J/MNRAS/474/4937 Interplanetary scintillation at 162 and 1400MHz (Chhetri+ 2018)
Interplanetary scintillation studies with the Murchison Widefield Array.
II. Properties of sub-arcsecond compact sources at low radio frequencies.
Chhetri R., Morgan J., Ekers R.D., Macquart J.-P., Sadler E.M.,
Giroletti M., Callingham J.R., Tingay S.J.
<Mon. Not. R. Astron. Soc., 474, 4937-4955 (2018)>
=2018MNRAS.474.4937C 2018MNRAS.474.4937C (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; Galaxies, radio ; Interferometry
Keywords: techniques: high angular resolution - techniques: interferometric -
galaxies: active - radio continuum: galaxies
Abstract:
We report the first astrophysical application of the technique of
wide-field interplanetary scintillation (IPS) with the Murchison
Widefield Array (MWA). This powerful technique allows us to identify
and measure sub-arcsecond compact components in low-frequency radio
sources across large areas of sky without the need for long-baseline
interferometry or ionospheric calibration. We present the results of a
5-min observation of a 30x30deg2 MWA field at 162MHz with 0.5s
time resolution. Of the 2550 continuum sources detected in this field,
302 (12 per cent) show rapid fluctuations caused by IPS. We find
that at least 32 per cent of bright low-frequency radio sources
contain a sub-arcsecond compact component that contributes over
40 per cent of the total flux density. Perhaps surprisingly,
peaked-spectrum radio sources are the dominant population among the
strongly scintillating, low-frequency sources in our sample. While
gamma-ray active galactic nuclei are generally compact, flat-spectrum
radio sources at higher frequencies (162MHz), the properties of
many of the Fermi blazars in our field are consistent with a compact
component embedded within more extended low-frequency emission. The
detection of a known pulsar in our field shows that the wide-field IPS
technique is at the threshold of sensitivity needed to detect new
pulsars using image plane analysis, and scaling the current MWA
sensitivity to that expected for SKA-low implies that large IPS-based
pulsar searches will be feasible with SKA. Calibration strategies for
the SKA require a better knowledge of the space density of compact
sources at low radio frequencies, which IPS observations can now
provide.
Description:
The data used in this study were taken by the MWA, located in Western
Australia, and consist of 2048 dual-polarization dipole antennas.
The work presented here uses a single 286s (∼5min) observation
made on 2016 May 1 at 02:25:20 UTC (during the daytime), with the Sun
placed in the first null of the primary beam. The pointing centre was
44 deg from the Sun (the minimum and maximum solar elongations for
sources detected in the field are 20.7 and 69.6°, respectively) at
RA=00:49:02 and Dec.=-19:58:54, and close to the south Galactic
pole. We split the MWA's instantaneous bandwidth into two 15.4MHz
bands. Only the upper half, centred at 162MHz, is discussed here.
The data were correlated in real-time on site, using the standard MWA
correlator (Ord et al., 2015PASA...32....6O 2015PASA...32....6O) with the maximum
available time resolution of 0.5s.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 138 2550 MWA IPS II catalogue
sed/* . 2550 Individual SED in pdf
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See also:
J/MNRAS/473/2965 : Interplanetary scintillation at 79 and 158MHz (Morgan+ 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Name GLEAM Source name from GLEAM catalogue,
JHHMMSS-DDMMSS
16- 17 I2 h RAh Right Ascension (J2000)
19- 20 I2 min RAm Right Ascension (J2000)
22- 26 F5.2 s RAs Right Ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32- 33 I2 arcmin DEm Declination (J2000)
35- 39 F5.2 arcsec DEs Declination (J2000)
41- 46 F6.3 Jy/beam S162 Estimated peak flux density at 162MHz
from GLEAM
48- 52 F5.3 Jy/beam e_S162 Uncertainty in 162MHz peak flux density
54- 58 F5.2 --- alpha Spectral index from GLEAM catalogue
60 A1 --- n_alpha Flag on alpha (1)
62- 65 F4.2 --- e_alpha ?=- Uncertainty in spectral index
67 I1 --- nNVSS Number NVSS of counterparts within 60arcsecond
of GLEAM position
69- 73 F5.3 Jy S1400 ?=- Integrated flux density from NVSS, only
when single counterpart listed in nNVSS
75- 78 F4.1 deg Elong Solar Elongation on date of observation
80- 85 F6.2 --- NormSNR Normalised signal to noise ratio
87 A1 --- l_SI Upper limit flag on SI
88- 91 F4.2 --- SI Scintillation index
93- 97 F5.3 --- e_SI ?=- Uncertainty in SI
99 A1 --- l_NSI Upper limit flag on NSI
100-103 F4.2 --- NSI Normalised Scintillation Index
105-109 F5.3 --- e_NSI ?=- Uncertainty in NSI
111-113 A3 --- Flag [AFP ] Flag (2)
115-138 A24 ---- SED Name of the file with SED in subdirectory sed
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Note (1): "*" indicates GLEAM does not provide spectral index, but a least
squares fit was used to estimate approximate spectral index across GLEAM band
Note (2): Flag as follows:
A = AT20G source
F = Fermi source
P = Peaked spectrum source
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History:
From electronic version of the journal
References:
Norgan et al., Paper I 2018MNRAS.473.2965M 2018MNRAS.473.2965M, Cat. J/MNRAS/473/2965
Chhetri et al., Paper III 2018MNRAS.479.2318C 2018MNRAS.479.2318C
Sadler et al., Paper IV 2019MNRAS.483.1354S 2019MNRAS.483.1354S
(End) Patricia Vannier [CDS] 11-Mar-2021