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

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  • 01/18/17--16:00: CEP4 in production
  • © RO, RUG CIT

    The RO is proud to announce our newest High Performance Computercluster: CEP4. It is used for the recording and offline processing of LOFAR data that is generated by the COBALT correlator. Production commissioning started last summer and in December we were ready for production. The project started halfway 2015 with the tender and the time thereafter was taken by installing the system according to the specs, designing, building and testing the software. ASTRON and CIT Teams of network and systems administrators, software engineers, telescope scientists and other specialists have worked hard to bring this to a successful conclusion.

    The time spent was significantly more than estimated at the start of this project because a number of unforeseen major hurdles had to be overcome. All critical issues have been addressed and the result is a technically up-to-date “workhorse” that will process LOFAR data for the coming 5 years. We will continue to explore and harvest the new opportunities this new cluster is able to offer to LOFAR and its community (e.g. unlocking the power of the GPU nodes).

    Specs for the tech-enthusiasts:

    Nodes: 1 management, 2 heads, 2 filesystem meta-data, 18 storage, 4 GPU compute and 50 regular CPU compute.

    Tflops (theoretical): 96 from CPUs, 68 from GPUs, Total 164 (CEP2 was 20)

    Filesystem: 3.5 PB

    New techniques and frameworks that have been incorporated in the LOFAR system as part of the migration to CEP4 are a.o.: Lustre (cluster file system), Docker (containerized applications), SLURM (batch scheduling), Qpid (message broker infrastructure), Ganglia (scalable distributed monitoring system), Spacewalk (systems management), Robin Hood (policy engine and reporting tool for large file systems) and a new standard for an OS: CentOS 7.


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    © ASTRON

    Last week we said goodbye to Arie Hin, who has been very important for the commissioning and smooth operation of ASTRON's succession of world-class radio telescopes for almost half a century. He started at Kootwijk (1950-1955), then moved to Dwingeloo (1955-1970), and finally to Westerbork (1970-1995).

    He understood "his" receivers in every detail and solved problems almost before they occurred. He taught us all. Being gentle, soft-spoken and highly respected, he was also a stabilising presence in the sometimes tense atmosphere of operating a cutting-edge telescope.

    The picture shows Arie explaining the WSRT to a group of Japanese scientists, who came to pay their respect to this exciting new instrument. Given the make-shift table, it must have been in the early 70's, when the telescope was being commissioned. By then he had already overseen two royal visits.

    His wife Truus was also very much part of the ASTRON family, and accompanied him to functions and activities like ice-skating. A few months ago, she died suddenly, just after they had moved to Leiden to be closer to their (grand)children. This was the worst possible blow for Arie, who did not survive her long. Thank you very much, old friend.


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    © TU/e, 2017.

    Focal-plane arrays (FPA) have become an interesting alternative for conventional horn-fed reflector antennas in a number of applications, e.g. in radio astronomy and in Ka-band satellite communication. However, there are limiting factors for using this technology at higher frequencies, such as bandwidth limitation. Nevertheless, the demand for wideband antenna arrays and focal-plane arrays is increasing especially in the Ku- and Ka-band.

    A fiber to RF-FREEspace multiBEAM converter (FREEBEAM) is an STW project, which investigates new multi-beam wideband antenna systems with optical beamforming. A demonstrator will be developed that generates four simultaneous beams in the 20-40 GHz band with an Effective Radiated Power of 100000 W. The partners in the project are ASTRON, NXP, Thales, TNO, Catena, SATRAX, ESO and ESA.

    In the framework of the FREEBEAM project, the design of wideband focal-plane arrays is carried out at the Eindhoven University of Technology (TU/e). With an essential help of ASTRON, two versions of wideband antennas have been manufactured successfully. This was a challenging task because the overall size of these antennas is only 15 x 12 mm, with gaps of 100 micron. But thanks to the craftsmanship of Albert van Duin, the prototypes were successfully manufactured.

