Selecting Quasars by their Intrinsic Variability

Understand

We present a new and simple technique for selecting extensive, complete and pure quasar samples, based on their intrinsic variability.

• We parametrize the single-band variability by a power-law model for the light-curve structure function, with amplitude A and power-law index gamma.
• We show that quasars can be efficiently separated from other non-variable and variable sources by the location of the individual sources in the A-gamma plane.
• We use ~60 epochs of imaging data, taken over ~5 years, from the SDSS stripe 82 (S82) survey, where extensive spectroscopy provides a reference sample of quasars, to demonstrate the power of variability as a quasar classifier in multi-epoch surveys.