J/AJ/152/82 Radio continuum survey of Kepler K2 mission Field 1 (Tingay+, 2016)
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 2016AJ....152...82T (SIMBAD/NED BibCode)
ADC_Keywords: Radio continuum ; Radio sources
Keywords: catalogs - galaxies: active - instrumentation: interferometers -
radio continuum: general
Abstract:
We present the first dedicated radio continuum survey of a Kepler K2
mission field, Field 1, covering the North Galactic Cap. The survey is
wide field, contemporaneous, multi-epoch, and multi-resolution in
nature and was conducted at low radio frequencies between 140 and
200MHz. 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 the
field. The multi-resolution aspect of the survey was provided by the
low resolution (4') MWA imaging, complemented by non-contemporaneous
but much higher resolution (20'') 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 1085 and 1468 detections in
the two MWA observation bands (centered at 154 and 185MHz,
respectively) and 7445 detections in the GMRT observation band
(centered at 148MHz), over 314 square degrees. The survey is presented
as a significant resource for multi-wavelength investigations of the
more than 21000 target objects in the K2 field. We briefly examine our
survey data against K2 target lists for dwarf star types (stellar
types M and L) that have been known to produce radio flares.
Description:
We describe contemporaneous observations of K2 Field 1 with the
Murchison Widefield Array (MWA) and historical (from 2010-2012)
observations from the Tata Institute of Fundamental Research (TIFR)
Giant Metrewave Radio Telescope (GMRT) Sky Survey (TGSS;
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
140-200MHz for the work described here). K2 mission Campaign 1 was
conducted on Field 1 (center at R.A.=11:35:45.51; decl.=+01:25:02.28;
J2000), covering the North Galactic Cap, between 2014 May 30 and
August 21.
The parameters of MWA observations are described in Table1, 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 30.72MHz bandwidth consisting of 24 contiguous
1.28MHz "coarse channels", each divided into 32 "fine channels" each
of 40kHz bandwidth (total of 768 fine channels across 30.72MHz). 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
185.60MHz, with two 296s 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 112s observations. The observed fields were tracked,
and thus, due to the fixed delay settings available to point the MWA
primary beam, the tracked R.A. and decl. 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 2.2TB.
A full survey of the radio sky at 150MHz as visible from the Giant
Metrewave Radio (GMRT) was performed within the scope of the PI-driven
TGSS project between 2010 and early 2012, covering the declination
range -55° to +90°. Summarizing the observational parameters
as given on the TGSS project website
(http://tgss.ncra.tifr.res.in/150MHz/obsstrategy.html), the survey
consists of more than 5000 pointings on an approximate hexagonal grid.
Data were recorded in full polarization (RR, LL, RL, LR) every 2s, in
256 frequency channels across 16MHz of bandwidth (140-156MHz). Each
pointing was observed for about 15 minutes, split over three or more
scans spaced in time to improve UV-coverage. Typically, 20-40
pointings were grouped together into single night-time observing
sessions, bracketed and interleaved by primary (flux density and
bandpass) calibrator scans on 3C48, 3C147, and/or 3C286. Interleaving
secondary (phase) calibrator scans on a variety of standard phase
calibrators were also included, but were typically too faint to be of
significant benefit at these frequencies.
A source catalog was produced from each of the two frequencies of MWA
data (see table2) and the single TGSS image (see table3). The final
set of MWA images after source finding yields a total of 1085 radio
sources at 154MHz, and 1468 at 185MHz over 314 square degrees, at
angular resolutions of ∼4'. The GMRT images, after source finding,
yields a total of 7445 radio sources over the same field, at an
angular resolution of ∼0.3'. Thus, the overall survey covers multiple
epochs of observation, spans approximately 140-200MHz, 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.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 60 86 Murchison Widefield Array (MWA) observation log
table2.dat 49 2556 Catalog from the Murchison Widefield Array (MWA)
at 154MHz and 184MHz
table3.dat 82 7445 *Catalog from the TGSS image
figure3.dat 34 42871 The light curves of all sources from the 154 and
185MHz catalogs
--------------------------------------------------------------------------------
Note on table3.dat: TGSS=Tata Institute of Fundamental Research (TIFR) Giant
Metrewave Radio Telescope (GMRT) Sky Survey (http://tgss.ncra.tifr.res.in/).
