We present results of single-epoch very long baseline interferometry ( VLBI ) observations of gamma-ray bright active galactic nuclei ( AGNs ) using the Korean VLBI Network ( KVN ) at 22 , 43 , 86 , and 129 GHz bands , which are part of a KVN key science program , Interferometric Monitoring of Gamma-ray Bright AGNs ( iMOGABA ) .
We selected a total of 34 radio-loud AGNs of which 30 sources are gamma-ray bright AGNs with flux densities of > 6 \times 10 ^ { -10 } ph cm ^ { -2 } s ^ { -1 } .
Single-epoch multi-frequency VLBI observations of the target sources were conducted during a 24-hr session on 2013 November 19 and 20 .
All observed sources were detected and imaged at all frequency bands with or without a frequency phase transfer technique which enabled the imaging of 12 faint sources at 129 GHz , except for one source .
Many of the target sources are resolved on milliarcsecond scales , yielding a core-jet structure with the VLBI core dominating the synchrotron emission on the milliarcsecond scale .
CLEAN flux densities of the target sources are 0.43-28 Jy , 0.32-21 Jy , 0.18-11 Jy , and 0.35-8.0 Jy in the 22 , 43 , 86 , and 129 GHz bands , respectively .
Spectra of the target sources become steeper at higher frequency with the mean of the spectral indices of -0.40 , -0.62 , and -1.00 in the 22-43 GHz , 43-86 GHz and 86-129 GHz bands , respectively , implying that the target sources become optically thin at higher frequency ( e.g. , 86-129GHz ) .