    The picture shows an experiment with probe measurements performed in the mm-wave anechoic chamber at the TU/e. The modified bow-tie antennas have been used as a first step in the design as a wideband array element to be used in a FPA. The presented simulation and measurement results demonstrate good agreement for both antenna versions and could be considered as a good confirmation of the selected antenna development strategy. These results will be used as a starting point for the wideband FPA design in the FREEBEAM project.


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    © Vanessa Moss & CAMRAS

    During my visit to ASTRON in September 2015, I met Harm Munk and Paul Boven who introduced me to the Dwingeloo telescope. We devised a plan to observe a supershell in neutral hydrogen that I'd studied with the Parkes 64m Radio Telescope (GSH 006-15+7, Moss et al. 2012), in order to see how the 25m observations compared and whether the structure of the shell had changed at all since it was observed several years ago (black line in left plot) as part of the Galactic All Sky Survey (McClure-Griffths et al. 2009). Our investigations with the Dwingeloo telescope took place over a few nights, during which we uncovered some interesting things! Firstly, the default line mode of the spectrometer was not high enough resolution to resolve the ~2 km/s HI absorption (yellow line in left plot), so we needed to switch to the 'raw mode' which is Fourier-transformed after the observations (red line in left plot). We were excited to see that we had resolved the line much better than in the original GASS data. The absorption at 7 km/s traces the wall of the supershell, and is produced by cold shell gas shadowing the bright Galactic background.

    Curiously we found that to get the correct spectral alignment, we needed to shift the Dwingeloo spectrum by 1 km/s. Some digging revealed something that was pretty surprising to me: most radio observatories around the world seem to use an old definition of the speed of the Sun (20 km/s from Blaauw & Schmidt 1965) rather than the updated version (16.5 km/s from Mihalis and Binney 1981). The Dwingeloo telescope software is using 16.5 km/s, and once this is carried through the various conversions, it produces the observed offset of 1 km/s - meaning that Parkes must use the older 20 km/s definition. The plot on the right shows the spectrum observed on different nights with slight adjustments to our observing method. The final spectrum (green line in right plot) represents our inclusion of a manual pointing correction to Dwingeloo (thus matching the Parkes spectrum most closely). The slightly raised plateau in the Parkes spectrum near 30 km/s is not clearly seen in our Dwingeloo data, most likely due to the difference in angular resolution between the two telescopes.


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    © Neal Jackson, Marco Iacobelli, Leah Morabito, for the Long Baseline Working Group Busy Week team.

    The 6th Long Baseline Working Group busy week was held at ASTRON in January and it was attended by 18 people, including a group of Latvian researchers in the framework of the 'BALTICS' project. A main goal of the busy week was to test and improve the current pipeline to map sources in a LOFAR Survey Tier-1 field region. LOFAR VLBI allows mapping at 0.3 arcsecond resolution, with sub-mJy sensitivity but data processing is a formidable challenge, especially if dealing with large datasets of the Surveys KSP.

    As a result, images were produced which went entirely through the pipeline, thus proving the goodness of the reduction strategy. The displayed picture is an example of mapped sources in the field (J132737+550406 and J132455+545406 in bottom right and left panels, respectively), made with 10 subbands only, not self-calibrated and with sub arcsec resolution.


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    © Karamanavis et al. 2016, A&A, 586, A60; Karamanavis et al. 2016, A&A 590, A48

    Blazars constitute the beamed population of AGN and are the most copious and variable emitters of radiation in the Universe. The detailed processes that give rise to those characteristics though are still under intense debate.

    In August 2008, Fermi/LAT discovered the distant blazar PKS 1502+106 (z=1.839) showing a strong gamma-ray outburst, followed by bright and variable flux over the next months. This activity at high energies triggered an intensive multi-wavelength campaign indicating that the outburst was accompanied by a significantly delayed counterpart at radio bands.

