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J/ApJ/689/108 MASIV survey. II. First four epochs (Lovell+, 2008)
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Beginning of ReadMe :J/ApJ/689/108 MASIV survey. II. First four epochs (Lovell+, 2008)
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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
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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 10-50muas. 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.