Radio Variability and Relativistic Beaming Effect for Blazars

Abstract

Abstract In this paper, using a database of the University of Michigan Radio Astronomy Observatory at the radio frequencies (8 GHz and 14.5 GHz), we determined the variability time scales, and calculated the brightness temperature for 86 radio sources (29 BL Lacertae objects—BLs and 57 flat spectrum radio quasars—FSRQs). The time scales were found in the range of from 3 months to 16.27 years with an averaged value scale of 2.34 years. We obtained the following results: (1) The brightness temperature is in the range of log $T_{\rm b,var}$$=$ 10.98 to $T_{\rm b,var}$$=$ 15.35, which suggests that the Doppler factors are in the range of $\delta$$=$ 0.73 to $\delta$$=$ 20.74. The averaged values are $\langle\delta\rangle$$=$ 5.95$\pm$2.93 for 57 FSRQs and $\langle\delta\rangle$$=$ 5.08$\pm$2.63 for 29 BLs. (2) The radio luminosity, $L_{\rm ob}$, is found to be correlated with the radio Doppler factor, $\delta$, log$L_{\rm ob}$$=$ (0.58$\pm$0.10) log$\delta^{3}$$+$ 43.49$\pm$0.21. (3) The viewing angles and the Lorentz factors were determined for 53 sources (15 BLs and 38 FSRQS) with available superluminal velocity (Zhang & Fan 2008, Chin. J. Astron. Astrophys, 8, 385). The averaged values are $\Gamma$$=$ 24.1$\pm$17.35 and $\theta$$=$ 8$.^\circ$7$\pm$3$.^{\circ}$5 for the FSRQs, and $\Gamma$$=$ 13.5$\pm$11.16 and $\theta$$=$ 12$^{\circ}\pm$7$^{\circ}$ for the BLs.