    Utilizing ultra-high resolution VLBI imaging at 15, 43, and 86 GHz, we attempt to shed light on the physics of the jet flow right after this high-energy flare.

    In this talk the findings of the mm-VLBI study, using the Global Millimeter VLBI Array (GMVA), will be presented. Additionally, light curves from the F-GAMMA monitoring program have been employed. The flare was quantified using a Gaussian process regression scheme and a cross-correlation analysis. The observed delays offer a tomography of the jet's opacity structure and allow the accurate localisation of the high-energy emission.


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    © ASTRON

    The Netherlands China Long Wavelength Explorer (NCLE) is a radio receiver aimed at observing the low frequency radio sky in lunar (Earth-Moon L2) orbit. NCLE is currently being designed, and is geared to launching with the Chinese Chang'e 4 relay satellite in 2018.

    At the end of 2016 the project passed the requirements review. Requirements stemming from the different science cases, including the Dark Ages and other unique scientific opportunities below 30 MHz, were derived, evaluated and agreed. The photo shows happy faces from the ASTRON part of the NCLE team, relieved by this success.

    In the meantime, the team is working very hard towards the PDR which will follow shortly. ASTRON's responsibilities include the design and production of the analogue input circuitry, the low-noise amplifiers, and the RF side of things of the antennas. With the help of our LESIA colleagues we had a head start in designing the LNA for which we currently have promising solutions. Still, as the time scales are very tight, the team is focused and determined to deliver on time.

    This project allows us to design and build low-frequency radio technology not only for NCLE, but this ground work will also form the basis for much larger future space-based radio instruments.

    The NCLE receiver project is a collaboration between ASTRON, Radboud University (PI), Innovative Solutions In Space (ISIS), the Chinese NAOC, and is supported by the Netherlands Space Office (NSO).


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    © Benito Marcote

    Since the first discovery of a Fast Radio Burst (FRB) in 2007 many searches have been conducted to unveil their nature. While the observed dispersion mesures of these objects pointed to an extragalactic origin, we could not confirm this origin without the precise localization of these fast events.

    The discovery of a repeating FRB (FRB 121102) provided a unique opportunity to carry out interferometric radio observations of these bursts for an accurate localization. A team lead by Shami Chatterjee (Cornell), including ASTRON and JIVE collaborators, was able to detect several bursts with the Karl G. Jansky Very Large Array (VLA) and imaged them. They found a faint 180-microJy persistent radio source as well, within ~0.1 arcsec of the bursts. The spectrum of this source indicated a non-thermal emission process. VLBI observations using the EVN and the VLBA revealed that the persistent radio source is compact at milliarcsecond scales.

    A faint 25-mag optical counterpart has also been found with the Keck and Gemini telescopes, consistent with a star-forming galaxy. No infrared or X-ray counterparts have been found so far.

    For the first time, thanks to the precise localization, we have strong evidence for the extragalactic origin of (at least some of the) Fast Radio Bursts. These results were published in Chatterjee et al. (2017, Nature, 541, 58; https://arxiv.org/abs/1701.01098 ).

    The figure shows the Nature cover representing the localization. The top figure shows the bursts as seen by the VLA compared with the previous localizations done by the Arecibo Telescope (open circles). The bottom figure shows these positions over the continuum image, with the persistent radio and optical sources coincident with the bursts.


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    © Astron

    An important milestone for the Westerbork Synthesis Radio Telescope: the first images have been made using a revolutionary new type of receiver, called Apertif. Because of these new receivers, much larger areas of sky can be mapped in a single observation. The 'old' Westerbork telescope could only map an area of sky comparable in size to that of the full moon in a single observation. The new Westerbork/Apertif system can image a region of sky 40 times larger, which is a great step forward. The new Apertif receivers, developed by ASTRON in Dwingeloo, were installed on the Westerbork telescope over the last year and will be fully operational this autumn.

