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We outline the prospects for performing pioneering radio weak gravitational lensing analyses using observations from a potential forthcoming JVLA Sky Survey program. A large-scale survey with the JVLA can offer interesting and unique opportunities for performing weak lensing studies in the radio band, a field which has until now been the preserve of optical telescopes. In particular, the JVLA has the capacity for large, deep radio surveys with relatively high angular resolution, which are the key characteristics required for a successful weak lensing study. We highlight the potential advantages and unique aspects of performing weak lensing in the radio band. In particular, the inclusion of continuum polarisation information can greatly reduce noise in weak lensing reconstructions and can also remove the effects of intrinsic galaxy alignments, the key astrophysical systematic effect that limits weak lensing at all wavelengths. We identify a VLASS "deep fields" program (total area ~10-20 square degs), to be conducted at L-band and with high-resolution (A-array configuration), as the optimal survey strategy from the point of view of weak lensing science. Such a survey will build on the unique strengths of the JVLA and will remain unsurpassed in terms of its combination of resolution and sensitivity until the advent of the Square Kilometre Array. We identify the best fields on the JVLA-accessible sky from the point of view of overlapping with existing deep optical and near infra-red data which will provide crucial redshift information and facilitate a host of additional compelling multi-wavelength science., Comment: Submitted in response to NRAO's recent call for community white papers on the VLA Sky Survey (VLASS)

VSOPシンポジウム(2000年1月19日-21日. 宇宙科学研究所(ISAS)）, 相模原市, 神奈川県, VSOP Symposium (January 19-21, 2000. Institute of Space and Astronautical Science(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000155014

The SKA at mid and low frequencies will be constructed in two distinct phases, the first being a subset of the second. This document defines the main scientific goals and baseline technical concept for the SKA Phase 1 (SKA_1). The major science goals for SKA_1 will be to study the history and role of neutral Hydrogen in the Universe from the dark ages to the present-day, and to employ pulsars as probes of fundamental physics. The baseline technical concept of SKA_1 will include a sparse aperture array operating at frequencies up to 450 MHz, and an array of dishes, initially operating at frequencies up to 3 GHz but capable of 10 GHz in terms of antenna surface accuracy. An associated Advanced Instrumentation Program (AIP) allows further development of new technologies currently under investigation. Construction will take place in 2016-2019 at a total capital cost of 350M\texteuro, including an element for contingency. The cost estimates of the SKA_1 telescope are now the subject of a more detailed and thorough costing exercise led by the SKA Project Development Office (SPDO). The 350 M\texteuro total for SKA_1 is a cost-constrained cap; an additional contingency is to reduce the overall scope of the project. The design of the SKA_1 is expected to evolve as the major cost estimates are refined, in particular the infrastructure costs at the two sites. The SKA_1 facility will represent a major step forward in terms of sensitivity, survey speed, image fidelity, temporal resolution and field-of-view. It will open up new areas of discovery space and demonstrate the science and technology underpinning the SKA Phase 2 (SKA_2)., 8 pages, 6 Figures. Talk presented at 'A New Golden Age for Radio Astronomy', International SKA Forum 2010, 10-14 June 2010, Hof van Saksen, NL. A higher resolution version of this paper is available at http://www.astron.nl/~mag/dokuwiki/doku.php?id=ska_phase_1_paper

We have studied the growth of the shell-like radio structure of supernova SN1993J in M81 from September 1993 through October 2003 with very-long-baseline interferometry (VLBI) observations at the wavelengths of 3.6, 6, and 18cm. For this purpose, we have developed a method to accurately determine the outer radius (R) of any circularly symmetric compact radio structure like SN1993J. The source structure of SN1993J remains circularly symmetric (with deviations from circularity under 2%) over almost 4000 days. We characterize the decelerated expansion of SN 1993J through approximately day 1500 after explosion with an expansion parameter $m= 0.845\pm0.005$ ($R \propto t^{m}$). However, from that day onwards the expansion is different when observed at 6 and 18cm. Indeed, at 18cm, the expansion can be well characterized by the same $m$ as before day 1500, while at 6cm the expansion appears more decelerated, and is characterized by another expansion parameter, $m_{6}= 0.788\pm0.015$. Therefore, since about day 1500 on, the radio source size has been progressively smaller at 6cm than at 18cm. These findings are in stark contrast to previous reports by other authors on the details of the expansion. In our interpretation the supernova expands with a single expansion parameter, $m= 0.845\pm0.005$, and the 6cm results beyond day 1500 are due to physical effects, perhaps also coupled to instrumental limitations. Two physical effects may be involved: (a) a changing opacity of the ejecta to the 6cm radiation, and (b) a radial decrease of the magnetic field in the emitting region. (Long abstract cut. Please, read full abstract in manuscript)., 21 pages, 19 figures, accepted in A&A

