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31. Optically Bright extragalactic Radio Sources II
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.
32. Pinpointing the SMBH in NGC1052
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.
33. PKS 1502+106 15, 43 and 86GHz images
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.
34. Precise astrometry with VLBA (VIPS)
ID:
ivo://CDS.VizieR/J/AJ/142/89
Title:
Precise astrometry with VLBA (VIPS)
Short Name:
J/AJ/142/89
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present accurate positions for 857 sources derived from the astrometric analysis of 16 eleven-hour experiments from the Very Long Baseline Array imaging and polarimetry survey at 5GHz (VIPS). Among the observed sources, positions of 430 objects were not previously determined at milliarcsecond-level accuracy. For 95% of the sources the uncertainty of their positions ranges from 0.3 to 0.9mas, with a median value of 0.5mas. This estimate of accuracy is substantiated by the comparison of positions of 386 sources that were previously observed in astrometric programs simultaneously at 2.3/8.6GHz. Surprisingly, the ionosphere contribution to group delay was adequately modeled with the use of the total electron content maps derived from GPS observations and only marginally affected estimates of source coordinates.
35. Precise Radio Source Positions from Mark III VLBI
ID:
ivo://CDS.VizieR/I/151
Title:
Precise Radio Source Positions from Mark III VLBI
Short Name:
I/151
Date:
21 Oct 2021
Publisher:
CDS
Description:
This catalog contains observations from 600 Mark III VLBI experiments from conducted between 1979 to 1988. These experiments resulted in 237681 acceptable pairs of group delay and phase delay rate observations. These have been used to derive positions of 182 extra-galactic radio sources with typical formal standard errors less than 1 mas. The right ascension zero point of this reference frame has been aligned with the FK5 by using the optical positions of 28 extragalactic radio sources whose positions are on the FK5 system. Also included are the Mark III VLBI stations and a summary of the analysis configuration.
36. QCAL-1 43 GHz Calibrator Survey
ID:
ivo://CDS.VizieR/J/AJ/144/150
Title:
QCAL-1 43 GHz Calibrator Survey
Short Name:
J/AJ/144/150
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents the catalog of correlated flux densities in three ranges of baseline projection lengths of 637 sources from a 43GHz (Q band) survey observed with the Korean VLBI Network. Of them, 14 objects used as calibrators were previously observed, but 623 sources have not been observed before in the Q band with very long baseline interferometry (VLBI). The goal of this work in the early science phase of the new VLBI array is twofold: to evaluate the performance of the new instrument that operates in a frequency range of 22-129GHz and to build a list of objects that can be used as targets and as calibrators. We have observed the list of 799 target sources with declinations down to -40{deg}. Among them, 724 were observed before with VLBI at 22GHz and had correlated flux densities greater than 200mJy. The overall detection rate is 78%. The detection limit, defined as the minimum flux density for a source to be detected with 90% probability in a single observation, was in the range of 115-180mJy depending on declination. However, some sources as weak as 70mJy have been detected. Of 623 detected sources, 33 objects are detected for the first time in VLBI mode. We determined their coordinates with a median formal uncertainty of 20mas. The results of this work set the basis for future efforts to build the complete flux-limited sample of extragalactic sources at frequencies of 22GHz and higher at 3/4 of the celestial sphere.
