The gamma/optical flares of 4FGL-DR3 blazars

We search for temporal relationships between optical and {gamma}-ray bands. Using a Bayesian Block Decomposition, we detect 1414 optical and 510 {gamma}-ray flares, we find a strong correlation between both bands. Among all the flares, we find 321 correlated flares from 133 blazars, and derive an average rest-frame time delay of only 1.1_-8.5_^+7.1^ d, with no difference between the flat-spectrum radio quasars, BL Lacertae-like objects or low, intermediate, and high-synchrotron peaked blazar classes.

Our time-delay limit rules out the hadronic proton-synchrotron model as the driver for non-orphan flares and suggests a leptonic single-zone model. Limiting our search to well-defined light curves and removing 976 potential but unclear 'orphan' flares, we find 191 (13 per cent) and 115 (22 per cent) clear 'orphan' optical and {gamma}-ray flares. The presence of 'orphan' flares in both bands challenges the standard one-zone blazar flare leptonic model and suggests multizone synchrotron sites or a hadronic model for some blazars.