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

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    © (not copyrighted)

    Jupiter, king (and, appropriately, largest) of the planets, is only outshone in the night sky by Venus and the Moon. Optically (color image) what we see is the outermost Jovian atmosphere: cloud bands and the great red spot (an immense storm system).

    To unveil what happens below the cloud tops, we need "radio eyes", as provided by the Karl G. Jansky Very Large Array in New Mexico. The new radio maps (monochrome image shows a 2-cm map) penetrate as much as 100 km through cloudy haze, to the level where clouds form.

    These images were recently published by Berkeley Professor Imke de Pater (Helena Kluyver Visitor to ASTRON/JIVE) and her colleagues (in "Science", Vol. 352, Issue 6290, pp. 1198-1201).

    Movie credits (Radio): Robert J. Sault (Univ. Melbourne), Imke de Pater and Michael H. Wong (UC Berkeley); (Optical): Marco Vedovato, Christopher Go, Manos Kardasis, Ian Sharp, Imke de Pater.


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  • 07/31/16--17:00: Testing APERTIF DCU boards
  • © ASTRON

    In April 2016, the last batch of WSRT/APERTIF DCU boards was delivered. The DC Power tests were done by the assembling company. To allow automatic testing, monitoring IC's were implemented on the boards, so we could read out the voltages and temperatures with I2C.

    The RF tests were done at ASTRON to allow RF engineers to be involved in searching for errors in defective modules. These errors were written on rework labels, which are visible in one of the pictures. To allow automatic testing here also, the RF measurement equipment was interfaced using GPIB. The measurement results were then compared with the limit dataset. The result showed the condition of the board (OK or REJECT).

    The last step was to assemble the DCU racks. They have a network (RJ45) interface. The racks were controlled by means of python test scripts, which made use of the official APERTIF software on the APERTIF server.


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    © Astron

    Every galaxy has a super massive black hole (a hundred million times as heavy as the Sun) in its centre. However, astronomers are left with the big puzzle of why some of these black holes are active (i.e. it emits enormous mounts of energy) while other are not and why the manifestation of the activity can take such a variety of forms. One of the likely reasons for this is the presence of gas near a super massive black hole. As part of the RadioLife project, we are trying to study the gas, and in particular neutral hydrogen, near super-massive black holes in a number of systems to understand under which conditions it turns the black hole from dormant to active.

    The nearby galaxy NGC 3998 was observed with the WSRT a few years ago as part of the study of a larger sample of galaxies (ATLAS3D, see Daily Images 22-11-2011 and 11-02-2011). It was found to have two faint, S-shaped radio lobes (see contours in the figure, superimposed to an image of the ionised gas). Such structures are seldom seen in galaxies of low radio luminosity like NGC 3998. The presence of a large HI disc in NGC 3998 suggested a possible link between the gas and the radio lobes, but it took us some time to come up with a good explanation to describe this system!

    The story of this intriguing galaxy is now in a paper accepted for publication by Astronomy & Astrophysics: "A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998"(http://arxiv.org/abs/1605.03873 ) by Bradley S. Frank, Raffaella Morganti, Tom Oosterloo, Kristina Nyland, Paolo Serra.

    There, we suggest that the HI disc was accreted through a minor merger. The fact that the S-shape of the inner gas disk mirrors the S-shape of the outer radio lobes is not a coincidence. The torques causing the gas disk to warp into an S-shape in the inner regions are also responsible for gas falling into the AGN, leading to a precessing jet. We think that the extended radio jets are poorly collimated and turbulent, and will, therefore, quickly fade. This explains the rarity of radio lobes in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via "discrete events", as suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.

    We are testing this idea using LOFAR observations where we have also detected the faint lobes. The spectral properties will tell us more about their age and their fate.


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  • 08/02/16--17:00: SKA-TSM environmental test
  • © Hiddo Hanenburg

    14 July 2016 these SKA-TSM Dipole antenna's were placed on the testfield in the backyard of ASTRON. This marks the start of an environmental test of the materials and the design.

    https://www.astron.nl/r-d-laboratory/completed-projects/ska-tsm/ska-tsm

    This project of the Samenwerkingsverband Noord-Nederland is partly financed by the Europian Fund for Regional Development, and by the province Drenthe.


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    © Eric Kooistra

    This low frequency antenna array operates at 16.10 to 16.25 MHz, but it is not related to Lofar or Astron, and not even to radio astronomy. It is owned by Rijkswaterstaat, the Dutch department of water management. I ran into it when camping near Ouddorp in Zeeland (NL).

