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A daily view of all the goings-on at ASTRON and JIVE.

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    © ASTRON

    The LOFAR working group on Nearby AGN has been active as part of the LOFAR Survey Key Science Project since the starting of the observations in Cycle 0. A number of famous objects - some shown in the picture - have been observed and many results have already been published.

    To discuss the status of the data reduction and analysis, how to publish it all and how to move forward with the project, the group had a face-to-face meeting, the second of its kind, this time in Cambridge. This follows on the one of last year at ASTRON (see Daily Image 23-2-2015). Judith Croston organised the logistics and we were hosted in a remarkable english mansion, part of the University of Cambridge.

    Part of the workshop was dedicated to discussing the results obtained so far in relation to the physics of nearby active nuclei and their energetics, a key parameter in order to understand the impact on the host galaxy. Participants presented their latest results on the data reduction and the methods used for the analysis, with ample time allowed for feedback and discussion on the best way to proceed with future work. Some presentations were dedicated to theoretical modelling, crucial for the interpretation of the results.

    A large fraction of the workshop and of the discussions were dedicated on how to move forward now that the data of the Tier 1 surveys start to become available. The work on single objects, which has been so far the focus of the group, can now be finally expanded to large samples and the group needs to prepare for that. The meeting was a good forum were ideas for projects using these new datasets were presented as well as how to optimize the coordination between groups and the development of tools, e.g. for optical identification of the radio sources.

    You can expect a large number of exciting results and Daily Images from this group!


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    © APERTIF

    After a succesfull hardware rollout (APERTIF-6) of the first 6 APERTIF dishes the rollout continues (APERTIF-12). Two pictures shown are taken at ITEQ Amersfoort in january 2016 during a visit. At that time the first parts for the frontends were ready. The other two pictures show the 6 remaining frontends in the building at Westerbork after delivery in the second part of January.

    ITEQ assembled and delivered very fast. The frontends are now waiting for the LNAs to be delivered at the end of March

    *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.


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    © ASTRON

    Last year, we established a new annual award for the best AJDI of the year. As is now the tradition, the winner was announced during the New Year's speeches.

    The winner for 2015 is ...(drrumm rroll)... Alexander Shulevski. Alexander presented a LOFAR movie of the entire sky using only the super-terp LOFAR stations during a significant thunder storm. The associated lightening discharges are clearly seen in the movie, including many near-simultaneous multiple events - see: http://www.astron.nl/dailyimage/pictures/20150721/movie.gif

    Also by a tradition of sorts, the winner of this award receives a bottle of Jameson's Irish Whiskey (see image above*). The Jameson distillery is very well connected to the world of radio science - born in Scotland, the famous distiller Andrew Jameson (1783 -1856) was the father of Annie Jameson (1840-1920), and Annie was the mother of one Guglielmo Marconi, Nobel prize winner in Physics (1909), and the father of wireless (radio) communication!


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    © Imke de Pater

    Despite the fact that Jupiter has been observed for decades from the ground, and in situ by spacecraft, we still do not know its bulk composition, nor do we understand its global atmospheric dynamics well.

    The sensitivity upgrade to the Very Large Array (VLA), combined with novel data reduction techniques, has enabled us to produce detailed longitude-resolved maps of Jupiter's atmosphere below the visible cloud layers.

    I will compare these (still embargoed) maps with visible-light amateur images, and present results from radiative transfer modeling. In addition to radio observations, we also investigate the planet's atmosphere using 5-micron spectroscopy, which provides information complementary to the radio data.


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    © Rik ter Horst

    Trapped heat inside an astronomical mirror deteriorates the image quality considerably. Sometimes cooling down takes hours and only after being thermally stabilized image quality will be optimal, seeing permitted of course.

    A year ago I started making a 19 mm thin, 400 mm diameter F/3 meniscus mirror for my new Wide Field telescope. This was very challenging as such a thin mirror is almost a guarantee for astigmatism due to its relative flexibility, something you don't want. The glass was slumped into an F/3 radius in an oven followed by grinding and polishing. Using a new technique I managed to rule out any astigmatism and after months of figuring my new telescope had its first light. The mirror cooled down within an hour (15 degrees) and performs very fine, so I’m very happy with the result of this experiment.

    The animation shows the mirror during a Foucault test at the centre of curvature, measuring several zones.


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    © ASTRON

    On the 18th of January, ASTRON welcomed a combined delegation of students of the northern universities for applied sciences: NHL Hogeschool Leeuwarden, Hanzehogeschool Groningen, and Hanze Institute of Technology in Assen.

