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

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  • 07/30/18--17:00: Summer break
  • © ASTRON

    The daily image is on a summer break. We will be back on 20 August. Don't forget to keep submitting images. We wish you all a great summer!

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    © Daysi Quinatoa

    In this project we used the EVN to investigate the magnetic fields in massive protostars to understand the role of B-fields in the launching of outflows. By measuring the Zeeman splitting effect we could detect the magnetic field in massive star-forming region G47.45+0.05. The field strength was -3.88 mG which is consistent with similar measurements made previously with the VLA. This suggests that the B-field does not suffer from feature blending at the VLA scale, i.e. the B-field properties do not change significantly between VLA and VLBI scales.

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    © ASTRON

    With the summer holidays underway and the current record breaking heat wave keeping us immobilized in front of our fans it may seem like all activity has halted. But we are still here! This one minute animation shows some of the 'frontend' features for the upcoming ALTA release.

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  • 08/02/18--17:00: ASTRON in Noord-Brabant?
  • © Koninklijke Bibliotheek (Delpher), ProfielActueel

    In the beginning of the 1950's the board of the Netherlands Foundation for Radio Astronomy (NFRA, the forerunner of ASTRON) was looking for a site for its planned 25 meter radio telescope. The first radio observatory of the NFRA was established at the site of Radio Kootwijk near Apeldoorn where a Würzburg-Riese radar dish was used for the first observations (see also this daily image). Using this dish the first radio map of the Milky Way was made. The diameter of the Würzburg-Riese dish was 7.5 meter. To make more detailed observations with increased sensitivity, the NFRA had plans to build a large radio telescope with a diameter of 25 meter.

    The search for a place to build the radio telescope was not easy. It should be far away from existing and planned highways, industrial areas and other possible sources of interference. One of the possible places was a site south of Eindhoven in the province of Noord-Brabant. The possible site in Noord-Brabant was mentioned in the booklet "Kootwijk hoort de Zon" (Kootwijk hears the sun) published in 1952. This booklet is part of the AO-series. In this series two other booklets about radio astronomy were published. The first one is "Radiostralen uit de sterrenwereld" (Radio rays from the world of stars) written by J. J. Raimond (the father of former ASTRON collegue Ernst Raimond) in 1946. The other one is "Hier... Radio-Melkweg!" (Here... Radio-Milky Way) published in 1956 just before the opening of the Dwingeloo radio telescope (see also this daily image).

    Another mention of the possible site in Noord-Brabant was made by the newspaper Algemeen Dagblad on the 27th of March 1953. In that article the radio observatory was caled a Mily Way monitoring station ("Melkweg-luisterpost"). Later in 1953 Dwingeloo was chosen as the definite site for the new radio telescope.

    One can speculate what the consequences would be if ASTRON was situated near the region of Eindhoven with a lot of high tech companies. At least it would mean less travelling for the current chairman of CAMRAS.

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    © Henk Mulder

    It is a well known fact that the Observers are the coolest people in the Astron building. But as you can see Jurjen Sluman took it to a whole new level, after all these years finally figuring out what those strange looking circular things in the floor are for.

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    © Amy Tuson

    Conventionally, pulsars have been discovered in blind, all-sky pulsation surveys. An alternative approach is to use radio continuum surveys in which pulsars show up as point sources. This proof of concept study has defined a set of selection criteria which can be used to discover new pulsars in the LOFAR Two-metre Sky Survey (LoTSS).

    LoTSS is an ongoing, deep, interferometric imaging survey of the Northern sky at a central frequency of 144 MHz. The survey resolution of 5" and sensitivity of 100uJy per beam will make it the deepest radio survey to date. Due to the fact pulsars are steep spectrum radio sources, with a mean spectral index of approximately -1.4+-1.0 for the known pulsar distribution, we have the unique opportunity to find pulsars missed by standard all-sky pulsation surveys. The figure above shows imaging and pulsation survey sensitivity limits and the typical range of pulsar spectral indices.

    Working with the LoTSS catalog of 320,000 sources, three pulsar properties can make it possible to distinguish them from other radio sources. Firstly, pulsar radio emission has a relatively high fraction of polarised flux. By searching through the preliminary catalog of 91 polarised LoTSS sources, no convincing pulsar candidates were found. Secondly is that pulsars have steep radio spectra. By computing spectral indices for LoTSS sources cross-matched to existing radio catalogs, such as WENSS, FIRST and NVSS, we found five pulsar candidates with spectral indices less than -1.5. Finally, scintillation causes variation of pulsar intensity as a function of both time and frequency. LoTSS sources were matched to sources in the TGSS catalog and we looked for those which showed a variation in total flux density. One source was measured as 6.9 times brighter in TGSS than LoTSS and this is a possible scintillating pulsar.

