Fukumura Keigo, Kazanas Demosthenes, Shrader Chris, Behar Ehud, Tombesi Francesco, Contopoulos Ioannis
Department of Physics and Astronomy, James Madison University, Harrisonburg, VA 22807.
Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771.
Astrophys J Lett. 2018 Sep 6;864(2). doi: 10.3847/2041-8213/aadd10.
Among a number of active galactic nuclei (AGNs) that drive ionized outflows in X-rays, a low-redshift ( = 0.184) quasar, PDS 456, is long known to exhibit one of the exemplary ultra-fast outflows (UFOs). However, the physical process of acceleration mechanism is yet to be definitively constrained. In this work, we model the variations of the Fe K UFO properties in PDS 456 over many epochs in X-ray observations in the context of magnetohydrodynamic (MHD) accretion-disk winds employed in our earlier studies of similar X-ray absorbers. We applied the model to the 2013/2014 spectra to determine the UFO's condition; namely, velocity, ionization parameter, column density and equivalent width (EW). Under some provisions on the dependence of X-ray luminosity on the accretion rate applicable to near-Eddington state, our photoionization calculations, coupled to a 2.5-dimensional MHD-driven wind model, can further reproduce the observed correlations of the UFO velocity and the anti-correlation of its EW with X-ray strength of PDS 456. This work demonstrates that UFOs, even without radiative pressure, can be driven as an extreme case purely by magnetic interaction while also producing the observed spectrum and correlations.
在众多能驱动X射线电离外流的活动星系核（AGN）中，一个低红移（z = 0.184）的类星体PDS 456，长期以来一直被认为展现出典型的超高速外流（UFO）之一。然而，其加速机制的物理过程尚未得到明确限制。在这项工作中，我们在磁流体动力学（MHD）吸积盘风的背景下，对PDS 456在多次X射线观测时期内Fe K UFO特性的变化进行建模，该模型曾用于我们早期对类似X射线吸收体的研究。我们将该模型应用于2013/2014年的光谱，以确定UFO的状态，即速度、电离参数、柱密度和等效宽度（EW）。在适用于近爱丁顿状态的X射线光度对吸积率的依赖性的某些条件下，我们的光电离计算与二维半MHD驱动风模型相结合，能够进一步重现PDS 456的UFO速度的观测相关性及其EW与X射线强度的反相关性。这项工作表明，即使没有辐射压力，UFO也可以作为一种极端情况，纯粹由磁相互作用驱动，同时还能产生观测到的光谱和相关性。
