Carbon Synthesis in Steady-State Hydrogen and Helium Burning On Accreting Neutron Stars

Abstract

Superbursts from accreting neutron stars probe nuclear reactions at extreme densities ($\rho \approx 10^{9}gc{m}^{-3}$) and temperatures ($T>10^{9}K$). These bursts ($\sim$1000 times more energetic than type I X-ray bursts) are most likely triggered by unstable ignition of carbon in a sea of heavy nuclei made during the rp-process of regular type I X-ray bursts (where the accumulated hydrogen and helium are burned). An open question is the origin of sufficient amounts of carbon, which is largely destroyed during the rp-process in X-ray bursts. We explore carbon production in steady-state burning via the rp-process, which might occur together with unstable burning in systems showing superbursts. We find that for a wide range of accretion rates and accreted helium mass fractions large amounts of carbon are produced, even for systems that accrete solar composition. This makes stable hydrogen and helium burning a viable source of carbon to trigger superbursts. We also investigate the sensitivity of the results to nuclear reactions. We find that the ${}^{14}$O($\alpha$,p)${}^{17}$F reaction rate introduces by far the largest uncertainties in the ${}^{12}$C yield.

8 pages, submitted to ApJ

References in corpus (8)

• Databases and tools for nuclear astrophysics applications BRUSsels Nuclear LIBrary (BRUSLIB), Nuclear Astrophysics Compilation of REactions II (NACRE II) and Nuclear NETwork GENerator (NETGEN)
• Possible Resonances in the 12C + 12C Fusion Rate and Superburst Ignition
• First superburst from a classical low-mass X-ray binary transient
• Intermediate long X-ray bursts from the ultra-compact binary source SLX 1737-282
• Superburst Models for Neutron Stars with Hydrogen and Helium-Rich Atmospheres
• Turbulent Mixing in the Surface Layers of Accreting Neutron Stars
• Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts
• The superburst recurrence time in luminous persistent LMXBs

Cited by in corpus (5)

• Dependence of X-Ray Burst Models on Nuclear Reaction Rates
• Carbon-oxygen-neon mass nuclei in superstrong magnetic fields
• Time-dependent, compositionally driven convection in the oceans of accreting neutron stars
• Constraining Accreted Neutron Star Crust Shallow Heating with the Inferred Depth of Carbon Ignition in X-ray Superbursts
• A search for the $835\text{Hz}$ superburst oscillation signal in the regular thermonuclear bursts of 4U 1636-536