We studied the radio structure of high-redshift (z>3) quasars with VSOP at 1.6 and 5 GHz. These sources are the most distant objects ever observed with Space VLBI, at rest-frame frequencies up to ~25 GHz. Here we give an account of the observations and briefly highlight the most interesting cases and results. These observations allowed us, among other things, to estimate the mass of the central black holes powering these quasars, to identify large misalignments between the milli-arcsecond (mas) and sub-mas scale radio structures, and to detect apparent superluminal motion at sub-mas scale., 3 pages; proceedings of the symposium "Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technology" (ISAS/JAXA, Sagamihara, Japan, 3-7 Dec 2007). Astronomical Society of the Pacific Conference Series, eds. Hagiwara Y., Fomalont E.B., Tsuboi M., Murata Y., in press

LOFAR, the Low Frequency Array, is a next-generation radio telescope that is being built in Northern Europe and expected to be fully operational at the end of this decade. It will operate at frequencies from 15 to 240 MHz (corresponding to wavelengths of 20 to 1.2 m). Its superb sensitivity, high angular resolution, large field of view and flexible spectroscopic capabilities will represent a dramatic improvement over previous facilities at these wavelengths. As such, LOFAR will carry out a broad range of fundamental astrophysical studies. The design of LOFAR has been driven by four fundamental astrophysical applications: (i) The Epoch of Reionisation, (ii) Extragalactic Surveys and their exploitation to study the formation and evolution of clusters, galaxies and black holes, (iii) Transient Sources and their association with high energy objects such as gamma ray bursts, and (iv) Cosmic Ray showers and their exploitation to study the origin of ultra-high energy cosmic rays. In this conference the foreseen LOFAR work on the epoch of reionisation has been covered by de Bruyn and on cosmic ray showers by Falcke. During this contribution we will first present the LOFAR project with an emphasis on the challenges faced when carrying out sensitive imaging at low radio frequencies. Subsequently, we will discuss LOFAR's capabilities to survey the low-frequency radio sky. Main aims for the planned surveys are studies of z>6 radio galaxies, diffuse emission associated with distant clusters and starbursting galaxies at z>2., 11 pages, 5 figures, to appear in the proceedings of the conference "Cosmology, galaxy formation and astroparticle physics on the pathway to the SKA", Oxford, April 10-12 2006

We present the results of a number of high resolution radio observations of the AGN 1156+295. These include multi-epoch and multi-frequency VLBI, VSOP, MERLIN and VLA observations made over a period of 50 months. The 5 GHz MERLIN images trace a straight jet extending to 2 arcsec at P.A. -18 degrees. Extended low brightness emission was detected in the MERLIN observation at 1.6 GHz and the VLA observation at 8.5 GHz with a bend of about 90 degrees at the end of the 2 arcsecond jet. A region of similar diffuse emission is also seen about 2 arcseconds south of the radio core. The VLBI images of the blazar reveal a core-jet structure with an oscillating jet on a milli-arcsecond (mas) scale which aligns with the arcsecond jet at a distance of several tens of milli-arcseconds from the core. This probably indicates that the orientation of the jet structure is close to the line of sight, with the northern jet being relativistically beamed toward us. In this scenario the diffuse emission to the north and south is not beamed and appears symmetrical. For the northern jet at the mas scale, proper motions of 13.7 +/-3.5, 10.6 +/- 2.8, and 11.8 +/- 2.8 c are measured in three distinct components of the jet (q_0=0.5, H_0=65 km /s /Mpc are used through out this paper). Highly polarised emission is detected on VLBI scales in the region in which the jet bends sharply to the north-west. The spectral index distribution of the source shows that the strongest compact component has a flat spectrum, and the extended jet has a steep spectrum. A helical trajectory along the surface of a cone was proposed based on the conservation laws for kinetic energy and momentum to explain the observed phenomena, which is in a good agreement with the observed results on scales of 1 mas to 1 arcsec., Comment: 19 pages with 18 figures. Accepted for publication in the A&A

