perform detailed periodicity analysis for the optical light curve and estimate the associated false alarm probability. In Section 5, we summarize the long-term variations of the broad H$\beta$ profile. A brief discussion on the possible periodicity is given in Section 6 and conclusion is given in Sections 7.

Observations and Historical Database
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New Observations between 2015-2017
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We carried out a two-year observation campaign between 2015 and 2017 using [the]{} Lijiang 2.4m telescope, located in Yunnan Province, China, operated by Yunnan Observatories. [We used the Yunnan Faint Object Spectrograph and Camera (YFOSC) with Grism 14, which covers a wavelength range of 3800-7200 [Å]{} and provides a resolution of 1.8 [Å]{} pixel$^{-1}$.]{} This spectrograph is equipped with a slit long enough to allow us to simultaneously observe a nearby comparison star (@Du2014). We use this comparison star as a reference standard to achieve accurate absolute and relative flux calibrations, whereas the absolute flux of the comparison star is calibrated by observations of spectrophotometric standards during nights of good weather conditions. This flux calibration method is better than the common way based on the flux constancy of the narrow \[\] line as described below. However, we confirm that the narrow \[\] 