J/ApJ/742/49 Variable and transient radio sources in FIRST (Thyagarajan+, 2011)
Variable and transient radio sources in the FIRST survey.
Thyagarajan N., Helfand D.J., White R.L., Becker R.H.
<Astrophys. J., 742, 49 (2011)>
=2011ApJ...742...49T 2011ApJ...742...49T
ADC_Keywords: Radio sources ; Radio continuum ; Surveys
Keywords: catalogs - methods: data analysis - methods: statistical -
radio continuum: general - surveys
Abstract:
A comprehensive search for variable and transient radio sources has
been conducted using ∼55000 snapshot images of the Faint Images of the
Radio Sky at Twenty-cm survey (Cat. VIII/90). We present an analysis
leading to the discovery of 1627 variable and transient objects down
to mJy levels over a wide range of timescales (a few minutes to
years). Variations observed range from 20% to a factor of 25.
Multi-wavelength matching for counterparts reveals the diverse classes
of objects exhibiting variability, ranging from nearby stars and
pulsars to galaxies and distant quasars. Interestingly, more than half
of the objects in the sample have either no classified counterparts or
no corresponding sources at any other wavelength and require
multi-wavelength follow-up observations. We discuss these classes of
variables and speculate on the identity of objects that lack
multi-wavelength counterparts.
Description:
The Faint Images of the Radio Sky at Twenty-centimeter (FIRST) survey
covered ∼9055deg2 (8444deg2 in the northern Galactic cap and
611deg2 in the southern Galactic cap) with observations conducted
between 1993 and 2004 using the NRAO VLA in its B-configuration
operating at a frequency of 1.4GHz (Becker et al., 1995ApJ...450..559B 1995ApJ...450..559B,
see Cat. VIII/90).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 139 1623 Summary of properties of variables and transients
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See also:
VIII/90 : The FIRST Survey Catalog, Version 12Feb16 (Becker+ 2012)
VII/269 : SDSS Quasar Catalog, DR9Q (Paris+, 2012)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/26 : Low-Frequency Variable Radio Sources Monitoring (Mitchell+, 1994)
J/ApJ/737/45 : Variable 1.4GHz radio sources from NVSS and FIRST (Ofek+, 2011)
J/ApJS/180/67 : Photometric selection of QSOs from SDSS. II. (Richards+, 2009)
J/AJ/127/2565 : Faint FIRST variable radio sources (de Vries+, 2004)
J/AJ/125/2411 : SIRTF First-Look Survey (Condon+, 2003)
J/ApJS/143/1 : FIRST-APM Source Catalog (McMahon+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of Right Ascension (J2000) (1)
4- 5 I2 min RAm Minute of Right Ascension (J2000) (1)
7- 12 F6.3 s RAs Second of Right Ascension (J2000) (1)
14 A1 --- DE- Sign of the Declination (J2000) (1)
15- 16 I2 deg DEd Degree of Declination (J2000) (1)
18- 19 I2 arcmin DEm Arcminute of Declination (J2000) (1)
21- 25 F5.2 arcsec DEs Arcsecond of Declination (J2000) (1)
27- 32 F6.2 mJy Fpeak [1/234.93] FIRST 1.4GHz peak flux density
34- 39 F6.2 mJy Fwmp Weighted mean 1.4GHz peak flux density
41 A1 --- l_Flow Limit flag on Flow
42- 47 F6.2 mJy Flow Lower limit of measured flux density range
49 A1 --- l_Fup Limit flag on Fup
50- 55 F6.2 mJy Fup Upper limit of measured flux density range
57- 66 F10.2 mJy Fnvss ?=-999999 NVSS 1.4GHz flux density (if match
found)
68 I1 --- N Number of observations in light curve
70 A1 --- l_sigma Limit flag on sigma
71- 74 F4.2 --- sigma [4/8] Variability indicator
σ(P(χ2,ν)) (2)
76- 80 F5.2 --- s.max Maximum deviation σmax from mean (3)
82- 86 F5.2 --- D.max Maximum deviation Δmax(σ) (4)
88 A1 --- l_Ratio Limit flag on Ratio
89- 93 F5.2 --- Ratio Maximum-to-minimum flux density ratio (5)
95- 98 I4 d Tmin ?=-999 Minimum significant timescale
100 A1 --- fN [N-] Neighbour flag (6)
102-109 F8.2 --- s.nbr [-6.2/3.6]?=-9999 Distance of neighbors flux
σnbr (7)
111 A1 --- Vt [VT] Variable or Transient light curve type
113-120 F8.2 mag imag ?=-9999 SDSS i-band magnitude
122-139 A18 --- Note Cross-ID with other catalogs and object type
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Note (1): The FIRST catalog used for positions, major and minor axes, etc.
with a complete description is available at the url
http://sundog.stsci.edu/first/catalogs/readme.html The "08jul16"
version was used at the time of this study.
Note (2): σ(P(χ2,ν)) in an equivalent normal distribution
corresponding to the χ-square probability associated with the
light curve to deviate from a constant light curve value given in
Fwmp. A value ">8.00" is assigned if the actual value is higher and/or
unable to be represented due to machine-precision limitations (a value
of 5 corresponds to a probability of 5.733x10-7 of non-variable source)
Note (3): σmax if the maximum deviation of any individual data
point in the light curve from a hypothetical light curve of constant
value given in Fwmp.
Note (4): Δmax(σ) is the difference (in σ) between any
two data points in the light curve.
Note (5): Ratio Max/Min for the pair of data points involved in D.max.
Note (6): N denotes presence of a neighbour brighter than 500mJy within 31'.
Note (7): distance by which the mean normalized peak flux density of the
outlier's neighbors departs from the mean of the distribution of such
normalized neighbor peak flux densities from all outliers. The higher
the absolute value is, the less ideal the quality of the field
surrounding the outlier and hence the less reliable the physical
variability of the outlier.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Apr-2013