# Intra-Day Variability Observations of Two Dozens of Blazars at 4.8 GHz
## 3 Results and Discussion  
### Variability Characteristics  
The results are listed in Tables 1 and 2. In the February IDV session, 16 targets from the RA observing session are observed, plus 4 additional targets from other samples and 5 calibrators. In the March IDV session, 14 targets from the RA observing session are observed, plus 3 additional targets from other samples and 5 calibrators. There are more than 20 data points sampled for the majority of sources in about three-day observation of each session, some sources have fewer data points due to their low declinations or bad data being deleted by the calibration software (e.g., when Full Width of Half Power of source profile \(>\) 120% of antenna beam width, or antenna pointing error \(>\) 1/6 of beam width, or error of Gaussian fit \(>\) 10% of peak of the Gaussian, or amplitude of a sub-scan profile \(>\) 110% of average amplitude of 4 + 4 sub-scans; these can be caused by too large source, too weak source or interference, etc.). After careful calibrations as introduced above, we obtained flux densities and light curves for each source. Here, we only show a few sources for example, three sources with strong variability--1357 + 769, J1128 + 5925 and WISE J092915.43 + 501336.0 in Figure 1, two counterexamples--B2 1239 + 376 and 1633 + 382 with no sign of variability in Figure 2.  
The same as our previous work [20], in order to ascertain whether or not an IDV is present, we applied a \(\chi^{2}\) test to each data set. We adopt the criterium that a data set with 'a probability of \(\leq\)0.1% to be constant' is considered to be variable (i.e., the 'null hypothesis' probability \(<\)1.0 \(\times\) 10\({}^{-3}\) in Table 1 or Table 2), which is equivalent to the confidence level of 99.9% to define the IDV. According to this definition, there are 14 out of 20 targets show IDV in session 1, all 17 targets show IDV in session 2.  
In Tables 1 and 2, we find there are a couple of prominent IDV sources from the two observing sessions, e.g., those with the modulation index \(m>3m_{0}\), the \(m_{0}\) is the average modulation index of the calibrators, which is 0.64 for session 1, and 0.45 for session 2.  
The modified modulation index \(m^{\prime}\) represents a variability strength, but not a real variability amplitude. The parameter \(Y\) is more like a variability amplitude, which ranges from a few per cent to \(\sim\)22% for the prominent IDV sources in Tables 1 and 2.  
We note that there are 11 common targets appeared in both session 1 and session 2, all of them have shown IDV in the two sessions except the quasar 1156 + 295 which only shows IDV in session 2, we give a short discussion for this in Section 3.3.  
Some of the IDV sources show relatively fast variability, e.g., the source J1128 + 5925, WISE J092915.43 + 501336.0 exhibit a short timescale of a few hours and some of them e.g., the source 1357 + 769 shows a relatively longer timescale. A full analysis on the IDV timescales along with the source structure and brightness temperature derived from the RA space VLBI measurements will be presented in a forthcoming paper.