Accepted Cycle 13 Theory Proposals

Proposal Number	Subject Category	PI Name	Title
13200475	STARS AND WD	Nancy Brickhouse	An Accurate EUV/X-ray Line Ratio Diagnostic
13200650	STARS AND WD	Ofer Cohen	3D MHD Modeling of Stellar Coronae
13400177	BH AND NS BINARIES	Dimitrios Psaltis	The Apparent Surface Areas of Spinning Neutron Stars
13700567	ACTIVE GALAXIES AND QUASARS	Laura Brenneman	Simulating Black Hole Eclipses
13800122	CLUSTERS OF GALAXIES	Eliot Quataert	The Thermal Stability of Galaxy Cluster Plasmas
13800553	CLUSTERS OF GALAXIES	Eric Hallman	The Properties of X-ray Tails in Galaxy Clusters as a Probe of the Intracluster Medium

Subject Category: STARS AND WD

Proposal Number: 13200475

Title: An Accurate EUV/X-ray Line Ratio Diagnostic

PI Name: Nancy Brickhouse

We propose to calculate accurate collisional excitation rate data for Fe XVIII. The EUV/X-ray line ratio is of particular interest to stellar coronae and other collisionally ionized sources observed with the Chandra LETG/HRC-S. Comparison of observations of Capella and other stellar coronal sources with predictions from existing atomic theory shows discrepancies of 30% and larger in the EUV/X-ray line ratios for Fe XVIII. With atomic data accurate to 10%, now achievable with atomic theory benchmarked by experiment, this line ratio from a single ionization state is useful for determining electron temperature and/or interstellar absorption.

Subject Category: STARS AND WD

Proposal Number: 13200650

Title: 3D MHD Modeling of Stellar Coronae

PI Name: Ofer Cohen

We propose to apply the BATSRUS global 3D MHD code, originally developed for studying the solar corona, to stellar systems studied by Chandra. We will apply MHD modelling to (1) probe the structure of rapidly rotating coronae only investigated to date using simple potential field approximations; (2) merge the MHD solution with a coronal heating model to produce realistic maps of coronal emission and test solar coronal heating scaling laws over a large dynamic range; and (3) make the first MHD models of mass loss and angular momentum loss constrained by both magnetogram and high resolution X-ray spectroscopy. The results will be used to test and extend a semi-empirical relation between mass and angular momentum loss vs coronal activity to high activity levels.

Subject Category: BH AND NS BINARIES

Proposal Number: 13400177

Title: The Apparent Surface Areas of Spinning Neutron Stars

PI Name: Dimitrios Psaltis

Observations of accreting neutron stars with Chandra have been instrumental in the spectroscopic measurements of their masses and radii. These neutron stars, however, spin at high rates, 100-650 Hz. Exploiting the full potential of the observations requires correcting for the effects of rotation on the gravitational lensing experienced by photons as they travel from the surface to the observer. These effects are larger than the 5-10 % accuracy necessary to distinguish among equations of state. In the proposed project, we will use the ray-tracing algorithm we have recently developed that incorporates the dipole and quadrupole deformation in the spacetimes of spinning neutron stars in order to calculate the corrections necessary to infer their radii from spectroscopic observations.

Subject Category: ACTIVE GALAXIES AND QUASARS

Proposal Number: 13700567

Title: Simulating Black Hole Eclipses

PI Name: Laura Brenneman

Multiple X-ray eclipses have been observed in several AGN (e.g., NGC 1365) with Chandra, and with XMM-Newton and Suzaku, verifying that they occur with reasonable frequency. We propose to create simulations of the lightcurves and time-dependent spectra during these eclipses, and to make these products available to the public as table models. These simulations will definitively address three crucial issues regarding the innermost regions of black hole systems: (1) the relativistic nature (or not) of the putative broad Fe K line and Compton hump; (2) whether a relativistic contribution to the soft excess exists in AGN; (3) whether the eclipser co- or anti-rotates with the disk and black hole. Our work will sow the seeds for a Chandra Large Observing Project in cycle 14.

Subject Category: CLUSTERS OF GALAXIES

Proposal Number: 13800122

Title: The Thermal Stability of Galaxy Cluster Plasmas

PI Name: Eliot Quataert

The interplay between radiative cooling and heating at the centers of massive halos remains one of the major problems in galaxy formation. Absent heating, theoretical models overpredict cooling and star formation rates in these systems by several orders of magnitude. Some process must heat the gas to offset cooling, but it is not yet clear how global thermal stability can be achieved; moreover, the plasma is likely to remain prone to local thermal instability on small scales. We propose to explore physically-motivated heating models that stabilize groups and clusters against cooling catastrophes. Our proposed work will determine both why clusters have the multiphase structure they do, and what role the cold and hot gas play in the thermal evolution of the intracluster medium.

Subject Category: CLUSTERS OF GALAXIES

Proposal Number: 13800553

Title: The Properties of X-ray Tails in Galaxy Clusters as a Probe of the Intracluster Medium

PI Name: Eric Hallman

We propose to study the morphological distribution and properties of X-ray tails resulting from the motion of galaxies and merging subgroups in galaxy clusters using high-resolution numerical simulations with the Enzo code and comparison to X-ray data. X-ray tails, which have been shown to indicate stripping of galactic gas, are unique probes of the environmental conditions in clusters, as well as the dynamics of the cluster. We will simulate 12 numerical galaxy clusters and their merger histories using various input physics. We will answer: What are the physical properties of the ICM as probed by X-ray tails? This study will provide key new insights to the properties of the ICM, as well as motivate future Chandra observational proposals by systematically examining what the data tell us.

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