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Introduction
Publications
Publications (239)
The missing baryons are usually thought to reside in galaxy filaments as
warm-hot intergalactic medium (WHIM). From previous studies, giant radio
galaxies are usually associated with galaxy groups, which normally trace the
WHIM. We propose observations with the powerful SKA1 to make a census of giant
radio galaxies in the southern hemisphere, which...
Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared
(nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute
Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope...
GRB 130427A was extremely bright due to a combination of its low redshift and
energetics typical of high-redshift gamma-ray bursts (GRBs). As a result, we
were able to obtain high-quality light curves across the electromagnetic
spectrum, providing an excellent opportunity for detailed broadband modeling.
We observed GRB 130427A with the Westerbork...
The discovery of neutral atomic hydrogen (HI) in the interstellar medium was based on a prediction by H. C. van de Hulst. The story of how Jan Oort suggested that the student Van de Hulst might investigate the question, who then reported his results at a wartime colloquium in Leiden, is well known. Recent archival research has turned up letters and...
The giant radio galaxy 4C 73.08 has been observed with the Westerbork Telescope at a wavelength of 21 cm. The radio map obtained
is a significant improvement upon previous maps in terms of the combination of high dynamic range, sensitivity and angular
resolution. The new map shows that the jet, previously thought to be one-sided, is probably symmet...
Van de Hulst's 1944 suggestion that 21-cm HI from the Milky
Way might be observable, Ewen and Purcell's 1951 detection and the
subsequent Kootwijk confirmation by Muller constitute the basic facts of
the HI line discovery. I will discuss some less well-known aspects of
the prediction and detection. There is concrete evidence as to when Oort
first b...
The optical field of the giant radio galaxy (GRG) 4C 73.08 has been spectroscopically investigated to look for companions
to the host 7Zw 292. We have taken spectra of 12 candidates and have determined redshifts for all of them. When combined with
the previously known redshift of 7Zw 292, we find that the radio source is accompanied by a small grou...
The brightest optical flash from a γ-ray burst (GRB) was, briefly, a naked-eye object. Several other GRBs have produced optical transients only slightly fainter. We argue that, based upon the recently accumulated data from hundreds of GRB transients, many such optical events should have been visible to the unaided eye in the course of human history...
We have investigated the environment of the giant radio galaxy NGC 315 with its associated group of galaxies selected by their
spectroscopic redshifts. Observations were made with the 2.16-m optical telescope at Xinglong Station of the National Astronomical
Observatories of China. In addition to 25 galaxies near NGC 315 with published redshifts, we...
The brightest optical flash from a gamma-ray burst (GRB) was, briefly, a
naked-eye object. Several other GRBs have produced optical transients only
slightly fainter. We argue that, based upon the recently accumulated data from
hundreds of GRB transients, many such optical events should have been visible
to the unaided eye in the course of human his...
Context. There is a group of about twenty galaxies around the giant radio galaxy (GRG) DA 240 which we are studying to investigate the environment of the radio source. We have noted that 11 members are aligned with the radio emission (Peng et al. 2004, A&A, 415, 487). The alignment occurs within a small angle similar to the width of the GRG radio l...
We have investigated galaxies around NGC 6251 to search for an associated group. Our main goal is to study the environment
around the giant radio galaxy to better understand the reasons for its size and structure. To this end, we have made spectroscopic
observations with the 2.16-m optical telescope at Xinglong Station of the National Astronomical...
For well over two millennia, Chinese astronomers observed and recorded a wide variety of phenomena in the heavens: eclipses,
comets, sunspots, aurorae, strange clouds and other meteorological phenomena. For a somewhat shorter period, there were also
recorded Japanese and Korean observations of the skies. In terms of numbers over the relevant time i...
The Centre for Astronomy at James Cook University (JCU) in Australia has been offering totally internet-delivered Master of Astronomy degrees since 2003 and Doctor of Astronomy and Ph.D. degrees since 2004. In 2005 a new dimension was added with unique offerings in the history of astronomy at both Masters and Doctoral levels. With the aid of 1 full...
This book provides readers with the results of recent research from some of the world's leading historians of astronomy on aspects of Arabic, Australian, Chinese, Japanese, and North and South American astronomy and astrophysics. It contains peer-reviewed papers gathered from the International Conferences on Oriental Astronomy 6 (ICO-6) with the ch...