37. Radio-optical reference frame link
ID:
ivo://CDS.VizieR/I/325
Title:
Radio-optical reference frame link
Short Name:
I/325
Date:
21 Oct 2021
Publisher:
CDS
Description:
Between 1997 and 2004 several observing runs were conducted mainly with the CTIO 0.9m to image ICRF counterparts (mostly QSOs) in order to determine accurate optical positions. Contemporary to these deep CCD images the same fields were observed with the USNO astrograph in the same bandpass. These provide accurate positions on the Hipparcos/Tycho-2 system for stars in the 10 to 16 magnitude range used as reference stars for the deep CCD imaging data. Here we present final optical position results of 413 sources based on astrograph data reductions using UCAC2 and UCAC4 type reference stars. These optical positions are compared to radio VLBI positions. The current optical system is not perfectly aligned to the ICRF radio system with rigid body rotation angles of 3 to 5 mas (3{sigma}) found between them for all 3 axes. Furthermore, statistically, the optical-radio position differences are found to exceed the total, combined, known errors in the observations. Systematic errors in the optical reference stars as well as physical offsets between the centers of optical and radio emissions are both identified as likely causes. A detrimental, astrophysical, random noise (DARN) component is postulated to be on about the 10mas level. If confirmed by future observations, this could severely limit the Gaia to ICRF reference frame alignment accuracy to an error of about 0.5mas per coordinate axis with the current number of sources envisioned to provide the link. A list of 36 ICRF sources without the detection of an optical counterpart to a limiting magnitude of about R=22 is provided as well.
38. Radio-optical scrutiny of compact AGN
ID:
ivo://CDS.VizieR/J/A+A/520/A62
Title:
Radio-optical scrutiny of compact AGN
Short Name:
J/A+A/520/A62
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the correlations between the VLBA (Very Long Baseline Array) radio emission at 15GHz, extended emission at 151MHz, and optical nuclear emission at 5100{AA} for a complete sample of 135 compact jets. We use the partial Kendall's tau correlation analysis to check the link between radio properties of parsec-scale jets and optical nuclear luminosities of host active galactic nuclei (AGN).
39. Radio properties of faint BL Lacs
ID:
ivo://CDS.VizieR/J/A+A/560/A23
Title:
Radio properties of faint BL Lacs
Short Name:
J/A+A/560/A23
Date:
21 Oct 2021
Publisher:
CDS
Description:
The advent of Fermi is changing our understanding on the radio and gamma-ray emission in Active Galactic Nuclei. Contrary to pre-Fermi ideas, BL Lac objects are found to be the most abundant emitters in the gamma-ray band. However, since they are relatively weak radio sources, most of their parsec-scale structure and their multi-frequency properties are poorly understood and/or have not been investigated in a systematically fashion. Our main goal is to analyze the radio and gamma-ray emission properties of a sample of 42 BL Lacs selected, for the first time in the literature, with no constraint on their radio and gamma-ray flux densities/emission. Thanks to new Very Long Baseline Array observations at 8 and 15GHz for the whole sample, we present here fundamental parameters such as radio flux densities, spectral index information, and parsec-scale structure. Moreover, we search for gamma-ray counterparts using data reported in the Second Catalog of Fermi Gamma-ray sources. Parsec-scale radio emission is observed in the majority of the sources at both frequencies. Gamma-ray counterparts are found for 14/42 sources. The comparison between our results in radio and gamma-ray bands points out the presence of a large number of faint BL Lacs showing "non classical" properties such as low source compactness, core dominance, no gamma-ray emission and steep radio spectral indexes. A deeper multiwavelength analysis will be needed.
40. Radio reference frame
ID:
ivo://CDS.VizieR/J/AJ/110/880
Title:
Radio reference frame
Short Name:
J/AJ/110/880
Date:
21 Oct 2021
Publisher:
CDS
Description:
A catalogue is presented based on the radio positions of 436 extragalactic sources distributed over the entire sky. The positional accuracy of the sources is better than 3 milliarcsec (mas) in both coordinates, with the majority of the sources having errors better than 1mas. This catalogue is based upon a general solution of all applicable dual frequency 2.3 and 8.4GHz Mark-III VLBI data available through the end of 1993 consisting of 1,015,292 pairs of group delay and phase delay rate observations. Details and positions are also given for an additional 124 objects that either need further observation or are currently unsuitable for the definition of a reference frame. The final orientation of the catalogue has been obtained by a rotation of the positions into the system of the International Earth Rotation Service and is consistent with the FK5 J2000.0 optical system, within the limits of the link accuracy.

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