    With the upgraded Westerbork telescope there are numerous possibilities for new studies. In particular, Apertif will be used to make radio images of large areas of sky that have not been studied before and to search the sky for new and interesting types of objects. In addition, with Apertif this can be done with an amount of detail that was not possible before. This unique capability will be used to image large parts of the northern sky and provide a public database of images and catalogues that will be used for many astronomical projects done by astronomers from all over the world.

    The first images made with the upgraded telescope that demonstrate this new 'wide-angle' capability is shown here. The first image shows the dwarf galaxy Leo T. The image is colour-coded and shows the gas (in blue) in this galaxy together with many distant radio galaxies in the background shown in orange. For comparison, the field of view of the previous Westerbork system and the size of the full moon are also indicated.

    To make this new capability possible, ASTRON developed and built the hardware in-house. 121 small receivers are used in each telescope whose signals are combined electronically to produce the large field of view.

    The upgraded telescope will also be used to search for and study new variable sources in the radio sky. With the new Apertif receivers, observations of large parts of the sky can be done much faster, and projects that used to be impossible as they would take tens of years can now be done in a much shorter time. Westerbork is therefore poised to make many new discoveries in the radio sky.


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    © Aleksandar Shulevski, Raffaella Morganti et al.

    One of the science cases for LOFAR is discovery and characterization of radio remnants of active galactic nuclei (AGN) - leftovers from past activity episodes. They are a key radio tracer of the total energy deposited in the (inter) galactic medium over cosmic time. As such, they provide key information about the feedback processes responsible for regulating galaxy (and super-massive black hole) growth over time. Also, remnants give us an insight into the AGN life-cycle.

    We investigated the prototypical AGN relic, B2 0924+30, to ascertain its activity history. LOFAR has fulfilled its potential, providing sensitive images at low frequencies which show the remnant lobes in their entirety.

    This data set, together with higher frequency data, has enabled the derivation of detailed age maps, helping to constrain the source history and energetics. We found that the oldest source regions are located around the host galaxy and are around 150 Myr old. The brightest and youngest regions are found within the twin lobes located on opposite sides of the AGN host galaxy and are around 40 Myr old, suggesting that that is the epoch when the activity in the lobes ceased. The overall source morphology suggests that this is a Fanaroff-Riley type II (FRII) remnant, in which case the youngest regions we see can represent the remnant hotspots.

    More such remnants are awaiting discovery in the era of the LOFAR syrveys such as the LOFAR Two meter Sky Survey (LoTSS) which is under way. Exciting times ahead! More in: A. Shulevski, R. Morganti, J .J. Harwood, P.D Barthel, M. Jamrozy, M.Brienza et al., Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective, 2017, A&A (arXiv:1701.06903)


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    © Pfrommer in prep.

    This image shows face-on and edge-on slices through a magneto-hydrodynamical simulation of a Milky Way-sized galaxy that self-consistently follows cosmic ray physics. Shown are gas density (left), cosmic-ray energy density (middle) and magnetic field strength (right) 1 Gyr after the onset of the simulation. The central starburst injects cosmic rays, which are able to drive a powerful outburst that is dominated by cosmic rays and magnetic fields (Pfrommer in prep.).

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  • 02/02/17--16:00: The AARTFAAC sky
  • © none?

    This is a mosaic of images taken from roughly 30 hours of observation with AARTFAAC over the autumn of 2016. AARTFAAC operates in parallel while other users observe with the LOFAR LBA. These snapshot images were recorded at 60MHz, bandwidth of 3.2 MHz, and image integration time of 1 second. Roughly 1400 all sky images were used cover the full northern celestial hemisphere.

    Initial image calibration removes Cas.A, Cyg.A, Tau.A, and Vir.A, as well as The Sun, and most of the diffuse galactic plane (red dotted line) emission, which would otherwise dominate. A further calibration step 'bootstraps' from currently published low frequency catalogs to correct the flux scaling for each image.

