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Start Over Subject very long baseline interferometry Validation Level 2
81. VLBI images of 2 binary AGN candidates
ID:
ivo://CDS.VizieR/J/A+A/588/A102
Title:
VLBI images of 2 binary AGN candidates
Short Name:
J/A+A/588/A102
Date:
21 Oct 2021
Publisher:
CDS
Description:
The sources SDSS J113126.08-020459.2 and SDSS J110851.04+065901.4 are two double-peaked [OIII] emitting AGN, identified as candidate binary AGNs by optical and near infrared (NIR) observations. We observed the two sources with high resolution Very Long Baseline Interferometry (VLBI) using the European VLBI Network at 5GHz, reduced VLA observations at three frequencies available for one of the sources, and used archival HST observations. For the source SDSS J113126.08-020459.2, the VLBI observations detected only one single compact component associated with the eastern NIR nucleus. In SDSS J110851.04+065901.4, the VLBI observations did not detect any compact components, but the VLA observations allowed us to identify a possible compact core in the region of the north-western optical/NIR nucleus. In this source we find kpc-scale extended radio emission that is spatially coincident to the ultraviolet continuum and to the extended emission narrow line region. The UV continuum is significantly obscured since the amount of extended radio emission yields a star formation rate of about 110M_{sun}_/yr, which is an order of magnitude larger than implied by the observed ultraviolet emission. Our analysis confirms the presence of only one AGN in the two candidate binary AGNs.
82. VLBI images of gamma-ray nova V407 Cygni
ID:
ivo://CDS.VizieR/J/A+A/638/A130
Title:
VLBI images of gamma-ray nova V407 Cygni
Short Name:
J/A+A/638/A130
Date:
21 Oct 2021
Publisher:
CDS
Description:
In 2010 March, the Large Area Telescope on board Fermi revealed a transient gamma-ray source that is positionally coincident with the optical nova in the symbiotic binary, V407 Cyg. This event marked the first discovery of gamma-ray emission from a nova. We aim to obtain resolved radio imaging of the material involved in the nova event, to determine the ejecta geometry and advance velocity directly in the image plane, and to constrain the physical conditions of the system. We observed the source with the European VLBI (Very Long Baseline Interferometry) Network in real time mode, at 1.6 and 5GHz, and the Very Long Baseline Array at 1.6, 5, and 8.4GHz. In total, we observed the source over 16 epochs, starting 20 days after the optical discovery and continuing for over six months. Milliarcsecond-scale radio emission is detected in 10/16 epochs of observations. The source is initially very dim but it later shows a substantial increase in brightness and a resolved shell-like structure 40-90 days after the optical event. The shell has a projected elliptical shape and is asymmetric in brightness and spectral index, being brighter and characterised by a rising spectrum at the south-eastern edge. We determine a projected expansion velocity of ~3500km/s in the initial phase (for an adopted 2.7kpc distance), and ~2100km/s between day 20 and 91. We also found an emitting feature about 350 mas (940AU) to the north-west, advancing at a projected velocity of ~700km/s along the polar axis of the binary. The total flux density in the VLBI images is significantly lower than that previously reported at similar epochs and over much wider angular scales with the VLA. Optical spectra convincingly demonstrated that in 2010 we were viewing V407 Cyg along the equatorial plane and from behind the Mira. Our radio observations image the bipolar flow of the ejecta perpendicular to the orbital plane, where deceleration is much lower than through the equatorial plane probed by the truncated profile of optical emission lines. The separated polar knot at 350 mas and the bipolar flow strictly resemble a similar arrangement seen in Hen 2-104, another symbiotic Mira seen equator-on that went through a large outburst ~5700yrs ago. The observed ~700km/s expansion constrains the launch date of the polar knot around 2004, during the accretion-fed active phase preceding the 2010 nova outburst.
83. VLBI imaging of 105 extragalactic radio sources
ID:
ivo://CDS.VizieR/J/A+A/526/A102
Title:
VLBI imaging of 105 extragalactic radio sources
Short Name:
J/A+A/526/A102
Date:
21 Oct 2021
Publisher:
CDS
Description:
The European space astrometry mission Gaia, to be launched by 2012, will construct a dense optical QSO-based celestial reference frame which will need to be linked to the International Celestial Reference Frame (ICRF; the IAU fundamental frame), with the highest accuracy. However, it has been found that only 10% of the ICRF sources (70 sources) are suitable to establish this link. The remaining sources are not useful 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 accuracy of this alignment, we have developed a program of VLBI observations based on three steps to detect, image and measure astrometric positions of weak extragalactic radio sources, with bright optical counterparts, from a sample of 447 candidate sources. The experiments devoted to VLBI detection, carried out with the European VLBI Network (EVN) in June and October 2007, were very successful, with 398 sources detected at both S- and X-bands. From these, 105 sources were observed in March 2008 with a global VLBI array (EVN and VLBA; Very Long Baseline Array) for imaging their VLBI structures. All sources were successfully imaged in both bands and about 50% (47 sources) were found to be point-like on VLBI scales. These images are available at http://www.obs.u-bordeaux1.fr/BVID/GC030/. VLBI positions of these sources will be measured accurately in future astrometric experiments.