--------------------------------------------------------------------------------
See also:
VIII/97 : 74MHz VLA Low-frequency Sky Survey Redux (VLSSr) (Lane+, 2014)
VIII/42 : Texas Survey of radio sources at 365MHz (Douglas+ 1996)
VIII/35 : Radio Sources observed with Culgoora Circular Array (Slee 1995)
VIII/16 : Molonglo Reference Catalogue of Radio Sources (Large+ 1991)
J/ApJ/734/L34 : 145MHz source measurements by PAPER (Jacobs+, 2011)
J/ApJ/648/629 : Radio observations of late M, L, and T dwarfs (Berger+, 2006)
J/ApJS/13/65 : Radio source flux densities at 750&1400MHz (Pauliny-Toth+ 1966)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 I10 --- MWA [1087724024/1090489536] Murchison Widefield
Array (MWA) observation identifier
12- 21 A10 "Y:M:D" Obs.date UT date of the observation
23- 30 A8 "h:m:s" Obs.time UT time of the observation
32- 34 I3 s Exp [112/296] Exposure time (112 or 296)
36- 39 A4 --- Target Observation target (K2, CenA, or HydA) (1)
41- 46 F6.2 MHz Freq [154.8/185.6] Center frequency (154.88 or
185.60)
48- 53 F6.2 deg RAdeg Right Ascension in decimal degrees (J2000)
55- 60 F6.2 deg DEdeg Declination in decimal degrees (J2000)
--------------------------------------------------------------------------------
Note (1): Observation targets defined as below:
K2 = K2 Field 1;
CenA = Centaurus A;
HydA = Hydra A.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 MHz Freq [154/185] Frequency of the observation (154 or
185)
5- 12 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000)
14- 19 F6.4 deg e_RAdeg Mean error in RAdeg
21- 27 F7.4 deg DEdeg Declination in decimal degrees (J2000)
29- 34 F6.4 deg e_DEdeg Mean error in DEdeg
36- 40 I5 mJy Savg [155/20006] Mean flux density across all
epochs
42- 44 I3 mJy e_Savg [1/716] Standard deviation of flux
(ΔFlux)
46- 49 I4 --- Source [0/2012] Source identifier (used in place of a
position based name) (G1)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000)
10- 15 F6.4 deg e_RAdeg Mean error in right ascension
17- 23 F7.4 deg DEdeg Declination in decimal degrees (J2000)
25- 30 F6.4 deg e_DEdeg Mean error in declination
32- 37 F6.3 Jy/beam Sp [0.01/16] Peak flux density
39- 43 F5.3 Jy/beam e_Sp [0.001/0.074] Mean error on Sp
45- 50 F6.2 arcsec a [16.95/237] Major axis
52- 56 F5.2 arcsec e_a [0.01/75.8] Mean error in a
58- 63 F6.2 arcsec b [16.75/105.4] Minor axis
65- 69 F5.2 arcsec e_b [0.01/27.2] Mean error in b
71- 73 I3 deg PA [-90/90] Position angle
75- 77 I3 deg e_PA [0/90]?=-1 Mean error on PA (a null error
indicates that the position angle was not
able to be estimated) (1)
79- 82 I4 --- Source [1/7445] Source running sequence identifier
(used in place of a position based name) (2)
--------------------------------------------------------------------------------
Note (1): When the source finding algorithm cannot assign a meaningful error on
the morphology parameters (in the low signal to noise detections), a null
value is entered into the relevant table entry.
Note (2): The identification numbers given for the Giant Metrewave Radio
Telescope (GMRT) data are specific to the GMRT data; they are not the same
as the identification numbers provided for the Murchison Widefield Array
(MWA) data (in Table2).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: figure3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 MHz Freq Frequency of the observation (154 or 185)
5- 8 I4 --- Source [0/2012] Source identifier (G1)
10- 21 F12.4 d JD Julian Date of the observation
23- 27 I5 mJy/beam S [151/20556] Flux density
29- 31 I3 mJy/beam e_S [37/604] Mean error in flux
33- 34 I2 --- Spot [45/80] Murchison Widefield Array (MWA) sweet
spot number (telescope pointing direction:
45, 56, or 80)
--------------------------------------------------------------------------------
Global Notes:
Note (G1): When the same identification number appears at both frequencies (154
and 185MHz), this indicates a source that is cross-matched at the two
frequencies.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
29-Nov-2016: Insert into VizieR
29-Mar-2019: Unit for Savg and e_Savg in Table 2 corrected for mJy.
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 25-Oct-2016