NGC 5548 43 year-long monitoring in H{beta}

This includes 12 years of new unpublished observations (2003 to 2015). We compiled about 1600 H{beta} spectra and analyzed the long-term spectral variations of the 5100 A continuum and the H{beta} line.

Our analysis is based on standard procedures, including the Lomb-Scargle method, which is known to be rather limited to such heterogeneous data sets, and a new method developed specifically for this project that is more robust and reveals a ~5700 day periodicity in the continuum light curve, the H{beta} light curve, and the radial velocity curve of the red wing of the H{beta} line. The data are consistent with orbital motion inside the broad emission line region of the source.