J/ApJ/740/65 VLA search for 5GHz radio transients (Ofek+, 2011)
A Very Large Array search for 5 GHz radio transients and variables at low
Galactic latitudes.
Ofek E.O., Frail D.A., Breslauer B., Kulkarni S.R., Chandra P., Gal-Yam A.,
Kasliwal M.M., Gehrels N.
<Astrophys. J., 740, 65 (2011)>
=2011ApJ...740...65O 2011ApJ...740...65O
ADC_Keywords: Radio continuum ; Radio sources
Keywords: radio continuum: general - stars: neutron - techniques: photometric
Abstract:
We present the results of a 5GHz survey with the Very Large Array
(VLA) and the expanded VLA, designed to search for short-lived
(≲1day) transients and to characterize the variability of radio
sources at milli-Jansky levels. A total sky area of 2.66deg2, spread
over 141 fields at low Galactic latitudes (b∼6-8°), was observed
16 times with a cadence that was chosen to sample timescales of days,
months, and years. Most of the data were reduced, analyzed, and
searched for transients in near real-time. Interesting candidates were
followed up using visible light telescopes (typical delays of 1-2hr)
and the X-ray Telescope on board the Swift satellite. The final
processing of the data revealed a single possible transient with a
peak flux density of fν∼2.4mJy. Furthermore, we use the data to
measure the source variability on timescales of days to years, and we
present the variability structure function of 5GHz sources.
Description:
141 fields (listed in table 2) were observed on 11 epochs using the
VLA in 2008 July and August and on five epochs using the Expanded VLA
(EVLA) during 2010 July. All observations were made in the compact
D-configuration, with a maximum baseline of 0.6km. For the 2008
observations, we added together two adjacent 50MHz bandwidths
centered at 4835 and 4885MHz with full polarization. For the 2010
observations, we added together two adjacent 128 MHz sub-bands
centered at 4896 and 5024MHz with full polarization.
The "Single epoch catalog" was generated by running SAD (Astronomical
Image Processing System (AIPS) task "search and destroy" (SAD)) on a
15 arcmin diameter region for each single-epoch image individually
(Table 5). A second "Master catalog" (Table 6) was created by
running SAD on the final Master images made from all available data
(16 epochs).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 34 141 List of survey pointings
table3.dat 52 16 List of the epochs
table5.dat 109 2953 Single epoch catalog
table6.dat 466 464 Master catalog
--------------------------------------------------------------------------------
See also:
VIII/87 : The Allen Telescope Array 20cm Survey (ATATS). I. (Croft+ 2010)
J/ApJ/725/1792 : Pi Ghz Sky Survey (PiGSS). I. (Bower+, 2010)
J/ApJ/704/652 : Radio transients in a 1.4GHz survey (Niinuma+, 2009)
J/PASP/120/339 : Nasu Radio-Transient Search Project (Takefuji+, 2008)
J/AJ/127/2565 : Faint FIRST variable radio sources (de Vries+, 2004)
J/ApJS/91/347 : A 5-GHz VLA Survey of the Galactic Plane (Becker+ 1994)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Field Field name (HHMM+DDMM; J2000)
12- 20 F9.5 deg RAdeg Field right Ascension (J2000)
22- 30 F9.5 deg DEdeg Field declination (J2000)
33- 34 I2 --- Nep [12/16] Number of epochs
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ep Epoch number
4- 7 I4 yr Obs.Y [2008/2010] Mid-time observation year (UTC)
9- 11 A3 "month" Obs.M Mid-time observation month (UTC)
13- 17 F5.2 d Obs.D Mid-time observation day (UTC)
20- 25 F6.2 d Exp Time elapsed
28- 30 I3 uJy Noise rms noise
33- 35 I3 --- Nf [109/141] Number of observed fields
38- 40 I3 --- Ns [151/363] Number of observed sources
43- 47 F5.3 --- GC [0.92/1.04] Gain correction
50- 52 F3.1 % CE [0/6] Cosmic error εcos (1)
--------------------------------------------------------------------------------
Note (1): measure of the VLA calibration error, assumed to be good to a
level of 3% or better; see section 6 for details.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ep [1/16] Epoch number
6- 8 I3 --- Seq [1/343] Source number
13- 21 A9 --- Field Field name (HHMM+DDMM; J2000)
26- 35 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
38- 47 F10.6 deg DEdeg Declination in decimal degrees (J2000)
50- 55 F6.2 mJy Fpc Corrected peak specific flux
57- 62 F6.2 mJy Fp [0.5/75.1] Peak specific flux uncorrected
for beam attenuation
65- 69 F5.2 mJy e_Fp [0.08/0.41] Error in UncF
72- 76 F5.2 --- Fi/Fp [0.04/4.57] Integrated flux divided by peak flux
79- 85 F7.2 arcsec amaj [7/69] Source major axis