Context. Ultra-high energy (UHE) neutrinos and cosmic rays initiate particle cascades underneath the Moon's surface. These cascades have a negative charge excess and radiate Cherenkov radio emission in a process known as the Askaryan effect. The optimal frequency window for observation of these pulses with radio telescopes on the Earth is around 15...
Ultra-high energy (UHE) neutrinos and cosmic rays initiate particle cascades underneath the Moon's surface. These cascades have a negative charge excess and radiate Cherenkov radio emission in a process known as the Askaryan effect. The optimal frequency window for observation of these pulses with radio telescopes on the Earth is around 150 MHz. By...
We observed the position of the broad-line Type Ic supernova PTF10bzf (ATel 2470) with the Westerbork Synthesis Radio Telescope at 4.8 GHz, at March 13 17.89 UT to March 14 1.45 UT. We do not detect a radio source at the position of the supernova (ATel #2470). The three-sigma rms noise in the map around that position is 126 microJy per beam, and th...
We observed the position of the Type Ibc supernova SN 2010br (CBET 2245, ATel #2587) with the Westerbork Synthesis Radio Telescope at 4.8 GHz, at May 11 14.34 UT to May 12 2.31 UT. We do not detect a radio source at the position of the supernova (CBET 2245). The three-sigma rms noise in the map around that position is 102 microJy per beam, and the...
Particle cascades initiated by ultrahigh energy neutrinos in the lunar regolith will emit an electromagnetic pulse with a time duration of the order of nanoseconds through a process known as the Askaryan effect. It has been shown that in an observing window around 150 MHz there is a maximum chance for detecting this radiation with radio telescopes...
Particle cascades initiated by ultra-high energy (UHE) neutrinos in the lunar regolith will emit an electromagnetic pulse with a time duration of the order of nano seconds through a process known as the Askaryan effect. It has been shown that in an observing window around 150 MHz there is a maximum chance for detecting this radiation with radio tel...
GRB 030329 displayed one of the brightest optical afterglows ever. We have followed the radio afterglow of GRB 030329 for over 5 years using the GMRT and WSRT at low radio frequencies. This is the longest as well as the lowest frequency follow up of any GRB afterglow ever.
Radio observations of a GRB afterglow provide a unique probe of the physics...
GRB 051022 was undetected to deep limits in early optical observations, but precise astrometry from radio and X-rays showed that it most likely originated in a galaxy at z ≈ 0.8. We report radio, optical, near-infrared, and X-ray observations of GRB 051022. Using the available X-ray and radio data, we model the afterglow and calculate its energetic...
We present a detailed spectral analysis of the prompt and afterglow emission of four nearby long-soft gamma-ray bursts (GRBs 980425, 030329, 031203, and 060218) that were spectroscopically found to be associated with Type Ic supernovae and compare them to the general GRB population. For each event, we investigate the spectral and luminosity evoluti...
G315.4-2.3 is an extended-shell supernova remnant (SNR) with some characteristics of evolutionarily young remnants and some of older ones. To further elucidate some of its characteristics, we present imaging and polarimetry of this SNR at a frequency of 1.34 GHz with a resolution of 8'' made with the Australia Telescope Compact Array. The indicator...
We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. First results are presented of an analysis of 20 hours of observation data for NuMoon project using the Westerbork Synthesis Radio Telescope to search for...
The NuMoon project uses the Westerbork Synthesis Radio Telescope to search for short radio pulses from the Moon. These pulses are created when an ultra high energy cosmic ray or neutrino initiates a particle cascade inside the Moon's regolith. The cascade has a negative charge excess and moves faster than the local speed of light, which causes cohe...
The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability and signatures of an inverse-Compton (IC) catastrophe during the states of extreme apparent brightness temperatures. The observing campaign involved simultaneous monitoring at radio to IR/optical wavelengths cen...
Oriental, especially Chinese, observations of transient celestial events are often compared with mundane objects: fruits, birds and containers are typical. The comparison is sometimes thought to indicate brightness of the heavenly object in question (for night-time apparitions). Here, the matter is examined in some detail. There is evidence that th...
An intensive radio frequency interference (RFI) monitoring campaign has been carried out at several proposed Square Kilometer Array (SKA) sites in China, based on the RFI measurement protocol for SKA candidate sites (hereafter RFI protocol), over a period of at least one year. In this paper we summarize the RFI equipment, data handling, and present...