    We have been granted time with LOFAR to follow-up the six sources of interest and the search for pulsations started last week.

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    © David McKenna

    Interplanetary scintillation is a phenomenon seen when a compact radio source is observed close to the Sun and manifests itself as variations of intensity on short time scales caused by density variations in the solar wind. The outflow of different solar wind streams with different densities and powerful events such as Coronal Mass Ejections (CMEs) cause variation in the strength of the scintillation, thus leading to measurements of this parameter being a valuable tool to probe the solar wind and observe CMEs in the interplanetary medium. However, extraction of a "scintillation index" as a measure of the strength of the scintillation with a phased array system such as LOFAR is not as straightforward as from using a traditional dish system.

    In this project we took observations of 3C48 and 3C147 with simultaneous interferometric imaging using the Dutch array (at sub 10th of a second, a first for LOFAR), tied-array beams using the full core, with a ring of off-source reference beams, and "fly's eye" observations using the international stations on various dates during the spring. The imaging data were initially processed using the method outlined by Morgan et al. (2017) for extracting scintillation indices with the MWA wide-field images, and used as a reference baseline to compare approaches for implementing similar methodologies to extract scintillation indices from the beam-formed data sets. Both data sets were then used to implement a power spectrum method introduced by Manoharan (1993), where the area under the spectrum is used to assess the amount of scintillation, a method typically applied to single station time series data but now also applicable to the fast imaging we undertook with LOFAR. We obtained consistent results between the imaging and beam-formed data, demonstrating both that reliable scintillation indices can be calculated from LOFAR data, and that the faster processing and less data-intensive beam-formed data are sufficient for this. The technique was applied also to 3C147 LOFAR data from September 2017 to identify and observe the passage of the fastest CME of the current solar cycle!

    The video is a WSClean image cube from an observation of 3C48 on the 18th of April, at a sampling rate of 12.04Hz and an excessively-detailed pixel resolution, showing the source scintillating due to the solar wind.

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  • 08/08/18--17:00: Summer Saturn
  • © Rik ter Horst

    Even at just 13 degrees above the southern horizon, Saturn remains mysteriously beautiful. The image below was taken under fine conditions with my 40 cm F / 12.8 telescope from my backyard in Zuidwolde, Groningen. Objects that are low in the sky suffer from atmospheric dispersion (caused by refraction of light through the Earth's atmosphere) and the use of an ADC (atmospheric dispersion corrector) is an absolute necessity for high resolution images of low standing planets. The 40 cm telescope is permanently equipped with an adjustable ADC to eliminate dispersion at all heights, even up to a height of 6 degrees above the horizon.

    This image is the result of 'Lucky Imaging' and is a Multi-stack of 5%, 15% and 30% of the best frames out of a 20000 frame AVI. While processing, I tried to avoid artefacts in order to keep the result as realistic as possible. The used camera was an ASI178MC (color).

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  • 08/09/18--17:00: Waiting for Wetter Times
  • © Madroon Community Consultants (MCC)

    A short walk from the observatory is a pond in the shape of a doughnut. In winter we cavort on the black ice at lunchtimes, as soon as it appears to be thick enough. We also put gentle pressure on our hapless foreign colleagues to grab this rare opportunity for an uniquely Dutchexperience.

    Now, during this very boring heat-wave, most of the nearby lakes and ponds on the Dwingelderveld are parched, cracked and dry. But our skating pond is still as full of water as ever, begging the question how deep it actually is.

    While you are pondering the secrets of this pond, you may click on the links and enjoy the refreshing sight of snow and ice. Lovely winter will be upon us before you know, and we might just be favoured with some passable ice.

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    © ASTRON

    Last week, the renowned Space Studies Programme (SSP) from the International Space University visited ASTRON/JIVE/NOVA in Dwingeloo. During the visit, participants learned about the institutes, got tours through the facilities, learned about telescope engineering, the James Webb Telescope, space VLBI and Space Weather, and visited the Low Frequency Array (LOFAR).

