Radio observations of the first three-month Fermi-AGN at 4.8 GHz

TL;DR

This study uses radio observations at 4.8 GHz to analyze gamma-ray bright AGN, revealing correlations between radio and gamma-ray emissions, and characterizing intra-day and inter-month variability in blazars.

Contribution

It provides new insights into radio variability patterns of gamma-ray AGN and compares IDV detection rates with previous samples.

Findings

Radio flux correlates with gamma-ray intensity.

60% of observed blazars show intra-day variability.

Pronounced inter-month variability observed in two BL Lac objects.

Abstract

Using the Urumqi 25m radio telescope, sources from the first three-month Fermi-LAT detected AGN catalog with declination >0 were observed in 2009 at 4.8 GHz. The radio flux density appears to correlate with the gamma-ray intensity. Intra-day variability (IDV) observations were performed in March, April and May in 2009 for selected 42 gamma-ray bright blazars, and 60% of them show evident flux variability at 4.8 GHz during the IDV observations, the IDV detection rate is higher than that in previous flat-spectrum AGN samples. The IDV appears more often in the VLBI-core dominant blazars, and the non-IDV blazars show relatively `steeper' spectral indices than the IDV blazars. Pronounced inter-month variability has been found in two BL Lac objects: J0112+2244 and J0238+1636.