    The individual snap images AARTFAAC makes every second are used to detect bright low frequency transients as quickly as possible for followup observing in near real time. Mosaics such as this one allow us to monitor the total observable source population over timescales of months to years allowing us to monitor for long term variability. This also provides beautiful view of the night sky, with radio eyes!


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  • 02/05/17--16:00: GALACTIC PLANE BUSY WEEK
  • © M Haverkorn, G. White, L. Driessen, R. Oonk, M. Arias

    The First Galactic Plane Imaging Busy Week is being held this week at the Muller room at ASTRON. The aim is to work on an imaging strategy for galactic-plane fields, which are often crowded, and present diffuse extended emission on large scales.

    Our first goal will be to achieve a robust calibration strategy for Galactic-plane fields. The combination of short and long baselines for LOFAR will allow for excellent imaging of the complex interplay between HII regions, supernovae and their surroundings thus providing a fantastic low-frequency view on our Galaxy.

    We will be working on HBA and LBA fields. For those interested, feel free to drop by at the Muller room.


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    © RossBurns

    Continuum image from Palau et al., 2011, ApJ, 743, L32 showing the millimeter cores in the massive star forming region AFGL 5142, where molecular outflows from the literature are indicated with long arrows. Overlain are the positions and proper motions of water masers which associate with protostellar jets in this region. Vector colours indicate the line of sight velocity, while vector lengths indicate proper motions (typically around 15 km/s). We used our VLBI maser data to measure the trigonometric distance to AFGL 5142, which was D = 2.14 +- 0.05 kpc, and reveal the presence of young jet-driven bowshocks emanating from the millimeter cores and aligned with the molecular outflows. These results were recently accepted for publication in MNRAS

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    © Benito Marcote

    The European VLBI Network (EVN) observed the repeating Fast Radio Burst FRB 121102 in eight sessions that span 1 February to 21 September 2016. These observations included the regular European EVN stations plus the 305-m William E. Gordon Telescope at the Arecibo Observatory. Using the new EVN software correlator (SFXC) we were able to correlate in real time the data transferred to JIVE via high-speed fiber networks but also to buffer the baseband EVN data, producing afterwards high-time-resolution correlations. Arecibo provided high-sensitivity data to search for bursts.

    From the eight epochs, only on 20 September 2016 we observed bursts from FRB 121102. Four bursts were detected within this 2.5-h observation. One of them showing a ~4 Jy peak, one order of magnitude larger than the other three bursts. This allowed us to localize FRB 121102 with a precision of a few milliarcseconds.

    Comparing the obtained positions with the persistent radio source we determined that both are coincident with a projected separation smaller than 40 pc, given the distance of the persistent source.

    A 5-GHz EVN observation allowed us to establish strong constraints on the compactness of the persistent radio source. This source remains unresolved in the EVN images, implying a projected size of 5 x 10^7 K.

    The EVN observations have provided strong evidence for a direct physical link between the bursts of FRB 121102 and the compact persistent radio source. Although the origin of the bursts remains unclear, two explanations arise as the most probable ones: a burst source associated with a low-luminosity active galactic nucleus (or massive black-hole related system), and a young neutron star energizing a supernova remnant.

    The Figure represents the persistent source at 1.7 GHz (contours) and at 5.0 GHz (color scale) compared to the localization of the bursts (crosses). The red cross represents the strongest burst, which is expected to exhibit the most accurate position. The black cross represents the weighted average position considering the four bursts.

    You can find the details of this study in Marcote, Paragi, Hessels et al. (2017, ApJL, 834,8).


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    © Amina Helmi/Jovan Veljanoski/Maarten Breddels/University of Groningen

    A new era has begun in Astrophysics driven by the launch of the European satellite Gaia. Gaia is currently mapping our Galaxy by measuring distances and motions of one billion stars with exquisite accuracy and unprecedented detail. It is fair to say that the impact of this space mission on our understanding of galaxy evolution and dynamics will be extraordinary.