We explore the physics behind one of the brightest radio afterglows ever, GRB 030329, at late times when the jet is non-relativistic. We determine the physical parameters of the blast wave and its surroundings, in particular the index of the electron energy distribution, the energy of the blast wave, and the density (structure) of the circumburst m...
Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a three-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radi...
Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a three-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radi...
The Dwingeloo 25-m telesope, inaugurated in 1956, has played a major role in research for half a century. We trace its history back to its conception in 1944, and summarize its main achievements. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
There are probably few radio astronomers who would be able to recall A.H. de Voogt, which is unfortunate, but at the same time unsurprising: for he published no original astronomical research, never carried out pioneering observations, nor is his name linked to either theoretical or instrumental breakthroughs. Yet he was described by the man who fi...
Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a 3-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Te...
When high-energy cosmic rays impinge on a dense dielectric medium such as the lunar re-golith, radio waves are produced through the Askaryan effect. At frequencies of the order of 100 MHz this is a very efficient way to detect Ultra-High Energy cosmic rays or neutrinos. The radio signals can be measured using the Westerbork Synthesis Radio Telescop...
The "guest star" of AD185, recorded in the ancient Chinese history the Houhanshu, has been widely regarded as a supernova. However, some authors have suggested that the guest star might have been a comet. It has also been proposed that the record is the concate-nation of a nova with a comet made by an early compiler. We have checked the record of t...
We present the results of EVN polarization observations of fourteen GHz-Peaked-Spectrum (GPS) radio sources at 5 GHz. These
sources were selected from bright GPS source samples and we aimed at finding Compact Symmetric Objects (CSOs). We have
obtained full polarization 5 GHz VLBI observations of 14 sources providing information on their source stru...
Context.Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding $10^{12}$ K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The violation of the IC limit, actually possible under non-stationary conditions, would lead to IC avalanches in...
We describe the kinematical character of optically emitting gas in a small area of the Cygnus Loop, as seen with moderately high resolution in Ha and [0III]. In both lines a number of different components contributing to the emission are recognized. The [0III] emission indicates that the gas may lie in a thin sheet, while from the H emission this i...
Recent data in several wavebands on the peculiar galactic object G70.7+1 .2 is reviewed. A new VLA map clearly shows the radio shell. Possible interpretations of the object include supernova remnant, nova shell, and nebula resulting from mass loss from a giant or supergiant, although each of these interpretations has its own difficulties.
The birth of Dutch radio astronomy can be rather precisely dated to 15 April 1944, when H.C. van de Hulst presented the results of his theoretical research into the origin of radio waves from space. We have investigated the events leading up to the momentous suggestion that hydrogen emission at 21 cm ought to be detectable. Both published material...
We present world-array VLBI observations of the blazar 1803+784 performed on May 29, 1993 at λ = 18 cm. A 17-station VLBI array, the phased VLA and the 7-station MERLIN array observed the source simultaneously for 11 h. We present the global VLBI map, the MERLIN map, and combined-array maps at different resolutions giving an overview of the morphol...
We present our centimeter wavelength (1.4, 2.3 and 4.8 GHz) light curves of the afterglow of GRB 030329, which were obtained with the Westerbork Synthesis Radio Telescope. Modeling the data according to a collimated afterglow results in a jet-break time of 10 days. This is in accordance with earlier results obtained at higher radio frequencies. How...
The EVN stations encompass elements with a range of diameters, even including an interferometer (the Westerbork Telescope, with up to 14 elements used together as a tied array). In combination, the various station pairs will each produce their own primary beam envelopes, with which the interferometer pattern is modulated. People sometimes forget th...
The history of early radio astronomy in the Netherlands is explored,
especially that which did not involve neutral hydrogen studies. Although
little of this early—mainly solar—work was published in
professional journals, there is some information in a popular Dutch
astronomy magazine. From this it is clear that the early radio
observations of the S...
I review the talks given during IAU Colloquium 196, sometimes in a revised order to suggest certain connexions. The AU now, its definition, value and uncertainty, and its modern determination are contrasted with the situation in 1640. While there are differences, not least in the value of the AU and its error, some things have not changed. As an en...
