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Start Over Subject very long baseline interferometry Validation Level 2
71. The VLBA Galactic Plane Survey (VGaPS)
ID:
ivo://CDS.VizieR/J/AJ/142/35
Title:
The VLBA Galactic Plane Survey (VGaPS)
Short Name:
J/AJ/142/35
Date:
21 Oct 2021
Publisher:
CDS
Description:
We presents accurate absolute positions from a 24 GHz Very Long Baseline Array (VLBA) search for compact extragalactic sources in an area where the density of known calibrators with precise coordinates is low. The goals were to identify additional sources suitable for use as phase calibrators for galactic sources, determine their precise positions, and produce radio images. In order to achieve these goals, we developed a new software package, PIMA, for determining group delays from wide-band data with much lower detection limit. With the use of PIMA we have detected 327 sources out of 487 targets observed in three 24 hour VLBA experiments. Among the 327 detected objects, 176 are within 10 degrees of the Galactic plane. This VGaPS catalogue of source positions, plots of correlated flux density versus projected baseline length, contour plots, as well as weighted CLEAN images and calibrated visibility data in FITS format, are available on the Web at http://astrogeo.org/vgaps. Approximately one half of objects from the 24GHz catalogue were observed at dual band 8.6GHz and 2.3GHz experiments. Position differences at 24GHz versus 8.6/2.3GHz for all but two objects on average are strictly within reported uncertainties. We found that for two objects with complex structure positions at different frequencies correspond to different components of a source.
72. The VSOP (the VLBI Space Observatory Programme) 5 GHz AGN (Active Galactic Nuclei) Survey Program Analysis Data
ID:
ivo://jvo/isas/darts/halca/halca_vsop_survey_program_data
Title:
The VSOP (the VLBI Space Observatory Programme) 5 GHz AGN (Active Galactic Nuclei) Survey Program Analysis Data
Short Name:
HALCA_AGN
Date:
19 Oct 2021 06:40:34
Publisher:
JVO
Description:
A significant fraction of the mission time of VSOP was to be dedicated to the VSOP Survey Programme of bright compact Active Galactic Nuclei (AGN) at 5 GHz, which was lead by ISAS. The VSOP Survey Sources are an unbiased dataset of 294 targets, of which 82% were successfully observed.
73. Time stability of the ICRF2 axes
ID:
ivo://CDS.VizieR/J/A+A/553/A122
Title:
Time stability of the ICRF2 axes
Short Name:
J/A+A/553/A122
Date:
21 Oct 2021
Publisher:
CDS
Description:
I assess the astrometric stability of the 295 defining sources of the current best realization of the International Celestial Reference System (ICRS): the second realization of the International Celestial Reference Frame (ICRF2), constructed and published in 2009 after the analysis of millions of VLBI observations at 2 and 8 GHz between 1979.6 and 2009.2. I also assess the time evolution of the ICRF2 axis stability. I derived coordinate time series of hundreds of quasars monitored by the regular geodetic VLBI program of the International VLBI Service for Geodesy and Astrometry (IVS). The axis stability was studied by constructing annual reference frames based on the ICRF2 defining sources. The time variable frame stability was obtained by computing the deformation parameters that lead from one frame to the next. I show that, although the astrometric stability of some of the ICRF2 defining sources has slightly degraded since 2009.2, the ensemble still constitutes a very stable reference frame. The current estimation of the axis stability over 1979.6-2013.1 remains at the same level as the one estimated over 1979.6-2009.2, i.e., on the order of 20uas for each axis.
74. TXS 2013+370 gamma-ray emitting region
ID:
ivo://CDS.VizieR/J/A+A/634/A112
Title:
TXS 2013+370 gamma-ray emitting region
Short Name:
J/A+A/634/A112
Date:
21 Oct 2021
Publisher:
CDS
Description:
The gamma-ray production mechanism and its localization in blazars are still a matter of debate. The main goal of this paper is to constrain the location of the high-energy emission in the blazar TXS 2013+370 and to study the physical and geometrical properties of the inner jet region on sub-pc scales. TXS 2013+370 was monitored during 2002-2013 with VLBI at 15, 22, 43, and 86GHz, which allowed us to image the jet base with an angular resolution of >=0.4pc. By employing CLEAN imaging and Gaussian model-fitting, we performed a thorough kinematic analysis at multiple frequencies, which provided estimates of the jet speed, orientation, and component ejection times. Additionally, we studied the jet expansion profile and used the information on the jet geometry to estimate the location of the jet apex. VLBI data were combined with single-dish measurements to search for correlated activity between the radio, mm, and gamma-ray emission. For this purpose, we employed a cross-correlation analysis, supported by several significance tests. The high-resolution VLBI imaging revealed the existence of a spatially bent jet, described by co-existing moving emission features and stationary features. New jet features, labeled as A1, N, and N1, are observed to emerge from the core, accompanied by flaring activity in radio/mm- bands and rays. The analysis of the transverse jet width profile constrains the location of the mm core to lie <=2pc downstream of the jet apex, and also reveals the existence of a transition from parabolic to conical jet expansion at a distance of ~54pc from the core, corresponding to ~1.5x10^6^ Schwarzschild radii. The cross-correlation analysis of the broad-band variability reveals a strong correlation between the radio-mm and gamma-ray data, with the 1mm emission lagging 49 days behind the rays. Based on this, we infer that the high energy emission is produced at a distance of the order of ~1pc from the VLBI core, suggesting that the seed photon fields for the external Compton mechanism originate either in the dusty torus or in the broad-line region.
