Accretion disks and coronae around massive black holes have been studied extensively, and they are known to be coupled. Over a period of 30 yr, 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 timescales 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 of 0.5 ≤ a ≤ 1, and the viewing angle to lie between 10 ≤ θ ≤ 22 (including 1σ 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.

大质量黑洞周围的吸积盘和日冕已被广泛研究，并且已知它们是耦合的。然而，在 30 年的时间里，Mrk 817 的 X 射线（日冕）通量增加了 40 倍，而其紫外线（盘状）通量保持相对稳定。最近的高节奏监测发现，Mrk 817 中的 X 射线和紫外线连续体也在数周和数月的时间尺度上解耦。这些发现可能需要对最里面的吸积流进行机械照射，和/或使用吸收器来保护圆盘和/或宽线区域 (BLR) 免受 X 射线日冕的影响。在此，我们报告了使用 NuSTAR 获得的对 Mrk 817 的 135 ks 观测，并辅以通过 Neil Gehrels Swift 天文台的同步 X 射线覆盖。X 射线数据强烈倾向于标准的相对论圆盘反射模型而不是合理的替代模型。a ≤ 1，视角介于 10 ≤ θ ≤ 22 之间（包括 1 σ统计误差和与模型差异相关的小系统误差）。光谱还揭示了中度电离吸收的有力证据，类似于 NGC 5548 和 NGC 3783 中的模糊事件，但可能没有那么极端。档案 Swift 数据表明吸收可能是可变的。特别是如果该吸收器的列密度沿磁盘平面较高，则可能会间歇性地掩盖或阻止 Mrk 817 中的中央引擎、磁盘和 BLR 之间的耦合。