Theoretical Models of Superbursts on Accreting Neutron Stars

Abstract

We carry out a general-relativistic global linear stability analysis of the amassed carbon fuel on the surface of an accreting neutron star to determine the conditions under which superbursts occur. We reproduce the general observational characteristics of superbursts, including burst fluences, recurrence times, and the absence of superbursts on stars with accretion rates below 10% of the Eddington limit. By comparing our results with observations, we are able to set constraints on neutron star parameters such as the stellar radius and neutrino cooling mechanism in the core. Specifically, we find that accreting neutron stars with ordered crusts and highly efficient neutrino emission in their cores (due to direct URCA or pionic reactions, for example) produce extremely energetic (> 10^44 ergs) superbursts which are inconsistent with observations, in agreement with previous investigations. Also, because of pycnonuclear burning of carbon, they do not have superbursts in the range of accretion rates at which superbursts are actually observed unless the crust is very impure. Stars with less efficient neutrino emission (due to modified URCA reactions, for example) produce bursts that agree better with observations. Stars with highly inefficient neutrino emission in their cores produce bursts that agree best with observations. All systems that accrete primarily hydrogen and in which superbursts are observed show evidence of H- and He-burning delayed mixed bursts. We speculate that delayed mixed bursts provide sufficient amounts of carbon fuel for superbursts and are thus a prerequisite for having superbursts. We compare our global stability analysis to approximate one-zone criteria used by other authors and identify a particular set of approximations that give accurate results for most choices of parameters. (abstract truncated)

arXiv comment43 pages, 18 figures, accepted by ApJ

References in corpus (26)

• Neutron Star Structure and the Equation of State
• Neutron Star Cooling
• Neutrino Emission from Neutron Stars
• The endpoint of the rp process on accreting neutron stars
• Evolutionary Binary Sequences for Low- and Intermediate-Mass X-ray Binaries
• Crustal Heating and Quiescent Emission from Transiently Accreting Neutron Stars
• Models for Type I X-Ray Bursts with Improved Nuclear Physics
• Cooling neutron stars and superfluidity in their interiors
• A Remarkable Three Hour Thermonuclear Burst From 4U 1820-30
• Carbon Flashes in the Heavy Element Ocean on Accreting Neutron Stars
• The rp Process Ashes from Stable Nuclear Burning on an Accreting Neutron Star
• The Ocean and Crust of a Rapidly Accreting Neutron Star: Implications for Magnetic Field Evolution and Thermonuclear Flashes
• Nuclear composition and heating in accreting neutron-star crusts
• Equation of state of fully ionized electron-ion plasmas
• Structure of the inner crust of neutron stars: crystal lattice or disordered phase ?
• X-ray bursts at extreme mass accretion rates from GX 17+2
• Evidence for a Millisecond Pulsar in 4U 1636-53 During a Superburst
• Models of Type I X-Ray Bursts in 4U 1820-30
• Nuclear heating and melted layers in the inner crust of an accreting neutron star
• Thermonuclear Stability of Material Accreting onto a Neutron Star
• A half-a-day long thermonuclear X-ray burst from KS 1731-260
• A superburst from 4U 1254-690
• Recurrent very-long type-I X-ray bursts in the low-mass X-ray binary 4U 1636-53
• The observers' view of (very) long X-ray bursts: they are super!
• Superburst Ignition and Implications for Neutron Star Interiors
• Superbursts at near-Eddington mass accretion rates

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• Evidence for crust cooling in the transiently accreting 11-Hz X-ray pulsar in the globular cluster Terzan 5
• The Latitude of Type I X-Ray Burst Ignition on Rapidly Rotating Neutron Stars
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• The Influence of Uncertainties in the 15O(alpha,gamma)19Ne Reaction Rate on Models of Type I X-Ray Bursts
• The Rates of type I X-ray Bursts from Transients Observed with RXTE: Evidence for Black Hole Event Horizons
• Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts
• A Two-Zone Model for Type I X-ray Bursts on Accreting Neutron Stars
• The Spectral and Temporal Properties of Transient Sources in Early-Type Galaxies
• On the Production and Survival of Carbon Fuel for Superbursts on Accreting Neutron Stars: Implications for Mass Donor Evolution
• Hydrodynamic Thermonuclear Runaways in Superbursts
• On the Physics of Type I X-ray Bursts on Accreting Neutron Stars at High Accretion Rates
• Helium Ignition on Accreting Neutron Stars with a New Triple-alpha Reaction Rate
• The efficiency of nuclear burning during thermonuclear (Type I) bursts as a function of accretion rate
• Impacts of the direct URCA and Superfluidity inside a Neutron Star on Type-I X-Ray Bursts and X-Ray Superbursts
• The superburst recurrence time in luminous persistent LMXBs
• Ignition column depths of helium-rich thermonuclear bursts from 4U 1728-34
• Unveiling the atmospheres of giant exoplanets with an EChO-class mission
• Consistency between deep crustal heating of strange stars in superbursters and soft X-ray transients
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