Determine whether lower-threshold candidates are genuine CLAGN transitions

Determine whether the additional sources selected with a reduced narrow-band chi-squared threshold of \(\chi_r^2>10\) represent genuine lower-amplitude changing-look active galactic nucleus transitions or an increasing fraction of continuum variability unrelated to changing-look transitions.

Background

The CLAS+ pipeline selects changing-look active galactic nucleus candidates by comparing S-PLUS narrow-band photometry with synthetic photometry derived from DESI or SDSS/BOSS spectra. The authors adopt $\chi_r^2>15$ as a conservative threshold for identifying high-confidence candidates, while noting that relaxing the threshold to $\chi_r^2>10$ would approximately double the catalog size.

The unresolved issue is whether the additional objects admitted by the lower threshold are astrophysical changing-look events with smaller amplitudes or instead ordinary continuum-variable quasars and other sources whose photometric–spectroscopic discrepancies do not correspond to changing-look behavior. The authors state that spectroscopic follow-up across the threshold range is required to distinguish these possibilities.