VIII/111 VCCS Epoch 1 Bright Catalog Release (Peters+, 2021)
The VLITE Commensal Sky Survey (VCSS):
A 340 MHz Companion to the VLA Sky Survey (VLASS).
Peters W., Polisensky E., Brisken W., Cotton W., Clarke T.,
Giacintucci, S., Kassim N.
< American Astronomical Society meeting No. 237, id. 211.06 >
=2022yCat.8111....0P 2022yCat.8111....0P
=2021AAS...23721106P 2021AAS...23721106P
ADC_Keywords: Surveys ; Radio sources
Keywords: radio astronomy - radio galaxies - radio source catalogs - sky survey
Abstract:
The VLA Low Band Ionosphere and Transient Experiment (VLITE) is a
commensal observing system on the Karl G. Jansky Very Large Array
(VLA). A 64MHz sub-band centered at 340MHz is recorded and
correlated for up to 18 antennas during nearly all regular VLA
operations. Pipeline software calibrates and images the data within a
few days after observation. Here we give a brief overview of the
instrument and present the first epoch of the VLITE Commensal Sky
Survey (VCSS). These data were taken simultaneously with the ongoing
VLA Sky Survey (VLASS; url: https://science.nrao.edu/vlass/). VLITE
breaks the continuous "on-the-fly" (OTF) VLASS scans into 2-second
integrations and correlates these at a central "pointing" position
every 1.5 degrees in right ascension. VLITE's field of view is 2
degrees across, while the declination rows are spaced by only 7.25',
so there is a large overlap between each row and a high tolerance for
failure. The data for each correlator position is imaged separately,
corrected and weighted by an appropriately elongated primary beam
model, and then combined in the image plane to create a mosaic of the
sky. Catalogs of the sources in both the individual pointing images
and the final mosaics are extracted using PyBDSF. In addition to
providing a sky model at 340MHz, VCSS complements VLASS by providing
source spectral indices and intermediate resolution images for
extended sources. The observations also provide a rich database for
transient searches
Description:
This document describes the first data release of the VLITE Commensal
Sky Survey Epoch 1 (VCSS1). This 340MHz survey was observed
simultaneously with Epoch 1 of the 3GHz VLA Sky Survey (VLASS). The
data for VCSS1 come from the VLA Low- band Ionosphere and Transient
Experiment (VLITE), and all data products reported here are produced
by the Naval Research Laboratory (NRL). The catalog consists of
components determined by PyBDSF fitting on individual mosaic images
where the fitted synthesized beams range from 10" (minor axis) to
30" (major axis). Details of the instrument, observing mode,
processing and data products are provided in this memo. This first
data release comprises only the bright (>5.0σ) sources due to
significant bias in flux for weaker sources as de scribed in the
document. We detail a number of known limitations on the catalog,
including the need to add a 15% flux scale uncertainty to cataloged
errors, and we adopt a positional uncertainty of 2" for the catalog.
The noise is not uniform across the sky for VCSS1, but the average
1σ noise is ∼3mJy/bm. We estimate that the 50σ catalog is
complete at >50% for sources with peak brightnesses above 200mJy/bm or
integrated fluxes above 300.
A summary of the basic observational parameters for the VCSS Epoch 1
bright catalog release is given in Table 1. The angular resolution
typically ranges from 10" (minor axis) to 30" (major axis) and varies
considerably across the sky; however it is on average equivalent to
the area of a 15" round beam. We assume typical VLA snapshot
sensitivity to extended sources in estimating the largest angular size
(LAS). The sensitivity varies considerably across the sky as detailed
below. The catalog covers most of the sky above dec -40°, but
there are gaps due to failed observations. The IAU naming convention
for the sources is VCSS1JHHMMSS.s+DDMMSS
Table 1: VCSS Epoch 1 Bright Catalog summary
----------------------------------------------
Central Frequency: 340 MHz
Bandwidth: 33.6 MHz
Angular Resolution: ∼15"
LAS: 8.5'
Average sensitivity (1σ): 3mJy/bm
Sky Coverage: 30000deg2
Sources: 52844
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
vcscat.dat 209 52844 VCSS Epoch 1 bright catalog release
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Byte-by-byte Description of file: vcscat.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Name Name, VCSS1 JHHMMSS.s+DDMMSS (Name)
24- 31 F8.4 deg RAdeg Right ascension (J2000) (RA)
33- 40 F8.4 deg DEdeg Declination (J2000) (DEC)
42- 53 E12.6 deg e_RAdeg Error on right ascension (E_RA)
55- 66 E12.6 deg e_DEdeg Error on declination (E_DEC)
68- 76 F9.2 mJy Ftot Total flux at 340MHz (Total_flux)
78- 83 F6.2 mJy e_Ftot Error on total flux at 340MHz
(ETotalflux)
85- 93 F9.2 mJy Ftotc Corrected total flux at 340MHz
(CorrectedTotalflux)
95-102 F8.2 mJy Fpeak Peak flux at 340MHz (Peak_flux)
104-109 F6.2 mJy e_Fpeak Error on peak flux at 340MHz (EPeakflux)
111-118 F8.2 mJy Fpeakc Corrected peak flux at 340MHz
(CorrectedPeakflux)
120-123 F4.1 arcsec Maj Major axis (Maj)
125-127 F3.1 arcsec e_Maj Error on major axis (E_Maj)
129-132 F4.1 arcsec Min Minor axis (Min)
134-136 F3.1 arcsec e_Min Error on minor axis (E_Min)
138-142 F5.1 deg PA Position angle (PA)
144-148 F5.1 deg e_PA Error on position angle (E_PA)
150-158 F9.2 mJy FtotIsl Island total flux at 340MHz
(IslTotalflux)
160-165 F6.2 mJy e_FtotIsl Error on island total flux at 340MHz
(EIslTotal_flux)
167-172 F6.2 mJy/beam Islrms Island rms (Isl_rms)
174-179 F6.2 mJy/beam Islmean Island mean (Isl_mean)
181-186 F6.2 mJy/beam ResIslrms Island rms residual (ResidIslrms)
188-194 F7.2 mJy/beam ResIslmean Island mean residual (ResidIslmean)
196 A1 --- SCode [CMS] A code that defines the source
structure (S_Code) (1)
198-201 F4.2 --- Compact Compactness (Compactness)
203-209 F7.2 --- SNR Signal-to-noise ratio (SNR)
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Note (1): Source structure code as follows:
S = for single Gaussian that is the only source in the island
M = for multiple Gaussian
C = single-Gaussian source in an island with other sources
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Acknowledgements:
Parthasarathy Venkataraman, p.venkataraman(at)utoronto.ca
References:
https://iopscience.iop.org/article/10.3847/0004-637X/832/1/60/pdf
https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9906/1/
Commensal-low-frequency-observing-on-the-NRAO-VLA--VLITE/10.1117/
12.2233036.full
(End) Patricia Vannier [CDS] 18-Nov-2022