    A group of almost 40 students, with an educational background in applied sciences (varying from mechatronics and sensor technology to digital and RF electronics), paid their first-time visit to ASTRON.

    A strictly scheduled program, consisting of a set of short presentations, a guided tour through the R&D-lab and a visit to the Dwingeloo-telescope, gave the students a good impression of the high-quality work done at ASTRON.

    Ronald de Wild explained in his talk “The Fourier Transform in 30 minutes” why Fourier plays such an important role in modern astronomical systems and Hajee Pepping explained to the students our digital signal processing applications as developed by ASTRON in which cutting edge beamforming technologies demand for Big Data processing platforms like Uniboard.

    An important visit, not only for the students but also for ASTRON’s R&D department, because among the students might be your colleagues of tomorrow!

    text: Ronald de Wild

    photos: Dagmar Hoogendorp


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    © JIVE

    On February 3rd, we conducted a very successful 2Gbit/s e-VLBI test. Many EVN stations participated; Effelsberg, Hartebeesthoek, Medicina, Noto, Onsala and Yebes all streamed data from their FILA10G boards at 2 Gbit/s while Torun used the traditional e-VLBI method with a Mark5B at 1 Gbit/s. We started our test by streaming "default" VDIF frames with a payload of 8000 bytes with multiple channels packed into a single frame (single-threaded, multi-channel). This worked really well (upon the first attempt!) thanks to recent optimizations in the SFXC software correlator and tuning of the Infiniband network of the correlator compute cluster. The total data rate was in excess of 13.5 Gbit/s, and it ran for more than an hour without any hiccups and with minimal packets loss. There were fringes to all participating stations. We pretty much maxed out one of our 10 Gbit/s links to SURFNet while doing this!

    We also tested VDIF frames with a payload of 2000 bytes using separate frames for each channel (multi-threaded, single-channel), where the FILA10G does the corner-turning. This took a bit more effort, but eventually we succeeded. It's interesting to note that while letting the FILA10G do the corner-turning saves some computation in the correlator, this is pretty much offset by the increased per-packet overhead as we need to process 4 times as many packets per second. The overhead of using smaller frames is nicely visible in the network throughput graph.

    This test proves that the SFXC correlator at JIVE can comfortably handle real-time correlation of 2 Gbit/s for six-and-a-half stations. There is probably enough spare capacity for adding one or two more stations as the cluster nodes were still partly idle and not all nodes were used for this test. There are still a number of technical issues to sort out to make sure the data streams can be started and stopped on demand. But we're getting really close to offering 2Gbit/s e-VLBI to our users.

    We'd like to thank the VLBI friends at the participating stations for their help with this test.

    Editor's note: It is not necessary to understand all the jargon to be really impressed with this stuff.


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    © Staveley-Smith, Kraan-Korteweg, Schr�der, Henning, Koribalski, Stewart and Heald

    A blind HI survey of the extragalactic sky behind the southern Milky Way has been conducted with the multibeam receiver on the 64-m Parkes radio telescope. The survey covers the Galactic longitude range 212 degr "Zone of Avoidance" because distant galaxies seemed to avoid the region � we now know that they are present there, but are obscured and confused by our own Galaxy in the foreground. The new survey provides an rms sensitivity of 6 mJy per beam per 27 km/s channel, and yields 883 galaxies to a recessional velocity of 12,000 km/s. One third of the detected galaxies had not been previously recognized. The survey covers the sky within the HI Parkes All-Sky Survey (HIPASS) area to greater sensitivity, finding lower HI-mass galaxies at all distances, and probing more completely the large-scale structures at and beyond the distance of the Great Attractor. Several newly identified mass concentrations have been uncovered with this new dataset.

    The image above shows the HI detections overlaid on the dust map in this region of sky (top) and on the continuum map (bottom), proving that the Parkes HI Zone of Avoidance Survey (HIZOA) is not affected by dust and only little by continuum emission in the foreground.

    A paper describing all of this work has been published today in the Astronomical Journal. The author list includes experts in the study of the Zone of Avoidance, some of whom used the Dwingeloo 25-m telescope for a similar, complementary survey in the 90s. In future, the SKA and its pathfinders will explore this region and the rest of the extragalactic HI sky to even greater detail.


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    © David Kaplan

    Explorations of the radio sky in the time-domain are an exciting frontier in astrophysics, and one where new observational capabilities will open up new windows on the universe. As one of a new generation of widefield, low-frequency radio telescopes, the Murchison Widefield Array has enormous potential to conduct blind searches for radio transients. We are working to develop capabilities for the MWA that will continue to serve the Australian Square Kilometer Array Pathfinder (ASKAP) Variables and Slow Transients (VAST), eventually allowing real-time transient detection and characterization. I will discuss the expected types of sources that we hope to discover with the full array, explore some of our initial results, and highlight plans for the next generation of facilities.

