Broad-line Region Characterization in Dozens of Active Galactic Nuclei Using Small-aperture Telescopes

We present the results of a nearly decade-long photometric reverberation mapping (PRM) survey of the Hα emission line in nearby (0.01 ≲ z ≲ 0.05) Seyfert galaxies using small (15-40 cm) telescopes. Broadband filters were used to trace the continuum emission, while narrowband filters tracked the Hα-line signal. We introduce a new PRM formalism to determine the time delay between continuum and line emission using combinations of auto- and cross-correlation functions. We obtain robust delays for 33/80 objects, allowing us to estimate the broad-line region (BLR) size. Additionally, we measure multiepoch delays for six objects whose scatter per source is smaller than the scatter in the BLR size-luminosity relation. Our study enhances the existing Hα size-luminosity relation by adding high-quality results for 31 objects, whose nuclear luminosities were estimated using the flux-variation gradient method, resulting in a scatter of 0.26 dex within our sample. The scatter reduces to 0.17 dex when the six lowest-luminosity sources are discarded, which is comparable to that found for the Hβ line. Single-epoch spectra enable us to estimate black hole masses using the Hα line and derive mass accretion rates from the iron-blend feature adjacent to Hβ. A similar trend, as previously reported for the Hβ line, is implied whereby highly accreting objects tend to lie below the size-luminosity relation of the general population. Our work demonstrates the effectiveness of small telescopes in conducting high-fidelity PRM campaigns of prominent emission lines in bright active galactic nuclei.