CORE-JET BLENDING EFFECTS IN ACTIVE GALACTIC NUCLEI UNDER THE KOREAN VLBI NETWORK VIEW AT 43 GHZ

Abstract

A long standing problem in the study of Active Galactic Nuclei (AGNs) is that the observed VLBI core is in fact a blending of the actual AGN core (classically defined by the ${\tau}=1$ surface) and the upstream regions of the jet or optically thin flows. This blending may cause some biases in the observables of the core, such as its flux density, size or brightness temperature, which may lead to misleading interpretation of the derived quantities and physics. We study the effects of such blending under the view of the Korean VLBI Network (KVN) for a sample of AGNs at 43 GHz by comparing their observed properties with observations obtained using the Very Large Baseline Array (VLBA). Our results suggest that the observed core sizes are a factor ~ 11 larger than these of VLBA, which is similar to the factor expected by considering the different resolutions of the two facilities. We suggest the use of this factor to consider blending effects in KVN measurements. Other parameters, such as flux density or brightness temperature, seem to possess a more complicated dependence.

Figure 1. Comparison of the flux densities (top) and core sizes (bottom) obtained using the iMOGABA model fitting script (red stars) and manual fitting (black dots).

Figure 2. Comparison of core sizes and brightness temperatures observed with VLBA (red squares) and KVN (black circles).

Figure 2. Continued.

Figure 3. Histograms for the measured fractional quantitiesfS , fd and fTb .

Figure 4. Scatter matrix for the proposed correlations. The correlation coefficients are shown in the top right corner of each panel.

Table 1 Sample Median Quantities

Table 4 Sample Fractional Quantities

Table 2 Sources Median Quantities

Table 3 Selected Sources Quasi-Simultaneous Median Quantities