Fermi Blazars in the Zwicky Transient Facility Survey: A Correlation Study

Abstract

We report on our correlation analysis for the γ-ray blazars detected with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi), for which we use the Fermi-LAT data and the optical zr and zg band data from the Zwicky Transient Facility survey in the time period approximately from 2018 July to 2022 February. We start from the full sample of the Fermi-LAT blazars and find ∼38% of them as significant variables in both γ-ray and optical bands. Among the variables, which are 705 blazars, 95 are selected as our targets based on the requirement for the γ-ray brightnesses. Then 15 out of the 95 blazars are found to show the γ-ray–optical correlations in the ∼3.7 yr time period. Most of the 15 blazars are classified as low synchrotron peaked (LSP) ones with the time lags between the γ-ray and optical bands in a range from −19 to +25 days. The results generally fit the often-considered emission scenario for the LSP blazars. Two cases of showing ∼−100 days time lags are discussed, which require further studies for confirmation. Our analysis results suggest that among the detected significant variables, ∼23% LSPs can show γ-ray and optical correlations, while their average γ-ray fluxes are above ∼4 × 10−8 photon cm−2 s−1.