We have investigated galaxies near the giant radio source DA 240 in a study of the source's environment. Spectroscopic observations were obtained with the 2.16 m optical telescope of the National Astronomical Observatories of China. We have measured the redshifts of 26 objects, and find that 16 have nearly the same value as the DA 240 galaxy, and h...
We have investigated galaxies near the giant radio source DA 240 in a study of the source's environment. Spectroscopic observations were obtained with the 2.16 m optical telescope of the National Astronomical Observatories of China. We have measured the redshifts of 26 objects, and find that 16 have nearly the same value as the DA 240 galaxy, and h...
We detected a correlation between optical and giant radio pulse emission from the Crab pulsar. Optical pulses coincident with the giant radio pulses were on average 3% brighter than those coincident with normal radio pulses. Combined with the lack of any other pulse profile changes, this result indicates that both the giant radio pulses and the inc...
We carried out a brief campaign in September 1998 to determine Jupiter’s radio spectrum at frequencies spanning a range from 74 MHz up to 8 GHz. Eleven different telescopes were used in this effort, each uniquely suited to observe at a particular frequency. We find that Jupiter’s spectrum is basically flat shortwards of 1–2 GHz, and drops off steep...
Unusual polarization properties of the high galactic latitude supernova
remnant (SNR) G4.8+6.2 are reported. The percentage polarization is
larger than 70% over the two main shells of G4.8+6.2 at 1400 MHz. It
is the second SNR with such high polarization at such a low frequency
among the known 225 SNRs. We show that this is very unusual for an
SNR....
We present our centimetre wavelength (1.4, 2.3 and 4.9 GHz) light curves of the afterglow of GRB030329, which were obtained with the Westerbork Synthesis Radio Telescope. Modelling the data according to a collimated afterglow results in a jet-break time t(sub j) of 17 days. This is in contrast with earlier results obtained at higher frequencies, wh...
Kreutz sungrazers consist of a handful of major comets and some 400 minor (faint) members found by satellite observations through 2001. Although they can be spectacular visual objects, many must be absent from historical records. Here I show that a dozen or so previously unrecognized sungrazers were probably recorded in Chinese solar observations,...
Using the Very Large Array and the Pie Town antenna, we have measured the position of the radio pulsar B1951+32 relative to nearby background radio sources at four epochs between 1989 and 2000. These data show a clear motion for the pulsar of (25 +/- 4) milliarcsec/yr at a position angle (252 +/- 7) degrees (north through east), corresponding to a...
The Westerbork Telescope has good low-frequency capability, with receivers covering much of the frequency range from 250 to 1800 MHz. For pulsar observations the array elements can be coherently summed to provide the equivalent of a 93 m aperture. To exploit this potential, a new backend, PuMa, has recently been commissioned. It can be configured i...
Using the Very Large Array, we have measured the position of the radio
pulsar B1951+32 relative to nearby background radio sources at four
epochs between 1989 and 2000. These data show a clear proper motion for
the pulsar of 25+/-4 mas/yr at a position angle 252+/-7 degrees (north
through east), corresponding to a transverse velocity 240+/-40 km/s....
We present observational results from long term monitoring of giant pulses from two pulsars. One of the pulsars (PSR 0950+08) has been observed simultaneously at three different observatories, at different radio frequencies. There is evidence to suggest that the giant pulse phenomenon is intrinsic to the pulsar.
Deep optical CCD imaging and spectroscopic observations of four new nebular structures have been performed for the first time. Filamentary and diffuse emission is detected in this field located to the north-east of the CTB 80 supernova remnant (SNR). Two long filaments are discovered to the north of LBN 156, while a 23 arcmin long filament, emittin...
The topics covered in this book include: Theory of Scattering and Scintillation, Distribution of Scattering Material, Intra-day Variability, Pulsars and their Magnetospheric Structure, Polarization of AGN, Interplanetary Scintillation, and Future Highly-Sensitive Radio Telescopes. The introductory papers emphasize the essential properties of diffra...
Based on our examination of the characteristics of about 280 known pulsars and 40 millisecond pulsars (MSPs), we have derived selection criteria for MSP candidates: steep spectrum, highly linearly polarized point sources. The first sample of 14 candidates from the NVSS at 1.4 GHz and the WENSS at 325 MHz has been observed by the WSRT using PuMa at...
It has been argued, for a number of reasons, that the next generation radio telescope should be a multi-element interferometer
with a collecting area of about 1 km2. The remaining parameters of such an instrument – frequency range, angular resolution, instantaneous bandwidth, etc. – will
be science driven. The requirements for propagation studies a...
