Abstract
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.
Highlights
The intra-day variability (IDV) of active galactic nuclei (AGNs) at centimeter wavelengths was first discovered in 1980s [1,2]
There are more than 20 data points sampled for the majority of sources in about three-day observation of each session, some sources have fewer data points due to their low declinations or bad data being deleted by the calibration software
We present the first results of the IDV observations of about two dozens of blazars with Urumqi 25 m radio telescope in 8–12 February 2014 and 7–9 March
Summary
The intra-day variability (IDV) of active galactic nuclei (AGNs) at centimeter wavelengths was first discovered in 1980s [1,2]. If the IDV is AGN-intrinsic, the timescale of a day or less will imply very high brightness temperatures of the jetemitting region, several magnitudes (typically 103−5 times) greater than the inverseCompton limit of TIC ∼ 1011.5 K [8] or the equipartition temperature of Teq = 5 × 1010 = 1010.7 K [9]. It becomes clear that the IDV at centimeter wavelengths is not AGN-intrinsic, but caused by the interstellar scintillation (ISS) effect in our Galaxy [17]. The flux fluctuations caused by the ISS-induced IDV, may have contributed partly to the RA SVLBI observed Tb excess (over the IC limit) of blazars [22].
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