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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 in the nIR/optical, and with the Chandra X-ray Observatory. We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimeter observations from the literature to perform broadband modeling, and determined the macro- and microphysical parameters of the GRB blast wave. By combining the broadband modeling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modeling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope, and Hubble Space Telescope (HST), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs., Comment: 11 pages, 4 figures, 4 tables; accepted for publication in MNRAS

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 concatenation of a nova with a comet made by an early compiler. We have checked the record of the guest star, comparing it with records of comets in the same history. We find that most descriptions of comets clearly indicate motion, whereas the record of the guest star does not. We further argue that the term ``yan'' used to describe the star's ``size'' might be short for yan-chuang (seat bed), and ``half a yan'' would be simply as an imaginary figuration of the ancient observer. Moreover, we show that the term ``hou -year" (hou-nian) most probably means the year after next. We argue that the asterism Southern Gate consisted of the stars α and β Cen. We conclude that the record describing the guest star of AD 185 is completely different from any comet record in the same history, and that it almost certainly was a supernova.

GRB 130427A was extremely bright as a result of occurring at low redshift whilst the energetics were more typical of high-redshift gamma-ray bursts (GRBs). We collected well-sampled light curves at 1.4 and 4.8 GHz of GRB 130427A with the Westerbork Synthesis Radio Telescope (WSRT); and we obtained its most accurate position with the European Very Long Baseline Interferometry Network (EVN). Our flux density measurements are combined with all the data available at radio, optical and X-ray frequencies to perform broadband modeling in the framework of a reverse-forward shock model and a two-component jet model, and we discuss the implications and limitations of both models. The low density inferred from the modeling implies that the GRB 130427A progenitor is either a very low-metallicity Wolf-Rayet star, or a rapidly rotating, low-metallicity O star. We also find that the fraction of the energy in electrons is evolving over time, and that the fraction of electrons participating in a relativistic power-law energy distribution is less than 15%. We observed intraday variability during the earliest WSRT observations, and the source sizes inferred from our modeling are consistent with this variability being due to interstellar scintillation effects. Finally, we present and discuss our limits on the linear and circular polarization, which are among the deepest limits of GRB radio polarization to date., 14 pages, 5 figures, 6 tables; accepted for publication in MNRAS

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 commonly used in astronomy. In 50 h of observation time with the Westerbork Synthesis Radio Telescope array we have set a new limit on the flux of neutrinos, summed over all flavors, with energies in excess of 4x10(22) eV.

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 Hα emission this indication is much less clear.

The discovery of X-ray, optical and radio afterglows of gamma-ray bursts (GRBs) and the measurements of the distances to some of them have established that these events come from Gpc distances and are the most powerful photon emitters known in the Universe, with peak luminosities up to 10^52 erg/s. We here report the discovery of an optical transient, in the BeppoSAX Wide Field Camera error box of GRB980425, which occurred within about a day of the gamma-ray burst. Its optical light curve, spectrum and location in a spiral arm of the galaxy ESO 184-G82, at a redshift z = 0.0085, show that the transient is a very luminous type Ic supernova, SN1998bw. The peculiar nature of SN1998bw is emphasized by its extraordinary radio properties which require that the radio emitter expand at relativistical speed. Since SN1998bw is very different from all previously observed afterglows of GRBs, our discovery raises the possibility that very different mechanisms may give rise to GRBs, which differ little in their gamma-ray properties.

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, possible under non-stationary conditions, would lead to IC avalanches in the soft-gamma-ray energy band during transient periods. For the first time, broadband signatures of possible IC catastrophes were searched for in S5 0716+71. A multifrequency observing campaign targetting S5 0716+71 was carried out in November 2003 under the framework of the European Network for the Investigation of Galactic nuclei through Multifrequency Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope (WEBT), involving a pointing by the soft-gamma-ray satellite INTEGRAL, optical, near-infrared, sub-millimeter, millimeter, radio, and Very Long Baseline Array (VLBA) monitoring. S5 0716+71 was very bright at radio frequencies and in a rather faint optical state during the INTEGRAL pointing; significant inter-day and low intra-day variability was recorded in the radio regime, while typical fast variability features were observed in the optical band. No correlation was found between the radio and optical emission. The source was not detected by INTEGRAL, neither by the X-ray monitor JEM-X nor by the gamma-ray imager ISGRI, but upper limits to the source emission in the 3-200 keV energy band were estimated. A brightness temperature Tb>2.1x10^{14} K was inferred from the radio variability, but no corresponding signatures of IC avalanches were recorded at higher energies. The absence of IC-catastrophe signatures provides either a lower limit delta>8 to the Doppler factor affecting the radio emission or strong constraints for modelling of the Compton catastrophes in S5 0716+71., 15 pages, 3 EPS figures, 3 tables, to appear in A&A

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. Its morphology and polarization are very similar to those of the supernova remnant DA530 (G93.0+6.5), which is another high Galactic latitude SNR.