    The SSP is a nine-week graduate top-level professional development program conducted by the International Space University (ISU). The curriculum covers the principal space related fields, both non-technical and technical and ranges from policy and law, business and management and humanities to life sciences, engineering, physical sciences and space applications. SSP participants are high potential scientists and engineers in the field of space in their early career from 35 different countries.

    This year, the SSP takes place from 25 June to 24 August in the Netherlands, hosted by the Netherlands Space Office (NSO), in close collaboration with Delft University of Technology, Leiden University and the European Space Research and Technology Centre (ESA-ESTEC) in Noordwijk. The program is packed with a wide variety of activities including lectures by renowned experts, hands-on activities and projects, team work assignments, and professional visits to industry and academia. ASTRON, JIVE and NOVA are sponsors of the SSP and collectively organized a visit to Dwingeloo on July 30th and August 5th.

    Because of the summer holidays it has been quite a challenge for the SSP Local Organising Committee to set up such a program, but when leaving Dwingeloo/Exloo the SSP visitors said that they were very grateful for the interesting program.

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  • 08/13/18--17:00: Total Lunar Eclipse 2018
  • © Zsolt Paragi

    Crowds gathered near the Dwingeloo telescope to watch the longest total lunar eclipse of the century, on 27-28 July 2018. What better place than the fields (Heide) near ASTRON/JIVE. The skies were clear, the views were spectacular. Soon following the sunset four bright planets were visible: Venus, Jupiter, Saturn and a bit later Mars was rising on the Eastern horizon. Mars itself appeared very bright as it reached opposition that very night (was not this bright since 2003). As it was getting darker, the already fully eclipsed, reddish/grey Moon was becoming visible above Mars. Together with the summer students we joined the big group of villagers and tourists to admire this spectacle.

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  • 08/14/18--17:00: A Summer Nebula
  • ©

    Nights are short during the summer months, so the big bright nebulae in and near the plane of the Milky Way are prime targets.

    This image of planetary nebula Messier 27 (aka the Dumbbell Nebula) is a simple RGB combination of four, 600s integrations for each filter with a 40cm telescope.

    11 years ago I made an image of this nebula with a much smaller telescope.

    The colour rendition of the new version is a bit more accurate and it shows a lot more detail.

    The full size image can be viewed here:

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  • 08/15/18--17:00: Today's Colloquium
  • © Sergei Gulyaev

    Starry night in New Zealand. The 30m (left) and 12m (middle) radio telescopes of the Warkworth Radio Astronomical Observatory. Photo by Mike MacKinven.

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  • 08/16/18--17:00: A Dutch Summer
  • © Cees Bassa, Joe Callingham, Gemma Janssen, David McKenna, Golam Shaifullah, Amy Tuson & Pietro Zucca

    As our summer in Dwingeloo comes to an end, we'd like to thank everybody at ASTRON and JIVE for making our stay so memorable.

    A special thanks goes to our supervisors - Cees Bassa, Ross Burns, Richard Fallows, Katharina Immer, Yogesh Maan, Zsolt Paragi, Tim Shimwell and Pietro Zucca - and everybody else who has helped us along the way. Your encouragement and support have been invaluable. We'd also like to mention Gemma Janssen and Golam Shaifullah, among many others, for making our summer so much fun! The collage above shows just some of the many things we have been up to. Starting from top left and moving across...

    - We visited the ESA's European Space Research and Technology Centre for a tour and a selection of interesting lectures. The capsule we are stood with has been in orbit around the Earth!

    - The Oogstdag is a traditional farming festival held in Lhee and, as we quickly found out, there is lots of tasty food.

    - We 'walked' to an island through mud at low tide. Needless to say, our shoes will never look the same again.

    - Some of us visited Cologne, Germany for a weekend. We climbed to the top of the cathedral in the background and the view was incredible!

    - We experienced an unconventional Dutch summer of continuous sunshine, so we were lucky enough to see many beautiful sunsets across Dwingelderveld National Park.

    - A boat trip around Giethoorn in "the world's slowest boat" (Pietro Zucca, 2018).

    - ASTRON students sat on the base of the Dwingeloo Radio Telescope.

    - The many clear nights during our stay made for some excellent stargazing. Mars is above the two silhouettes.

    - We were taken to explore the Westerbork Synthesis Radio Telescope and LOFAR Superterp.

    - Cycled to the Hunebedden near Havelte; despite the fact this looks like a child's playground, it is a Neolithic burial chamber!

    - Some of us visited Brussels, Belgium for a weekend, enjoying foreign delicacies known as 'fries' and 'waffles'.

