Accepted Cycle 16 Theory Proposals

Proposal Number	Subject Category	PI Name	Title
16200289	STARS AND WD	Vikram Dwarkadas	Further Advances in Our Understanding of the X-Ray Emission from Wind-Driven Nebulae around Massive Stars
16200696	STARS AND WD	Gabriela Montes	WR 20A: A HIGH ENERGY WINDOW INTO RADIATIVELY DRIVEN STELLAR WINDS FROM HOT STARS
16400746	BH AND NS BINARIES	Edward Brown	Neutrino Cooling in the Crusts of Quiescent Neutron Star Transients: A New Mechanism
16400800	BH AND NS BINARIES	Sourav Chatterjee	Modeling Black Hole X-Ray Binaries in Globular Clusters
16500277	SN, SNR AND ISOLATED NS	George Pavlov	Modeling neutron star atmospheres with moderate magnetic fields
16500802	SN, SNR AND ISOLATED NS	ANDREY TIMOKHIN	Heating of pulsar polar caps: a modern view
16610303	NORMAL GALAXIES: DIFFUSE EMISSION	Anna Rosen	To Leak or Not to Leak: Where are the Missing X-ray Photons from Massive Star Clusters?
16800554	CLUSTERS OF GALAXIES	Rukmani Vijayaraghavan	The Survival of Hot Galactic Coronae in Groups and Clusters

Subject Category: STARS AND WD

Proposal Number: 16200289

Title: Further Advances in Our Understanding of the X-Ray Emission from Wind-Driven Nebulae around Massive Stars

PI Name: Vikram Dwarkadas

Stellar mass-loss leads to the formation of wind-driven nebulae (WDNe) around the star, with an extremely hot interior that should be observable as diffuse X-ray emission. Instead if diffuse X-ray emission is detected at all, both the luminosity and temperature are significantly lower than expected. Herein we propose multi-dimensional ionization-gasdynamic simulations to model the complex structure of WDNe around massive stars and compute the X-ray spectra, which can be directly compared to observations. We will expand on our previous calculations to investigate the spatial production of X-rays within the nebula, and compute models for bubbles that show appreciable X-ray emission, such as NGC 6888. This work will enable us to systematically address the X-ray observations with confidence.

Subject Category: STARS AND WD

Proposal Number: 16200696

Title: WR 20A: A HIGH ENERGY WINDOW INTO RADIATIVELY DRIVEN STELLAR WINDS FROM HOT STARS

PI Name: Gabriela Montes

Separated by only a few stellar radii, WR 20a serves as a critical test-case for how radiatively-driven stellar winds initiate and interact. Although our previous simulations provided a relatively good description of the available Chandra data, they are still incomplete. To accurately model WR 20a we need a multidimensional approach that attempts to resolve the underlying physics, which in the case of WR 20a is heavily dependent on hydrodynamics and radiation transport, both of which have yet to be included. This will help answer crucial remaining questions about the properties of the wind-wind interaction region, which are key for understanding the reprocessing of the X-ray radiation and the radiative driven wind processes.

Subject Category: BH AND NS BINARIES

Proposal Number: 16400746

Title: Neutrino Cooling in the Crusts of Quiescent Neutron Star Transients: A New Mechanism

PI Name: Edward Brown

We propose to explore how a newly discovered, and potentially powerful, neutrino emissivity affects the observed cooling from quiescent neutron star transients. This neutrino cooling is due to rapid electron-capture/beta-decay cycles in the accreted neutron star crust and has not been taken into account in previous models. The work proposed herein will implement this new cooling mechanism into our neutron star thermal evolution code, and generate new predictions for the long-term cooling behavior of bright transients like XTE J1701-462. Our code will enable the use of Chandra observations of transients to constrain the strength of this newly discovered cooling mechanism. This opens up the exciting prospect of testing nuclear models of neutron-rich nuclei.

