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Collaboration tools in the LOFAR2.0 Station Team

March 29, 2020, 5:00 pm
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© ASTRON

The LOFAR2.0 Station project is a complex project with several work packages and people spread over the AG, R&D and RO divisions of ASTRON. Work packages such as System Engineering, RCU2, Cabinet and Clock and Station Control are executed by colleagues with varying technical skills and with different ways of working. Our software developers prefer an Agile/Scrum method, whereas hardware engineers prefer waterfall approaches. Despite these different approaches, the project as a whole has to be able to keep track of overall progress and planning. Within each of the work packages, the work must be planned, organized and prioritized in three-week increments. To help streamline all those processes, we use JIRA and Confluence.

JIRA is an advanced and widely used issue tracking tool that enables us to prepare, plan and track all the work that must be done. Confluence is a collaboration tool to share information, documents, drawings, decisions, meeting notes, etc. JIRA enables a highly structured overview of all coming and running activities in complex projects. Confluence enables co-working and sharing of information in a way that is superior to a shared disk or a cloud storage solution. Confluence and JIRA, being from the same company, are well integrated with each other and together allow simple linking between issues, meeting action points, discussions from meetings, documents, task lists, planning, etc.

We have provided JIRA and Confluence training sessions to get up to speed and many engineers are now actively involved. JIRA and Confluence support the LOFAR2.0 Station project management and workpackage management, planning, and project execution quality. They can benefit many other project in ASTRON as well. Feel free to contact Arno Schoenmakers or Rene Kaptijn if you would like to learn more.

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End of EMBRACE

March 30, 2020, 5:00 pm
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© JP

With a little sadness are we taking this test antenna apart. At the start in 2008, we thought that we would need this "proof of principle" for only one, maximum two years of operation.

Now the third Midden-Drenthe temporary building permit will expire end this year, and with no longer active users for this system, the decision is made to remove the antennas, radome and Faraday cage. On the photo is Peter Gruppen, separating the different types of materials, to enable an environmently friendly disposal.

The Westerbork Electronic Multi Beam Radio Astronomy Concept, EMBRACE, was a prototype of the aperture array concept, built in 2008. See also the daily image of 23-05-2008. In Nancay (Fr.) is a second EMBRACE antenna, but also no longer in operation.

EMBRACE had a frequency range of 500-1500 MHz, with single polarisation. The 17x17m radome is made of 19cm expanded polystyreen. The 20x22m platform is made of 118 2x2m concrete tiles.

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LOFAR maintenance @ safe distance

March 31, 2020, 5:00 pm
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© L.vd Bult/D.Schrama

In these strange times of working from home LOFAR maintenace goes on! In the field it's not so hard to keep safe distance.

With our new collegues Denis Schrama and Derkjan Pepping in the field,supported by Lute frome home, LOFAR observations will not be beaten by Corona.

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Virtual ASTRON office with virtual LOFAR room

April 1, 2020, 5:00 pm
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© ASTRON

Instead of the LOFAR room and ASTRON building we are trying a virtual office called Sococo. In this virtual office we work, have social chats, and run our daily Station team standup meetings. To some extend it is similar to using Slack. The difference is that during the day we keep our virtual headset icon in Sococo open, so that we can hear it if somebody speaks in the room. This is especially nice for shared coffee breaks and ad hoc collaboration. It is also possible to meet and greet in another room or to remain quite, almost just like in the real world.
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Luis Henry Quiroga-Nuñez defended his thesis in style

April 2, 2020, 5:00 pm
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© photo credit to Andres Perez

He came to Dwingeloo from Colombia for the first time in 2012 as a JIVE summer student and on March 12 2020, Luis Henry Quiroga-Nuñez successfully defended his PhD thesis in Leiden. The title of the thesis was “Stellar Radio Beacons for Galactic Astrometry”. Under this title featured contributions to both the BeSSeL and BAaDE projects, as well as a chapter on radio flare stars. For all subjects, Luis pioneered combining the radio results with Gaia astrometry. In fact, his work stands out because he used many different techniques and data from many different wavelength regimes and different telescopes. All with a clear link to VLBI astrometry.

The ceremony became somewhat special with early Corona measures taking effect and two committee members joining by video. The committee examined the thesis and took note of the compelling answers by the candidate. Then our Luis received the doctorate. In the ‘laudatio’ the breadth of the thesis was praised, which is also a credit to the many collaborators working on these projects, from JIVE, ASTRON, Leiden and indeed around the world. It was also noted that, besides his doctorate, Luis had achieved some exceptional goals in exceptional circumstances during his time in the Netherlands; with his family now being Dutch, he started a prestiguous Jansky fellowship in New Mexico.

