• Received : 2018.06.29
  • Accepted : 2019.02.24
  • Published : 2019.04.30


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.

CMHHBA_2019_v52n2_31_f0001.tif 이미지

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).

CMHHBA_2019_v52n2_31_f0002.tif 이미지

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

CMHHBA_2019_v52n2_31_f0003.tif 이미지

Figure 2. Continued.

CMHHBA_2019_v52n2_31_f0004.tif 이미지

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

CMHHBA_2019_v52n2_31_f0005.tif 이미지

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

CMHHBA_2019_v52n2_31_t0001.tif 이미지

Table 4 Sample Fractional Quantities

CMHHBA_2019_v52n2_31_t0002.tif 이미지

Table 2 Sources Median Quantities

CMHHBA_2019_v52n2_31_t0003.png 이미지

Table 3 Selected Sources Quasi-Simultaneous Median Quantities

CMHHBA_2019_v52n2_31_t0004.png 이미지


Supported by : National Research Foundation (NRF), National Research Council of Science and Technology


  1. Algaba, J.-C., Zhao, G-Y., Lee, S. S., et al. 2015, Interferometric Monitoring of Gamma-Ray Bright Active Galactic Nuclei II: Frequency Phase Transfer, JKAS, 48, 237
  2. Algaba, J.-C., Lee, S. S., Kim, D. W., et al. 2018, Exploring the Variability of the Flat Spectrum Radio Source 1633+382. I. Phenomenology of the Light Curves, ApJ, 852, 30
  3. Algaba, J.-C., Lee, S. S., Rani, B., et al. 2018, Exploring the Variability of the Flat-spectrum Radio Source 1633+382. II. Physical Properties, ApJ, 859, 128
  4. Asada, K., Nakamura, M., & Pu, H. Y. 2016, Indication of the Black Hole Powered Jet in M87 by VSOP Observations, ApJ, 833, 56
  5. Boccardi, B., Krichbaum, T. P., Bach, U., et al. 2016, First 3 mm-VLBI Imaging of the Two-sided Jet in Cygnus A. Zooming into the Launching Region, A&A, 588, 9
  6. Bruni, G., Gomez, J. L., Casadio, C., et al. 2017, Probing the Innermost Regions of AGN Jets and Their Magnetic Fields with RadioAstron. II. Observations of 3C 273 at Minimum Activity, A&A, 604, 111
  7. Hada, K., Kino, M., Doi, A., et al. 2013, The Innermost Collimation Structure of the M87 Jet Down to ${\sim}10$ Schwarzschild Radii, ApJ, 775, 70
  8. Hodgson, J., Lee, S. S., Zhao, G.-Y., et al. 2016, The Automatic Calibration of Korean VLBI Network Data, JKAS, 49, 137
  9. Gomez, J. L., Lobanov, A. P., Bruni, G., et al. 2016, Probing the Innermost Regions of AGN Jets and Their Magnetic Fields with RadioAstron. I. Imaging BL Lacertae at 21 Microarcsecond Resolution, ApJ, 817, 96
  10. Hovatta, T., Valtaoja, E., Tornikoski, M., et al. 2009, Doppler Factors, Lorentz Factors and Viewing Angles for Quasars, BL Lacertae Objects and Radio Galaxies, A&A, 494, 527
  11. Hovatta, T., Lister, M. L., Aller M. F., et al. 2012 MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VIII. Faraday Rotation in Parsecscale AGN Jets, AJ, 144, 105
  12. Hovatta T., Aller, M. F., & Aller, H. D. 2014, MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. XI. Spectral Distributions, AJ, 147, 143
  13. Jorstad, S. G., Marscher, A. P., Morozova, D.A., et al. 2017, Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program, ApJ, 846, 98
  14. Kang, S.-C., et al. 2019, in preparation
  15. Kardashev, N. S., Alakoz, A. V., Andrianov, A. S., et al. 2017, RadioAstron Science Program Five Years after Launch: Main Science Results, Solar Syst. Res., 51, 535
  16. Kim, D.-W., Trippe, S., Lee, S. S., et al. 2017, The Millimeter-Radio Emission of BL Lacertae During Two ${\gamma}$-ray Outbursts, JKAS, 50, 167
  17. Kim, J.-Y., Lee, S. S., Hodgson, J. A., et al. 2018, Long-term Millimeter VLBI Monitoring of M 87 with KVN at Milliarcsecond Resolution: Nuclear Spectrum", A&A, 610, 5
  18. Kim, J.-Y., et al. 2019, in preparation
  19. Kovalev, Y. Y., Lobanov, A. P., Pushkarev, A. B., et al. 2008, Opacity in Compact Extragalactic Radio Sources and Its Effect on Astrophysical and Astrometric Studies, A&A, 483, 759
  20. Lee, S. S., Han, M. H., Kang, S. C., et al. 2013, Monitoring of Multi-frequency Polarization of Gamma-ray Bright AGNs, Eur. Phys. J. Web Conf., 6107007L
  21. Lee, S. S. 2014, Intrinsic Brightness Temperatures of Compact Radio Jets as a Function of Frequency, JKAS, 47, 303
  22. Lee, S. S., Wajima, K., Algaba, J. C., et al. 2016, Interferometric Monitoring of Gamma-Ray Bright AGNs. I. The Results of Single-epoch Multifrequency Observations, ApJS, 227, 8
  23. Lee, J. W., Lee, S. S., Hodgson, J. A., et al. 2017, Interferometric Monitoring of Gamma-Ray Bright AGNs: S5 0716+714, ApJ, 841, 119
  24. Ly, C., Walker, R. C., & Junor, W. 2007, High-Frequency VLBI Imaging of the Jet Base of M87, ApJ, 660, 200
  25. Mahmud, M., Coughlan, C. P., Murphy, E. et al. 2013, Connecting Magnetic Towers with Faraday Rotation Gradients in Active Galactic Nuclei Jets, MNRAS, 431, 695
  26. Pilipenko, S. V., Kovalev, Y. Y., Andrianov, A. S., et al. 2018, The High Brightness Temperature of B0529+483 Revealed by RadioAstron and Implications for Interstellar Scattering", MNRAS, 474, 3523
  27. Pushkarev, A. B., Hovatta, T., Kovalev Y. Y., et al. 2012, MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. IX. Nuclear Opacity, A&A, 545, 113
  28. Rioja, M., Dodson, R., Jung, T. H., et al. 2014, Verification of the Astrometric Performance of the Korean VLBI Network, Using Comparative SFPR Studies with the VLBA at 14/7 mm, AJ, 148, 84
  29. Wagner, S. J. & Witzel, A. 1995, Intraday Variability In Quasars and BL Lac Objects, ARA&A, 33, 163
  30. Walker, R. C., Hardee, P. E., Davies, F. B., et al. 2018, The Structure and Dynamics of the Subparsec Jet in M87 Based on 50 VLBA Observations over 17 Years at 43 GHz, ApJ, 855, 128