ASKAPBETA - BETA Pilot Multi-Epoch Continuum Survey of Spitzer SPT Deep Field

Overview

The Boolardy Engineering Test Array (BETA) is a 6 x 12m-dish interferometer and the prototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped with the first generation of ASKAP's phased array feed (PAF) receivers. These facilitate rapid wide-area imaging via the deployment of simultaneous multiple beams within an ~30 deg² field of view. By cycling the array through 12 interleaved pointing positions and using nine digitally formed beams, the authors have effectively mimicked a traditional 1 hours x 108 pointing survey, covering ~150 deg² over 711-1015 MHz in just 12 hours of observing time. Three such observations were executed over the course of a week. The authors verified the full bandwidth continuum imaging performance and stability of the system via self-consistency checks and comparisons to existing radio data. The combined three epoch image has arcminute resolution and a 1-sigma thermal noise level of 375 µJy/beam, although the effective noise is a factor of ~3 higher due to residual sidelobe confusion. From this, the authors have derived a catalog of 3,722 discrete radio components, using the 35% fractional bandwidth to measure in-band spectral indices for 1037 of them. A search for transient events reveals one significantly variable source within the survey area. The survey covers approximately two-thirds of the Spitzer South Pole Telescope (SPT) Deep Field. This pilot project demonstrates the viability and potential of using PAFs to rapidly and accurately survey the sky at radio wavelengths.

The target field was observed with BETA on three separate occasions as part of the commissioning and verification of the instrument. The telescope delivers 304 MHz of instantaneous bandwidth and for these observations the sky frequency range was 711-1015 MHz, corresponding to a fractional bandwidth of 35%. The data were captured with a frequency resolution of 18.5 kHz, using 16,416 frequency channels across the band.

The PYBDSM source finder was used to extract a component catalog from the deep mosaic image formed from a combination of all epochs and sub-bands. Components were fit to islands of emission that had a peak brightness of >5 sigma and an island boundary threshold of >3 sigma, where sigma is the local estimate of the background noise level. Component spectral indices were assigned by matching positions at which spectral indices were successfully fit (Section 4.5 of the reference paper). Following the excision of some spurious detections at the noisy edge of the mosaic, the final catalog contains 3,722 components, 1,037 of which have in-band spectral index measurements.

Catalog Bibcode

2016MNRAS.457.4160H

References

Wide-field broad-band radio imaging with phased array feeds:
a pilot multi-epoch continuum survey with ASKAP-BETA.
    Heywood I., Bannister K.W., Marvil J., Allison J.R., Ball L., Bell M.E.,
    Bock D.-J., Brothers M., Bunton J.D., Chippendale A.P., Cooray F.,
    Cornwell T.J., De Boer D., Edwards P., Gough R., Gupta N., Harvey-Smith L.,
    Hay S., Hotan A.W., Indermuehle B., Jacka C., Jackson C.A., Johnston S.,
    Kimball A.E., Koribalski B.S., Lenc E., Macleod A., McClure-Griffiths N.,
    Mcconnell D., Mirtschin P., Murphy T., Neuhold S., Norris R.P., Pearce S.,
    Popping A., Qiao R.Y., Reynolds J.E., Sadler E.M., Sault R.J.,
    Schinckel A.E.T., Serra P., Shimwell T.W., Stevens J., Tuthill J.,
    Tzioumis A., Voronkov M.A., Westmeier T., Whiting M.T.
   <Mon. Not. R. Astron. Soc., 457, 4160-4178 (2016)>
   =2016MNRAS.457.4160H    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in March 2017 based on CDS Catalog J/MNRAS/457/4160 file table3.dat, the list of source components found in the ASKAP-BETA Survey covering two-thirds of the Spitzer SPT Deep Field.

Parameters

Name
The J2000.0 position-based radio source designation, '[HBM2016] JHHMMSS.ss-DDMMSS.ss', where the prefix stands for Heywood, Bannister, Marvil 2016. This naming convention was created by the HEASARC using the style recommended by the Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the radio source component in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 10^-4 degrees (0.36 arcseconds) in the original table.

