J/MNRAS/482/2502 AARTFAAC flux density calibration (Kuiack+, 2019)
AARTFAAC flux density calibration and Northern hemisphere catalogue at 60 MHz.
Kuiack M., Huizinga F., Molenaar G., Prasad P., Rowlinson A.,
Wijers R.A.M.J.
<Mon. Not. R. Astron. Soc., 482, 2502-2514 (2019)>
=2019MNRAS.482.2502K 2019MNRAS.482.2502K (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio continuum
Keywords: methods: data analysis - catalogues - surveys -
radio continuum: general
Abstract:
We present a method for calibrating the flux density scale for images
generated by the Amsterdam ASTRON Radio Transient Facility And
Analysis Centre (AARTFAAC). AARTFAAC produces a stream of all-sky
images at a rate of 1s in order to survey the Northern hemisphere for
short duration, low-frequency transients, such as the prompt
electromagnetic counterpart to gravitational wave events, magnetar
flares, blazars, and other as of yet unobserved phenomena. Therefore,
an independent flux density scaling solution per image is calculated
via bootstrapping, comparing the measured apparent brightness of
sources in the field to a reference catalogue. However, the lack of
accurate flux density measurements of bright sources below 74MHz
necessitated the creation of the AARTFAAC source catalogue, at 60MHz,
which contains 167 sources across the Northern hemisphere. Using this
as a reference results in a sufficiently high number of detected
sources in each image to calculate a stable and accurate flux scale
per 1s snapshot, in real-time.
Description:
By creating an all-sky image every second, AARTFAAC has the capability
of generating a large amount of data. Therefore, the intended
operational mode is to perform a transient search on the stream of
images, saving only those data where an interesting event has been
detected. However, in order to test the calibration method and fully
characterize the data quality a set of observations was recorded and
stored for analysis offline.
Additionally, full LST coverage was required to generate the catalogue
of calibrator sources across the Northern hemisphere. Therefore,
nearly 33h of observations were recorded to test the flux density
calibration method and generate the AARTFAAC catalogue. This allowed
the analysis of sources for many hours, across separate observations,
while maintaining a manageable data volume. These observations were
recorded between 2016 August and December. During this period of time,
the final stages of commissioning with the real-time imaging pipeline
were completed, leaving only the image calibration.
The AARTFAAC catalogue of calibration sources is presented in table A1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 106 167 AARTFAAC Northern hemisphere catalogue at 60MHz
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Nmeas Number of images used to generate light curve
8- 16 A9 --- ID ID derived from the positions measured as in the
VLSSr (JHHMM+DDd)
18- 23 F6.2 deg RAdeg Right ascension (J2000)
25- 28 F4.2 deg e_RAdeg Error on RAdeg
30- 34 F5.2 deg DEdeg Declination (J2000)
36- 39 F4.2 deg e_DEdeg Error on DEdeg
41- 46 F6.2 Jy Fint Flux density at 60MHz (1)
48- 51 F4.2 Jy e_Fint Error on Fint (1)
53- 58 F6.2 --- Loc Skew normal distribution location parameter
(ξ) (2)
60- 63 F4.2 --- e_Loc Error on Loc (2)
65- 69 F5.2 --- Scale Skew normal distribution scale parameter
(ω) (2)
71- 74 F4.2 --- e_Scale Error on Scale (2)
76- 80 F5.2 --- Shape Skew normal distribution shape parameter
(α) (2)
82- 85 F4.2 --- e_Shape Error on Shape (2)
87-106 A20 --- OName Matching common name or 3C label, where
available
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Note (1): The flux density values, and uncertainties, are calculated from the
mode of a skew-normal distribution fit to the population of
measurements.
Note (2): The mode of the skew normal distribution is not analytic, but can be
approximated numerically, Mo~ξ+ωmo(α),
where ξ, ω, and α, are the fit parameters location,
scale, and shape, of the distribution.
The function mo(α) is the degree to which the skew modifies
the mode from the mean, which for a normal distribution is equal to 0.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 29-Jun-2022