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  • 02/11/16--16:00: PAASAR
  • © Bart Peeters, Ursa Minor B.V.

    The proof-of-concept prototype of the Phased Array Antenna for SAR (PAASAR) project is currently being tested in the assembly area. The aim of the project is to develop and test an active antenna that can simultaneously receive Search And Rescue (SAR) signals relayed by at least four different Galileo navigation satellites. These SAR signals (not to be confused with synthetic aperture radar) may be transmitted by distress beacons on boats, aircraft and handhelds. By measuring the time of arrival of these four (or more) signals, and using the known locations of the satellites, the origin of the distress signal can be determined.

    Presently, SAR ground stations use steerable dish antennas to track satellites as they move across the sky, with each dish tracking only a single satellite at a time. Obviously, it is much more efficient to track all the visible satellites with a single antenna. PAASAR uses ASTRON/JIVE UniBoard technology to combine the signals received by 50 antenna elements to form multiple independent beams that track different satellites simultaneously. Thus creating a solid-state ground station without any moving parts!

    We have moved PAASAR to the ASTRON premises because the 3rd harmonic of UMTS and television saturated our LNA (amplifier) at our previous test location in Amsterdam. Since the RF environment near Dwingeloo is much less hostile, we soon hope to capture our first satellite signal. After we have finished doing some basic tests, and some Front End (FE) upgrades in the lab, we will mount the FE on the frame that is already being placed next to Huisje West at ASTRONs Open Area Test site.

    During the next weeks you will see Dion Kant(*) and Bart Peeters of Ursa Minor working on this project, assisted by two Zoran's from the Spanish company TTI. They are all partners in the PAASAR project. For more information and the full list of project partners, see https://artes.esa.int/projects/paasar

    What makes this project special is that technology and know-how that was developed for astronomical research (e.g. the LOFAR and SKA radio telescopes) can also be applied to save lives.

    (*) Dion Kant has of course been involved in developing phased array technology as an ASTRON employee in the past. It is good to see him again.


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  • 02/14/16--16:00: APERTIF DCU Powercard
  • © E.Mulder

    Another nice piece of hardware ready for APERTIF-12. the picture shows 24 Powercards for 24 DCUs (Down Convertor Units http://www.astron.nl/dailyimage/main.php?date=20160125 ) for the second rollout phase of APERTIF, nicely put together by Eim Mulder.

    Whilst the first part of hardware is being tested, APERTIF is already preparing for the second building phase.

    *APERTIF-12 is the second 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.


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    © ASTRON

    Recently, we invited our Scientific Advisory Committee (SAC) to visit Dwingeloo, in order to discuss some important issues that included the Science Data Centre (SDC) initiative, the APERTIF survey plan, LOFAR 2.0 and several other significant topics. The role of the SAC is to provide scientific advice to the ASTRON director but in this instance the SAC was also explicitly asked by our Board to comment on the SDC. The SAC report will be presented to the ASTRON Board at their upcoming meeting towards the end of this month. We also intend to hold a staff plenary session shortly thereafter, in order to present some of the SAC/Board's main conclusions, and how we plan to take things further forward.

    The image above shows members of the SAC and senior ASTRON mgt in the Oort room (from left to right around the table): Marco de Vos, Anita Loots (SKA SA), a hidden Steven Tingay (INAF/ICRAR), Michael Wise, Ralph Wijers (API), Leon Koopmans (RuG), Huub Rottgering (Leiden), Michiel van Haarlem, Martha Haynes (Cornell), Gert Kruithof, the SAC chair - Sean Dougherty (DRAO), and Rene Vermeulen.


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    © Astron & ATH

    Station Baldy was the first POLFAR station to be commissioned. It received a lot of media attention because it was not only the first Polish LOFAR station, but it also contained the 100.000th LOFAR dipole (See http://www.astron.nl/dailyimage/index.html?main.php?date=20150824 ).

    As a final test after connecting the new station to our European network, we decided to make an all-sky image with it, remotely from Dwingeloo. Since the HBA tile beam is only 20 degrees wide, we used a single dipole (out of 16) per tile, thus extending the view to 140 degrees. A program written by Michiel Brentjens selected the set of dipoles that minimised the station beam sidelobe level. After correcting for the dipole position offsets w.r.t. the center of their tiles, and applying the calibration tables, we could finally generate all-sky images.