We present a status report of dedicated circular polarization (CP) global VLBI observations of SS433. The total intensity image of the source is presented. We do not detect linear polarization in the core region of the source. We estimate the errors in D-terms for the EVN, and its effect on the final right-left circular polarization gain calibration. The data from this and earlier observations are analyzed with the "zero-V" self-calibration technique, in order to obtain indications for detectable CP in different regions of the source. Our data show no evidence for strong gyro-synchrotron (GS) emission on the size scale probed by our beam., Comment: 4 pages. 1 figures. Proceedings of the 7th European VLBI Network Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R. Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico Nacional), p. 221-224. Needs evn2004.cls

Compact Steep Spectrum (CSS) sources are known to show strong optical line emission \citep{Gelderman1994} which is generally considered to be due to the interaction between the radio jet and the ISM. This argument is strengthened by the HST observations of \citet{Axon-2000} which show this emission is frequently associated with the radio jet. Previous observations of the CSS quasar 3C 138 \citep{Cotton1997} have shown that the bulk of the jet has very low amounts of Faraday rotation whereas the inner jet shows very high Faraday rotation (~ -5000 rad m-2). The inner jet is dominated by moving components which allows observing the fine scale of the Faraday screen as the components move behind it. We report the results of such a monitoring campaign which indicated that there is structure in the Faraday screen on the pc and possibly sub pc scale. Motions of the polarized component slowed dramatically during the course of these observations, limiting the region probed. The observations also strongly suggest that the polarized emission from the inner jet is seen through limited holes in a dense Faraday screen. In this case, the observed variations in Faraday rotation are possibly the result of jet-ISM interactions.

We summarize the results of VLBA and global VLBI observations of SS433 between 1995 and 2000. With these observations we resolve the inner jet of the source and identify an absorption region (~25 AU), the "central radio gap". The radio gap is caused by free-free absorption of the jet radio emission by a flattened outflow from the binary system. Radio emission is detected on 100 AU scales perpendicular to the normal jets ("equatorial emission region"; "equatorial outflow"). At some epochs the emission is smooth but compact features are frequently detected. We suggest that equatorial outflows may be common in microquasars., Comment: Talk + two posters presented at the 4th Microquasar Workshop, Cargese, Corsica, 27-31 May 2002. Altogether 8 pages with 7 figures

We present VLBI imaging results for SS433 from the period 1995-2000. An equatorial emission region is detected and confirmed in 7 experiments at 1.6 and 5 GHz. The structure of the region changes with time on scales of weeks to months. The nature of emission is unknown, but it is certainly non-thermal, maybe optically thin synchrotron. The spectrum however might be attenuated by a thermal population of electrons. There were previous indications for an equatorial outflow from the system. We do detect outward motion of a radio component, and estimate a speed of 1200/sin(i) km/s. Theoretical work and IR observations suggest that the mass-loss rate in SS433 is much higher in this region than in the jets. We suggest that the high-mass microquasars might all have equatorial outflows; in fact, it is the dominant form of mass-loss in these systems., 4 pages, 3 figures (from 6 ps files), presented at the 6th EVN Symposium in Bonn, Germany, 25-28 June 2002. Note that fig. 2 is a compressed version and hence its quality is poorer. Paper compiled again with an updated EVN2002 class file - requested by the editors of the proceedings

We present and discuss observations made with MERLIN and VLBI at 1.7 and 5 GHz of the two CSS quasars 3C 43 and 3C 298. They show quite different morphologies, the former being a very distorted triple radio source, the latter a small FRII type object. Relativistic effects and structural distortions are discussed. Source ages are evaluated to be of the order of ~10^5 years, therefore 3C 43 and 3C 298 can be considered fairly ''young'' radio sources. Some inference is also derived on the properties of the medium surrounding the radio emitting regions in these sub-galactic objects, whose density could be as low as 10^-3 cm^-3., 14 pages, A&A accepted

