Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz
  Two dozens of radio loud active galactic nuclei (AGNs) have been observed
with Urumqi 25 m radio telescope in order to search for intra-day variability
(IDV). The target sources are blazars (namely flat spectrum radio quasars and
BL Lac objects) which are mostly selected from the observing list of
RadioAstron AGN monitoring campaigns. The observations were carried out at 4.8
GHz in two sessions of 8-12 February 2014 and 7-9 March respectively. We report
the data reduction and the first results of observations. The results show that
the majority of the blazars exhibit IDV in 99.9% confidence level, some of them
show quite strong IDV. We find the strong IDV of blazar 1357 + 769 for the
first time. The IDV at centimeter-wavelength is believed to be predominately
caused by the scintillation of blazar emission through the local interstellar
medium in a few hundreds parsecs away from Sun. No significant correlation
between the IDV strength and either redshift or Galactic latitude is found in
our sample. The IDV timescale along with source structure and brightness
temperature analysis will be presented in a forthcoming paper.
