Multi-Zone Models of Superbursts from Accreting Neutron Stars

Abstract

Superbursts are rare and energetic thermonuclear carbon flashes observed to occur on accreting neutron stars. We create the first multi-zone models of series of superbursts using a stellar evolution code. We self-consistently build up the fuel layer at different rates, spanning the entire range of observed mass accretion rates for superbursters. For all models light curves are presented. They generally exhibit a shock breakout, a precursor burst due to shock heating, and a two-component power-law decay. Shock heating alone is sufficient for a bright precursor, that follows the shock breakout on a short dynamical time scale due to the fall-back of expanded layers. Models at the highest accretion rates, however, lack a shock breakout, precursor, and the first power law decay component. The ashes of the superburst that form the outer crust are predominantly composed of iron, but a superburst leaves a silicon-rich layer behind in which the next one ignites. Comparing the model light curves to an observed superburst from 4U 1636-53, we find for our accretion composition the best agreement with a model at three times the observed accretion rate. We study the dependence on crustal heating of observables such as the recurrence time and the decay time scale. It remains difficult, however, to constrain crustal heating, if there is no good match with the observed accretion rate, as we see for 4U 1636-53.

18 pages, 17 figures, submitted to ApJ

References in corpus (7)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• X-ray bursting neutron star atmosphere models: spectra and color corrections
• Fusion reactions in multicomponent dense matter
• Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen Burning
• First superburst from a classical low-mass X-ray binary transient
• Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts
• The superburst recurrence time in luminous persistent LMXBs

Cited by in corpus (40)

• Dependence of X-Ray Burst Models on Nuclear Reaction Rates
• Strong neutrino cooling by cycles of electron capture and ${\beta }^{-}$ decay in neutron star crusts
• Nucleosynthesis in Type I X-ray Bursts
• Thermonuclear X-ray bursts
• Nuclear Physics of the Outer Layers of Accreting Neutron Stars
• Nuclear Reactions in the Crusts of Accreting Neutron Stars
• The influence of accretion rate and metallicity on thermonuclear bursts: predictions from KEPLER models
• Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-Driven Convection
• X-ray Reflection and An Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143
• Urca cooling pairs in the neutron star ocean and their effect on superbursts
• Thermonuclear burst observations for model comparisons: a reference sample
• Reaction Rate and Composition Dependence of the Stability of Thermonuclear Burning on Accreting Neutron Stars
• Characterizing the Evolving X-Ray Spectral Features During a Superburst from 4U 1636-536
• Multi-epoch X-ray burst modelling: MCMC with large grids of 1D simulations
• A superburst candidate in EXO 1745--248 as a challenge to thermonuclear ignition models
• Mass measurement of 56Sc reveals a small A=56 odd-even mass staggering, implying a cooler accreted neutron star crust
• Simulating X-ray bursts during a transient accretion event
• Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars
• Deep crustal heating for realistic compositions of thermonuclear ashes
• Carbon production on accreting neutron stars in a new regime of stable nuclear burning
• Effects of Nuclear Equation of State on Type-I X-ray Bursts: Interpretation of the X-ray Bursts from GS 1826-24
• Carbon Synthesis in Steady-State Hydrogen and Helium Burning On Accreting Neutron Stars
• The imprint of carbon combustion on a superburst from the accreting neutron star 4U 1636-536
• A Survey of Chemical Separation in Accreting Neutron Stars
• Relativistic outflow from two thermonuclear shell flashes on neutron stars
• The efficiency of nuclear burning during thermonuclear (Type I) bursts as a function of accretion rate
• Relativistic ocean $r$-modes during type-I X-ray bursts
• The Regulated NiCu Cycles with the new ${}^{57}$Cu(p,$\gamma$)${}^{58}$Zn reaction rate and the Influence on Type-I X-Ray Bursts: GS 1826$-$24 Clocked Burster
• Discovery of transition from marginally stable burning to unstable burning after a superburst in Aql X-1
• Burning in the tail: implications for a burst oscillation model
• Accreting neutron stars: heating of the upper layers of the inner crust
• The Impacts of Neutron-Star Structure and Base Heating on Type I X-Ray Bursts and Code Comparison
• Model of heat diffusion in the outer crust of bursting neutron stars
• Superburst oscillations: ocean and crustal modes excited by Carbon-triggered Type I X-ray bursts
• Cooling of neutron stars in soft X-ray transients with realistic crust composition
• Net reaction rate and neutrino emissivity for the Urca process in departure from chemical equilibrium
• The Great Wall: Urca Cooling Layers in the Accreted NS Crust
• Thermonuclear Type-I X-ray Bursts and Burst Oscillations from the Eclipsing AMXP Swift J1749.4-2807
• Tracing the outburst decay of soft X-ray transients Aql X-1 and 4U 1608-52 with XSPECT
• A "Hyperburst" in the MAXI J0556-332 Neutron Star: Evidence for a New Type of Thermonuclear Explosion