75. VBLA observations of W51 Main/South
ID:
ivo://CDS.VizieR/J/ApJ/720/1055
Title:
VBLA observations of W51 Main/South
Short Name:
J/ApJ/720/1055
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report measurement of the trigonometric parallax of W51 Main/South using the Very Long Baseline Array. We measure a value of 0.185+/-0.010mas corresponding to a distance of 5.41^+0.31^_-0.28_kpc. W51 Main/South is a well-known massive star-forming region near the tangent point of the Sagittarius spiral arm of the Milky Way. Our distance to W51 yields an estimate of the distance to the Galactic center of R_0_=8.3+/-0.46(statistical)+/-1.0(systematic)kpc by simple geometry. Combining the parallax and proper motion measurements for W51, we obtained the full-space motion of this massive star-forming region. We find W51 is in a nearly circular orbit about the Galactic center. The H_2_O masers used for our parallax measurements trace four powerful bipolar outflows within a 0.4pc size region, some of which are associated with dusty molecular hot cores and/or hyper- or ultra-compact HII regions.
76. VLBI and VLA obs. of Seyfert galaxies
ID:
ivo://CDS.VizieR/J/A+A/425/99
Title:
VLBI and VLA obs. of Seyfert galaxies
Short Name:
J/A+A/425/99
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have obtained mas-scale resolution very long baseline interferometry (VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5GHz (wavelength, {lambda}=6cm). The Seyferts of the two types were chosen to be matched in several orientation-independent properties, primarily in order to rigorously test predictions of the unified scheme. We detected all the 15 objects that we observed. In this paper we describe the observations and data reduction procedures, and present the VLBI radio images as well as simultaneous Very Large Array images that we obtained for these 15 Seyferts.
77. VLBI detection of 398 extragalactic radio sources
ID:
ivo://CDS.VizieR/J/A+A/520/A113
Title:
VLBI detection of 398 extragalactic radio sources
Short Name:
J/A+A/520/A113
Date:
21 Oct 2021
Publisher:
CDS
Description:
The European space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames with the highest possible accuracy. It has been found that only 70 (10%) of the sources from the International Celestial Reference Frame (ICRF) are suitable for establishing this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of 447 optically- bright (magnitude <=18) extragalactic radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating an optical quasar catalog with the NRAO VLA Sky Survey (NVSS, Cat. VIII/65). This paper presents the observing strategy to detect, image, and measure accurate radio positions for these sources. It also provides results on the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, a high detection rate of 89% is found, which is promising for the continuation of this project. This high VLBI detection rate for sources from the NVSS catalog is probably due to the selection process, suggesting that optically-bright quasars have compact radio structures.
78. VLBI Ecliptic Plane Survey: VEPS-1
ID:
ivo://CDS.VizieR/J/ApJS/230/13
Title:
VLBI Ecliptic Plane Survey: VEPS-1
Short Name:
J/ApJS/230/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present here the results of the first part of the VLBI Ecliptic Plane Survey (VEPS) program. The goal of the program is to find all compact sources within 7.5{deg} of the ecliptic plane that are suitable as calibrators for anticipated phase referencing observations of spacecraft, and determine their positions with accuracy at the 1.5 nrad level. We run the program in two modes: search and refine. In the search mode, a complete sample of all sources brighter than 50mJy at 5GHz listed in the Parkes-MIT-NRAO and Green Bank 6cm (GB6) catalogs, except those previously detected with VLBI, is observed. In the refining mode, the positions of all ecliptic plane sources, including those found in the search mode, are improved. By 2016 October, thirteen 24hr sessions that targeted all sources brighter than 100mJy have been observed and analyzed. Among 3320 observed target sources, 555 objects have been detected. We also conducted a number of follow-up VLBI experiments in the refining mode and improved the positions of 249 ecliptic plane sources.
79. VLBI ICRF2
ID:
ivo://CDS.VizieR/J/AJ/150/58
Title:
VLBI ICRF2
Short Name:
J/AJ/150/58
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years of Very Long Baseline Interferometry observations. ICRF2 contains precise positions of 3414 compact radio astronomical objects and has a positional noise floor of ~40{mu}as and a directional stability of the frame axes of ~10{mu}as. A set of 295 new "defining" sources was selected on the basis of positional stability and the lack of extensive intrinsic source structure. The positional stability of these 295 defining sources and their more uniform sky distribution eliminates the two greatest weaknesses of the first realization of the International Celestial Reference Frame (ICRF1). Alignment of ICRF2 with the International Celestial Reference System was made using 138 positionally stable sources common to both ICRF2 and ICRF1. The resulting ICRF2 was adopted by the International Astronomical Union as the new fundamental celestial reference frame, replacing ICRF1 as of 2010 January 1.
80. VLBI ICRF. II
ID:
ivo://CDS.VizieR/J/AJ/127/3587
Title:
VLBI ICRF. II
Short Name:
J/AJ/127/3587
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use very long baseline interferometry data obtained between mid-1995 and the end of 2002 May together with older data to extend and revise the International Celestial Reference Frame (ICRF). Revised positions of ICRF candidate and "other" sources, based on inclusion of the additional data, are presented. Positions, in the frame of the ICRF, for an additional 109 new sources are also presented. All but four of the new sources are located north of {delta}=-30{deg}. Positions of the ICRF defining sources remain unchanged. We present a summary of current astrometric and geodetic observing programs and discuss the evolution and future of the ICRF.