X-ray and UV Monitoring of the Seyfert 1.5 Galaxy Markarian 817

Abstract

We report the results of long-term simultaneous X-ray and UV monitoring of the nearby (z=0.03145) Seyfert 1.5 galaxy Mrk 817 using the Neil Gehrels Swift Observatory XRT and UVOT. Prior work has revealed that the X-ray flux from Mrk 817 has increased by a factor of 40 over the last 40 years, whereas the UV emission has changed by a factor of 2.3. The X-ray emission of Mrk 817 now compares to some of the brightest Seyferts, but it has been poorly studied in comparison. We find that the X-ray (0.3-10.0 keV) and the UVM2 (roughly 2000--2500 Angstrom) fluxes have fractional variability amplitudes of 0.35 and 0.18, respectively, over the entire monitoring period (2017 Jan. 2 to 2018 Apr. 20). A cross-correlation analysis is performed on the X-ray (0.3-10.0 keV) and UVM2 light curves over the entire monitoring period, a period of less frequent monitoring (2017 Jan. 2 to 2017 Dec. 11), and a period of more frequent monitoring (2018 Jan. 12 to 2018 Apr. 20). The analysis reveals no significant correlation between the two at any given lag for all monitoring periods. Especially given that reverberation studies have found significant lags between optical/UV continuum bands and broad optical lines in Mrk 817, the lack of a significant X-ray-UV correlation may point to additional complexities in the inner or intermediate disk. Mechanical (e.g.,a funnel in the inner disk) and/or relativistic beaming of the X-ray emission could potentially explain the lack of a correlation. Alternatively, scattering in an equatorial wind could also diminish the ability of more isotropic X-ray emission to heat the disk itself.

Accepted for publication in ApJ

References in corpus (6)

• The AGN Black Hole Mass Database
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• A Long, Hard Look at the Low-Hard State in Accreting Black Holes
• A fast and long-lived outflow from the supermassive black hole in NGC 5548
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548

Cited by in corpus (11)

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• UV/optical disk thermal reverberation in AGN: an in-depth study with an analytic prescription for the time-lag spectra
• Reverberation Mapping Measurements of Black Hole Masses and Broad-Line Region Kinematics in Mrk 817 and NGC 7469
• EUCLIA. II. On the puzzling large UV to X-ray lags in Seyfert galaxies
• AGN STORM 2. III. A NICER view of the variable X-ray obscurer in Mrk 817
• The Inner Accretion Flow in the Resurgent Seyfert-1.2 AGN Mrk 817
• Populations of highly variable X-ray sources in the XMM$-$Newton slew survey
• The Relation between X-ray and Ultraviolet Variability of Quasars
• AGN STORM 2: I. First results: A Change in the Weather of Mrk 817
• Probing the rest-frame wavelength dependence of quasar variability : Insights from the Zwicky Transient Facility Survey