    The antenna array is located in the dunes, and points at the North Sea off Hook of Holland. It has a counterpart about 30 km to the North, at the other side of the port entrance. At both sites, 4 antennes transmit and 12 receive. Together they form a radar system that measures the sea currents. This information is used by the ships to safely enter the port of Rotterdam.


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    © ASTRON

    Last Thursday, we received good news from the European Commission that the H2020 proposal AENEAS, which ASTRON is leading, has been accepted and will now enter into grant negotiations. AENEAS is a 3M euro project intended to develop a design and operational model for a distributed, network of large-scale regional data centres for the SKA and includes partners from 13 countries and 28 institutions around the world. AENEAS stands for the ''Advanced European Network of E-infrastructures for Astronomy with the SKA'' and is designed to address the challenges the community will face in extracting science from the incredible amounts of data the SKA will produce.

    The AENEAS project will seek to integrate e-infrastructures across Europe with those in other SKA member countries to provide a seamless platform for international science with the SKA and its precursors, and will explore techniques and technologies to provide data services to the astronomical community. It represents a great opportunity to continue the work begun in the DOME project, build on the unique experience we've gained with LOFAR, and kickstart our local efforts to form the nucleus of a Science Data Centre here at ASTRON. Like the Science Data Centre activities themselves, AENEAS will be an ASTRON-wide project involving staff from the AG, RO, and R&D groups.


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    © Harm-Jan Stiepel

    In collaboration with Anne Veendijk and Edwin Stuut, the ASTRON-JIVE PV organized a motorcycle tour on 22 April. Fourteen motorcycle fanatics toured under a sunny sky through the provinces of Drenthe and Overijssel. The tour was surely not a speeding tour, did not have a competitive element, but more to get a kick out of the ride, have fun at the break locations and enjoy the beautiful surroundings.

    The participants, as well as the motors, varied in age and style. Men and women geared in leather or dressed in more modern motorcycle clothing, drove on sports motorbikes, touring machines and cruisers. We were soon immersed in a varied landscape, small roads between charming villages and fine Hanseatic cities like Hasselt and Zwolle. We went over dikes along meandering rivers and straight canals and even the motor tourists had to cross two rivers (Zwarte Water and IJssel) by boat. For some of us the ferry was a new experience.

    After the lunch in the small village called Herxen, we visited the American Motorcycle Museum in Raalte. The highest point of the route was on the Holterberg (berg is Dutch for mountain and 60 m above sea level is high is the Netherlands) where our photographer made the last photos of our tour.


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    © James McKee, Gemma Janssen

    In the hunt for low-frequency gravitational waves, the European Pulsar Timing Array (EPTA) collaboration is always looking for more data to include in their timing solutions. Both timing precision as well as a long total baseline are important to get the best results. For several pulsars we have included data from Jodrell Bank (precluding our EPTA data release by Desvignes et al. 2016) to extend the timing baseline to cover earlier epochs.

    Surprisingly, as can be seen in the figure, for PSR J0613-0200, the early data did not line up with the very stable EPTA timing solution which used data from WSRT, Jodrell Bank, Effelsberg and Nancay, covering the period between 1999-2015. A careful comparison with other pulsars to exclude instrumentational issues, and adding early data from the Effelsberg EPOS instrument proved that this must be a pulsar-intrinsic effect: we found a micro-glitch in a millisecond pulsar!

    The figure shows the timing residuals for PSR J0613-0200. Different observing systems are shown in different colours. The timing model does not accurately predict the arrival times before March 1998 (MJD 50888), due to an unmodelled glitch occurring shortly before the epoch over which the EPTA ephemeris (1999-2015) was derived.

    A glitch is a sudden spin-up of the pulsar and is believed to be caused by transfer of angular momentum from the superfluid interior of the neutron star to its solid crust. This is the second glitch ever found in a millisecond pulsar, and moreover is the smallest glitch known to date showing a change in the rotational frequency of the pulsar of only 8E-10Hz. This result is in particular interesting as this pulsar is also used as an element in a pulsar timing array, with which we ultimately hope to detect gravitational waves. Having a glitch in one of our most stable pulsars was worrying at first, but we were able to prove that including the glitch in the timing model did not affect the long-term quality of this pulsar.

    Our paper can be found at: Mckee, Janssen et al. 2016; http://adsabs.harvard.edu/abs/2016MNRAS.461.2809M.


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    © Benito Marcote , Liying Wei

    It is well-known that astronomers usually avoid crowded places, and hide behind their computers to stare at images and codes, or hide in labs to test for instance the new APERTIF.

