Second Epoch Vlba Calibrator Survey Observations: VCS-Ii

Abstract

Six very successful VLBA calibrator survey campaigns were run between 1994 and 2007 to build up a large list of compact radio sources with positions precise enough for use as VLBI phase reference calibrators. We report on the results of a second epoch VLBA Calibrator Survey campaign (VCS-II) in which 2400 VCS sources were re-observed at X and S bands in order to improve the upcoming third realization of the International Celestial Reference Frame (ICRF3) as well as to improve their usefulness as VLBI phase reference calibrators. In this survey, some 2062 previously detected sources and 324 previously undetected sources were detected and revised positions are presented. Average position uncertainties for the re-observed sources were reduced from 1.14 and 1.98 mas to 0.24 and 0.41 mas in RA and Declination, respectively, or by nearly a factor of 5. Minimum detected flux values were approximately 15 and 28 mJy in X and S bands, respectively, and median total fluxes are approximately 230 and 280 mJy. The vast majority of these sources are flat-spectrum sources, with ~82% having spectral indices greater than -0.5.

Resolving the Decades-long Transient FIRST J141918.9+394036: An Orphan Long Gamma-Ray Burst or a Young Magnetar Nebula?

“…where the quoted uncertainties represent the 1-σ confidence interval and take into account the statistical uncertainties in the image (0.2 mas in both α and δ), the uncertainty in the phase calibrator position (0.1 mas; Beasley et al 2002;Gordon et al 2016), and the estimated uncertainties associated with the phase referencing technique (0.06 and 0.04 mas for α and δ, respectively; Pradel et al 2006 consistent with the one reported from the FIRST survey (Law et al 2018), as well as the preliminary results published in Marcote et al (2018). The measured flux density on 2018 September 18 follows the declining trend of the light-curve reported from observations with the Karl G. Jansky Very Large Array, VLA (see Fig.…”

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

“…The precise location of A-2 is α=19:59:28.32345, δ=+40:44:01.9133 (J2000, ±1 mas), referenced to the previously known astrometric position of the nucleus (established to be α nuc =19:59:28.35648, δ nuc =+40:44:02.0963, Gordon et al 2016) in the ICRF2 frame (Fey et al 2015). The projected offset from the nucleus is 418 mas, or 458 pc.…”

Statistical Analysis of the Results of 20 Years of Activity of the International VLBI Service for Geodesy and Astrometry

“…The jumps in the number of sources ( Fig. 1f) are caused mainly by special observing programs VLBA Calibrator Survey (VCS) at the VLBA network 7 (Gordon et al (2016) and references therein).…”