Densification of the VLBA Calibrator Survey (VCS8)


Densification of the VLBA Calibrator Survey (VCS8) project has several goals: population analysis, community service, and extension of the legacy list of compact radio sources. Proposed observations will allow to homogenize the sample of compact extragalactic radio sources with correlated flux densities at baseline projection lengths greater than 3000 km. The goal is to reach completeness at 3/4 of the celestial sphere at 150 mJy level. Such a sample will allow to investigate various statistics:
  1. to measure the brightness temperature for the core and jet components in order to populate a model of the distribution of the observed core brightness temperature in terms of the intrinsic properties of relativistic jets such as the brightness temperature, bulk motion, viewing angle. The data will also provide the unbiased sample needed to investigate the unified scheme between quasars, BL Lacs and galaxies.
  2. to analyze the relationship between the core optical depth as measured by the spectral index and other properties of the jet emission and optical properties.
  3. to analyze the distribution of source compactness index, defined as the ratio of correlated flux densities at long baseline projection lengths to short baseline projection lengths, and its relationship to other source characteristics.
  4. to test the dependence between the angular size of the core-jet region and the redshift. This dependence can be interpreted as a measure of the cosmological term qo.
Completeness of the sample will allow to generalize conclusions to the general population.

The second goal, is to improve the position accuracy of the Pan-STARRS catalog, which is currently under construction. The PanSTARRS survey covers the δ > -31° portion of the sky, with field of view (FoV) of approximately 7 square degrees. The current astrometric accuracy of PanSTARRS catalog has been achieved using a general purpose pipeline and referencing to the 2MASS catalog. However, this methodology significantly underperforms compared to the expected photon noise error floor. We propose a new method to do the PanSTARRS astrometry, a so-called "global astrometry" method, which was originally developed for the (now defunct) SIM project. In the past, the grid of extragalactic sources with high position accuracies has been too sparse to implement this global astrometry technique. However, using numerical simulations, we find that when at least 1 source with milliarcsecond VLBI position accuracy is present in a field, then a robust, one-step astrometric adjustment of source positions over the entire 3π sky can be successfully performed. An accurate PanSTARRS astrometric catalog is important for various applications, such as correct identification of transient X-ray and gamma-ray sources, a proper astrometric calibration of the Kepler telescope field, detection of nearby faint stars and high-proper motion halo population, Galactic dynamics studies, characterization of tidal streams of stars on the outskirts of the Galaxy, as well as other specific US DoD applications. We propose to observe candidate sources in the areas that have less than 1 source per PanSTARRS FoV, especially at higher Galactic latitudes to avoid crowding and extinction issues.

The third goal, community service, is to improve the list of calibrators for phase referencing. These observations will allow us to produce the accumulative list of calibrators that are strong enough at longest baselines for being detected for less than one minute at 2048 Mbps. The list will be dense enough to guarantee finding a calibrator in a circle of a radius of 2° at any target. Proposed organization of observations will also allow a user to order a candidate for a calibrator for his or her proposal.

The fourth goal is to extend the legacy source list. The calibrator list with positions known at a milli-arcsecond level of accuracy accompanied with brightness distributions in fits format at several frequencies is used for many studies beyond phase-calibration and population analysis. This includes identification of AGNs, generation of parent lists for high frequency surveys, lists of targets for space navigation, etc. For 18 years, VLBA spent ~1000 hours for intensive surveys, or about 1%. But this 1% observing time yielded 2/3 of the total number of objects ever detected with VLBA. In a long term, the list of detected sources, their positions and images will be treated as a legacy of the array.

Community Service

If you cannot find a suitable calibrator for your VLBI project, you may request observations of candidate calibrator sources by filling this form.


The list of observed sources.

The number of segments observed: 10
The number of sources observed: 1218
The number of segments correlated: 10
The number of target sources correlated: 1208
The number of target sources detected at any band: 753
The number of target sources detected at C-band: 750
The number of target sources detected at X-band: 714
Detection rate: 62%

The catalogue of source positions from C-band observations: vcs8_c.sou
The catalogue of source positions from X-band observations: vcs8_x.sou

Change Log

  1. 2014.02.14 Competed analysis of experiment BP177A

  2. 2014.04.23 Released preliminary astrometric catlaogues from analysis of 10 experients BP177A-BP177J

  3. 2014.04.23 Released results of analysis of experiment BP177B

  4. 2014.05.28 Released results of analysis of experiments BP177C, BP177D, BP177E

  5. 2014.06.05 Released results of analysis of experiments BP177F and BP177G

  6. 2014.06.07 Released results of analysis of experiment BP177H

  7. 2014.06.16 Released results of analysis of experiment BP177I

  8. 2014.06.26 Released results of analysis of experiment BP177J

Experiment Correlator output (FITS-IDI)   Log-files     Key file     Flux file C-band     Flux file X-band     Position sol.     Prelim. map  
bp177a 2014_01_07_bp177a_01.fits bp177a   logs bp177a   key bp177a C-band flux bp177a X-band flux bp177a   sol bp177a   maps
bp177b 2014_01_27_bp177b_01.fits bp177b   logs bp177b   key bp177b C-band flux bp177b X-band flux bp177b   sol bp177b   maps
bp177c 2014_01_28_bp177c_01.fits bp177c   logs bp177c   key bp177c C-band flux bp177c X-band flux bp177c   sol bp177c   maps
bp177d 2014_01_29_bp177d_01.fits bp177d   logs bp177d   key bp177d C-band flux bp177d X-band flux bp177d   sol bp177d   maps
bp177e 2014_01_30_bp177e_01.fits bp177e   logs bp177e   key bp177e C-band flux bp177e X-band flux bp177e   sol bp177e   maps
bp177f 2014_02_03_bp177f_01.fits bp177f   logs bp177f   key bp177f C-band flux bp177f X-band flux bp177f   sol bp177f   maps
bp177g 2014_02_07_bp177g_01.fits bp177g   logs bp177g   key bp177g C-band flux bp177g X-band flux bp177g   sol bp177g   maps
bp177h 2014_02_17_bp177h_01.fits bp177h   logs bp177h   key bp177h C-band flux bp177h X-band flux bp177h   sol bp177h   maps
bp177i 2014_02_18_bp177i_01.fits bp177i   logs bp177i   key bp177i C-band flux bp177i X-band flux bp177i   sol bp177i   maps
bp177j 2014_02_23_bp177j_01.fits bp177j   logs bp177j   key bp177j C-band flux bp177j X-band flux bp177j   sol bp177j   maps

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This web page was prepared by Leonid Petrov ()
Last update: 2015.08.21_10:06:34