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Proposal Number: 09200657

Title: Highly Accurate Line Ratio Diagnostics from Helium-Like Ions

PI Name: Nancy Brickhouse

We propose to calculate highly accurate atomic data for the Helium-like systems O VII, Mg XI, Si XIII, and Fe XXV. Chandra and XMM-Newton grating data of cool stars have shown that the temperatures derived from He-like systems are inconsistent with other measures, due to inaccurate atomic data. Recent calculations of Ne IX by our team demonstrate that accuracy in the calculations of line ratios can now be achieved at the 5 to 10 percent level, confirmed by laboratory measurements. We will use the Breit-Pauli and DIRAC R-matrix codes, along with the GRASP code to produce the accurate data for these systems. Our results will generate the best line ratio temperature diagnostics accurate to about 20 percent. These data will be placed in ATOMDB for public distribution in a timely manner.

Proposal Number: 09400238

Title: Learning How Globular Cluster LMXBs and MSPs Evolve

PI Name: Saul Rappaport

Globular clusters are factories for the production of interesting systems such as low-mass X-ray binaries (LMXBs) and recycled millisecond radio pulsars (MSPs). While neutron star binaries can be formed via a variety of dynamical encounters, no one understands in any detail what the evolutionary paths are. Such incipient cluster neutron star binaries have never been evolved in significant numbers with a proper Henyey stellar evolution code. We will, for the first time, follow the evolution of a large number of binary X-ray sources formed in clusters with a Henyey code. In addition to understanding the cluster LMXBs, one of our main goals will be to understand the origin of their descendant MSPs with M_companion and P_orb in the ranges 0.02-0.1 Msun and 2-5 hrs, respectively.

Proposal Number: 09400439

Title: Spectrum Synthesis Modeling of GRO J1655-40

PI Name: Timothy Kallman

We propose to make synthetic spectral models which can be used to measure element abundances and other parameters describing the outflow from the warm absorber in the black hole X-ray transient GRO J1655-40. The HETG spectrum from this object obtained in 2005 is notable as a laboratory for the study of warm absobers, and for the presence of many lines from odd-Z elements between Na and Co (and Ti and Cr) not previously observed in X-rays. In order to do so, we will gather and calculate, where necessary, the atomic cross sections and rate coefficients needed to calculate the ionization balance and spectrum from these elements. These atomic quantities will be publicly available as part of the modeling code xstar, and associated database and xspec models warmabs and photemis.

Proposal Number: 09400526

Title: Disk Winds in X-ray Binaries

PI Name: Daniel Proga

We propose to study winds from accretion disks in X-ray binaries. We will focus on hydrodynamical simulations of an X-ray absorbing wind in the X-ray transient GRO J1665-40. Three key factors motivate our study: (1) high quality X-ray spectra of this source taken with Chandra, (2) controversy about whether the wind in this system is magnetically and thermally driven, and (3) the fact that our previous disk wind simulations have been successful in explaining line absorption in other systems with disk winds. We propose to explore effects of thermal driving on a disk wind. Our goal is to test whether thermal winds can account for observed spectra. This study will yield insights into the problem of disk winds not only in GRO J1665-40 but also other systems such as H~1743-322, and 4U 1630-472.

Proposal Number: 09400687

Title: EXTENDING THE NON-EQUILIBRIUM IONIZATION MODEL FOR PHOTOIONIZED PLASMAS

PI Name: Li Ji

We propose extending our collisional non-equilibrium ionization code to photoionized plasmas, by taking advantage of the atomic data and physics from the equilibrium photoionization model of XSTAR. The expanded model will allow us to probe various physical processes in a wider range of astrophysical objects, such as colliding winds in X-ray binaries, outflows in AGNs and shock flows in the IGM. We will gain insights into the non-equilibrium state of those ionization plasmas. The code will be publicly available for use within a spectral analysis system, facilitating direct comparisons with Chandra HETGs observations. By modularizing our code, we also aim to enable flexible use of its internal physics in wider contexts.

Proposal Number: 09500324

Title: Spectral Line Formation in Magnetic Neutron Stars

PI Name: Dong Lai

Recent observations (e.g. by Chandra) have revealed absorption lines at around 0.2-1 keV in a number of isolated neutron stars (NSs), and some of these show intriguing evidence of harmonics. There has also been some evidence for line features in the spectra of several magnetars during outbursts. Understanding these spectral lines is very important as it would lead to direct measurement of the NS surface magnetic fields and compositions, shedding light on the nature of these objects. We propose to model the proton/ion cyclotron line transfer in various NS environments and to construct partially ionized NS atmosphere models of heavy elements. We will produce atmosphere model spectra and confront our results with observational data.

