J/ApJ/689/108 MASIV survey. II. First four epochs (Lovell+, 2008)
The micro-arcsecond scintillation-induced variability (MASIV) survey. II. The first four epochs. Lovell J.E.J., Rickett B.J., Macquart J.-P., Jauncey D.L., Bignall H.E., Kedziora-Chudczer L., Ojha R., Pursimo T., Dutka M., Senkbeil C., Shabala S. <Astrophys. J., 689, 108-126 (2008)> =2008ApJ...689..108L
ADC_Keywords: Active gal. nuclei ; Interstellar medium ; Radio continuum ; Surveys Keywords: ISM: structure - radiation mechanisms: non-thermal - radio continuum: ISM - galaxies: active Abstract: We report on the variability of 443 flat-spectrum, compact radio sources monitored using the VLA for 3 days in four epochs at ∼4 month intervals at 5GHz as part of the Micro-Arcsecond Scintillation-Induced Variability (MASIV) survey. Over half of these sources exhibited 2%-10% rms variations on timescales over 2 days. We analyzed the variations by two independent methods and find that the rms variability amplitudes of the sources correlate with the emission measure in the ionized interstellar medium along their respective lines of sight. We thus link the variations with interstellar scintillation of components of these sources, with some (unknown) fraction of the total flux density contained within a compact region of angular diameter in the range 10-50µas. We also find that the variations decrease for high mean flux density sources and, most importantly, for high-redshift sources. The decrease in variability is probably due either to an increase in the apparent diameter of the source or to a decrease in the flux density of the compact fraction beyond z∼2. Description: The VLA observations took place over four periods during 2002 January 19, May 9, and September 13 and 2003 January 10. All epochs were 72hr in duration except 2002 September, which included an additional 24hr. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 118 475 MASIV source variability characteristics
See also: VIII/67 : Catalogue of scintillating radio sources (Artyukh+, 1996-1998) J/AZh/72/291 : Variability at Frequencies 3.9 and 7.5 GHz (Gorshkov+, 1995) J/MNRAS/325/1411 : ATCA Intraday Variability Survey (Kedziora-Chudczer+, 2001) J/AJ/128/1570 : 8.4GHz VLBA observations of scintillating sources (Ojha+, 2004) J/ApJS/165/439 : Interstellar scintillation at 2 and 8GHz (Rickett+, 2006) J/AZh/85/314 : Complete sample of flat-spectrum radio sources (Gorshkov+, 2008) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 10 A10 --- MASIV Source identification (JHHMM+DDMM) 12- 13 I2 h RAh Hour of Right Ascension (J2000) 15- 16 I2 min RAm Minute of Right Ascension (J2000) 18- 22 F5.2 s RAs Second of Right Ascension (J2000) 24 A1 --- DE- Declination sign (J2000) 25- 26 I2 deg DEd Degree of Declination (J2000) 28- 29 I2 arcmin DEm Arcminute of Declination (J2000) 31- 34 F4.1 arcsec DEs Arcsecond of Declination (J2000) 36- 40 F5.1 10+10ph/m2/s Ha WHAM Hα flux in Rayleighs 42- 47 F6.3 Jy <S1> Mean epoch 1 (2002.05) 5GHz flux density (G1) 49- 54 F6.3 Jy <S2> Mean epoch 2 (2002.35) 5GHz flux density (G1) 56- 61 F6.3 Jy <S3> Mean epoch 3 (2002.70) 5GHz flux density (G1) 63- 68 F6.3 Jy <S4> Mean epoch 4 (2003.02) 5GHz flux density (G1) 70- 73 F4.1 % mod1 Raw epoch 1 (2002.05) modulation index (G1) 75- 78 F4.1 % mod2 Raw epoch 2 (2002.35) modulation index (G1) 80- 83 F4.1 % mod3 Raw epoch 3 (2002.70) modulation index (G1) 85- 88 F4.1 % mod4 Raw epoch 4 (2003.02) modulation index (G1) 90- 93 F4.2 % e_mod The 1σ error in raw modulation index 95 A1 --- C1 [ync] variable (y) for epoch 1 (1) 96 A1 --- C2 [ync] variable (y) for epoch 2 (1) 97 A1 --- C3 [ync] variable (y) for epoch 3 (1) 98 A1 --- C4 [ync] variable (y) for epoch 4 (1) 100-108 E9.2 --- D(2d) Standard characterization of intra-day variation from fit to epoch average structure function 110-116 E7.1 --- e_D(2d) ? Error in D(2d) (2) 118 I1 --- tau Timescale classification (3)
Note (1): Classification as follows: y = variable; n = non-variable; c = non-variable source used as a secondary calibrator. Note (2): A blank error indicates a non-convergent fit. Note (3): Timescale classification as follows: 2 = τchar<0.5d; 3 = 0.5d<τchar<3d; 4 = τchar>3d; 0 = D(2d) below threshold of 4e-4.
Global notes: Note (G1): Epochs as follows: Epoch 1 = 2002-01-19 January 19, 72hr duration. Epoch 2 = 2002-05-09 May 9, 72hr duration. Epoch 3 = 2002-09-13 September 13, 72hr+24hr duration. Epoch 4 = 2003-01-10 January 10, 72hr duration.
History: From electronic version of the journal References: Lovell et al. Paper I. 2003AJ....126.1699L
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 19-Jan-2011
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