After a few elbow shakes and a somewhat socially-distanced party, Luis and family made it back to Albuquerque just before travel came to a halt.

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Lunar craters

April 5, 2020, 5:00 pm
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© Rik ter Horst

It has been a while since I had the chance to use my telescope. The night of March 31 promised to be a good one, so I took my 250 mm Schmidt-Cassegrain telescope outside. With the moon high in the sky, it was an excellent opportunity for an imaging session of the moon.

This image shows some interesting areas of the moon; some parts are smooth, almost without craters or mountains while other areas are dotted with craters and mountains. Especially the image at the right, showing the area around crater Albategnius. Interesting to see are the long shadows on its craterfloor.

Telescope: homebuilt 250 mm F/15 Schmidt Cassegrain. Camera: ASI120MM, with red filter to reduce the effects of the seeing.

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ERC Advanced Grant for Erwin de Blok

April 6, 2020, 5:00 pm
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© credit: South African Radio Astronomical Observatory

Prof. Dr. Erwin de Blok from the Astronomy Group has been awarded a 2.5 MEuro European Research Council (ERC) Advanced Grant for his "MeerGas" project. The aim of this research project is to use the SKA precursor telescope MeerKAT in South Africa to make extremely deep observations of the neutral hydrogen in 30 nearby galaxies.

Neutral hydrogen is the gas from which the stars are formed in galaxies. Most galaxies, however, contain only enough gas to form stars for just a fraction of their life. This means they have to get gas from somewhere else. Computer simulations suggest that this gas is located in the space between the galaxies and is slowly captured by the galaxies. The radio emission from this gas is very faint and has therefore never been unambiguously observed.

MeerGas will also use and develop new techniques with which the large data volumes that MeerKAT will produce can be efficiently analysed. The research program will help prepare for the even larger amount of data that the SKA will produce.

The ERC Advanced Grant is awarded on the basis of both the applicant's scientific excellence and the research proposal and is the largest personal grant that the ERC awards.

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The timing stability of three Black Widow pulsars

April 7, 2020, 5:00 pm
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© Ann-Sofie Bak Nielsen, Gemma Janssen, Golam Shaifullah, Cees Bassa

Black widow pulsars are binary systems where the high energy emission from the millisecond pulsar is ablating the surface of their low-mass binary companion. The resulting matter, lost in the form of a wind, is usually observed to block or 'eclipse' the radio signal of the pulsar when the companion passes closest to the line-of-sight with the pulsar. Due to the ablation, the binary companions are bloated, which leads to tidally induced changes in the orbital period of the binary.

A European and global effort to use high precision pulsar timing of an ensemble of radio millisecond pulsars is ongoing, aimed at detecting gravitational waves from supermassive binary black holes. The sensitivity to detecting these waves depends crucially on the number of pulsars that can be timed to high precision. Including more pulsars will improve the detection sensitivity.

In a new publication, we used pulsar timing observations of the European Pulsar Timing Array, which includes data from the Effelsberg, Lovell, Nancay and Westerbork Synthesis Radio Telescope, to investigate the timing stability of three black widow pulsars. By using 7 to 8 years of pulsar timing observations (see lefthand panels), we found that none showed radio eclipses, which, if present, would lead to increased timing residuals near orbital phase 0.25 (see righthand panels). We also find that only one of the pulsar, J0023+0923, shows significant orbital variations, indicating tidal locking. As these variations are, so far, well described by higher order derivatives of the orbital period, the pulsar timing of all three pulsars is considered precise enough to be included in the pulsar timing programme of the European Pulsar Timing Array.

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Venus passes the Pleiades above Dwingeloo

April 8, 2020, 5:00 pm
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© CC-BY-4.0 Tammo Jan Dijkema

Like every 8 years, Venus passed the Pleiades on the evening of April 3rd. I went to the Dwingelderveld (keeping 1.5 km distance) to take a photo with the Dwingeloo telescope in the foreground.
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Unknown unknowns: MeerKAT discovers strange filaments connecting the radio lobes of ESO 137-006

April 14, 2020, 5:00 pm
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© published in A&A. Ramatsoku et al, 2020

When dealing with data from a new telescope, one routinely expects surprises of the technical variety. But sometimes the Universe itself throws a curveball, just to remind us who’s in charge.

