- ID:
- ivo://CDS.VizieR/J/A+A/574/A73
- Title:
- LOFAR long baselines at 140MHz Calibrators
- Short Name:
- J/A+A/574/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140MHz. We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/Sci/338.355
- Title:
- 1.3mm VLBI detections of M87
- Short Name:
- J/other/Sci/338.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by the accretion of matter onto supermassive black holes. Although the measured width profiles of such jets on large scales agree with theories of magnetic collimation, the predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations, at a wavelength of 1.3 millimeters, of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5+/-0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/4992
- Title:
- MOJAVE XIV. AGN jet shapes & opening angles
- Short Name:
- J/MNRAS/468/4992
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 15 GHz stacked VLBA images of 373 jets associated with active galactic nuclei (AGN) having at least 5 observing epochs within a 20yr time interval 1994-2015 from the MOJAVE programme and/or its precursor, the 2 cm VLBA Survey. These data are supplemented by 1.4 GHz single-epoch VLBA observations of 135 MOJAVE AGNs to probe larger scale jet structures. The typical jet geometry is found to be close to conical on scales from hundreds to thousands of parsecs, while a number of galaxies show quasi-parabolic streamlines on smaller scales. A true jet geometry in a considerable fraction of AGNs appears only after stacking epochs over several years. The jets with significant radial accelerated motion undergo more active collimation. We have analyzed total intensity jet profiles transverse to the local jet ridgeline and derived both apparent and intrinsic opening angles of the flows, with medians of 21.5{deg} and 1.3{deg}, respectively. The Fermi LAT-detected gamma-ray AGNs in our sample have, on average, wider apparent and narrower intrinsic opening angle, and smaller viewing angle than non LAT-detected AGNs. We have established a highly significant correlation between the apparent opening angle and gamma-ray luminosity, driven by Doppler beaming and projection effects.
- ID:
- ivo://CDS.VizieR/J/A+A/484/119
- Title:
- Multi-epoch VLBI survey of CJF sources
- Short Name:
- J/A+A/484/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second in a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-spectrum (hereafter CJF) sources and their analysis. We obtain a consistent motion dataset large enough to allow the systematic properties of the population to be studied. We present detailed kinematic analysis of the complete flux-density limited CJF survey. We computed 2-D kinematic models based on the optimal model-fitting parameters of multi-epoch VLBA observations. This allows us to calculate not only radial, but also orthogonal motions, and thus to study curvature and acceleration. Statistical tests of the motions measured and their reliability were performed. A correlation analysis between the derived apparent motions, luminosities, spectral indices, and core dominance and the resulting consequences is described. With at least one velocity in each of the 237 sources, this sample is much larger than any available before, so it allows a meaning ful statistical investigation of apparent motions and any possible correlations with other parameters in AGN jets. The main results to emerge are as follows: * In general motions are not consistent with a single uniform velocity applicable to all components along a jet. * We find a slight trend towards a positive outward acceleration and also adduce some evidence for greater acceleration in the innermost regions. * We find a lack of fast components at physical distances less than a few pc from the reference feature. * Only ~4% of the components from galaxies and <2% of those from quasars undergo large bends i.e. within 15{deg} of +/-90{deg}. * The distribution of radial velocities shows a broad distribution of velocities (apparent velocities up to 30c). Fifteen percent of the best-sampled jet components exhibit low velocities that may need to be explained in a different manner to the fast motions. * Some negative superluminal motions are seen, and in 15 cases (6%) these are definitely significant. * We find a strong correlation between the 5 GHz luminosity and the apparent velocity. * The CJF galaxies, on average, show slower apparent jet-component velocities than the quasars. * The mean velocity in the VLBA 2cm survey (Kellermann et al. 2004) is substantially higher than in the CJF survey, the ratio could be roughly a factor of 1.5-2. This supports the observed trend toward increasing apparent velocity with in creasing observing frequency. This AGN survey provides the basis for any statistical analysis of jet and jet-component properties.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A27
- Title:
- NGC1052 twin-jet VLBI images
- Short Name:
- J/A+A/623/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Few active galactic nuclei (AGN) reveal double-sided jet systems. However, these systems are crucial to understand basic physical properties of extragalactic jets. We address the questions whether jets in AGN are symmetric in nature, how well they are collimated on small scales, and how they evolve with time. We monitored the sub-parsec scale morphology of NGC 1052 with the Very Long Baseline Array at 43GHz from 2005 to 2009. A detailed study of 29 epochs show a remarkable asymmetry between both jets. A kinematic analysis of the outflows reveals higher apparent velocities for the eastern (approaching) jet as compared to the western (receding) jet, i.e., {beta}_ej_=0.529+/-0.038 and {beta}_wj_=0.343+/-0.037, respectively. Contradictory to previous studies, we find higher flux densities for the western jet as compared to the eastern. The distribution of brightness temperature and jet width features well-collimated jets up to 1 mas distance to the dynamic center and a nearly conical outflow further outward. By combining flux density ratios and velocities of the jet flows, we were unable to find a combination of intrinsic velocities and inclination angles of the jets that is consistent for all four years of observation; this contradicts findings for symmetrically evolving jets. Spectral index maps between quasi-simultaneous 22GHz and 43GHz observations support the existence of an optically thick absorber covering the innermost ~=1.6mas around the 43GHz central feature and an optically thin jet emission with a spectral index of <=-1. Our results fit into a picture in which we expect larger internal energy and/or magnetic flux in the western jet and higher kinetic energy in the eastern jet. Previous observations at lower frequencies have found slower velocities of the moving jet features as compared to this work. Considering the different velocities in different areas, we suggest a spine-sheath structure with a faster inner layer and slower outer layer.
