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

Abstract 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.