Found near the centre of the Great Attractor, in the Norma galaxy cluster, ESO 137-006 is one of the brightest radio galaxies in the southern hemisphere. ESO 137-006 was *not* the scientific target of this observation. We were ready for it to show up as an annoyingly bright source, with nothing particularly interesting about it apart from the usual trouble of subtracting such a source accurately.

The very first continuum maps immediately showed that we were dealing with something far more curious. The MeerKAT L-band map shown above, recently published in A&A https://www.aanda.org/articles/aa/abs/2020/04/aa37800-20/aa37800-20.html demonstrates some very unusual collimated synchrotron threads (CST) apparently connecting the radio emission lobes of the galaxy.

The finding is, at present, rather bewildering. It is very difficult to explain why and when and how these threads could have formed, or why they are so collimated and uniform. They could be magnetically connected with particles flowing into these magnetic channels. Whatever their origin, this brings up some questions such as: how common are these features in radio galaxies? Are they specific to the case of ESO 137-006 and its environment? Or, on the contrary, are these threads common in radio galaxies, but have so far not been detected because of sensitivity and resolution limits? Or is the Universe simply playing a cosmic joke on us, and the threads are a completely unrelated feature elsewhere in the cluster, which just happens to project onto ESO 137-006 so neatly?

Whatever the astrophysical causes, this image highlights MeerKAT’s exquisite sensitivity to extended low surface brightness emission. Perhaps we should start expecting such surprises more routinely.

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Queen Juliana on the Dwingeloo Radio Telescope

April 16, 2020, 5:00 pm
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© CC0, foto: Joop van Bilsen, Nationaal Archief / Anefo

Today exactly 64 years ago, on 17 April 1956, Queen Juliana opened the Dwingeloo telescope, guided by Professor Oort. The image shows Her Majesty and Prof Oort on the balcony of the telescope.
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LOFAR4SW reach an important milestone

April 19, 2020, 5:00 pm
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© C. Baldovin

The project LOFAR4SW (funded by the EC program H2020) will deliver a fully documented design to enable LOFAR to be used as a space weather instrument, in parallel to radio astronomy observations. In 2019, the project went through two main reviews: the Preliminary Design Review in Cardiff (January), and the mid-term review in Brussels (September).

Recently (March 30 and 31) LOFAR4SW achieved another important milestone: the Detailed Design Review (DDR), originally planned to be a face to face meeting at ASTRON. However, when the strict corona measurements were announced, the meeting was changed into a videoconference.

The big question was if such a review could work in this format. Happily, the answer is yes, the meeting worked very well. Although we had a very tight schedule, the panel chair (André Gunst) made sure that the main issues were discussed.

The review focused on the design of the hardware (WP5 - ASTRON) and software (WP6 - Chalmers), the system design work package (WP4 - UKRI) was also involved. Despite the strange circumstances of the review; not only being at home but for many of us having also children running around, the efficiency of the meeting was not affected. Our team is satisfied by the constructive and open discussions that took place during the two days of the review.

The LOFAR4SW team is grateful of the dedication showed by the review panel: André Gunst (ASTRON), David Prinsloo (ASTRON), Menno Norden (ASTRON), Hans van der Marel (ASTRON), Mark Oude Alink (University of Twente), Federico Perini (INAF), and Henrik Olofsson (Onsala Space Observatory). Our team is now digesting the findings and recommendations from the panel and putting in place the actions agreed at the meeting. LOFAR4SW will continuing maturing the design towards the Critical Design Review, scheduled in February 2021.

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Thumbs up for TMSS!

April 21, 2020, 5:00 pm
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© TMSS team

A team of software engineers and telescope scientists at ASTRON is realizing a brand-new software application for the specification, administration, and scheduling of LOFAR observations. The new platform is called TMSS: Telescope Manager Specification System. Its realization is crucial, as it will enable the required support for LOFAR2.0 use cases, while also streamlining LOFAR operations and improving the adaptability and maintainability of software for future extensions. TMSS is an important component of the Telescope Manager of LOFAR2.0, the system that will control all aspects of the telescope, including proposal handling, observation execution, and system monitoring.

The TMSS project started in January 2020. In its first quarter, it has implemented the important system foundations in terms of telescope model and database. The system has already been also enhanced with the capability to perform a survey-type observation. We have witnessed this during the demo at the sprint review on 21 April, when the picture here was taken. It shows the team of happy TMSS team members and various stakeholders framed within the most relevant screenshots of the TMSS system taken during the successful observation.

This is a very important milestone for the project and the first of several more expected in the next months.