84. VLBI International Celestial Reference Frame (ICRF)
ID:
ivo://CDS.VizieR/I/251
Title:
VLBI International Celestial Reference Frame (ICRF)
Short Name:
I/251
Date:
21 Oct 2021
Publisher:
CDS
Description:
of the 1998AJ....116..516M paper: A quasi-inertial reference frame is defined based on the radio positions of 212 extragalactic sources distributed over the entire sky. The positional accuracy of these sources is better than about 1mas in both coordinates. The radio positions are based upon a general solution for all applicable dual-frequency 2.3 and 8.4GHz Mark III very long baseline interferometry data available through the middle of 1995, consisting of 1.6 million pairs of group delay and phase delay rate observations. Positions and details are also given for an additional 396 objects that either need further observation or are currently unsuitable for the definition of a high-accuracy reference frame. The final orientation of the frame axes has been obtained by a rotation of the positions into the system of the International Celestial Reference System and is consistent with the FK5 J2000.0 optical system, within the limits of the link accuracy. The resulting International Celestial Reference Frame has been adopted by the International Astronomical Union as the fundamental celestial reference frame, replacing the FK5 optical frame as of 1998 January 1.
85. VLBI monitoring of NGC 4258
ID:
ivo://CDS.VizieR/J/ApJ/659/1040
Title:
VLBI monitoring of NGC 4258
Short Name:
J/ApJ/659/1040
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report a 3yr, 18 epoch, VLBI monitoring study of H_2_O masers in the subparsec, warped, accretion disk within the NGC 4258 AGN. Our immediate goals are to trace the geometry of the underlying disk, track rotation via measurement of proper motion, and ascertain the radii of masers for which centripetal acceleration may be measured separately. The monitoring includes 4 times as many epochs, 3 times denser sampling, and tighter control over sources of systematic error than earlier VLBI investigations. Coverage of a 2400km/s bandwidth has also enabled mapping of molecular material 30% closer to the black hole than accomplished previously, which will strengthen geometric and dynamical disk models. Through repeated observation we have also measured for the first time a 5uas (1sigma) thickness of the maser medium.
86. VLBI observations of NRAO 530 at 22, 43 and 86GHz
ID:
ivo://CDS.VizieR/J/MNRAS/418/2260
Title:
VLBI observations of NRAO 530 at 22, 43 and 86GHz
Short Name:
J/MNRAS/418/2260
Date:
21 Oct 2021
Publisher:
CDS
Description:
NRAO 530 is an optically violent variable source and has been studied with multi-epoch multifrequency high-resolution very long baseline interferometry (VLBI) observations. NRAO 530 was monitored with the Very Long Baseline Array (VLBA) at three frequencies (22, 43 and 86GHz) on 10 consecutive days in 2007 May during observations of the Galactic Centre (Sgr A*). Furthermore, analysis of archival data of NRAO 530 at 15GHz over the last 10 years allows us to study its detailed jet kinematics. We identified the compact component located at the southern-end of the jet as the VLBI core, consistent with previous studies.
87. VLBI Position Measurements
ID:
ivo://CDS.VizieR/J/AZh/81/1032
Title:
VLBI Position Measurements
Short Name:
J/AZh/81/1032
Date:
21 Oct 2021
Publisher:
CDS
Description:
A large number (~2 million) of VLBI observations have been reduced in order to re ne the measured coordinates of the observed radio sources. The data reduction was carried out in the OCCAM package using the least squares colocation method. Corrections to the coordinates of 642 objects were derived. The accuracy of the catalog is no worse than 0.2 milliseconds of arc for stable sources.
88. VLBI suvey around B0218+357 at 90cm
ID:
ivo://CDS.VizieR/J/ApJ/673/78
Title:
VLBI suvey around B0218+357 at 90cm
Short Name:
J/ApJ/673/78
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on the first wide-field, very long baseline interferometry (VLBI) survey at 90cm. The survey area consists of two overlapping 28deg^2^ fields centered on the quasar J0226+3421 and the gravitational lens B0218+357. A total of 618 sources were targeted in these fields, based on identifications from Westerbork Northern Sky Survey (WENSS) data. Of these sources, 272 had flux densities that, if unresolved, would fall above the sensitivity limit of the VLBI observations. A total of 27 sources were detected as far as 2{deg} from the phase center. The results of the survey suggest that at least 10% of moderately faint (S~100mJy) sources found at 90 cm contain compact components smaller than ~0.1"-0.3" and stronger than 10% of their total flux densities.
89. W49N H2O masers
ID:
ivo://CDS.VizieR/J/ApJ/429/253
Title:
W49N H2O masers
Short Name:
J/ApJ/429/253
Date:
21 Oct 2021
Publisher:
CDS
Description:
VLBI observations of a H2O maser were done at five epochs in 1980-82 with a 5 station VLBI network (see 1992ApJ...393..149G). A model was fitted to each peak in any spectral channel exceeding 5 times the rms background. The minimum level of this background, due to system noise at the antennas, was about 0.2Jy at each epoch. The model parameters include right ascension and declination offset (x, y) relative to a reference position; the total flux density, S; and the angular diameter {theta}_H_, of the best-fitting Gaussian distribution of intensity. The fitted parameters are in table1.