    However, on Sunday 31th of July, a group of 15 ASTRON/JIVE astronomers gathered in Giethoorn to enjoy a day in the "Venice of the North", which is also known as one of the most touristic places of the Netherlands. Although intending just a relaxing day out, they showed again that astronomers are hardworking and dedicated people by punting and kayaking through Giethoorn instead of hiring motorized boats. The weather even allowed some brave JIVE astronomers to venture a swim!

    In the collage you can spot the following people:

  • Jeanette Bast

  • Jay Blanchard

  • Roy Smits

  • Antonia Rowlinson

  • Yuping Huang

  • Anjali Piette

  • Liying Wei

  • Akoto-danso Alexander

  • Richard Fallows

  • David Prinsloo

  • Benito Marcote

  • Lerato Sebokolodi

  • Ross Burns

  • Xiaoxi Song

  • Floor Broekgaarden.


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    © Van Diepen & Broekema

    During the first week of July, the members of the SKA Science Data Processor (SDP) consortium met on Malta for a week to discuss progress and to look forward and plan the work leading up to the Critical Design Review in early 2018.

    The great environment (which is shown in several of the pictures above) and the illness of a significant fraction of the participants didn't prevent this meeting from being fruitful. This was, to a great extent, due to the focus on small-group discussions instead of plenary presentation sessions.

    The bottom picture shows the meeting participants. The three top pictures depict (from left to right) the social interaction between several project partners, the skyline of Valetta (the city hosting this event) and an ASTRON employee inspired by the statue of the founder of the city.


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    © L. Morabito, A. Deller, H. Rottgering, et al.

    Using the International Low Frequency Array (LOFAR) Low Band Antenna we achieved sub-arcsecond imaging resolution at 55 MHz with VLBI techniques.

    The image of radio galaxy 4C 43.15 on the left was made using 15.6 MHz of bandwidth centred on 55 MHz. We used the multiscale function of the CLEAN task in CASA with Briggs weighting (robust -1.5) and no inner uv cut. The image noise achieved is 59 mJy/bm while the expected noise given the amount of flagged data and image weighting is 25 mJy/bm. The final restoring beam is 0.9 arcsec × 0.6 arcsec with PA -33 deg.

    The image on the right is the same image, but smoothed with a Gaussian kernel 1.2 times the size of the restoring beam. The contours in both images are drawn at the same levels, which are 3σ, 5σ, 10σ, and 20σ of the unsmoothed image.

    This radio galaxy was selected as part of a pilot study of 10 high redshift radio galaxies. The correlation between radio spectral index and redshift has been exploited to discover high redshift radio galaxies, but its underlying cause is unclear. It is crucial to characterise the particle acceleration and loss mechanisms in high redshift radio galaxies to understand why their radio spectral indices are steeper than their local counterparts. Low frequency information on scales of ~1 arcsec are necessary to determine the internal spectral index variation. This daily image shows the first spatially resolved studies at frequencies below 100 MHz of the z=2.4 radio galaxy 4C 43.15 which was selected based on its ultra-steep spectral index (α=1.4 GHz, implying a break frequency between 500 MHz and 1.4 GHz. These spectral properties are similar to those of local radio galaxies. We conclude that the initially measured ultra-steep spectral index is due to a combination of the steepening spectrum at high frequencies with a break at intermediate frequencies.

    Published in "LOFAR VLBI studies at 55 MHz of 4C 43.15, a z= 2.4 radio galaxy", 2016, MNRAS, 461, 2676


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  • 08/14/16--17:00: LOFAR universe
  • © Hiddo Hanenburg

    LOFAR surprises everyday. This time it does so with a new "universe" of colorful lichen! It was found on the antenna head located in the testfield in the ASTRON backyard.


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  • 08/15/16--17:00: Subtle Disincentives
  • © Madroon Community Consultants (MCC)

    It is not actually forbidden to drive your car over the old road across the Dwingelerveld to ASTRON, it is just gently discouraged. Of course, some people then squeeze their vehicle onto the nice new bicycle path, which unfortunately is just wide enough for such uncouth behaviour. It is great fun to refuse to move out of the way, and watch the rainbow of conflicting emotions unfold on their faces.

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    © Cees Bassa

    On July 18, the ASTRON/JIVE summer students visited the WSRT and LOFAR telescopes. They were joined by the Leiden/ESA Astrophysics Program for Summer Students (LEAPS), with whom they visited ESA/ESTEC, as well as most of the ASTRON/JIVE summer visitors.