    The movie shows a 24h observation. It consists of 5s snapshots, taken at one-hour intervals. Only a single 1.2 kHz subband around 115 MHz was used.

    The strong radio sources CasA and CygA, and our own Milky Way are clearly visible. Notice also our closest star (the Sun), moving from south-east to south-west. Most importantly, the horizon and the rest of the image are free from Radio Frequency Interference (RFI), even with a security camera installed on-site.

    So the station is ready to be included in the International LOFAR Telescope (ILT). The three new POLFAR stations will definitely improve the LOFAR image quality, especially the spatial resolution.


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    © Laura Perez

    Planet formation is a natural outcome of the star formation process. With the advent of sensitive observations -- particularly of circumstellar disks at radio wavelengths -- and together with developments in theory, rapid progress is being made in understanding how planet formation proceeds. In this talk, I will discuss three projects to observationally characterize the assembly of planetary systems in circumstellar disks.

    First, I will present results from an observational program aimed at tracing the growth and migration of solids in disks; one of the first steps toward forming terrestrial planets and the rocky cores of gas giants. The systems studied reveal that larger particles are segregated to the inner disk regions, consistent with theoretical barriers that limit further growth.

    Second, I will discuss a possible solution to the posited barriers for growth: regions of local pressure maxima that can efficiently trap grains and create appropriate conditions for further evolution of solids. I will present recent ALMA observations that reveal large-scale asymmetries in the solid distribution of material within the disk, and which may be the observational signature of these regions.

    Third, I will discuss observational constraints obtained from recent ALMA and VLA observations that resolve the structure of disks with dust-depleted cavities, in both gas and solid components. This program aims to test theoretical predictions for disk structure during the epoch of planet formation: the expected radial segregation by particle size and the expected difference in cavity size as traced by dust and gas emission.

    Finally, I will conclude with new avenues of observational work aimed at directly witnessing the hallmarks of planet formation, particularly with ALMA and next-generation facilities.


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    © ASTRON

    The ASTERICS project held its second General Assembly in Amsterdam recently. The project is making good progress with all deliverables submitted on time, and with some developments even ahead of schedule. One point of concern is that in some projects staff recruitment is lagging behind a bit (a common problem with new European projects) but hopefully we can redress this issue in the coming 6 months. The ASTERICS External Advisory Board (AEAB) also attended the GA, and were able to provide some useful feedback on how they see the project from an independent perspective. In short, the project is in good shape for the next major milestone - the 18 month project review at the end of the year.

    ASTERICS brings together the large ESFRI astronomy and astro-particle physics facilities for the first time in a single EC project. It was therefore very appropriate that the meeting concluded with the live streaming of the NSF announcement of the discovery of gravitational waves. The elegancy of this profound result made a deep impression on all the participants. This followed on from the detection of neutrinos from a AGN (blazar) published on astro-ph earlier in the week, not to mention the growing expectation that fundamental progress is about to be announced on our understanding of the transient radio sky, and the nature of Fast Radio Bursts.

    All-in-all, one can safely say that the era of multi-wavelength/multi-messenger astronomy has truly begun, making ASTERICS a very timely initiative indeed!

    For more information on ASTERICS, see: https://www.asterics2020.eu


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  • 02/21/16--16:00: Proper SKA footwear
  • © ASTRON

    After a successful LFAA AAVS1 DDR, we were eager to surprise the international panel with a unique present.

    Therfore, we're happy to present the first edition of proper SKA footwear!

    Looking forward to another year of fruitful SKA developments, enjoying these Dutch power-shoes.


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  • 02/22/16--16:00: LOFAR Science Highlights
  • © ASTRON

    With the LOFAR telescope now into its fifth cycle of regular operations and examples of the amazing science being done with it becoming more numerous in the published literature, it is time that these achievements were celebrated more publicly on ASTRON's website.

    Examples of these achievements have now been gathered together in a single "LOFAR Science Highlights" page which can be found on the ASTRON website at:

    http://www.astron.nl/general/lofar/lofar-science-highlights/lofar-science-highlights

    All the images can be downloaded for use in presentations (with the appropriate image credits of course!). The page also links to a separate item where general presentations about LOFAR and selected science highlights can also be found.

    This page is not meant to be exhaustive, but we hope to keep it up-to-date as more results are published. Anyone with a result that they would like to see highlighted on this page is of course very welcome to email an appropriate image and brief explanatory caption to sciencesupport@astron.nl.


