CAZ catalog and optical light curves of 7918 blazar-selected AGN

TL;DR

The CAZ project delivers the largest blazar-focused catalog (7918 sources) and the most extensive optical light-curve compilation to date by combining RFC, 4LAC-DR3, 3HSP, CGRaBS, and 5BZC sources with nightly CRTS, ATLAS, and ZTF data. It introduces a unified blazar classification, collects key physical parameters, and provides long, multi-survey light curves with careful cross-survey calibration. Variability is quantified with fractional variability and Bayesian-block based methods to identify periods of enhanced emission (BB95) and major flaring (BBHOP), revealing that optical flares rise faster than they decay, and that variability is strongest near the synchrotron peak frequency ν_sy and increases with the radio Doppler factor. The results show FSRQs and BLLs exhibit similar variability at the same ν_sy, and provide a rich foundation for population-level jet physics, multiwavelength studies, and neutrino association analyses, supported by companion X-ray results.

Abstract

Active Galactic Nuclei (AGN) are some of the brightest and most variable objects in the universe. Those with relativistic jets observed at small viewing angles are blazars. Due to Doppler-boosting, blazars exhibit extreme stochastic variability. While the origin of this variability is thought to be changes in the accretion flow and jet dynamics, much about blazar variability remains unknown. In this paper we use several blazar-dominated AGN samples to form a catalog of 7918 blazars and candidates -- the largest to date. We also collect source types, redshifts, spectral energy distribution (SED) peak frequencies, radio variability Doppler factors, and X-ray flux densities for as many sources as possible. We use all-sky surveys (CRTS, ATLAS, and ZTF, abbreviated as ``CAZ'') to extract their optical multiband flux density on a nightly basis between 2007 and 2023, and construct as long and as high cadence light curves as possible for as many sources as attainable. The catalog and its light curves are provided in the accompanying electronic tables, enabling many analyses involving AGN variability with unprecedented sample-sizes. We quantify the variability of the light curves, and apply the Bayesian blocks algorithm to determine their flaring periods. We find: (1) optical flares generally have a faster rise than decay; (2) optical brightness and variability are strongly dependent on the synchrotron peak frequency; (3) flat spectrum radio quasars and BL Lac objects have comparable optical variability and flare characteristics at the same synchrotron peak frequency; and (4) optical flare times tend to decrease and amplitudes increase with increasing radio variability Doppler factor.

Figures (23)

• Figure 1: Sky distribution of 7918 sources in the CAZ catalog using the equatorial coordinate system (J2000 epoch).
• Figure 2: Distributions of (i) redshift, (ii) LE and HE peak frequencies (shown in green and red, respectively), (iii) radio variability Doppler factor, and (iv) median X-ray flux density of sources in the CAZ catalog. "MED" refers to median, "CAZ #" to the number of available parameters.
• Figure 3: Global distributions of 8130 merged CAZ light curves (7722 of AGN and 408 of WDs) with $\ge$10 data points and $\ge$30 d duration. Panel (i) shows the mean shift factor across all filters per light curve, (ii) median flux density per light curve, (iii) median flux density error per light curve, (iv) data count per light curve, (v) length of each light curve, (vi) cadence per light curve. The solid orange vertical line shows the median, and the dashed red line the 90$^\mathrm{th}$ percentile.
• Figure 4: Example merged light curves. The name of the source is given on the top left corner of each panel. We note that some light curves are of much higher quality than others (e.g., plot i compared to iv; the former is of the well-known, highly variable TXS 0506+056, while the latter is of a host-galaxy-dominated source). A zoomed-in version of these light curves (including identified periods of enhanced emission and flares) is given in Fig. \ref{['fig_eg_LCs_eg_flares']}.
• Figure 5: Example zoomed-in light curves with BB95 periods (Sect. \ref{['sec_identifying_critically_bright_BBs']}) and BBHOP flares (Sect. \ref{['sec_identifying_flares']}) identified. The merged light curves on the left are zoomed-in versions of those shown in Fig. \ref{['fig_eg_LCs']}. The light curves on the right are their corresponding BB light curves. The grey vertical area on the left show BB95 periods, which are BB whose flux density is larger than $S_{95\%}$ (shown as the grey horizontal line in the left). BBHOP flares are shown on the right using green lines connecting their start to the peak then to the end BB. Prominent BBHOP flares are further distinguished with a purple or cyan background. The red horizontal solid line in the right panels represents the reference flux density for determining the global amplitude $\mathcal{G}$ (i.e., $S_{25\%}$; the dotted lines represent its error). The grey horizontal dotted line in the right plots represents $S_{75\%}$, which is needed when determining prominent BBHOP flares. We note that CAZJ1635+0907 and CAZJ0131+5545 are determined to be non-variable and WD140409.96+045739.9 is non-variable by definition, thus, we do not identify BB95 and prominent BBHOP flares in their light curves.