    Roy Smits and I gave the WSRT tours, showing the telescopes and the new APERTIF, as well as the old MFFE, frontends. We also visited the (very warm) EMBRACE hall and enjoyed a nice lunch in the WSRT canteen. At the LOFAR superterp we were hosted by Richard Fallows, who expertly explained the LOFAR antennas, the station hardware and the correlator/beamformer. The summer students even fixed one of the LBA dipoles (ID LBA 24551-00084), which had fallen over.

    The ASTRON/JIVE summer students will present their research at Wednesday astro lunch. Today, Xiaoxi Song and Anoj Khadka will give a lunchtalk, followed by Aarthi Ramesh, Anjali Piette and Floor Broekgaarden, who will present their work next week (August 24). Finally, Yuping Huang will give a lunch talk on September 7. You are welcome to attend these talks. Each student will also post a daily image here in the near future.


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    © Xiaoxi Song, Vlad Kondratiev, Anya Bilous

    My summer project focused on single-pulse analysis of PSR B0809+74 using LOFAR Low Band Antennas. While analysing single-pulse spectra, we spotted a distinct 50-pulse sequence of emission patches. We dubbed it as a ''super-sequence''. The super-sequence snapshot (upper panel) shows the band-averaged profiles of pulses (right top subplot) with spectrum of all pulses superimposed (left top subplot, showing intensities with S/N > 3.5 only). For clarity, the pulses are divided in 5 groups represented by different colours. The apparent emission patch starts at frequency of about 15 MHz, drifting in phase and growing in spectral width towards high frequencies. It essentially drifts in both frequency and time.

    We argue that the super-sequence is very unlikely to be pulsar-intrinsic. With the dispersion measure of 5.7 pc/cm^3, single pulses from B0809+74 are dispersed for about 100 s between 15 and 62 MHz. Thus, any broadband brightness variations across this 100-s time scale will present itself as ''patches'' in pulse spectra (see cartoon at the bottom of the image). At lower frequencies, smaller portion of pulse spectrum is affected. Thus, after de-dispersion we observe the sequence of patchy pulses with ''emission patch'' moving up in frequency and growing in spectral width. In addition, PSR B0809+74 exhibits the phenomenon of drifting subpulses, thus the patches move also in phase.

    Observed broadband brightness variations can be potentially related to the apparent source position jitter due to the ionosphere. It is important to be aware of this non-pulsar-intrinsic spectrum modulation when carrying out single-pulse analysis at low frequencies. Similar phenomenon is also observed with High Band Antennas, where modulation is in turn caused by interplanetary scintillations (see daily image on 07-05-2014).


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    © Yogesh Maan and Roy Smits

    The Apertif Radio Transient System (ARTS) is an advanced and real-time backend for time-domain studies with Apertif. It is being designed specifically to detect Fast Radio Bursts (FRBs) and make use of the Westerbork array to localise these enigmatic sources better than single dishes have so far been able to. ARTS can also carry out deep searches of pulsars, and time known pulsars. This requires handling high data-rates and the ability of different modes of observation.

    The initial set of hardware, firmware and software in ARTS, for the pulsar timing module, has recently been installed at the WSRT site. After a number of commissioning steps to test and iron out wrinkles in the various required processing steps, we saw a pulse profile come through on Wednesday 11 August at 12:37:00 CEST and we proclaimed first light!

    The first image captures the moment that ARTS team members Daniel, Roy, Yogesh and Apertif commissioning engineer Boudewijn witnessed this great milestone -- the folded profile of a 3-minute, 18.75-MHz-bandwidth observation of pulsar B0329+54, the go-to commissioning pulsar in the Northern Sky. We used only the central Apertif dipole elements from 3 WSRT dishes in this first and most basic step and the signal to noise ratio was in the expected range.

    The second image shows an even better profile of a 15-minute observation, revealing the characteristic components of this bright pulsar.

    The final image shows the first hardware component of ARTS, called ARTS-0, which has the high precision pulsar timing pipeline implemented on it. This machine is capable of performing real-time coherent dedispersion of radio pulsars of the full 300 MHz (twice the bandwidth of the pre-upgrade WSRT), as well as storing up to 30 hours of raw voltages. That will allow for the continuation of the high-precision pulsar timing programme. By expanding on the pre-upgrade timing baseline, WSRT will contribute to projects like neutron-star mass measurements, studies of binary pulsar evolution and, eventually, gravitational wave detection with a pulsar timing array in the nanohertz regime.


