MWAK2F1LFC - Murchison Widefield Array Low-Frequency Radio Survey of Kepler K2 Field 1

Overview

This table contains some of the results from the first dedicated radio continuum survey of a Kepler K2 mission field, Field 1, covering the North Galactic Cap. The survey was wide-field, contemporaneous, multi-epoch, and multi-resolution in nature and was conducted at low radio frequencies between 140 and 200 MHz. The multi-epoch and ultra-wide-field (but relatively low-resolution) part of the survey was provided by 15 nights of observation using the Murchison Widefield Array (MWA) over a period of approximately a month, contemporaneous with K2 observations of this field. The multi-resolution aspect of the survey was provided by the low-resolution (4 arcminutes) MWA imaging, complemented by non-contemporaneous but much higher resolution (20 arcseconds) observations using the Giant Metrewave Radio Telescope (GMRT). The survey is, therefore, sensitive to the details of radio structures across a wide range of angular scales. Consistent with other recent low radio frequency surveys, no significant radio transients or variables were detected in the survey. The resulting source catalogs consist of 1,085 and 1,468 detections in the two MWA observation bands (centered at 154 and 185 MHz, respectively) and 7445 detections in the GMRT observation band (centered at 148 MHz), over 314 square degrees. The survey is presented as a significant resource for multi-wavelength investigations of the more than 21,000 target objects in the K2 field. In the reference paper, the authors briefly examined their survey data against K2 target lists for dwarf star types (stellar types M and L) that had been known to produce radio flares.

This survey included contemporaneous observations of the K2 Field 1 made with the MWA and historical (from 2010-2012) observations made with the Tata Institute of Fundamental Research (TIFR) GMRT Sky Survey (TGSS; see http://tgss.ncra.tifr.res.in/), via the TGSS Alternative Data Release 1 (ADR1; Intema et al. 2016, in prep.). The MWA and GMRT are radio telescopes operating at low radio frequencies (approximately 140-200 MHz for the work described here). The K2 mission Campaign 1 was conducted on Field 1 (center at J2000.0 coordinates RA of 11:35:45.51 and Dec of +01:25:02.28;), covering the North Galactic Cap, between 2014 May 30 and August 21.

The details of the MWA observations are described in Table 1 of the reference paper (available at https://cdsarc.cds.unistra.fr/ftp/cats/J/AJ/152/82/table1.dat), showing the 15 observations conducted over a period of approximately one month in 2014 June and July. All observations were made in a standard MWA imaging mode with a 30.72-MHz bandwidth consisting of 24 contiguous 1.28-MHz "coarse channels", each divided into 32 "fine channels" each of 40-kHz bandwidth (a total of 768 fine channels across 30.72 MHz). The temporal resolution of the MWA correlator output was set to 0.5s. All observations were made in full polarimetric mode, with all Stokes parameters formed from the orthogonal linearly polarized feeds. Observations were made at two center frequencies, 154.88 and 185.60 MHz, with two 296-s observations of the K2 field at each frequency on each night of observation, accompanied by observations of one of three calibrators (Centaurus A, Virgo A, or Hydra A) at each frequency, with 112-s observations. The observed fields were tracked, and thus, due to the fixed delay settings available to point the MWA primary beam, the tracked RA and Dec changes slightly between different observations (always a very small change compared to the MWA field of view). The total volume of MWA visibility data processed was approximately 2.2 TB. The synthesized beam at 154 MHz is approximately 4.6 x 4.2 arcminutes at a position angle of 105 degrees, and approximately 4 x 3 arcminutes at a position angle of 109 degrees at 185 MHz. The 154 MHz images have a typical noise of 100 mJy/beam, while the 184 MHz images have a typical noise of 70 mJy/beam.

A source catalog was produced from each of the two frequencies of MWA data and given in Table 2 of the reference paper. The final set of MWA images after source finding yielded a total of 1,085 radio sources at 154 MHz, and 1,471 sources at 185 MHz over 314 square degrees, at an angular resolutions of ~4 arcminutes: this MWA catalog is contained in this HEASARC table, which thus has 1,085 + 1,471 = 2,556 entries. The GMRT images, after source finding, yielded a total of 7,445 radio sources over the same field, at an angular resolution of ~0.3 arcminutes: the GMRT catalog is contained in a separate HEASARC table GMRTK2F1LF which is available at http://heasarc.gsfc.nasa.gov/W3Browse/radio-catalog/gmrtk2f1lf.html. Thus, the overall survey covers multiple epochs of observation, spans approximately 140-200 MHz, is sensitive to structures on angular scales from arcseconds to degrees, and is contemporaneous with the K2 observations of the field over a period of approximately one month.

Catalog Bibcode

2016AJ....152...82T

References

A multi-resolution, multi-epoch low radio frequency survey of the Kepler K2
mission campaign 1 field.
    Tingay S.J., Hancock P.J., Wayth R.B., Intema H., Jagannathan P., Mooley K.
   <Astron. J., 152, 82-82 (2016)>
   =2016AJ....152...82T    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in December 2016 based on CDS Catalog J/AJ/152/82 file table2.dat (the MWA Kepler 2 Field 1 source catalog).

Parameters

Frequency
The frequency of the observation, either 154 MHz or 185 MHz, in MHz.

Source_Number
A unique identification number for each radio source at the specified frequency in the catalog. The ID numbers given in this tables for sources detected at 154 and 185 MHz appear to be completely independent, since their positions are in general quite different (even though, in the reference paper, it states that they are common to this table, and that when the same ID number appears at both frequencies, this indicates the source is cross-matched at the two frequencies). The ID numbers given for the GMRT data in Table 3 of the reference paper (available in the HEASARC database as the GMRTK2F1LF table) are specific to the GMRT data, i.e., they are not the same as either of the ID numbers provided for the MWA data in the present table.

Name
The name of the radio source, using the '[THW2016] MWA nnnMHz' prefix (for Tingay, Hancock, Wayth 2016 Murchison Widefield Array, nnn MHZ, where nnn is either 154 or 185) and the source number, e.g., '[THW2016] MWA 185MHz 997'. These names were created by the HEASARC in the style recommended by the Dictionary of Nomenclature of Celestial Objects.

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

RA_Error
The mean error in the Right Ascension of the radio source, in degrees.

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

Dec_Error
The mean error in the Declination of the radio source, in degrees.

LII
The Galactic Longitude of the radio source.

BII
The Galactic Latitude of the radio source.

Flux
The mean flux density across all epochs of the radio source at the frequency specified by the frequency parameter, in mJy/beam. There are no extended or resolved sources in the MWA catalog so only the flux density is reported (equal to the peak brightness in the image for a point source).

Flux_Error
The standard deviation of the mean flux density of the radio source at the frequency specified by the frequency parameter, in mJy/beam.

Contact Person

Questions regarding the MWAK2F1LFC database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Friday, 08-Nov-2024 14:52:25 EST