Our BeppoSAX observations of IC 443 were primarily directed toward isolating and studying its previously known hard component, thereby to test the hypothesis that this is direct evidence for very energetic (≃100 TeV) cosmic rays. Although our analysis is at an early stage, it was immediately obvious that we have, with the BeppoSAX/PDS, detected a very hard (from 14 to >30 keV) component which is almost certainly the counterpart of the EGRET γ-ray source 2 EGJ0618+2234. This object is offset from the prominent soft thermal emission in IC 443. In the same field we found with the BeppoSAX/MECS two hard (5–10 keV) hot spots. Both the hot spots and the 2EG source appear to be evidence for energetic cosmic rays produced where the SNR shock is interacting with a dense molecular cloud.

The remnant of Tycho's supernova of 1572 has been polarimetrically imaged using the 4 configurations of the VLA at wavelengths of 22 and 6 cm. A few data were also obtained at wavelengths of 21, 19, and 18 cm in the B configuration to check for any ambiguities in the Faraday rotation measurements and to look for deviations from the λ2 dependence of the Faraday rotation which would indicate significant internal Faraday effects. Although the total intensity shows structure on a scale of about 1 arcsecond the polarized emission appears to be resolved into cells of perhaps 10-arcsec size (1 arcsec corresponds to 0.011 pc at the 2.2 kpc distance to Tycho's SNR). We have therefore convolved the map shown in Figure 1 to a resolution of 4 arcsec to improve the signal-to-noise ratio. The contours represent the total intensity at 6-cm wavelength and the vectors show the position angle of the magnetic field with a length corresponding to the polarized intensity at 6 cm. In order to be seen, the vectors have a separation of 6 arcsec but no significant information is lost on this spacing.

We present the R_c band light curve of the optical transient (OT) associated with GRB970228, based on re-evaluation of existing photometry. Data obtained until April 1997 suggested a slowing down of the decay of the optical brightness. However, the HST observations in September 1997 show that the light curve of the point source is well represented by a single power law, with a ``dip'', about a week after the burst occured. The exponent of the power law decay is $\alpha$ = --1.10 $\pm$ 0.04. As the point source weakened it also became redder., Comment: 5 pages, latex, to appear in Gamma-Ray Bursts, 4-th Huntsville Symposium, eds Meegan, Preece, Koshut

The X-ray radiation from inverse Compton scattering of CMB photons by the relativistic electrons in ‘radio’ lobes provides a direct measure of their column density at a known energy, unlike synchrotron radiation which also depends on the unknown magnetic field. Thus by combining inverse Compton and radio data we can separately determine the particle energies and field strengths, rather than having to rely on uncertain estimates like minimum energy. The predicted flux is $$S_{IC} \alpha \left( {S_{\nu rad} \nu _{rad}^\alpha } \right)B^{ - (\alpha + 1)} \left( {1 + z} \right)^{\alpha + 3} $$ (1) and strong IC signal requires high radio flux and low magnetic field, properties of giant radio galaxies. On the other hand the minimum detectable count rate, I min , increases with the target size due to the larger background contribution. As a result the detectability of IC X-rays for ROSAT PSPCB measurements is roughly $${{I_{min} }}\alpha \left( {S_{rad} \cdot \theta \cdot z} \right)^{1/2} (1 + z)^{15/4} $$ (2) assuming a spectral index of 0.75. After making detailed prediction of S IC for a number of objects of the 3CR sample, the best candidates were 3C 236, 3C 326, and 4C 73.08.

Our Atlas of Extragalactic Radio Sources will present high-quality images of the nearer half of “3CRR”, the sample defined by Laing, Riley & Longair (1983). This is the best-studied complete sample of extragalactic radio sources. All 173 members have secure redshifts and most have been imaged in the radio at high resolution. There is also copious information on their optical line emission, and many have been detected in the sub-mm, FIR, and in X-rays. 3CRR is widely used as a baseline against which fainter, higher-redshift samples can be compared to define the evolution of the population (e.g. Neeser et al. 1995; Law-Green, this conference).

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 14 candidates has been observed by the WSRT using PuMa at both 92 and 21 cm in May 1999. From our preliminary analysis of the 382 MHz data, we find no evidence for MSPs in the first sample.