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  • 08/21/16--17:00: LOFAR wandeling
  • © streekblad

    Apart from being a major astronomical instrument, LOFAR also presents an amazing sight, set in an unusual landscape. And, as with everything, you appreciate it more as you know more about it.

    The advertisement shown here was published in a local paper, and offers a guided walk to the LOFAR core near Exloo. It is organised by local organisations that are very proud to have (the core of) the largest telescope in the world in their backyard.

    Note that there is still time to join this adventure.


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    © Anoj Khadka

    HIZOA J0836-43 is an HI massive galaxy hidden by the galactic dust and Vela supernova remnant in the southern sky. Its high star formation rate (SFR ~20MΘ/yr) combined with the huge HI gas reservoir makes it interesting for understanding the relationship between the gas dynamics and star formation going on inside it which ultimately can shed light into galaxy formation and evolution models.

    In these images I have laid HI (Neutral Hydrogen) contours over the IR (infrared) images to understand the distribution of HI gas in the galaxy. As one can see, in both the images distribution of the HI gas is much more extended beyond the central star forming regions indicated by bright emissions at the center. Data to make these HI contours out of zero moment map was taken from observations made from ATCA (Australian Telescope Compact Array). Contour levels moving outside in are at 20, 50, 90, 135, 170 times the rms value for noise (0.014). Corresponding HI column densities for the contours are 0.36, 0.88, 1.60, 2.40 and 3.02 times 1021 atoms/cm2.

    Laying HI contours over the IR images helps us to know how the distribution of gas is in the galaxy and in which regions the star formation is concentrated. It also helps us to identify any possible merger interactions or companion galaxies nearby. These two infrared images taken at 3.6 micron and 8 micron wavelengths by IRAC (Infra-red Array Camera) on the Spitzer space telescope tell us about the star formation/old stars and the emission from PAH (Polycyclic Aromatic Hydrocarbon) molecules occurring in the galaxy respectively.


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  • 08/23/16--17:00: Best of luck Adam!
  • © ASTRON

    As most of you know, Adam Deller will be leaving ASTRON at the end of the month and returning to Australia to take up a prestigious Future Fellowship at Swinburne University of Technology. In particular, Adam will be leading a new project to upgrade the Molongo telescope to turn into a premier instrument for detecting and localizing fast radio bursts (FRBs).

    We are naturally sad to see Adam leave, but of course wish him all the best in this next phase of his career. Fortunately, astronomy is a truly global endeavor these days and, as with all ASTRON alumni, Adam isn't planning to disappear on us completely. His new project on FRBs is a nice complement to our own local efforts to localize FRBs, and of course he hopes to continue to contribute to the development and exploitation of LOFAR's long-baseline capabilities. So although we'll miss having him around on a day to day basis, we hope to see him frequently here in Dwingeloo in the future.

    I hope you will all join me in wishing Adam well in his new position and new project. Best of luck Adam!


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    © Anjali Piette, Antonia Rowlinson, Jess Broderick

    With the two recent gravitational wave (GW) detections from Advanced LIGO - GW150914 and GW151226; both binary black hole mergers - this is an extremely exciting time in Astrophysics. Multiple telescopes, including LOFAR, have performed follow-up observations in an attempt to localise and better understand these events. The aim of my summer project was to look for electromagnetic (EM) counterparts to GW events in LOFAR's follow-up observations at 145 MHz, which were taken 1 week, 1 month and 3 months after each GW alert.

    Although EM radiation is not expected from binary black hole mergers, various theories propose that, under certain conditions, a synchrotron afterglow could be observed (e.g. Loeb 2016). Moreover, using the very wide total field of view of the LOFAR observations (~200 deg^2), we also conducted a more general search for low-frequency transients, in particular by comparing our data with the 150 MHz TGSS survey (Intema et al. 2016) to look for transients on a longer average time-scale of about 4.5 years.

    In the top panel, we have plotted fractional variability (V_nu) vs. the significance of variability (eta_nu) for the first and third runs of each follow-up observation, using output from the Transients Pipeline (TraP; Swinbank et al. 2015). Strong transient candidates should appear as outliers in the top right corner of the plot. However, we found that the single outlier in this case is not a real transient; no LIGO EM counterparts or other transients were detected down to a median 6 sigma level of ~30 mJy. Nonetheless, this still allows us to place valuable constraints on radio transient surface densities (bottom panel). In particular, this is one of the first deep, very-low-frequency transient searches probing time-scales longer than one year.

    LOFAR observations of future GW events will be needed to continue this exciting and potentially ground-breaking search.


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