Academy of Sciences (CBK-PAN), Warshaw. She represented the station owner on behalf of the POLFAR consortium.
So the SAT was passed, to mutual satisfaction. Many thanks to all co-workers from CBK, Trans-Tronic company from Poland (who performed a great job in the roll-out), our roll-out team, and of course the commissioning team!
© ASTRON / Hiddo HanenburgToday at 15.00, the Christmas High Tea will be held. This marks the end of the year for ASTRON, JIVE and NOVA. Retired & current personnel, students and visitors come together to celebrate Christmas. The ASTRON/ JIVE choir will sing a couple of Christmas songs and people catch up with each other over drinks and festive snacks.
At the end of he celebrations the Christmas parcels will be handed out and many people will start their holidays.
© Marjan TibbeThe International LOFAR Telescope has been officially extended to the East! On Wednesday 9 December 2015 the ILT board admitted POLFAR, the Polish LOFAR Consortium, as a new member. Three LOFAR stations have been built in 2015, at Baldy near Olzstyn in the North, at Borowiec near Poznan in the West, and at Lazy near Krakow in the South. They will become fully operational in early 2016, along with the Polish node in Poznan for the LOFAR long term archive.
The chair of the ILT board, Heino Falcke, and the POLFAR representative, Andrzej Krankowski, signed the participation certificate, after which there was time to celebrate the extension of the ILT to the east. The picture shows, from left to right, Huub Roettgering (NL-LAC), Marcus Brueggen (GLOW), Philip Best (LOFAR-UK), John Conway (LOFAR-Sweden), Heino Falcke (NL-LAC, Chair), Andrzej Krankowski (POLFAR), Rene Vermeulen (ILT Director), Hanna Rothkaehl (representing Borowiec station), Peter Gallagher (observer from I-LOFAR), Michel Tagger (FLOW), and Michael Garrett (ASTRON).
This significant expansion will tightly connect the diverse and experienced Polish community into the wider LOFAR family. Meanwhile, the Irish consortium I-LOFAR is hoping for its turn to build a LOFAR station, extending the ILT to the West and thereby qualifying to become the next member.
© Jan Rinze PetersonOn the 26th of November we celebrated the measurement of the first fringe (08/10/2015) on the sky with the final APERTIF correlator, using 6 WSRT dishes for the moment.
The APERTIF team also took the oppertunity to thank Wim van Cappellen for his role as project manager. His effort and energy, together with the rest of the team, made WSRT/APERTIF into the magnificent instrument it is.
© AstronFor some of their modules, the Netherlands Space Research Organisation (SRON) decided to take the frequency down a tiny notch to 'more decent' frequencies. So, in the past year, there has been some exchange of knowledge between our groups. In addition, SRON used the facilities in our lab to measure their designs.
Based on the knowledge gained, some more modules were designed, and passed all initial tests. To see the hardware in action, the Radio Group of Astron paid a visit to SRON in Groningen on Nov 30th. Unfortunately, the cryostat in which these modules are used was closed just a few days before our visit. Nevertheless, during a lab tour lots of impressive hardware was shown.
Specially to meet us, also some guys from SRON Utrecht came over. Several presentations had been prepared. There was great interaction between our groups, both during the presentations as during discussions on the lab-tour.
When leaving they also thanked us for coming, lets hope it was not just for the banketstaaf (https://en.wikipedia.org/wiki/Banket_%28food%29) we brought along.
© Harris familyDan Harris was the first astronomical postdoc(*) in Dwingeloo, between 1975 and 1978. He died last week, after four-score fully-lived years. According to his children (Justine, Seth and Leila): A passionate and world-traveling astronomer, Dad conformed to no social norm. His adventures are legion, but include sailing across the Atlantic in 1964, rafting down the Amazon with our mom, and climbing Mt. Washington with the entire family last year on his 80th birthday.
He ended his scientific orbit at Harvard CfA. In the words of Jim Moran: Dan was the High Energy Division's "in house" radio astronomer, having worked at several of the major radio observatories including Arecibo and Westerbork, before expanding his wavelength coverage to X-rays. He brought a remarkable enthusiasm and love of astronomy to all his projects. Over his career, Dan's interests spanned supernova remnants, interplanetary scintillation, cluster magnetic fields and inverse Compton emission, radio galaxies, and AGN. Most recently, he was studying jets from extragalactic sources (see his Annual Review article "X-ray Emission from Extragalactic Jets" in 2006) and surveying the 3CR Catalog using Chandra.
But of course there was more. For instance, as related by Tony Willis, Dan was one of the authors of the Caltech A survey back in 1961. A source in the survey, CTA 102, was one of the first radio sources to show variability, and the Russian astronomer N.S. Kardashev caused a sensation when he suggested that it might be a signature of an alien civilization. This suggestion turned out to be wrong, but Dan remains the only radio astronomer that I know of to have one of his discoveries become the theme of a song by a famous pop group, The Byrds, in 1967. You can listen to it on YouTube (www.youtube.com/watch?v=P1mXIiM9QjA)
The two side-by-side images show him and his Barbara(**) in the same setting, punting on the Cam, but 35 years apart. They mated for life. A memorial service will be scheduled in the Boston area some months from now. Dates and details will be provided as plans develop.
See also: http://www.atnf.csiro.au/people/bkoribal/ATNF-DailyImage/archive/2015/19-Dec-2015.html
(*) It was not easy to persuade the astronomical community that SRZM needed active astronomers on-site in Dwingeloo, to help build the right kind of instruments. The first batch (Harris, Strom, Schilizzi, De Bruyn, Kapahi, Robertson) all went on to greatness, each in their own way.
(**) It is not easy to be larger than life, unless you have a significant other that makes it all possible.
© ASTRONASTRON wishes you all a merry Christmas and a prosperous 2016!
© image copyright: Paul Boven, Harm-Jan Stiepel, Huib van LangeveldeThe year 2015 has been a special year for JIVE, as the ERIC was inaugurated and the old foundation transferred its activities to the new legal entity.
Looking forward to 2016, the ERIC is ready to carry out the VLBI operations and provides opportunities to innovate the astronomical capabilities of the research infrastructure we offer with the EVN partners.
We wish all of you a great holiday break and all the best for 2016!
The JIVE staff.