The radio emission from the remnant of Tycho's supernova of 1572 arises in a nearly circular, clumpy shell. A very distinct, thin bright rim just outside the main shell can be seen around most of the periphery of the remnant. The outer edge of radio emission, usually defined by this bright rim, coincides perfectly with the outer X-ray boundary. Most of the emission is polarized by a modest amount, with the outer rim particularly prominent. Observations at several wavelengths are used to map out the rotation measure at high angular resolution, and determine the intrinsic magnetic field direction. The magnetic field shows a somewhat cellular pattern but with a net radial orientation and a generally fairly low degree of polarization.

The Westerbork Synthesis Radio Telescope (WSRT) has now been used to make source surveys at frequencies of 610 and 1415 MHz. This paper summarizes the results concerning source counts and anisotropies in the distribution of sources from those surveys not concerned with clusters of galaxies.

NGC 6251, a 14th mag elliptical galaxy, was shown by Waggett et al. (1977) to have large-scale radio emission features with a total angular extent of ∼ 1.1°, which corresponds to a projected linear size of about 1.7 Mpc (HO = 75 km s−1 Mpc−1). A bright radio jet links a central core source embedded in NGC 6251 to the extended emission on the northwest side of the galaxy.

Continuum observations of IC 443 were made at 21 cm with a resolution of 23″×59″. The appearance in the radio continuum is very similar to the optical appearance. Since the radio emission is nonthermal, this requires a mechanism that can enhance the synchrotron volume emissivity within thermal filaments, which emit strong optical radiation. We suggest compression of gas and magnetic fields in a shock.Tycho's remnant has been observed both at 21 cm (resolution 24″ × 27″) and at 6 cm (resolution 7″ × 8″). Most of the fine scale structure is resolved. The similarity at the two wavelengths indicates a remarkable constancy in the spectral index of features down to a scale of 20″.

A giant radio source with an unusual Z-shaped structure extending over nearly one degree on the sky has been detected around the nearby elliptical galaxy NGC315. The source has structure aligned with the minor axis of the optical galaxy on linear scales ranging from a few tens of kpc to ~ 1.7 Mpc. There is also a bright compact (

Pulsar-like emission has been detected from the flat-spectrum component of the galactic radio source CTB80. The consequences for the source are discussed.

A high resolution study has been made of faint and very extensive radio components associated with the galaxies 3C236 and DA240. Their respective linear dimensions of 5.7 Mpc and 2 Mpc are without precedent. Their properties are compared with those of other radio galaxies and the consequences for present models of the evolution of these objects are briefly discussed.

The very fact that supernovae produce remnants has long been compelling evidence for their interaction with an ambient medium. Recent work using the Westerbork Telescope and IRAS now firmly establishes the presence of both neutral hydrogen and dust in or near the shock front of a variety of supernova remnants (SNR). HI has been found in a handful of “mature” SNR (all the objects thus far investigated), the detailed correlation of cloud morphology with radio continuum and Hα filaments providing incontrovertible evidence for an association. The overall velocity spread observed indicates that some neutral hydrogen has been accelerated by interaction with the shock front. In the best studied case, IC443, the velocity structure of several features suggests clouds with shocks passing through them. The presence of infrared emission and hence dust appears more ubiquitous. IRAS observations of both young and “mature” SNR reveal structures which correlate well with the radio and optical morphology. The emission typically peaks in the 25 to 50 micron range, and the data appear to be consistent with dust heated by the SNR shock. The observations are considered in the context of the SNR environment.

NGC 6251, a 14th mag elliptical galaxy, was shown by Waggett et al. (1977) to have large-scale radio emission features with a total angular extent of ~ 1.1°, which corresponds to a projected linear size of about 1.7 Mpc (HO = 75 km s-1 Mpc-1). A bright radio jet links a central core source embedded in NGC 6251 to the extended emission on the northwest side of the galaxy.

The Westerbork Synthesis Radio Telescope has made observations of some galactic supernova remnants at 21 cm continuum. The observations of Tycho’s remnant were carried out by Strom and Duin. Further details about the instrument and the measurements can be found in Strom and Duin (1973).

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.

Continuum observations of IC 443 were made at 21 cm with a resolution of 23″ × 59″. The appearance in the radio continuum is very similar to the optical appearance. Since the radio emission is nonthermal, this requires a mechanism that can enhance the synchrotron volume emissivity within thermal filaments, which emit strong optical radiation. We suggest compression of gas and magnetic fields in a shock.

The large-scale emission present in IRAS maps is usually dominated by zodiacal light, with a spectrum that resembles dust at ~ 190 K, and emission from cold interstellar dust at ~ 20 K. The confusion due to this background tends to obscure other, weaker emission, such as e.g. the emission from the shock-heated dust (T ~ 60 K) we have been looking for in supernova remnants (Braun et al 1986).