    Last September, Gaia produced its first data release. In this talk I will present some first results from the exploration of this dataset. This first analysis reveals a rather complex and rich structure for the halo of our Galaxy, indicating that mergers have played an important role in the build-up of the Galaxy.

    About the image: The Milky Way disk is embedded in a roundish halo of stars. The stars (in purple) are from a computer simulation of the remains from a merger with a small galaxy. The arrows indicate the motion of these stars that are now part of the halo. We expect that tens to hundreds of such flows of stars are crisscrossing the Milky Way.


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    © Alex Clarke et al.

    LOFAR's Multifrequency Snapshot Sky Survey (MSSS) has resulted in the discovery and detailed study of a new 2.56 Mpc giant radio galaxy (GRG) associated with a disturbed galaxy group (UGC 9555). This image illustrates the huge extent of radio emission, stretching larger on the sky than the full moon. LOFAR contours are displayed in white, and the VLA's NVSS 1.4 GHz survey in red. The inset shows the host galaxy group. Lime green contours from FIRST show compact radio emission from the AGN and its jet. Coloured contours are smoothed SDSS bands, indicating the disturbed nature of the group that hosts this interesting radio source.

    The paper describing the discovery of the GRG, along with a description of the very interesting host galaxy group and the large-scale structure in that region of the cosmos, has recently been accepted for publication in A&A (Clarke et al. 2017; http://arxiv.org/abs/1702.01571 ). It will be followed up with a detailed analysis of the morphology and evolution of the source, based on a high-resolution LOFAR observation motivated by the MSSS discovery.


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    © ASTRON

    How should we develop the software architecture of such a complex system as the Square Kilometre Array (SKA)? How can we document it in a clear and concise manner? These were the central questions during the SKA Software Architecture Workshop organised by the SKA Office in the beginning of 2017.

    The twenty-five participants included representatives from several SKA consortia and the SKA Office. ASTRON was present with two people working in the Science Data Processor and Central Signal Processor consortia.

    The backbone of the workshop consisted of tutorials given by two instructors from the Software Engineering Institute of the Carnegie Mellon University (SEI). After the lectures, the theoretical knowledge was put into practice. The participants developed so-called mission threads, worked on quality attribute scenarios and documented parts of the SKA using various views. An important aspect of the work was integrating the knowledge scattered across the various consortia into a system-level view of the SKA. A lot of open architectural questions were identified during the process which will need to be addressed in the near future.

    As a follow-up, the consortium designing the Science Data Processor, which is one of the most software-intensive parts of the SKA, is organising a similar SEI workshop for its members. The newly acquired knowledge will be put to the test during the preparation of the SKA Critical Design Review documentation which needs to follow the SEI guidelines.


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    © R&D Compute group

    The image shows a possible analysis of the resource usage by pipelines. Understanding how pipelines affect the underlying hardware in a uniform way can for example be used to measure improvement of new pipelines or efficiently do observation scheduling.

    The top-left image is a graphical representation of the pipeline we used (kindly provided by Marco Iacobelli). Underneath, a plot shows the usage of CPU and memory. The image of the right shows how much time is spent in each part of the pipeline in a hierarchical way.

    The work has been presented at the Astronomical Data Analysis Software and Systems (ADASS) conference. A PDF version of the poster can be found on the website of the conference. The presented results, which will also appear in the conference proceedings, can be found on arXiv.


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    © Francesco de Gasperin - Maaijke Mevius

    Observing at

    From top-left to bottom-right:

  • Clock delay (in s)

  • TEC (in TECU)

  • RM (in radians)

  • third order ionospheric effect (in arbitrary unit)

    Each line is a station, blue to red from core to remote. All plots show differential values w.r.t. CS001.

    The sum of these effects (clock+ionospheric 1st, 2nd and 3rd order) seems to describe all the phase systematic errors present in LBA data when solving in the direction of a strong calibrator. Correlation between nearby stations and between different ionospheric orders is expected and observed.


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