We describe, and present preliminary results from the analysis of 1.6 GHz VLBI observations, made in Cluster-Cluster mode between subgroups of antennas from the WSRT, VLA and MERLIN arrays. We observed for two 6-hour periods on consecutive days, simultaneously monitoring 4 compact radio sources with angular separations ranging from ~1 to 9 degrees. The data were recorded in a non-standard MkIII mode using special set-ups, and correlated at the MPIfR MkIIIa correlator. The preliminary results from standard and phase reference analyses are very encouraging. The experiment has provided a useful database for investigating the potential of this new observing technique at low frequencies., Comment: Proceedings of the 6th European VLBI Network Symposium (p57-60), Ros, E., Porcas, R.W., Lobanov, A.P., & Zensus, J.A. (eds.), MPIfR, Bonn, Germany (2002). 4 pages, 5 figures

This paper describes the selection of a new southern/equatorial sample of Gigahertz Peaked Spectrum (GPS) radio galaxies, and subsequent optical CCD imaging and spectroscopic observations using the ESO 3.6m telescope. The sample consists of 49 sources with -4020 degrees, and S(2.7GHz)>0.5 Jy, selected from the Parkes PKSCAT90 survey. About 80% of the sources are optically identified, and about half of the identifications have available redshifts. The R-band Hubble diagram and evolution of the host galaxies of GPS sources are reviewed., Comment: Latex, 12 pages, 8 figures, accepted for publication in MNRAS

We summarize the results of VLBA and global VLBI observations of SS433 between 1995 and 2000. With these observations we resolve the inner jet of the source and identify an absorption region (~25 AU), the "central radio gap". The radio gap is caused by free-free absorption of the jet radio emission by a flattened outflow from the binary system. Radio emission is detected on 100 AU scales perpendicular to the normal jets ("equatorial emission region"; "equatorial outflow"). At some epochs the emission is smooth but compact features are frequently detected. We suggest that equatorial outflows may be common in microquasars., Talk + two posters presented at the 4th Microquasar Workshop, Cargese, Corsica, 27-31 May 2002. Altogether 8 pages with 7 figures

We have determined the central velocity dispersion and surface brightness profiles for a sample of powerful radio galaxies in the redshift range 0.06, Comment: LaTeX, 13 pages, 10 figures: submitted to MNRAS

We report results of a VSOP (VLBI Space Observatory Programme) observation of a high redshift quasar PKS 2215+020 (z=3.572). The ~1 milliarcsecond resolution image of the quasar reveals a prominent `core-jet' structure on linear scales from 5/h to 300/h pc ($H_0=100*h km/(s*Mpc). The brightness temperatures and sizes of bright features identified in the jet are consistent with emission from relativistic shocks dominated by adiabatic energy losses. The jet is powered by the central black hole with estimated mass of ~4*10^9 solar masses. Comparisons with VLA and ROSAT observations indicate a possible presence of an extended radio/X-ray halo surrounding 2215+020., Comment: 15 pages, 6 figures, aastex macros; accepted for publication in The Astrophysical Journal, V.546, N.2 *(January 10 2001)

We report on the investigation of a complete sample of young radio-loud AGN at z, LaTeX, 4 pages, 2 figs: To appear in the Proceedings of the 5th EVN Symposium. Eds. J. Conway, A. Polatidis, R.Booth., Onsala Space Observatory, Chalmers Technical University, Gothenburg, Sweden (2000)

We present multi-frequency VLBA+VLA observations of SS433 at 1.6, 5 and 15 GHz. These observations provide the highest angular resolution radio spectral index maps ever made for this object. Motion of the components of SS433 during the observation is detected. In addition to the usual VLBI jet structure, we detect two radio components in the system at an anomalous position angle. These newly discovered radio emitting regions might be related to a wind-like equatorial outflow or to an extension of the accretion disk. We show that the radio core component is bifurcated with a clear gap between the eastern and western wings of emission. Modelfitting of the precessing jets and the moving knots of SS433 shows that the kinematic centre -- i.e. the binary -- is in the gap between the western and eastern radio core components. Spectral properties and observed core position shifts suggest that we see a combined effect of synchrotron self-absorption and external free-free absorption in the innermost AU-scale region of the source. The spatial distribution of the ionized matter is probably not spherically symmetric around the binary, but could be disk-like., Accepted for publication by Astronomy and Astrophysics