RA_Error
The 1-sigma uncertainty in the Right Ascension of the radio source component, in arcseconds. The listed values are derived from the uncertainty in the component fitting and are thus sensitive only to the statistical component discussed in Section 4.4 of the reference paper. A more rigorous estimation of the positional errors can be achieved by the quadrature sum of the listed values and the astrometric uncertainties that are tied to those of SUMSS (see Section 4.4, ibid).

Dec
The Declination of the radio source component in the selected equinox. This was given in J2000.0 equatorial coordinates to a precision of 10^-4 degrees (0.36 arcseconds) in the original table.

Dec_Error
The 1-sigma uncertainty in the Declination of the radio source component, in arcseconds. The listed values are derived from the uncertainty in the component fitting and are thus sensitive only to the statistical component discussed in Section 4.4 of the reference paper. A more rigorous estimation of the positional errors can be achieved by the quadrature sum of the listed values and the astrometric uncertainties that are tied to those of SUMSS (see Section 4.4, ibid).

LII
The Galactic Longitude of the radio source component.

BII
The Galactic Latitude of the radio source component.

Flux_863_MHz
The peak flux density of the radio source component computed at the band center reference frequency of 863 MHz, in milliJansky/beam (mJy/beam).

Flux_863_MHz_Error
The 1-sigma uncertainty in the peak flux density of the radio source component computed at the band center reference frequency of 863 MHz, in milliJansky/beam (mJy/beam).

Int_Flux_863_MHz
The integrated flux density of the radio source component computed at the band center reference frequency of 863 MHz, in milliJansky (mJy).

Int_Flux_863_MHz_Error
The 1-sigma uncertainty in the integrated flux density of the radio source component computed at the band center reference frequency of 863 MHz, in milliJansky (mJy).

RMS_863_MHz
The estimated local rms noise (sigma) at the position of the radio source component, in milliJansky/beam (mJy/beam).

Alpha
The spectral index (alpha) of the radio source component assuming S ~ nu^alpha, where S is the flux density and nu is the frequency. This is formed via a fit to the component flux densities across the four sub-bands. See Section 4.5 of the reference paper for further details.

Major_Axis_Limit
This limit flag parameter is set to '<' if the quoted deconvolved major axis size is an upper limit, rather than an actual value.

Major_Axis
The deconvolved major axis size of the Gaussian model fitted to the radio source component, in arcseconds. A value of zero indicates that the source is unresolved.

Major_Axis_Error
The 1-sigma uncertainty in the deconvolved major axis size of the Gaussian model fitted to the radio source component, in arcseconds

Minor_Axis_Limit
This limit flag parameter is set to '<' if the quoted deconvolved minor axis size is an upper limit, rather than an actual value.

Minor_Axis
The deconvolved minor axis size of the Gaussian model fitted to the radio source component, in arcseconds. A value of zero indicates that the source is unresolved.

Minor_Axis_Error
The 1-sigma uncertainty in the deconvolved minor axis size of the Gaussian model fitted to the radio source component, in arcseconds

Position_Angle_Limit
This limit flag parameter is set to '<' if the quoted position angle of the Gaussian model fitted to the radio source component is an upper limit, rather than an actual value.

Position_Angle
The position angle (measured eastwards from north) of the Gaussian model fitted to the radio source component, in degrees

Position_Angle_Error
The 1-sigma uncertainty in the position angle (measured eastwards from north) of the Gaussian model fitted to the radio source component, in degrees

Zi_Un_Id_Component
The zero-indexed unique identifier for the radio source component.

Zi_Un_Id_Source
The zero-indexed unique identifier for the radio source. Sources can consist of one or more components.

Zi_Un_Id_Island
The zero-indexed unique identifier for the island with which the radio source component is associated. Components were fit to islands of emission that had a peak brightness of >5 sigma and an island boundary threshold of >3 sigma, where sigma is the local estimate of the background noise level.

Contact Person

Questions regarding the ASKAPBETA database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:24:30 EDT