# Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz
## 3 Results and Discussion
### Comment on Individual Sources  
We comment briefly on some prominent IDV sources which showed a modulation index \(m>3m_{0}\) in one or two observing sessions, in the following. We note that all the target sources are blazars with core-dominated radio structures in milliarcsecond scales from the VLBI images (e.g., [28; 29]). **PKS 0528 + 134**: the source shows IDV in both sessions, see Tables 1 and 2, the IDV strength is slightly increased from session 1 to session 2, while the mean flux density of 1.710 \(\pm\) 0.034 Jy in session 1 decreases to 1.525 \(\pm\) 0.034 Jy, at 4.8 GHz. Figure 1: Three strong IDV sources with \(m\geq 3\) in both observations. **(Left upper panel)** the light curve of 1357 + 769 at 4.8 GHz in 8–12 February 2014, the flux density \(I\) (left \(y\)-axis) and the ratio of flux density over mean flux density \(<I>\) (right \(y\)-axis) versus time (MJD) in this and following figures; **(right upper panel)** the light curve of 1357 + 769 at 4.8 GHz in 7–9 March 2014. **(Left middle panel)** the light curve of J1128 + 5925 at 4.8 GHz in 8–12 February 2014; **(right middle panel)** the light curve of J1128 + 5925 at 4.8 GHz in 7–9 March 2014. **(Left bottom panel)** the light curve of J0929 + 5013 at 4.8 GHz in 8–12 February 2014; **(right bottom panel)** the light curve of J0929 + 5013 at 4.8 GHz in 7–9 March 2014. Figure 2: Two example sources with no variability. **(Left panel)** the light curve of B2 1239 + 376 at 4.8 GHz in 8–12 February 2014; **(right panel)** the light curve of 1633 + 382 at 4.8 GHz in 8–12 February 2014. **0716 + 714**: this BL Lac object is a well known IDV source, although its IDV strength is moderate with relatively longer IDV timescales from previous observations and its IDV timescales can be fitted with the annual modulated ISS model [20]. It shows IDV in both sessions, and its IDV strength in session 1 is less than that in session 2. The total flux density of 1.255 \(\pm\) 0.016 Jy in session 1 decreases to 1.193 \(\pm\) 0.017 Jy in session 2. **0748 + 126**: this blazar shows IDV in both sessions, its IDV strength in session 1 is higher than that in session 2. Its mean flux density is similar from session 1 to session 2. **OJ287**: this is a BL Lac object, which is thought to be a supermassive binary black hole system from long-term optical periodic flux variations [30], but even the RA space VLBI still cannot resolve the binary. It is observed in session 2 only and shows an IDV. **1044 + 719**: this blazar shows IDV in both sessions. The IDV strength increases from session 1 to session 2. Its mean flux density also increases from 2.581 \(\pm\) 0.035 Jy in session 1 to 2.786 \(\pm\) 0.049 Jy in session 2. **1357 + 769**: this blazar shows strong IDVs in both sessions (upper panel of Figure 1), the \(m^{\prime}\) decreases from 5.28 in session 1 to 3.02 in session 2, while the mean flux density decreases from 0.461 \(\pm\) 0.025 Jy in session 1 to 0.411 \(\pm\) 0.013 Jy in session 2. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** \\
**Source** & **Type** & **N** & \(<\) 5 \(>\) \(\pm\) \(\sigma_{\star}\) & **m/m\({}^{\prime}\)** & **Y** & **A**\({}^{2}\) & **A**\({}^{2}\) & **P**\({}_{\rm{\small{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{                    }}}}}}}}}}\) & **R**\({}_{\rm{\small{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{       }}}}}}}}}}}}}\) & **R**\({}_{\rm{\small{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{     }}}}}}}}}}}}}}\) & **m/m\({}^{\prime}\)** & **J**\({}^{\prime}\)** & **R**\({}_{\rm{\small{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{      }}}}}}}}}}}}}}\) \\
**[Jy]** & [Jy]** & [Jy]** & [Jy]** & [Jy] & & & & \\ \hline
0202 + 319 & FSRQ & 27 & 1.675 \(<\) 0.020 & 1.19/0.95 & 3.02 & 74.8 & 9.9 & 1.3 \(\times\) 10\({}^{-6}\) (9) \({}^{\star}\) & 1.466 & n.a.