J/ApJ/737/45 Variable 1.4GHz radio sources from NVSS and FIRST (Ofek+, 2011)
The structure function of variable 1.4GHz radio sources based on NVSS and FIRST
observations.
Ofek E.O., Frail D.A.
<Astrophys. J., 737, 45 (2011)>
=2011ApJ...737...45O 2011ApJ...737...45O
ADC_Keywords: Radio sources ; Radio continuum ; Surveys
Keywords: ISM: general - quasars: general - radio continuum: general
Abstract:
We augment the two widest/deepest 1.4GHz radio surveys, the NRAO VLA
Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty
centimeters (FIRST), with the mean epoch in which each source was
observed. We use these catalogs to search for unresolved sources that
vary between the FIRST and NVSS epochs. We find 43 variable sources
(0.1% of the sources) that vary by more than 4σ, and we
construct the mean structure function of these objects. This enables
us to explore radio variability on timescales between several months
and about five years. We find that, on these timescales, the mean
structure function of the variable sources is consistent with a flat
structure function. A plausible explanation to these observations is
that a large fraction of the variability at 1.4GHz is induced by
scintillations in the interstellar medium, rather than by intrinsic
variability. Finally, for a subsample of the variables for which the
redshift is available, we do not find strong evidence for a
correlation between the variability amplitude and the source redshift.
Description:
The NVSS observations (NRAO VLA Sky Survey; Condon et al. 1998,
Cat. VIII/65) were carried out between 1993 June and 1999 April, while
the FIRST survey observations (Faint Images of the Radio Sky at Twenty
Centimeters; Becker et al. 1995ApJ...450..559B 1995ApJ...450..559B, see Cat. VIII/90) were
conducted between 1993 March and 2002 September. The FIRST catalog
contains 816331 sources, brighter than about 1mJy, mainly in the North
Galactic cap. The NVSS catalog contains 1773484 objects with
DEC>-30°, brighter than about 3.5mJy.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 1773484 Observing times of NVSS sources
table2.dat 63 816331 Observing Times of FIRST Sources
table3.dat 104 43 Variable sources
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See also:
VIII/90 : The FIRST Survey Catalog, Version 12Feb16 (Becker+ 2012)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/26 : Low-Frequency Variable Radio Sources Monitoring (Mitchell+, 1994)
J/AJ/127/2565 : Faint FIRST variable radio sources (de Vries+, 2004)
J/MNRAS/315/839 : Compact variable radio sources at 151MHz. I. (Minns+, 2000)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
12- 21 F10.6 deg DEdeg Declination in decimal degrees (J2000)
23- 30 F8.2 mJy Sp 1.4GHz peak flux
32- 38 F7.2 mJy e_Sp The rms in PFlux
40- 42 I3 --- Nobs Number of observations
44- 54 F11.3 d t ? Mean Julian day of the observation (1)
56- 63 F8.3 d dt ? Time span of the observations δt (1)
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Note (1): In table 1, -99.999 = NaN.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
11- 18 F8.5 deg DEdeg Declination in decimal degrees (J2000)
20 A1 --- Rem [a-h ] Comment on individual source (1)
22- 26 F5.2 mJy S1 FIRST peak specific flux
28- 31 F4.2 mJy e_S1 The rms in S1
33- 36 F4.1 mJy S2 NVSS peak specific flux
38- 40 F3.1 mJy e_S2 The rms in S2
41 A1 --- f_S2 [C] C: complex source in NVSS (2)
43- 48 F6.1 d Dt Time between the FIRST and NVSS observation
50- 53 F4.1 mag B2mag ? USNO-B1 B2-band magnitude (3)
55- 58 F4.1 mag R2mag ? USNO-B1 R2-band magnitude (3)
60- 64 F5.2 mag Jmag ? 2MASS J-band magnitude (3)
66- 70 F5.2 mag Hmag ? 2MASS H-band magnitude (3)
72- 76 F5.2 mag Kmag ? 2MASS K-band magnitude (3)
78- 81 F4.1 arcsec rX ? Distance from ROSAT source (3)
83- 87 F5.2 mag gmag ? SDSS g-band magnitude (3)
89- 93 F5.2 mag rmag ? SDSS r-band magnitude (3)
95- 99 F5.3 --- zsp ? SDSS spectroscopic redshift
101-104 F4.2 --- zph ? SDSS photometric redshift (4)
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Note (1): Flag as follows:
a = The peak flux we measure in the NVSS image is a factor of two lower than
the flux stated in the NVSS catalog, so this may be a constant source.
b = Near the strong source 3C 340 - NVSS and FIRST images are noisy.
c = Radio images are noisy.
d = This is possibly a radio supernova in the outskirts of NGC 3310 (Argo et
al. 2004MNRAS.351L..66A 2004MNRAS.351L..66A).
e = NVSS image shows a double source.
f = Extended emission 15 arcmin from source.
g = Extended emission 4 arcmin from source.
h = FIRST flux may be influenced by sidelobes from 3C 343 (4.5Jy, 9 arcmin to
the NW).
Note (2):
C = Sources number 2, 4, 20, 24, and 39 are indicated as complex sources
with a high peak in the NVSS catalog. We note that these sources are
brighter in the NVSS catalog than in the FIRST catalog.
Note (3): The position of each source was cross correlated with various
catalogs, including the USNO-B1 (Monet et al. 2003, Cat. I/284),
2MASS (Skrutskie et al. 2006, Cat. VII/233 - see also Cat. II/246),
ROSAT bright and faint source catalogs (Voges et al. 1999, Cat. IX/10,
2000IAUC.7432....3V 2000IAUC.7432....3V), and the Sloan Digital Sky Survey (York et al.
2000AJ....120.1579Y 2000AJ....120.1579Y - see also Cat. II/294). In case counterparts are
found we list their USNO-B1 B2 and R2 magnitudes, 2MASS J, H, and K
magnitudes, distance from ROSAT source, and SDSS g and r point-spread
function magnitudes and redshifts. We use search radius, relative to
the FIRST catalog position, of 60" for ROSAT and 2.5" for all the
other catalogs.
Note (4): We use a photometric redshift estimator for quasars which is
described in Ofek et al. (2002MNRAS.337.1163O 2002MNRAS.337.1163O). The photometric
redshift is calculated only if the source is indicated as a possible
quasar in the SDSS database.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 07-Jan-2013