Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz

TL;DR

This study observed 24 blazars at 4.8 GHz to investigate intra-day variability, finding most exhibit significant IDV likely caused by interstellar scintillation, with some showing notably strong variability.

Contribution

First comprehensive intra-day variability observations of 24 blazars at 4.8 GHz, demonstrating widespread IDV and identifying the first strong IDV in blazar 1357+769.

Findings

99.9% of blazars show IDV at 4.8 GHz

Some blazars exhibit strong IDV

No correlation between IDV strength and redshift or galactic latitude

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.