Do the Kepler AGN Light Curves Need Re-processing?

TL;DR

This study assesses the impact of spacecraft effects on Kepler AGN light curves, finding that re-processing alters the inferred variability properties but does not change the main scientific conclusions about AGN variability models.

Contribution

It demonstrates that re-processing Kepler AGN data affects the PSD slope estimates, highlighting the importance of data reduction methods in variability analysis.

Findings

Re-processed light curve shows a steeper PSD slope ($\,\,\gamma=2.90$) than the standard pipeline ($\,\,\gamma=2.65$).

Turnover timescales are nearly identical (~27 days) in both light curves.

Standard pipeline data still contains significant spacecraft-induced effects.

Abstract

We gauge the impact of spacecraft-induced effects on the inferred variability properties of the light curve of the Seyfert 1 AGN Zw 229-15 observed by \Kepler. We compare the light curve of Zw 229-15 obtained from the Kepler MAST database with a re-processed light curve constructed from raw pixel data (Williams & Carini, 2015). We use the first-order structure function, $SF(\delta t)$, to fit both light curves to the damped power-law PSD of Kasliwal, Vogeley & Richards, 2015. On short timescales, we find a steeper log-PSD slope ($\gamma = 2.90$ to within $10$ percent) for the re-processed light curve as compared to the light curve found on MAST ($\gamma = 2.65$ to within $10$ percent)---both inconsistent with a damped random walk which requires $\gamma = 2$. The log-PSD slope inferred for the re-processed light curve is consistent with previous results (Carini & Ryle, 2012, Williams & Carini, 2015) that study the same re-processed light curve. The turnover timescale is almost identical for both light curves ($27.1$ and $27.5$~d for the reprocessed and MAST database light curves). Based on the obvious visual difference between the two versions of the light curve and on the PSD model fits, we conclude that there remain significant levels of spacecraft-induced effects in the standard pipeline reduction of the Kepler data. Re-processing the light curves will change the model inferenced from the data but is unlikely to change the overall scientific conclusion reached by Kasliwal et al. 2015---not all AGN light curves are consistent with the DRW.