Subject Category: BH AND NS BINARIES

Proposal Number: 16400800

Title: Modeling Black Hole X-Ray Binaries in Globular Clusters

PI Name: Sourav Chatterjee

Numerical simulations of globular cluster dynamics will be used to study the formation and evolution of black hole (BH) X-ray binaries. Our simulation code is based on Henon s Monte Carlo method, providing much greater computational speed and convenience than direct N-body methods. Our code includes all dynamical and stellar evolution processes (for single stars and binaries) relevant to BH formation and evolution. The main goal of the project is to provide to the community a large database of cluster models focusing specifically on the properties of BHs and varying systematically all physical parameters and theoretical assumptions affecting the BHs most strongly.

Subject Category: SN, SNR AND ISOLATED NS

Proposal Number: 16500277

Title: Modeling neutron star atmospheres with moderate magnetic fields

PI Name: George Pavlov

Central Compact Objects (CCOs) in Supernova Remnants have been recognized as a class of isolated neutron stars with moderate magnetic fields, 10^{10} - 10^{11} G,and a lack of pulsar activity. At such magnetic fields and typical effective temperatures of 1 - 3 million kelvins, the electron cyclotron energy exceeds the thermal energy, and spectral features at the harmonics of the cyclotron energy can be observed in the Chandra and XMM-Newton energy range. We propose to develop atmosphere models for neutron stars with such parameters and apply the model spectra and angular dependences to interpreting X-ray data on CCOs and other neutron stars with moderate magnetic fields.

Subject Category: SN, SNR AND ISOLATED NS

Proposal Number: 16500802

Title: Heating of pulsar polar caps: a modern view

PI Name: ANDREY TIMOKHIN

Recently, significant progress has been made in the theoretical understanding of magnetospheres of rotationally powered pulsars. New self-consistent pulsar models have shown that some of the basic assumptions of previous models are incorrect. In particular, new pair cascade models show that particle acceleration near polar caps (PCs) happens in a qualitatively different way than in previous models, implying that existing predictions about heating of the neutron star PCs by relativistic plasma are unreliable. We propose to revise the theory of PC heating using recently developed self-consistent models of particle acceleration and pair cascades. We will improve our numerical code and use it to create models of PC cascades and provide new estimates for the temperature of pulsar PCs.

Subject Category: NORMAL GALAXIES: DIFFUSE EMISSION

Proposal Number: 16610303

Title: To Leak or Not to Leak: Where are the Missing X-ray Photons from Massive Star Clusters?

PI Name: Anna Rosen

The observed diffuse X-ray emission from massive star clusters (MSCs) is far weaker than predicted by theoretical models. There are several energy-loss mechanisms that can account for this but which mechanism dominates determines the importance of stellar winds as a feedback mechanism that regulates star formation. Existing observations have been unable to settle this question, so we propose to address it by performing radiation-magnetohydrodynamic simulations of the formation of MSCs, including radiation and stellar wind feedback, and then making mock Chandra images from our simulations that we can compare to archival and future images of 30 Doradus. This will enable us to determine the observable signatures of the various loss mechanisms and to search for such signatures in the archives.

Subject Category: CLUSTERS OF GALAXIES

Proposal Number: 16800554

Title: The Survival of Hot Galactic Coronae in Groups and Clusters

PI Name: Rukmani Vijayaraghavan

Recent Chandra observations have revealed the ubiquitous presence of hot extended X-ray coronae centered on cluster galaxies. In cluster environments, tidal and ram pressure stripping, along with thermal heat conduction, are expected to remove these coronae. Their survival in these harsh environments is puzzling, and implies the existence of shielding mechanisms like magnetic fields and kinematic viscosity, or replenishment processes, due to stellar and AGN feedback. The goal of our proposal is to model the stripping, shielding, and replenishment in hot galactic coronae using hydrodynamical numerical simulations, and quantify the balance between the various physical phenomena at play.

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