87- 93 F7.2 arcsec bmin [1/27] Source minor axis
96-100 F5.1 deg PA [0/180] Position angle of major axis
105-109 F5.2 arcmin DC [/10.5] Distance of source from beam center
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Mseq [1/464] Source index in Master catalog
6- 14 A9 --- Field Field name (HHMM+DDMM; J2000)
19- 28 F10.6 deg RAdeg Right Asecnsion in decimal degrees (J2000)
31- 40 F10.6 deg DEdeg Declination in decimal degrees (J2000)
42- 48 F7.2 mJy Fpc Corrected peak specific flux
50- 55 F6.2 mJy Fp [0.12/57.18] Peak specific flux uncorrected
for beam attenuation
57- 62 F6.2 mJy e_Fp [0.04/0.13] Error in UncF
65- 69 F5.2 --- Fi/Fp [0.27/3.68] Integrated flux divided by peak flux
73 I1 --- Lobe [0/1] SAD sidelobe warning flag
76- 82 F7.2 arcsec amaj [10/43] Source major axis
84- 90 F7.2 arcsec bmin [4/29] Source minor axis
93- 97 F5.1 deg PA [0/180] Position angle of major axis
99-103 F5.2 arcmin DC [0/91] Distance of source from beam center
106-107 I2 --- Nobs [14/16] Number of observations of the field
110-111 I2 --- Ndet [0/16] Number of source detections in
individual epochs by SAD
114-119 F6.2 --- Chi2 The χ2 measured from Single epochs
121-126 F6.2 --- S/M Flux standard deviation in Single epochs
divided by mean flux
130-135 F6.2 --- Chi2Y The χ2 measured from Yearly epochs
137-142 F6.2 --- S/MY Flux standard deviation in Yearly epochs
divided by mean flux
148-152 F5.2 --- VR [1/7] Variability index VR in Yearly epochs (1)
154-158 F5.2 --- VF [0/1] Variability index VF in Yearly epochs (1)
161-164 F4.1 arcsec r(N) [0.1/14.5]? Distance from nearest NVSS source;
15" search radius
166-173 F8.1 mJy Fref ? NVSS peak specific flux (Cat. VIII/65)
175-182 F8.1 mJy e_Fref ? Error in NVSS peak specific flux
184-188 F5.2 --- alpha [-1.12/3.53]? 1.4-4.9GHz spectral slope α
defined by fν∝να
192-195 F4.1 arcsec r(U) [0.1/2]? Distance from nearest USNO-B1 source;
2" search radius
197-201 F5.1 mag Bmag ? USNO-B1 B2 magnitude
203-207 F5.1 mag Rmag ? USNO-B1 R2 magnitude
210-213 F4.1 arcsec r(2M) [0.3/2]? Distance from nearest 2MASS source;
2" search radius
215-219 F5.2 mag Jmag ? 2MASS J-band magnitude
221-225 F5.2 mag Hmag ? 2MASS H-band magnitude
227-231 F5.2 mag Kmag ? 2MASS Ks-band magnitude
234-239 F6.2 mJy f2008 Uncorrected peak flux in Yearly 2008 image
241-245 F5.2 mJy e_f2008 Error in f2008
247-252 F6.2 mJy f2010 Uncorrected peak flux in Yearly 2010 image
254-258 F5.2 mJy e_f2010 Error in f2010
260-265 F6.2 mJy f1 Uncorrected peak flux in Single epoch number 1
267-271 F5.2 mJy e_f1 Error in f1
273-278 F6.2 mJy f2 Uncorrected peak flux in Single epoch number 2
280-284 F5.2 mJy e_f2 Error in f2
286-291 F6.2 mJy f3 Uncorrected peak flux in Single epoch number 3
293-297 F5.2 mJy e_f3 Error in f3
299-304 F6.2 mJy f4 Uncorrected peak flux in Single epoch number 4
306-310 F5.2 mJy e_f4 Error in f4
312-317 F6.2 mJy f5 Uncorrected peak flux in Single epoch number 5
319-323 F5.2 mJy e_f5 Error in f5
325-330 F6.2 mJy f6 Uncorrected peak flux in Single epoch number 6
332-336 F5.2 mJy e_f6 Error in f6
338-343 F6.2 mJy f7 ? Uncorrected peak flux in Single epoch number 7
345-349 F5.2 mJy e_f7 ? Error in f7
351-356 F6.2 mJy f8 Uncorrected peak flux in Single epoch number 8
358-362 F5.2 mJy e_f8 Error in f8
364-369 F6.2 mJy f9 Uncorrected peak flux in Single epoch number 9
371-375 F5.2 mJy e_f9 Error in f9
377-382 F6.2 mJy f10 Uncorrected peak flux in Single epoch number 10
384-388 F5.2 mJy e_f10 Error in f10
390-395 F6.2 mJy f11 Uncorrected peak flux in Single epoch number 11
397-401 F5.2 mJy e_f11 Error in f11
403-408 F6.2 mJy f12 Uncorrected peak flux in Single epoch number 12
410-414 F5.2 mJy e_f12 Error in f12
416-421 F6.2 mJy f13 ? Uncorrected peak flux in Single epoch number 13
423-427 F5.2 mJy e_f13 ? Error in f13
429-434 F6.2 mJy f14 ? Uncorrected peak flux in Single epoch number 14
436-440 F5.2 mJy e_f14 ? Error in f14
442-447 F6.2 mJy f15 Uncorrected peak flux in Single epoch number 15
449-453 F5.2 mJy e_f15 Error in f15
455-460 F6.2 mJy f16 ? Uncorrected peak flux in Single epoch number 16
462-466 F5.2 mJy e_f16 ? Error in f16
--------------------------------------------------------------------------------
Note (1): the variability indicators VR and VF are defined from the
observed fluxes fi of a source on the different epochs i as:
VR = max(fi)/min(fi)
VF = [max(fi)-min(fi)]/[max(fi)+min(fi)]
= (VR-1)/(VR+1)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 04-Feb-2013