Michael Zingale: X-ray bursts

We are pursing several different models of X-ray bursts using our Castro and Maestro codes. Our current work involves studying flame propagation across the surface of the neutron star, focusing on the dynamics and nucleosynthesis. Our earlier XRB convection
studies looked at the convection preceding the outburst.
Supported by the DOE Office of Nuclear Physics.
All of the source code for reproducing these simulations is available on github

Simulations of X-ray Bursts

Flame spreading in X-ray bursts

We are using Castro to model the flame spreading across the surface of the neutron star. Our simulations resolve the burning front and the Rossby length (the scale where the Coriolis force and lateral spreading balance), allowing us to model the development and propagation of realistic flames moving through the neutron star atmosphere. Realistic nuclear reaction networks and conductivities are used.

Our goal of these studies is to learn how fast these flames can acceleration, understand any multidimensional effects that might help explain burst oscillations, and to explore the nucleosynthesis.

A time-series of a pure He flame moving across the surface of a neutron star, from Eiden et al. 2020.

volume renderings of the 3D flame view from above showing abar and nuclear energy generation

Volume renderings viewed from above of the 3D flame spreading simulation showing mean-molecular weight and nuclear energy generation rate, from Zingale et al. 2023.

Our results are described in the following papers:

Dynamics of Laterally Propagating Flames in X-Ray Bursts. I. Burning Front Structure, Eiden, Kiran, Zingale, Michael, Harpole, Alice, Willcox, Donald, Cavecchi, Yuri, & Katz, Max P. 2020, ApJ, 894, 1, p. 6
Dynamics of Laterally Propagating Flames in X-Ray Bursts. II. Realistic Burning & Rotation, Harpole, A., Ford, N. M., Eiden, K., Zingale, M., Willcox, D. E., Cavecchi, Y., & Katz, M. P. 2021, ApJ, 912, p. 36
Comparing Early Evolution of Flames in X-ray Bursts in Two and Three Dimensions, Zingale, M. Eiden, K., & Katz, M. 2023, submitted to ApJ

Convection in X-ray bursts

We are modeling mixed H/He X-ray bursts with our low Mach number hydrodynamics code Maestro. The nucleosynthesis is described by a 10-nuclei network that approximates hot-CNO, 3-alpha, and rp-process breakout. These simulations are done in a plane-parallel geometry, with a 6 cm resolution. These calculations follow on from our initial pure He simulations. Our goal is to understand how a multi-dimensional treatment of the convection alters the nucleosynthesis.

Our results are described in the following papers:

Multidimensional Modeling of Type I X-ray Bursts. I. Two-Dimensional Convection Prior to the Outburst of a Pure He Accretor, Malone, C. M., Nonaka, A. J., Almgren, A. S., Bell, J. B., & Zingale, M., 2011, ApJ, 728, 118
Multidimensional Modeling of Type I X-ray Bursts. II. Two-Dimensional Convection in a Mixed H/He Accretor, Malone, C. M., Zingale, M., Nonaka, A., Almgren, A. S., & Bell, J. B., 2014, ApJ, 788, 115
Comparisons of Two- and Three-Dimensional Convection in Type I X-ray Bursts, Zingale, M., Malone, C. M., Nonaka, A., Almgren, A. S., & Bell, J. B., 2015, ApJ, 807, 60

Here's a model of the three-dimensional convection: