(Nilsson et al. in prep.). While there are several peaks (features) in the LCCF, shown in Figure \[lccf\], none of them reach the $2\,\sigma$ significance level. We also calculated the cross-correlation functions between the optical-37GHz and 37-15GHz. The only significant correlation is between 37-15GHz, with significance $>3\sigma$. The peak is rather broad from -40 to +30 days (Fig. \[lccf\]) and is consistent with zero lag. Typically, for evolving synchrotron self-absorbed components [e.g. @1994ApJ...437...91S; @2014MNRAS.441.1899F], one would expect the higher frequency to lead the lower frequency variations, which is consistent with our finding. However, as stated the peak is rather wide and also consistent with zero time lag. These results may indicate co-spatiality.

The optical-radio correlations of this source have been previously studied by and @2004MNRAS.348.1379C. Both works found several weak peaks in the correlations with lags 190, 400 days , and 190, 789 and 879 days [@2004MNRAS.348.1379C]. In Figure \[lccf\], there is a single ‘feature’ covering all these lags, peaking at $\sim$500 days. This feature is not significant and in general the results of our calculation agree with those by and @2004MNRAS.348.1379C.

We also searched for common long-term trends from the optical and radio data by fitting linear trends to 