    - We placed our flags on the summer student world map.

    Dank u wel en tot ziens!

    Amy, Iuliana, David, Anshu, Daysi and Alexander

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    © Henk Mulder

    As the Apertif system keeps getting more spectacular and goes through its software releases so does the Westerbork monitoring.

    Since around September Henk Mulder and Arthur Coolen have been working hard on designing, building, coding and testing our new Monitoring System for monitoring all of Westerbork. The All-Round Telescope Array Monitoring and Information System (ARTAMIS) monitors all the WSRT systems (Dish control, Weather Sensors, Radio Astron, Galileo, (e)VLBI, ARTS, Apertif..) giving us the capability to see everything we need in one monitoring system. Load data points in graphs, look back in time to spot anomalies, find failing fans, firmware problems, failing dishes.. you name it.

    We have recently had our first feedback session were we ask for input from the people building the hardware, enthusiastic astronomers, software engineers, field engineers and other future users to see what needs to be monitored, what can be monitored and who needs what data points to be displayed in what way. And of course show everyone what fancy features we are working on for the future. We also sent out our first WinCC OA newsletter which shows some of the new features we just released, where to find them, and how they can improve your day to day work straight away (its been a productive few months).

    The monitoring is developed and designed in-house and is being updated constantly. Like LOFAR has the Navigator thats become a piece of monitoring software that is invaluable for making sure we get the best out of our systems and get alerted to critical system problems before they happen. The Westerbork monitoring system has already given us new insights on how the Apertif hardware is performing and what needs extra attention. Building a SCADA system from scratch has also been a great way for us to really see what is now possible with WinCC OA, and this will also give us a head start for future projects like LOFAR 2.0.

    So to the developers, users and WinCC OA friends many thanks, and continue giving us your feedback, only then you will get the product that is able to make your day to day life easier.

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    © Iuliana Nitu

    An ongoing question in pulsar emission is whether pulsars have some intrinsic 'off-pulse' emission, outside their main pulse region. While any such off-pulse emission would be too faint to detect directly, the ISM can help by acting as a lens. In the right conditions, the signal from a pulsar could show scintillation, or intensity fluctuations, due to the irregularities in the ISM as it propagates through. If the pulsar's magnetosphere is not resolved, and thus the pulsar looks like a point source, the off-pulse emission should show correlated intensity variations to the ones of the main-pulse.

    On the basis of this, we used a new technique ( Ravi and Deshpande 2018 ) to estimate off-pulse emission from pulsars.

    A major part of this project was the implementation of this technique in Python. Then, we analysed various observations. The image here shows the main plots of the analysis of PSR J1713+0747 data taken with the Green Bank Telescope, as part of the 24-hour campaign (with thanks to Joeri van Leeuwen and Timothy Dolch for providing these data). On the right, the dynamic spectrum of the main pulse region shows bright regions (or scintles) due to interstellar scintillation. On the top-left, the 2D auto-correlation of the main pulse dynamic spectrum is shown, with the corresponding 1D cuts at zero frequency and time lag respectively. The widths of the Gaussian distributions are representative of the dimensions of the scintles. On the bottom-left, the cross-correlation between the main pulse and the off-pulse dynamic spectra is shown, with the corresponding cuts. Our analysis places a limit on the off-pulse emission as (0.0 +/- 0.4)% of the main pulse emission.

    We hope that in the near future, the software developed this summer will lead to a systematic search of off-pulse emission in many pulsars, and eventually help improve our understanding of pulsar emission.

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    © Alexander Plavin

    Fast Radio Bursts is a phenomenon that produces brief (few millisecond duration) dispersed signals of unknown origin. Of the two dozens or so FRB pulses detected to date, only one of them showed repeated bursts, FRB121102. This allowed interferometric follow-up observations with the VLA and the European VLBI Network (EVN) and finally precise localization in the sky, for the first time for any FRB. The source is located in the outskirts of a dwarf galaxy at a redshift of z=0.193 (Chatterjee et al. 2017, Tendulkar et al. 2017, Marcote et al. 2017). There is an associated faint, persistent radio source at the location within the positional errors of the FRB pulses. This persistent radio source is either a very peculiar, magnetar-powered nebula (with an unusually high radio power), or it is related to a low-luminosity AGN off-center in the dwarf galaxy.

