Apparent oiii variability in the narrow line Seyfert I Mrk142

In this letter, we checked spectral properties of the well-known narrow line Seyfert I Mrk142, in order to try to find effects of narrow line variability on BLR radius of Mrk142 which is an outlier in the R-L plane. Although, no improvement can be found on BLR radius, apparent narrow line variability can be confirmed in Mrk142. Using the public spectra collected from the Lick AGN Monitoring Project, the spectral scaling method based on assumption of constant \oiii line is firstly checked by examining broad and narrow emission line properties. We find that with the application of the spectral scaling method, there is a strong correlation between the \oiii line flux and the \oiii line width, but weaker correlations between the broad H$\alpha$ flux and the broad H$\beta$ flux, and between the broad H$\alpha$ flux and the continuum emission at 5100\AA. The results indicate that the assumption of constant \oiii line is not preferred, and caution should be exercised when applying the spectral scaling calibration method. And then, we can find a strong correlation between the \oiii line flux and the continuum emission at 5100\AA, which indicates apparent short-term variability of the \oiii line in Mrk142 over about two months.