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INTRINSIC BRIGHTNESS TEMPERATURES OF COMPACT RADIO JETS AS A FUNCTION OF FREQUENCY
이상성 한국천문학회 2014 Journal of The Korean Astronomical Society Vol.47 No.6
We present results of our investigation of the radio intrinsic brightness temperatures of compactradio jets. The intrinsic brightness temperatures of about 100 compact radio jets at 2, 5, 8, 15, and86 GHz are estimated based on large VLBI surveys conducted in 2001-2003 (or in 1996 for the 5 GHzsample). The multi-frequency intrinsic brightness temperatures of the sample of jets are determinedby a statistical method relating the observed brightness temperatures with the maximal apparent jetspeeds, assuming one representative intrinsic brightness temperature for a sample of jets at each observingfrequency. By investigating the observed brightness temperatures at 15 GHz in multiple epochs, we findthat the determination of the intrinsic brightness temperature for our sample is affected by the fluxdensity variability of individual jets at time scales of a few years. This implies that it is important to usecontemporaneous VLBI observations for the multi-frequency analysis of intrinsic brightness temperatures. Since our analysis is based on the VLBI observations conducted in 2001-2003, the results are not stronglyaffected by the flux density variability. We find that the intrinsic brightness temperature T0 increases asT0 ∝ νξobs with ξ = 0.7 below a critical frequency νc ≈ 9 GHz where the energy loss begins to dominate theemission. Above νc, T0 decreases with ξ = −1.2, supporting the decelerating jet model or particle cascademodel. We also find that the peak value of T0 ≈ 3.4 × 1010 K is close to the equipartition temperature,implying that the VLBI cores observable at 2-86 GHz may be representing jet regions where the magneticfield energy dominates the total energy in jets.