    The main goal of this summer project was to process the three epochs of EVN data at two frequencies to establish the properties of the persistent radio source. We studied its variability and found that the flux density is constant at the 10% level. The location is very stable as well at the level of 0.1 mas. The position does not depend on observing frequency, and we obtain the most accurate localization to date. We get an upper limit of 25% on fractional polarization for the persistent source at 5 GHz, which is much lower than for individual burst, that are almost 100% polarized at the same frequency. This proves beyond doubt that the persistent radio emission is not due to a large number of very weak repeating pulses.

    In addition the project included the study of the brightest pulse detected for this source at 1.6 GHz. We got preliminary results on its polarization, which is less than 30% in contrast to highly polarized C-band pulses. The detected rotation measure is the highest ever reported for this source.

    The image above shows the following (left to right, top to bottom):

    - Comparison of localization accuracy achieved in this project in comparison to previous observations.

    - The strongest pulse profile at 1.6 GHz.

    - EVN image of the persistent source.

    - Mindmap of this project including properties we studied and instruments used.

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    © (c) Erwin de Blok

    M81 and M82 are two well-known galaxies in the northern sky, and together with NGC 3077 form the M81 triplet. They have been been extensively observed in the radio, and observations of their neutral hydrogen (HI) distribution, done with the VLA in the early '90s, have become the poster child for showing the importance of interactions between galaxies.

    Those old observations were made some 25 years ago, and cover only a small part of the volume of the triplet. In fact, recent single-dish observations show that there is twice as much HI present in the group than previously observed with the VLA.

    We therefore decided to revisit this group, again using the VLA whose capabilities have improved enormously over the past decades. We covered a 3 x 3 degree area surrounding M81 with 105 pointings, increasing the survey area by almost a factor of ten. These new observations also increased the spatial and velocity resolution significantly, so that these new observations can now resolve individual HI clouds around these galaxies.

    The left-hand image shows our new high-resolution HI mosaic in blue, superimposed on a Sloan Digital Sky Survey colour image. M81 is in the center, M82 toward the top, NGC 3077 is visible on the left, and dwarf galaxy NGC 2976 at the bottom-right. The spiral arms in M81 are clearly visible, as is the chaotic HI distribution around M82, and the offset HI near NGC 3077. Throughout the field, bright and faint HI streams and filaments are visible, connecting these galaxies. The right-hand image shows only the HI distribution. Here the complexity of the HI filaments and clouds is clearly visible.

    These observations are described in a paper recently accepted for the Astronomical Journal by de Blok et al., also available at .

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    © RTL Nieuws/Frank Nuijens

    "On Saturday 11 August the Parker Solar Probe will be launched by NASA. Will the employees at ASTRON watch the launch on a big screen, cheering it on?"

    The Communications team gets the most diverse questions. This particular one came from a journalist of RTL Nieuws, the national news broadcast. My answer was: "Probably not, but let me check and get back to you."

    As it turns out, Richard Fallows has observing time on LOFAR to co-observe the solar activity as the Solar Probe orbits the Sun. RTL Nieuws thought this was an interesting alternative to a launch-watching party and interviewed Richard.

    The news broadcast was watched by almost 750,000 people and can be viewed on (from 12:58).

    Unfortunately the reporter didn't have the time to include Richard's quotes on his work with LOFAR in the report. As Richard is on holiday, I asked Pietro Zucca to explain what LOFAR will do:

    The combination of in-situ spacecraft measurements and ground-based remote-sensing observations of coronal and heliospheric plasma parameters is extremely useful for space-weather studies. Ground-based observations can be used to infer a global picture of the inner heliosphere, providing the essential context into which in-situ measurements from spacecraft can be placed. Conversely, remote-sensing observations usually contain information from extended lines of sight, with some deconvolution and modelling necessary to build up a three-dimensional (3-D) picture. Precise spacecraft measurements, when calibrated, can provide ground truth to constrain these models.

    Up until now, spacecraft have rarely travelled very close to the Sun. The launch over the next couple of years of two dedicated solar missions represents the first opportunity in 40 years to directly combine remote-sensing observations of the solar corona and inner heliosphere with in-situ measurements close-in to the Sun. The Parker Solar Probe (PSP) launched this August 2018, with Solar Orbiter currently scheduled not earlier than February 2020.

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    © ASTRON

    Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere emitting radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) reaching speeds higher than the local magneto-sonic speed. Radio imaging of decameter wavelengths (20-90 MHz) allow us to study coronal shocks which leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs.

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