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Title: Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-driven Convection

Abstract

Thermonuclear flashes of hydrogen and helium accreted onto neutron stars produce the frequently observed Type I X-ray bursts. It is the current paradigm that almost all material burns in a burst, after which it takes hours to accumulate fresh fuel for the next burst. In rare cases, however, bursts are observed with recurrence times as short as minutes. We present the first one-dimensional multi-zone simulations that reproduce this phenomenon. Bursts that ignite in a relatively hot neutron star envelope leave a substantial fraction of the fuel unburned at shallow depths. In the wake of the burst, convective mixing events driven by opacity bring this fuel down to the ignition depth on the observed timescale of minutes. There, unburned hydrogen mixes with the metal-rich ashes, igniting to produce a subsequent burst. We find burst pairs and triplets, similar to the observed instances. Our simulations reproduce the observed fraction of bursts with short waiting times of ∼30%, and demonstrate that short recurrence time bursts are typically less bright and of shorter duration.

Authors:
 [1];  [2]
  1. X-ray Astrophysics Laboratory, Astrophysics Science Division, NASA/GSFC, Greenbelt, MD 20771 (United States)
  2. Monash Center for Astrophysics, School of Physics and Astronomy, Monash University, Victoria, 3800 (Australia)
Publication Date:
OSTI Identifier:
22663475
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 842; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ACCRETION DISKS; COSMIC X-RAY BURSTS; HELIUM; HYDROGEN; METALS; NEUTRON STARS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ONE-DIMENSIONAL CALCULATIONS; OPACITY; SIMULATION; X RADIATION

Citation Formats

Keek, L., and Heger, A., E-mail: laurens.keek@nasa.gov. Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-driven Convection. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA7748.
Keek, L., & Heger, A., E-mail: laurens.keek@nasa.gov. Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-driven Convection. United States. doi:10.3847/1538-4357/AA7748.
Keek, L., and Heger, A., E-mail: laurens.keek@nasa.gov. Tue . "Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-driven Convection". United States. doi:10.3847/1538-4357/AA7748.
@article{osti_22663475,
title = {Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-driven Convection},
author = {Keek, L. and Heger, A., E-mail: laurens.keek@nasa.gov},
abstractNote = {Thermonuclear flashes of hydrogen and helium accreted onto neutron stars produce the frequently observed Type I X-ray bursts. It is the current paradigm that almost all material burns in a burst, after which it takes hours to accumulate fresh fuel for the next burst. In rare cases, however, bursts are observed with recurrence times as short as minutes. We present the first one-dimensional multi-zone simulations that reproduce this phenomenon. Bursts that ignite in a relatively hot neutron star envelope leave a substantial fraction of the fuel unburned at shallow depths. In the wake of the burst, convective mixing events driven by opacity bring this fuel down to the ignition depth on the observed timescale of minutes. There, unburned hydrogen mixes with the metal-rich ashes, igniting to produce a subsequent burst. We find burst pairs and triplets, similar to the observed instances. Our simulations reproduce the observed fraction of bursts with short waiting times of ∼30%, and demonstrate that short recurrence time bursts are typically less bright and of shorter duration.},
doi = {10.3847/1538-4357/AA7748},
journal = {Astrophysical Journal},
number = 2,
volume = 842,
place = {United States},
year = {Tue Jun 20 00:00:00 EDT 2017},
month = {Tue Jun 20 00:00:00 EDT 2017}
}
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