A remarkable long-term light curve, and deep, low-state spectroscopy: Swift & XMM-Newton monitoring of the NLS1 galaxy Mkn 335

TL;DR

This study presents extensive UV and X-ray monitoring of the NLS1 galaxy Mkn 335, revealing its long-term variability, spectral changes during low states, and the complexity of its X-ray spectra.

Contribution

It provides one of the longest simultaneous UV/X-ray light curves for an AGN and analyzes spectral variability with phenomenological models during low states.

Findings

Mkn 335 exhibits strong X-ray and UV variability.

No significant UV-X-ray correlation or lag was found.

X-ray low-state spectra show significant spectral variability.

Abstract

The Narrow-line Seyfert 1 galaxy (NLS1) Mkn 335 is remarkable because it has repeatedly shown deep, long X-ray low-states which show pronounced spectral structure. It has become one of the prototype AGN in deep minimum X-ray states. Here we report on the continuation of our ongoing monitoring campaign with Swift and the examination of the low state X-ray spectra based on a 200 ks triggered observation with XMM in June 2009. Swift has continuously monitored Mkn 335 since May 2007 typically on a monthly basis. This is one of the longest simultaneous UV/X-ray light curves so far obtained for an active galactic nucleus (AGN). Mkn 335 has shown strong X-ray variability even on time scales of hours. In the UV, it turns out to be one of the most variable among NLS1s. Long-term Swift monitoring allow us to examine correlations between the UV, X-rays and X-ray hardness ratios. We find no significant correlation or lag between the UV and X-ray variability; however, we do find distinct trends in the behavior of the hardness ratio variability. The hardness ratio and count rate are correlated in the low-flux state, but no correlation is seen in the high-state. The X-ray low-state spectra of the 2007 and 2009 XMM observations display significant spectral variability. We fit the X-ray spectra with a suite of phenomenological models in order to characterize the data. The broad band CCD spectrum can be fitted equally well with partial absorption and blurred reflection models. These more complicated models are explored in further detail in upcoming work.