Thumbs up for TMSS!!

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An AJDI integration for Slack

April 22, 2020, 5:00 pm
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© -

The Astron/JIVE Daily Image (AJDI) is now also available in the Slack channel #ajdi. For all home workers who miss the big screen in the canteen, the Slack channel can provide an alternative means of enjoying the daily image.

An extra benefit of the Slack channel is that comments can be posted on a daily image, and reactions can be given in the form of emoticons. The Slack integration was written as a Python script, which runs daily at 8:45. The script is available at https://git.astron.nl/dailyimagebot.

After implementing this script, I learned that there is also an RSS-version of the daily image, as well as an RSS plugin for Slack. So that would probably have been an easier solution (which is also less fun to develop).

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Guiding users on the scheduling of EVN observations

April 23, 2020, 5:00 pm
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© –

Very long baseline interferometry (VLBI) observations, including the ones conducted with the European VLBI Network (EVN), have been traditionally scheduled using the NRAO SCHED program. Users are requested to prepare their EVN scheduling files ahead of the observations. JIVE provides support to all EVN users in order to help them during the schedule preparation. However, we are aware that the first time astronomers approach these tools can be a bit appalling.

Recently, JIVE has built a new tool, pySCHED, that takes advantage of newer and more-sophisticated tools based on Python, and also simplifies the scheduling of these observations.

As a next step, the EVN webpage now includes a page explaining how to schedule regular EVN observations. A detailed explanation of how to prepare the schedule, including some initial template files, is now in place. We also include a detailed description of the main points to be considered during scheduling. Examples of how the observing scans can be arranged and calibrator sources can be selected are also provided, covering the most common types of EVN observations: continuum, phase-referencing, spectral-line, or polarization observations.

We hope this documentation will make the scheduling of your future EVN observations easier and more intuitive than before. In any case, we are always happy to get feedback from the EVN community and provide support for any observation.

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Predictions for prompt low-frequency radio emission from gamma-ray bursts

April 28, 2020, 5:00 pm
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© Starling et al. 2020 (MNRAS in press)

Gamma-ray bursts (GRBs) are the explosive end states of massive stars and some compact binary mergers. The prompt pulses (Fig 1, UK Swift Science Data Centre) arise in a relativistic jet, but whether this jet is matter- or magnetically-dominated remains a central outstanding question.

Some magnetic models predict low-frequency radio emission alongside the initial high energy pulses. We suggest a test for the magnetically-dominated wind model of Usov & Katz (2000) using the LOFAR rapid-response mode, on-target within 5 minutes. Fig 2 (Starling et al. 2020) shows the predicted detections as green stars for a sample of Swift GRB X-ray flares from Yi et al. (2016). We find LOFAR could have detected 44% of the flares at 144 MHz, adopting this model and negligible absorption and scattering effects. Several such detections could be accessible to LOFAR each year, enabling triggered LF observations to play a key role in establishing the mechanism responsible for GRB prompt emission.

This work was made possible by an ASTRON Helena Kluyver visiting fellowship during the summer of 2019, and appears in ”LOFAR detectability of prompt low-frequency radio emission during gamma-ray burst X-ray flares”, 2020, Starling, Rowlinson, van der Horst & Wijers, MNRAS in press, https://arxiv.org/abs/2004.11209

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The GLEAM 4-Jy (G4Jy) Sample: the ‘brightest’ radio-sources in the southern sky

April 29, 2020, 5:00 pm
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© Copyright © 2020 Sarah White, accepted for publication in PASA, https://arxiv.org/abs/2004.13125

Low-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few ‘radio-loud’ galaxies for robust, detailed studies in terms of redshift-evolution and/or environment. Hence our use of observations from the Murchison Widefield Array -- a precursor telescope for the Square Kilometre Array -- to construct the GLEAM 4-Jy (G4Jy) Sample (1,863 sources at S_151MHz > 4.0 Jy; White et al. 2020a, 2020b). This sample is dominated by AGN and is over 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S_178MHz > 10.9 Jy; Laing et al. 1983) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way in which galaxies evolve, it is crucial to correctly identify the galaxy hosting the radio emission. This has been completed for the G4Jy Sample -- through repeated visual inspection and extensive checks against the literature -- forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment. The first two papers detailing the sample are now on arXiv, and you can keep up-to-date by bookmarking the following repository: https://github.com/svw26/G4Jy . Note that 140 G4Jy sources have been observed using Open Time on MeerKAT (PI: White), and that 564 G4Jy sources lie within the footprint of the LOFAR Two-metre Sky Survey (Shimwell et al. 2017).

