Identifying QSOs/AGNs by Variability Seen in Difference Images
Abstract
Most quasars are known to be variable and they show larger variability on longer timescales of months to years. In this study, we generate g-band difference images and construct light curves for QSO/AGN candidates listed in Stripe 82 public catalogs complied from different methods, including spectroscopy, colors, variability, and X-ray detection. To separate QSOs/AGNs from other (non-)variable sources, we quantify their variability in the characteristic timescales (τ) and amplitude (SF∞) using the first-order structure function (SF) for the damped random walk (DRW) model. We find that QSOs occupy a specific region in the SF parameter space, enabling us to identify them with high efficiency and completeness. Since difference imaging excels at identifying variable sources embedded in complex or blended emission regions, it is one of the best tools to examine the variability of active nuclei surrounded by host galaxy emission, i.e. type II AGNs, and lower-luminosity AGNs. For the first time, we probe the variability of X-ray detected extended sources using their difference imaging light curves. Contrary to the AGN unification model prediction, some type II AGNs show detectable variability on long-term timescales like typical QSOs/AGNs.
- Publication:
-
American Astronomical Society Meeting Abstracts #221
- Pub Date:
- January 2013
- Bibcode:
- 2013AAS...22133903C