Chapter 5
Thermonuclear X-ray Bursts
Duncan K. Galloway and Laurens Keek
Contents
5.1 Overview . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 210
5.1.1 Theory of Burst Ignition and Nuclear
Burning Regimes . .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 211
5.1.2 Status of Burst Observations . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 217
5.2 X-ray Burst Ignition .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 221
5.2.1 Thin-Shell Instability and Electron Degeneracy . .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 222
5.2.2 Reignition After a Short Recurrence Time . .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 222
5.2.3 Ignition Latitude .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 224
5.3 The Burst Spectral Energy Distribution .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 225
5.3.1 The Continuum Spectrum .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 225
5.3.2 Discrete Spectral Features . . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 228
5.4 Interaction with the Accretion Environment . .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 230
5.4.1 Reflection by the Accretion Disk . .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 233
5.4.2 Anisotropic Emission . .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 234
5.5 Burst Oscillations and the Neutron Star Spin .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 235
5.6 mHz Oscillations and Marginally Stable Burning . .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 236
5.6.1 Observations of mHz QPOs . . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 237
5.6.2 Theoretical Interpretation: Marginally Stable Burning .. ... .. .. .. .. .. .. .. .. .. .. .. .. 238
5.7 Burst Duration and Fuel Composition . . .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 239
5.7.1 Intermediate Duration Bursts. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 240
5.7.2 Superbursts . . .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 242
5.8 Thermonuclear Burst Simulations . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 244
5.8.1 Single-Zone Models .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 245
5.8.2 One-Dimensional Multi-Zone Models . . .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 245
5.8.3 Multi-Dimensional Models. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 248
D. K. Galloway ()
School of Physics & Astronomy, Monash University, Clayton, VIC, Australia
e-mail: duncan.galloway@monash.edu
L. Keek
CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD, USA
Department of Astronomy, University of Maryland, College Park, MD, USA
e-mail: laurens@xrb.space
© Springer-Verlag GmbH Germany, part of Springer Nature 2021
T. M. Belloni et al. (eds.), Timing Neutron Stars: Pulsations, Oscillations
and Explosions, Astrophysics and Space Science Library 461,
https://doi.org/10.1007/978-3-662-62110-3_5
209
Thermonuclear X-ray Bursts
Duncan K. Galloway and Laurens Keek
Contents
5.1 Overview . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 210
5.1.1 Theory of Burst Ignition and Nuclear
Burning Regimes . .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 211
5.1.2 Status of Burst Observations . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 217
5.2 X-ray Burst Ignition .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 221
5.2.1 Thin-Shell Instability and Electron Degeneracy . .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 222
5.2.2 Reignition After a Short Recurrence Time . .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 222
5.2.3 Ignition Latitude .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 224
5.3 The Burst Spectral Energy Distribution .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 225
5.3.1 The Continuum Spectrum .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 225
5.3.2 Discrete Spectral Features . . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 228
5.4 Interaction with the Accretion Environment . .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 230
5.4.1 Reflection by the Accretion Disk . .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 233
5.4.2 Anisotropic Emission . .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 234
5.5 Burst Oscillations and the Neutron Star Spin .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 235
5.6 mHz Oscillations and Marginally Stable Burning . .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 236
5.6.1 Observations of mHz QPOs . . ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 237
5.6.2 Theoretical Interpretation: Marginally Stable Burning .. ... .. .. .. .. .. .. .. .. .. .. .. .. 238
5.7 Burst Duration and Fuel Composition . . .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 239
5.7.1 Intermediate Duration Bursts. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 240
5.7.2 Superbursts . . .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 242
5.8 Thermonuclear Burst Simulations . .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 244
5.8.1 Single-Zone Models .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 245
5.8.2 One-Dimensional Multi-Zone Models . . .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 245
5.8.3 Multi-Dimensional Models. .. ... .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. .. .. .. 248
D. K. Galloway ()
School of Physics & Astronomy, Monash University, Clayton, VIC, Australia
e-mail: duncan.galloway@monash.edu
L. Keek
CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD, USA
Department of Astronomy, University of Maryland, College Park, MD, USA
e-mail: laurens@xrb.space
© Springer-Verlag GmbH Germany, part of Springer Nature 2021
T. M. Belloni et al. (eds.), Timing Neutron Stars: Pulsations, Oscillations
and Explosions, Astrophysics and Space Science Library 461,
https://doi.org/10.1007/978-3-662-62110-3_5
209