We have carried out a series of measurements at some locations in Guizhou Province and one additional site at the Urumqi Astronomical Station in the Xinjiang autonomous region, to check on their suitability, from the point of view of interference, for the construction of a Five-hundred-meter Aperture Spherical Telescope (FAST). This large facility...
We first very briefly introduce the major radio facilities for astronomical research in China, and then report on the present interference situation at major radio observatories. Some of the radio interference problems are caused by paging services, mobile phone satellites, telemetry services for power supply, waterpower and earthquake activity, or...
It has been argued, for a number of reasons, that the next generation radio telescope should be a multi-element interferometer with a collecting area of about 1 km 2 . The remaining parameters of such an instrument – frequency range, angular resolution, instantaneous bandwidth, etc. – will be science driven. The requirements for propagation studies...
High resolution radio observations of the composite supernova remnant (SNR) G326.3-1.8 or MSH 15-56 with the Australia Telescope Compact Array show details of both the shell and the bright plerion which is offset about 1/3 of the distance from the center of the SNR to the shell. The shell appears to be composed of thin filaments, typical of older s...
Seven millisecond pulsars (MSPs) have been identified from the NVSS by positional coincidence. Our examination of the characteristics of about, 280 known pulsars and 40 MSPs has shown that they have high polarization and a steep spectrum. We identify likely MSP candidates from both the NVSS at 1.4 GHz and the WENSS at 325 MHz. The first sample of 1...
The 39.5 ms pulsar PSR 1951+32 and the remnant with which it is associated, CTB 80, have both been observed with the recently upgraded Westerbork synthesis array (WSRT). Parts of CTB 80 have been observed over the frequency coverage from 0.3 to 8 GHz, while PSR 1951+32 has been observed from 0.3 to 1.6 GHz. The results are described and discussed i...
A Five hundred meter Aperture Spherical Telescope (FAST) is proposed to
be built in the unique karst area of southwest China, and will act, in a
sense, as a prototype for the Square Kilometer Array (SKA). It will be
over twice as large as Arecibo coupled with much wider sky coverage.
Large radio telescopes have a distinguished record of foundamenta...
We present the results of VLBI observations of OH masers in the direction of the Galactic star forming region W51. The aim of this exercise was to measure the distribution of the apparent angular broadening of these maser sources. The maser spots lie in two patches covering some 8'' NS. Individual spots are extended by up to 50 m.a.s., with axial r...
this paper we try to understand the radio emission from the shell of the nova GK Per in order to check the concepts described in the series of papers on the origin of cosmic rays, and develop them further.
We report on Westerbork 1.4 GHz radio observations of the radio counterpart to $\gamma$-ray burst GRB~970508, between 0.80 and 138 days after this event. The 1.4 GHz light curve shows a transition from optically thick to thin emission between 39 and 54 days after the event. We derive the slope $p$ of the spectrum of injected electrons ($dN/d\gamma_...
We report on the results of optical follow-up observations of the counterpart of the gamma-ray burst GRB 970508, starting 7 hr after the event. Multicolor U-, B-, V-, Rc-, and Ic-band observations were obtained during the first three consecutive nights. The counterpart was monitored regularly in Rc until ~ 4 months after the burst. The light curve...
We report on the results of optical follow-up observations of the counterpart of GRB 970508, starting 7 hours after the event. Multi-color U, B, V, R$_{c}$ and I$_{c}$ band observations were obtained during the first three consecutive nights. The counterpart was monitored regularly in R$_{c}$ until $\sim$ 4 months after the burst. The light curve a...
During the impacts of the fragmented Comet D/Shoemaker–Levy 9, Jupiter's synchrotron radio emission at λ90 cm was monitored using the Very Large Array (VLA) and Westerbork Synthesis Radio Telescope. The dramatic infall of the comet onto Jupiter temporarily induced significant changes in the planet's radiation belts. The total flux density of Jupite...
Radio telescope observations taken with the VLA and WSRT during the period June-October 1994 show an East-West asymmetry which evolves over time. The E/W asymmetry is induced immediately following the first fragment impact of comet Shoemaker-Levy 9. Following an impact, enhancements are seen over a =~100? range of Jovicentric longitudes at lambdaII...