The Seyfert 1.2 Mrk 817 is in a Very Heavily Obscured State

ATel #15323; J. M. Miller, M. K. Zak, P. Draghis, M. T. Reynolds (Univ. of Michigan), A. Zoghbi (Univ. Maryland, College Park), E. Kammoun (IRAP/OMP Toulouse)
on 12 Apr 2022; 15:43 UT
Credential Certification: Jon Miller (jonmm@umich.edu)

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Mrk 817 is a Seyfert 1.2 AGN, recently noted for an unusual lack of connection between its UV and X-ray flux trends (Morales et al. 2019). On the time scales of days and weeks, at least some of this unusual phenomenology can likely be attributed to a disk wind (Miller et al. 2021, Kara et al. 2021). It is unclear if the same mechanism might also explain why the source was about 40 times fainter in X-rays in the distant past (e.g., Winter et al. 2011).

Following the recent detection of a very low X-ray flux (Zak et al. 2022, ATEL #15316), we triggered observations with Swift, NuSTAR, and XMM-Newton. The Swift and NuSTAR observations have been completed. Swift XRT exposures were made on April 07 and April 08 2022 (6.2 ks and 3.8 ks, respectively). NuSTAR observed the source on April 07 2022 (46.9 ks).

We fit the Swift and NuSTAR spectra jointly using a model consisting of neutral absorption in the Milky Way, ionized partial covering absorption of a power-law continuum, neutral reflection, and ionized diffuse plasma emission. In XSPEC parlance, the model was: tbabs*(zxipcf*pow+pexmon+apec). The reflection model, pexmon, was fit to only include reflection, and its parameters were matched to the power-law. An overall normalizing constant was allowed to float between the spectra. Minimizing a Cash statistic, we measure the following key model parameters and 1-sigma errors:

Gamma = 1.85(5)
Log xi = 2.11(6)
N_H = 4.9(4) E+23 cm^-2
F_cov = 0.92(2)
R (Omega/2pi) = 0.67 +/- 0.15
kT = 0.89 +/- 0.13 keV
Flux = 2.1(4) E-12 erg/cm2/s (2-10 keV)
Flux = 1.0(2) E-11 erg/cm2/s (0.3-40 keV)
Flux = 1.8(3) E-11 erg/cm2/s (0.3-40 keV, unabsorbed)

Relative to the largely typical state previously observed with Swift and NuSTAR by Miller et al. (2021), the continuum flux is now an order of magnitude lower, while the obscuring column density and ionization are an order of magnitude higher. Comparing absorbed and unabsorbed flux levels, it is clear that the obscuration does not account for all of the flux decrement, likely pointing to a substantial actual drop in the mass accretion rate. Upcoming observations with XMM-Newton will help to determine whether or not the obscuring gas is an outflow. It is possible that the gas is a failed wind that has enveloped the central engine, similar to the stellar-mass black hole GRS 1915+105 (Miller et al. 2020).

We thank the Swift and NuSTAR teams and directors for executing these observations.

Kara, E., et al., 2021, ApJ, 922, 151
Miller, J. M., et al., 2020, ApJ, 904, 30
Miller, J. M., et al., 2021, ApJ, 911, L12
Morales, A., et al., 2019, ApJ, 870, 54
Winter, L., et al., 2011, ApJ, 728, 28