- ID:
- ivo://CDS.VizieR/J/A+AS/116/473
- Title:
- Nutation modeling and VLBI observations
- Short Name:
- J/A+AS/116/473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using geodetic and astrometric VLBI acquired between 1984-1994, we have determined coefficients in the nutation series with uncertainties of 10microarcseconds. This level of accuracy is quite sufficient to differentiate between alternate theories of nutation. We show that small terms predicted using the Kinoshita & Souchay (1990) rigid Earth theory of nutation revised by Souchay & Kinoshita (1996), agree well with the VLBI results at periods where the non rigid Earth corrections are reliable. These terms are different or absent from the Kinoshita (1977) theory that is the basis for the standard IAU 1980 model. We propose a nutation series based on the Kinoshita & Souchay theory using the Wahr (1979) transformation for a non rigid Earth that can be useful where the physical interpretation of the smaller terms is important. This series, called VKSNRE95.1, includes corrections to the nine largest terms derived from VLBI observations.
- ID:
- ivo://CDS.VizieR/J/AJ/142/105
- Title:
- Optically Bright Extragalactic Radio Sources
- Short Name:
- J/AJ/142/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is expected that the European Space Agency mission Gaia will make possible to determine coordinates in the optical domain of more than 500,000 quasars. In 2006, a radio astrometry project was launched with the overall goal to make comparison of coordinate systems derived from future space-born astrometry instruments with the coordinate system constructed from analysis of the global very long baseline interferometry (VLBI) more robust. Investigation of their rotation, zonal errors, and the non-alignment of the radio and optical positions caused by both radio and optical structures are important for validation of both techniques. In order to support these studies, the densification of the list of compact extragalactic objects that are bright in both radio and optical ranges is desirable. A set of 105 objects from the list of 398 compact extragalactic radio sources with declinations >-10{deg} was observed with the VLBA+EVN with the primary goal of producing their images with milliarcsecond resolution. These sources are brighter than 18 magnitude at V band, and they were previously detected at the European VLBI network. In this paper coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these VLBI observations following the method of absolute astrometry. The catalog of positions of 105 target sources is presented. The accuracies of sources coordinates are in the range of 0.3 to 7mas, with the median 1.1mas.
- ID:
- ivo://CDS.VizieR/J/AJ/146/5
- Title:
- Optically Bright extragalactic Radio Sources II
- Short Name:
- J/AJ/146/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Future space-borne astrometry missions, such as Gaia, will be able to determine the optical positions of hundreds of quasars with submilliarcsecond accuracies comparable to those achieved in radio by very long baseline interferometry (VLBI). Comparisons of coordinate systems from space-borne missions and VLBI will be very important, first for investigations of possible systematic errors and second for investigations of possible shifts between centroids of radio and optical emissions in active galactic nuclei. In order to make such a comparison more robust, a program for densification of the grid of radio sources detectable with both VLBI and Gaia was launched in 2006. Program sources are 398 quasars with declinations >-10{deg} that are brighter than 18mag at the V band. The first two observing campaigns were run in 2007-2008. In the third campaign, a set of 291 objects from that list was observed with the VLBA+EVN in 2010-2011 with the primary goal of producing their images with milliarcsecond resolution. In this paper, following the method of absolute astrometry, coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these observations. The catalog of positions of 295 target sources, estimates of their correlated flux densities at 2.2 and 8.4GHz, and their images are presented. The accuracies of source coordinates are in a range of 2-200mas, with a median of 3.2mas.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A47
- Title:
- Pinpointing the SMBH in NGC1052
- Short Name:
- J/A+A/593/A47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical models based on Blandford & Znajek (1977MNRAS.179..433B) extract the rotational energy from a Kerr black hole, which could be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 1000G to 10000G. We imaged the vicinity of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the magnetic field at 1 Schwarzschild radius to lie between 200G and ~83000G consistent with Blandford & Znajek (1977MNRAS.179..433B) models.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A60
- Title:
- PKS 1502+106 15, 43 and 86GHz images
- Short Name:
- J/A+A/586/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Blazars are among the most energetic objects in the Universe. In 2008 August, Fermi/LAT detected the blazar PKS 1502+106, which showed a rapid and strong gamma-ray outburst followed by high and variable flux over the next months. This activity at high energies triggered an intensive multi-wavelength campaign that also covered the radio, optical, UV, and X-ray bands, indicating that the flare was accompanied by a simultaneous outburst at optical/UV/X-rays and a delayed outburst at radio bands. We explore the phenomenology and physical conditions within the ultra-relativistic jet of the gamma-ray blazar PKS 1502+106. Additionally, we address the question of the spatial localization of the MeV/GeV-emitting region of the source. We used ultra-high angular resolution mm-VLBI observations at 43 and 86GHz complemented by VLBI observations at 15GHz. We also employed single-dish radio data from the F-GAMMA program at frequencies matching the VLBI monitoring. PKS 1502+106 shows a compact core-jet morphology and fast superluminal motion with apparent speeds in the range 5-22c. Estimating Doppler factors along the jet yields values of between ~7 up to ~50. This Doppler factor gradient implies an accelerating jet. The viewing angle towards the source differs between the inner and outer jet, with the former at {theta}~3{deg} and the latter at {theta}~1{deg}, after the jet bends towards the observer beyond 1mas. The de-projected opening angle of the ultra-fast magnetically dominated jet is found to be (3.8+/-0.5){deg}. A single jet component can be associated with the pronounced flare both at high energies and in radio bands. Finally, the gamma-ray emission region is localized at <=5.9pc away from the jet base.
