English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

With upcoming all sky surveys such as LSST poised to generate a deep digitalmovie of the optical sky, variability-based AGN selection will enable theconstruction of highly-complete catalogs with minimum contamination. In thisstudy, we generate $g$-band difference images and construct light curves forQSO/AGN candidates listed in SDSS Stripe 82 public catalogs compiled fromdifferent methods, including spectroscopy, optical colors, variability, andX-ray detection. Image differencing excels at identifying variable sourcesembedded in complex or blended emission regions such as Type II AGNs and otherlow-luminosity AGNs that may be omitted from traditional photometric orspectroscopic catalogs. To separate QSOs/AGNs from other sources using ourdifference image light curves, we explore several light curve statistics andparameterize optical variability by the characteristic damping timescale($\tau$) and variability amplitude. By virtue of distinguishable variabilityparameters of AGNs, we are able to select them with high completeness of 93.4%and efficiency (i.e., purity) of 71.3%. Based on optical variability, we alsoselect highly variable blazar candidates, whose infrared colors are consistentwith known blazars. One third of them are also radio detected. With the X-rayselected AGN candidates, we probe the optical variability of X-ray detectedoptically-extended sources using their difference image light curves for thefirst time. A combination of optical variability and X-ray detection enables usto select various types of host-dominated AGNs. Contrary to the AGN unificationmodel prediction, two Type II AGN candidates (out of 6) show detectablevariability on long-term timescales like typical Type I AGNs. This study willprovide a baseline for future optical variability studies of extended sources.

Variability-based AGN selection using image subtraction in the SDSS and LSST era