The Inner Accretion Flow in the Resurgent Seyfert-1.2 AGN Mrk 817

Abstract

Accretion disks and coronae around massive black holes have been studied extensively, and they are known to be coupled. Over a period of 30 years, however, the X-ray (coronal) flux of Mrk 817 increased by a factor of 40 while its UV (disk) flux remained relatively steady. Recent high-cadence monitoring finds that the X-ray and UV continua in Mrk 817 are also decoupled on time scales of weeks and months. These findings could require mechanical beaming of the innermost accretion flow, and/or an absorber that shields the disk and/or broad line region (BLR) from the X-ray corona. Herein, we report on a 135 ks observation of Mrk 817 obtained with NuSTAR, complemented by simultaneous X-ray coverage via the Neil Gehrels Swift Observatory. The X-ray data strongly prefer a standard relativistic disk reflection model over plausible alternatives. Comparable fits with related models constrain the spin to lie in the range 0.5 < a < 1, and the viewing angle to lie between 10 deg. < theta < 22 deg. (including 1-sigma statistical errors and small systematic errors related to differences between the models). The spectra also reveal strong evidence of moderately ionized absorption, similar to but likely less extreme than obscuring events in NGC 5548 and NGC 3783. Archival Swift data suggest that the absorption may be variable. Particularly if the column density of this absorber is higher along the plane of the disk, it may intermittently mask or prevent coupling between the central engine, disk, and BLR in Mrk 817.

Accepted for publication in ApJ Letters

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• AGN STORM 2. III. A NICER view of the variable X-ray obscurer in Mrk 817
• AGN STORM 2: II. Ultraviolet Observations of Mrk817 with the Cosmic Origins Spectrograph on the Hubble Space Telescope
• Multi-wavelength observations of the obscuring wind in the radio-quiet quasar MR 2251-178
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• Update of the INTEGRAL/IBIS AGN catalogue: deeper on the Galactic plane and wider beyond
• A Systematic Search for X-ray Eclipse Events in Active Galactic Nuclei Observed by Swift
• Comparing Reflection and Absorption Models for the Soft X-ray Variability in the NLS1 AGN UGC 11763