Tim Waters
To model the temperature evolution of optically thin astrophysical environments at MHD scales, radiative and collisional cooling rates are typically either pre-tabulated or fit into a functional form and then input into MHD codes as a…
The AGN STORM 2 collaboration targeted the Seyfert 1 galaxy Mrk 817 for a year-long multiwavelength, coordinated reverberation mapping campaign including HST, Swift, XMM-Newton, NICER, and ground-based observatories. Early observations with…
The solar corona is the prototypical example of a low density environment heated to high temperatures by external sources. The plasma cools radiatively, and because it is optically thin to this radiation, it becomes possible to model the…
We present the results of the XMM-Newton and NuSTAR observations taken as part of the ongoing, intensive multi-wavelength monitoring program of the Seyfert 1 galaxy Mrk 817 by the AGN Space Telescope and Optical Reverberation Mapping 2 (AGN…
In disk wind models for active galactic nuclei (AGN) outflows, high-energy radiation poses a significant problem wherein the gas can become overionized, effectively disabling what is often inferred to be the largest force acting on the gas:…
An intensive reverberation mapping campaign on the Seyfert 1 galaxy Mrk817 using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) revealed significant variations in the response of the broad UV emission lines to…
The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this…
The literature on thermal instability (TI) reveals that even for a simple homogeneous plasma, the nonlinear outcome ranges from a gentle reconfiguration of the initial state to an explosive one, depending on whether the condensations that…
Observations of ionized AGN outflows have provided compelling evidence that the radiation field transfers both momentum and energy to the plasma. At parsec scale distances in AGN, energy transfer can dominate, in which case the only force…
We present reverberation mapping measurements for the prominent ultraviolet broad emission lines of the active galactic nucleus Mrk817 using 165 spectra obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our…
Local thermal instability can plausibly explain the formation of multiphase gas in many different astrophysical environments, but the theory is only well understood in the optically thin limit of the equations of radiation hydrodynamics…
Acceleration can change the ionization of X-ray irradiated gas to the point that the gas becomes thermally unstable. Cloud formation, the expected outcome of thermal instability (TI), will be suppressed in a dynamic flow, however, due to…
We present the first results from the ongoing, intensive, multi-wavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this AGN was, in part, selected for its historically unobscured nature, we discovered that the…
The warm absorbers observed in more than half of all nearby active galactic nuclei (AGN) are tracers of ionized outflows located at parsec scale distances from the central engine. If the smallest inferred ionization parameters correspond to…
The mechanism of thermal driving for launching mass outflows is interconnected with classical thermal instability (TI). In a recent paper, we demonstrated that as a result of this interconnectedness, radial wind solutions of X-ray heated…
One of the main mechanisms that could drive mass outflows on parsec scales in AGN is thermal driving. The same X-rays that ionize and heat the plasma are also expected to make it thermally unstable. Indeed, it has been proposed that the…
The classic Bondi solution remains a common starting point both for studying black hole growth across cosmic time in cosmological simulations and for smaller scale simulations of AGN feedback. In nature, however, there will be inhomogenous…
Many studies have considered the roles of clouds, outflows, and turbulence in producing the broad emission and absorption lines in the spectra of active galactic nuclei (AGNs). However, these are often treated as separate or even competing…
One of the main mechanisms that could drive mass outflows in AGNs is radiation pressure due to spectral lines. Although straightforward to understand, the actual magnitude of the radiation force is challenging to compute because the force…
The mass and size distributions are the key characteristics of any astrophysical objects, including the densest clumps comprising the cold phase of multiphase environments. In our recent papers, we showed how individual clouds of various…