In this image, GLEAM contours (170-231 MHz; red), NVSS contours (1.4 GHz; blue), and TGSS contours (150 MHz; yellow) are overlaid onto a mid-infrared image from AllWISE (W1). Also plotted are positions from GLEAM (red squares), NVSS (blue crosses), TGSS (yellow diamonds), and 6dFGS (magenta diamonds). The white plusses indicate the host-galaxy positions (identified in the mid-infrared) for two G4Jy radio-sources.

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Commemorating war victims with the Westerbork telescope

May 7, 2020, 5:00 pm
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© ASTRON/Herinneringscentrum Kamp Westerbork

Every year on May 5, we celebrate our freedom in The Netherlands. And every year on May 4, we commemorate the victims who fought for our freedom during the Second World War and other wars.

We also commemorate this with the Westerbork telescope. Every year on May 4 we put our telescope dishes in a mourning position. In this video, made in collaboration with Herinneringscentrum Kamp Westerbork, you can see the dishes being put into that position by our operator Jurjen Sluman (who was operating the telescope from home due to the national coronavirus restrictions). An impressive sight with an impressive instrument.

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Imaging RFI issues at RS210

May 11, 2020, 5:00 pm
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© CC-BY-4.0 Tammo Jan Dijkema

Recently some intermittent interference was spotted at RS210 near Weerselo. Menno downloaded some single subband correlation matrices off the station, to diagnose the origin of the RFI. Using the imaging code by Vanessa Moss he quickly diagnosed that the source, with apparent brightness comparable to Cassiopeia A, was located at a farm about 600 meters from the station.

While in the neighborhood of the station, he dropped by the farm to ask if they recently installed new equipment. Over a cup of coffee, he found out that recently new LED lamps were installed. Using his laptop on the coffee table, Menno took some data (panel 1), and then asked to switch off the lamps. And lo and behold, a new observation revealed that the RFI disappeared (panel 2). After he switched the lamps back on, the RFI showed up again as well (panel 3).

Tammo Jan updated the code to support plotting on top of aerial photos, to easier spot the origin of the RFI, and annotating celestial sources. The updated source code is here.

New radio quiet LED lamps were recently bought by ASTRON. These lamps have been tested at a LOFAR station and are proven invisible. They will be traded for the not so RFI friendly LED lamps at the farm, which can be reused as noise sources.

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In Memoriam Wout Beerekamp (1941-2020)

May 12, 2020, 5:00 pm
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© Beerekamp family

Wout joined ASTRON (then called SRZM) in 1965, as part of the team that looked after the famous 25m radio telescope in Dwingeloo, which was once the largest in the World. He was trained in digital electronics, but was greatly interested in using the rapidly encroaching computers. He was the driving force of the new HP2114, and gave programming lessons (in machine language) to the rest of the staff. Due to his social and organisatorial skills he soon became Head of the Technical workshop.

During the building of the much larger Westerbork Synthesis Radio Telescope (WSRT), Wout was elected as the first chairman of the new "Personeelsraad" (staff representation committee) of the vigorously growing institute in Dwingeloo. In this capacity he played a smoothing role in the difficult reorganisation of 1971/2.

In 1974 he prevailed over 20 applicants for the function of Head of Observations for the WSRT. He held this post for the duration of the "dizzy decade", when the WSRT was the foremost radio telescope in the World.

Looking for new challenges, he then became Head of Operations during the startup of the Isaac Newton Group of optical telescopes, which was part of the multi-wavelength UK/NL collaboration with Great Britain. In that context, he spent 1984/5 on La Palma, the westernmost Canary island. Back in Dwingeloo, he was entrusted with easing the invigorating secondment of an increasing number of ASTRON staff to our various interests on La Palma, Hawaii, and in England.

After his retirement in 1988, Wout deployed his teaching skills in public outreach at the new Planetron in Dwingeloo, where he planted the seeds of many a future career in astronomy. He also played an important role in the collaboration with CAMRAS, an organisation of radio "hams" that eventually took over the care (and new use) of the venerable Dwingeloo telescope. (NB: One of the hams at the opening of the refurbished telescope in 2014 was the Nobel Prize winner Joe Taylor).

So Wout was a multi-faceted man with a multi-faceted career, in which he helped make things happen by motivating people. This valuable skill also manifested itself in his busy private life, where he typically was chairman of organisations like the tennisclub, the church, the bridge club etc. Thank you, Wout.

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