Recent Swift Monitoring of Mrk 817 Reveals an Extremely Low Flux State

ATel #15316; M. K. Zak, J. M. Miller, M. T. Reynolds, B. Gediman, C. Han, Y. Hemrattaphan (Univ. of Michigan)
on 7 Apr 2022; 18:23 UT
Credential Certification: Jon Miller (jonmm@umich.edu)

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Mrk 817 is a Seyfert 1.2 galaxy (Koss et al. 2017) at a redshift of 0.03145 (Strauss & Huchra 1988). The mass of its central black hole is (4.9 +/- 0.8) E+7 solar masses (Peterson et al. 2004).

Previous studies have shown that Mrk 817 lacks the correlation between X-ray and UV emission that is typical in Seyfert galaxies (Morales et al. 2019). This may be due to a disk wind inhibiting communication between the X-ray and UV portions of the accretion flow (Miller et al. 2021, Kara et al. 2021).

To characterize the flux evolution of the source, we made spectral fits to recent Neil Gehrels Swift Observatory observations with the X-ray Telescope (XRT), assuming a canonical Gamma = 1.7 power-law index and minimizing a Cash statistic. The table below summarizes results for an early observation wherein the low flux state is detected, and the most recent observation:

ObsID Date c/s Flux (0.3-10 keV, E-12 cgs)
00096450063 02/24/2022 0.070 +/- 0.007 3.7 +/- 0.4
00096727003 04/06/2022 0.050 +/- 0.006 1.5 +/- 0.2

Although the observations have a very low number of counts, there is evidence that the power-law index is flatter, or that the spectrum is significantly more complex.

Morales et al. reported a mean XRT count rate of 0.5466 +/- 0.0025 c/s from 2017 January 2 to 2018 April 20. The count rates from our recent observations are roughly an order of magnitude smaller. This low flux state could be related to the historic low X-ray flux of Mrk 817 observed several decades ago (e.g., Winter et al. 2011).

We have triggered observations with NuSTAR, Swift, and XMM-Newton aimed at understanding the nature of this extremely low flux state; we will report early results from those observations via ATEL, and full results in subsequent papers. We acknowledge support for undergraduate research from the Michigan Institute for Research in Astrophysics (MIRA), and we thank the Swift, NuSTAR, and XMM-Newton directors and teams.

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