We report on high sensitivity, spectral line VLBI observations of the HI absorption feature in the radio galaxy NGC4261. Although absorption is only detectable on the most sensitive baseline, it can be unambiguously associated with the counterjet and is interpreted to originate in a thin atomic circumnuclear disk. This structure is probably a continuation of the dusty accretion disk inferred from HST imaging, which could be feeding the massive black hole. HI column densities in front of the counterjet of the order of 10^{21}(T_sp/100 K) cm^{-2} are derived, consistent with X-ray data and VLBI scale free-free absorption. The data presented here are the result of the first scientific project processed on the new EVN MkIV data processor., Comment: 4 pages, 3 postscript figures, Astronomy and Astrophysics Letters, in press

A relativistic radio component, which moves in a direction close to the sky plane, will increase in flux density when it decelerates. This effect is the basis for the qualitative model for GPS galaxies we present in this paper, which can explain their low-variability convex spectrum, their compact double or compact symmetric morphology, and the lack of GPS quasars at similar redshifts. Components are expelled from the nucleus at relativistic speeds at a large angle to the line of sight, and are decelerated (eg. by ram-pressure or entrainment of the external gas) before contributing to a mini-lobe. The young components are Doppler boosted in the direction of motion but appear fainter for the observer. The non-relativistic mini-lobes dominate the structure and are responsible for the low variability in flux density and the convex radio spectrum as well as the compact double angular morphology. Had the same source been orientated at a small angle to the line of sight, the young components would be boosted in the observer's direction resulting in a flat and variable radio spectrum at high frequencies. Hence the characteristic convex spectrum of a GPS source would not be seen. These sources at small angles to the line of sight are probably identified with quasars, and are not recognized as GPS sources, but are embedded in the large population of flat spectrum variable quasars and BL Lac objects. This leads to a deficiency in GPS/CSOs identified with quasars., Comment: 11 pages, LaTeX, accepted by A&A 26/Jan/1998

Compact Steep Spectrum (CSS) radio sources are defined as having straight steep spectra typical of extended double-lobed radio sources and structures unresolved by conventional interferometers (Peacock and Wall 1982; van Breugel et al., 1984; Fanti et al., 1985). Their spectra remain straight up to quite high frequencies, indicating that no dominant core is present. Sometimes the spectrum bends at frequencies lower than 1 GHz. The angular sizes imply projected linear sizes generally < 10 kpc.

We present deep WSRT 1.4 GHz observations of the Hubble Deep Field region. At the 5 sigma level, the WSRT clearly detects 85 regions of radio emission in a 10' x 10' field centred on the HDF. Eight of these regions fall within the HDF itself, four of these are sources that have not previously been detected at 1.4 GHz, although two of these are VLA detections at 8.5GHz. The two new radio sources detected by the WSRT are identified with relatively bright (I, To appear in Astronomy and Astrophysics Letters (accepted); 4 Pages, 1 figure. See http://www.nfra.nl/~mag/hdf for a useful but preliminary web based catalogue, colour (pretty) figures and more information

SN1993J is to date the radio supernova whose evolution has been monitored in greatest detail and the one which holds best promise for a comprehensive theoretical-observational analysis. The shell-like radio structure of SN1993J has expanded in general accord with models of shock excited emission, showing almost circular symmetry for over 8 years, except for a bright feature at the south-eastern region of the shell that has been observed at every epoch. The spectrum of SN1993J has flattened from alpha =-1 to alpha =-0.67 (S_(\nu) propto nu**(alpha)). The decelerated expansion can be modeled well with a single slope but apparently better with two slopes. There are also intriguing hints of structure in the expansion curve. The results by the two VLBI groups carrying out this research show general agreement, but also some differences. A comparison of the optical and VLBI results about the details of the deceleration show some discrepancies., Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E., Porcas R.W., Lobanov A.P., Zensus J.A. (eds.), MPIfR, Bonn, Germany, pp. 239-242 (2002). 4 pages, 6 figures, needs evn2002.cls