Proposal Number: 09620368

Title: Models for the Evolution of X-Ray Binaries in a Young Stellar Population

PI Name: Michael Eracleous

We will model the evolution of X-Ray binaries (XRBs) formed in episodes of vigorous star formation, using an established population synthesis code and compare with the luminosity functions of different ages observed by Chandra in nearby dwarfs. We will predict the number counts, X-ray luminosity, and luminosity function, of a population of XRBs. We will follow evolution of these properties over, during, and after the star-formation episode and we will connect them to other observable properties of the system, such as the optical emission-line luminosity. Such models are important for the interpretation of Chandra observations of nearby galaxies, as well as high-redshift, star-forming galaxies found in deep X-ray surveys.

Proposal Number: 09700835

Title: Understanding the Flares of Sgr A* Through 3D Radiative Magnetohydrodynamic Simulations

PI Name: Dimitrios Psaltis

We propose to study the physical origin of the flares observed from Sgr A* using ab initio, time-dependent, 3D, radiative, magnetohydrodynamic simulations of accretion flows around supermassive black holes. We will employ the spectral numerical algorithm that we have recently developed and incorporate, for the first time, a time-dependent radiative transport scheme that is suitable for the physical conditions of Sgr A*. We will compare our results directly to Chandra and long-wavelength observations in order to distinguish between different mechanisms for the flares that have been recently proposed.

Proposal Number: 09800190

Title: Simulations of the Merging Bullet Cluster: Testing LCDM and the Dynamics of Cluster Plasma

PI Name: Paul Shapiro

The cluster halo-subhalo collision in 1E0657-56 shows an intracluster bow shock that trails the merging subhalo, evidence for collisionless dark matter (DM). Halo collisions as fast as this shock are unlikely in LCDM, but high-resolution (~ 1 kpc) simulations show the shock velocity can exceed the halo collision velocity, thus increasing the likelihood. Since proper interpretation of Chandra data requires these high-resolution simulations, we will generalize them from 2D to 3D, with off-axis collisions, realistic cosmological boundary conditions and DM dynamics, and the possibility of SIDM.

Proposal Number: 09800271

Title: Quantifying Cluster Temperature Substructure

PI Name: Mark Voit

Precision measurements of dark energy from cluster evolution require an understanding of both the scatter in the mass-observable relations used to measure cluster mass and the redshift evolution of that scatter. Much of the scatter probably stems from a dispersion in cluster relaxation. One promising quantitative measure of cluster relaxation is the ratio between a cluster's hard-band temperature and its broad-band temperature. We are proposing to calibrate the relationship between temperature ratio and a cluster's degree of relaxation using a large sample of simulated clusters. If the temperature ratio indeed correlates closely with cluster relaxation, then Chandra observers will have a new tool for quantifying scatter in the mass-observable relations essential for cosmology.

Proposal Number: 09800293

Title: Cosmic ray bubbles and abundance gradients in clusters

PI Name: Mateusz Ruszkowski

Chandra observations of cool core clusters reveal that the abundance profiles appear much broader than the stellar light distributions of the brightest cluster galaxies. A possible solution to this puzzle is that active galactic nuclei (AGN) help to uplift the metal-enriched gas. However, the nature of this process remains very poorly understood. Numerical simulations performed to date do not capture the essential physical processes that are needed to properly model this effect such as magnetic fields, radiative cooling and cosmic ray diffusion from buoyant bubbles inflated by the AGN. We will perform numerical simulations including these effects and compare the expected abundance distributions with Chandra observations.

Proposal Number: 09910209

Title: Simulations of Collisions between Infalling Material and the Milky Way

PI Name: Robin Shelton

Observations of High Velocity Clouds suggest that some of these clouds are interacting with Galaxy's extended gaseous halo. Larger objects, such as the Sagittarius Dwarf Galaxy, have punched through the Milky Way's disk and halo. According to existing hydrodynamic simulations, high velocity cloud collisions with the Milky Way shock heat gas, evacuate large cavities, and splash up material. More recent simulations that include the halo's magnetic field show that the halo absorbs the brunt of the impact. In order to determine if the fastest collisions may have contributed significantly to the hot halo gas seen by Chandra, we need magnetohydrodynamic simulations coupled with spectral calculations. Here, we propose to perform the necessary simulations.