Several large (at least 0.°5 diameter) supernova remnants (SNR) located at 2. °5 or more from the galactic plane have been mapped with the Westerbork Synthesis Radio Telescope (WSRT) at 49 cm. The sample, which includes IC443, DA530, VR042.05.01, CTA1 and OA184, is particularly suitable for complementary studies in other spectral regimes. By choosing objects at relatively high galactic latitudes we have consciously selected SNR which are likely to suffer less than average extinction and are probably nearer to the sun than most. This makes them particularly attractive for optical and X-ray studies which, along with IR and further radio observations, are either in progress or being planned. These are summarized in Table 1.

Infrared emission in young supernova remnants is interpreted as coming from shock-heated dust. Using models and data from other wavelength regimes, many physical parameters of the remnants can accurately be derived.

IN the field of an observation of the cluster Abell 478 made with the Westerbork Synthesis Radio Telescope1 at 21 cm, we have discovered and report here a weak radio source coincident with the 6.2-mag B8Vn star2 HD26676. The source positions derived from both the 21-cm observation, and measurements made later at 6 cm, agree within the errors with the AGK3 position of the star (Table 1). The 21-cm data were obtained during a single 8-h observation, while at 6 cm three measurements, each lasting for 10 h, were made over a period of 6 weeks. There is no significant indication of variability from the three flux densities derived at 6 cm (Table 2). The global 6-cm flux density, as well as the position in Table 1, were obtained by combining the three observations in a single map.

New and confirmed optical identification of 12 3CR radio sources are reported, along with redshifts for nine of them. Seven have redshifts in excess of 1, with the highest being 1.841 for 3C454.1; the remaining three sources are also likely to be at z of greater than 1. One of the newly identified sources, 3C 194, shows a moderately strong Ly-alpha emission, and may be a member of the new class of objects, possible young/forming galaxies, typified by 3C 326.1 and 3C 294. The optical identification of the 3CR sources are now complete, and only six are lacking redshifts. Practically all of the new identifications are galaxies whose light appears to be dominated by stars, rather than nonthermal active nuclei, although their powerful radio emission argues that they are likely to be highly unusual objects. Their observed properties are similar to those of previously identified high-redshift powerful radio galaxies. 39 references.

The complex X-ray and radio structures of the cluster of galaxies Abell 478 have been observed in the 2-11-keV energy band by the rotating modulation collimators on the SAS-3 X-ray observatory and at 1415 MHz by the Westerbork synthesis radio telescope. The X-ray data imply an extended source (X-ray luminosity of the order of 10 to the 45th power erg/s) and are consistent with the presence of a coincident pointlike source X-ray luminosity of the order of 10 to the 45th power erg/s. The X-ray source position is also coincident with a cD radio galaxy at the core of the cluster.

The extended cloud complex containing members of the Gem OB1 association, the supernova remnant IC443, and the H II region S249 has been studied with IRAS observations at 12,25,60 and 100 microns and WSRT observations at 327 and 1400 MHz and in the 21-cm H I line. A skeleton-like framework of cool dust delineates the boundaries of the region, and physical parameters have been derived for the entire complex, individual H II regions and the shocked and recombined gas within IC443 using the radio and infrared data. IC443 is shown to consist of three interconnected, roughly spherical subshells of vastly different radii and centroids. The geometry is fully constrained by the structural and kinematic data. Two of the subshells together define the usually assumed boundaries of IC443, while the third includes the optical filaments which extend beyond the northeastern rim and which are shown to have well-correlated nonthermal radio components. The available evidence implies that the SNR shock has encountered a pre-existing high density shell. It is shown that the system of subshells is fully consistent with formation by stellar wind driven bubbles generated by association members within the inhomogeneous environment of the complex.

Radio observations at 610 MHz with the Westerbork Synthesis Radio Telescope (WSRT) are combined with optical data from the 48 inch Palomar telescope to search for radio-optical candidates for five high-latitude Uhuru X-ray sources (3U 0042+32, 0917+63, 1443+43, 1555+27, and 1809+50). From the data for two of these fields we suggest the following: (1) The rich cluster of galaxies A2142 (zapprox. =0.1), which is found to contain several extended radio sources in its central region, is a likely candidate for 3U 1555+27, as first suggested from purely optical observations. (2) The ''near'' Zwicky cluster, Zw 1810.2+4949, which contains a complex radio source associated with a 15 mag galaxy, is a candidate identification for 3U 1809+50. The unusual radio galaxy OU 516, as well as the double galaxy NGC 6582, both located in the cluster, are also candidates for 3U 1809+50, especially if the X-rays indicate variability. (AIP)