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  • 02/23/16--16:00: Ghost hunting
  • © ASTRON / Rhodes University

    In radio astronomy, ghosts are not just a figment of our imagination. Although their nature has eluded us for a long time after their first spotting in a WSRT 92-cm observation by Ger de Bruyn, ghosts were explained as the result of missing sources in the sky model used for self-calibration by simulations developed at Rhodes University and SKA South Africa (see the AJDI of 28 february 2014). Those simulations were tailored to arrays with a regular East-West layout, such as the WSRT. This obviously makes one wonder whether ghosts can also emerge when we use irregular array layouts, such as the layout of LOFAR and those envisaged for the SKA and, if they do, how we can detect them without confusing them with real emission.

    In a recently published paper, we extended the geometrical description underlying the simulations to arbitrary array layouts and introduced a perturbation analysis treating the self-calibration error as a perturbation on the true gain values. The extension of the geometrical description permitted us to apply our simulations to the KAT-7 array, which has an irregular array configuration. As in the case of the WSRT, we found that each baseline produces its own ghost pattern, but that this pattern can be complex valued. An example is shown in the top panels of today's image. In this example, a 1-Jy modelled source was placed in the phase center while a 0.2-Jy unmodelled source was located at (1, 0). Since a single baseline already produces a seemingly complicated structure, finding an intuitive explanation felt like a daunting task.

    Fortunately, we were able to predict the location as well as the baseline causing a specific ghost by introducing the perturbation analysis. The results are shown in the bottom left panel. They reveal that ghosts form in two distinct types of symmetrically opposite pairs. Intuitively, one would already expect the ghost associated with baseline (r,s) to form a pair with the ghost associated with baseline (s,r). These ghost pairs, which are symmetrically opposite around the phase center, can indeed be found. However, it turns out that for the ghost pattern of baseline (p,q) the baselines (p,s) and (r,q) also form ghost pairs, which are symmetrically opposite around the mid-point of the line connecting the modelled and the unmodelled source. These ghosts can be considered to be associated with phase closure errors introduced by the incomplete sky model.

    In our perturbation analysis, we also found that the fluxes of some ghosts scale inversely proportional to the number of elements in the array, while the fluxes of others scale inversely proportional to square of the number of elements in the array. We refer to the first category as proto-ghosts and to the second as deutero-ghosts. Proto-ghosts are typically brighter than deutero-ghosts. The bottom righ plot shows which ghosts fall into which category.

    Armed with these new insights, we will continue our hunt for ghosts, so watch this space!


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    © Katherine Alatalo (The Carnegie Observatories)

    Modern day galaxies are found to be in a bimodal distribution, both in terms of their morphologies, and in terms of their colors, and these properties are inter-related. In color space, there is a genuine dearth of intermediate colored galaxies, which has been taken to mean that the transition a galaxy undergoes to transform must be rapid. Given that this transformation is largely one-way (at z=0), identifying all initial conditions that catalyze it becomes essential.

    I will discuss a new way we have identified to find such transitioning galaxies (through the Shocked POststarburst Galaxy Survey), which is able to pinpoint transitioning galaxies at an earlier stage of transition than other traditional searches. I will also discuss the case study of AGN-driven molecular outflow NGC1266, and new findings about the feedback between the interstellar medium in transforming galaxies and their transformations, in particular, the presence of star formation suppression being discovered taking place in the molecular gas reservoirs of these sources.

    Between identifying new transforming galaxies, and providing new insights into the internal processes within transforming galaxies, a new window has been opened into this nearly one-way process.


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    © Image credit D. Kaplan (UWM), E. F. Keane (SKAO)

    A real-time fast radio burst discovered at the Parkes telescope has led to the first identification of a host galaxy and redshift for these mysterious sources. Fast radio bursts (FRBs) are bright, millisecond radio pulses of unknown origin believed to come from outside our Galaxy. The large uncertainty in the sky position of all previously published FRBs makes pinpointing a host galaxy difficult, so no burst to-date has an accurate redshift measurement.

    FRB 150418 was detected less than 10 seconds after it occurred by the SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB). Follow-up with the Australia Telescope Compact Array identified a fading radio transient lasting ~6 days in the field of the burst. From the precise location of the fading source a host galaxy was found with redshift z = 0.492 ± 0.008. The fading afterglow suggests a cataclysmic origin for FRB 150418 and the timescale of the radio transient is roughly consistent with the radio afterglow of a short gamma-ray burst.

    The image shows an optical image of the field with the full-width half-maximum of the 13 Parkes beams superimposed as white circles. Insets show subsequent zooms of the field and the highly dispersed pulse of the burst arriving at a range of frequencies across the Parkes bandwidth over ~1 second.

    The results are published in Nature this week.


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