On the impact of the carbon fusion rate over the properties of superbursts -- Numerical simulations of superbursts with MESA

Abstract

Context: Superbursts are very energetic explosions in the crust of neutron stars in Low-Mass X-ray Binaries (LMXBs). These are triggered by unstable carbon burning at $T\leq 10^{9}$ K. In recent years, there has been a re-examination of the carbon fusion rate, finding that at these temperatures it might be either smaller or higher with respect to the classic rate from Caughler \& Fowler (1988) by a factor $10^{3}$. Aims: We explore the consequences changing the carbon fusion rate has over the physics of superbursts. Methods: For simulating superbursts, we employ the public code MESA v.24.08.1, as well as four versions of the carbon fusion reaction rate. Results: An enhancement of the reaction rate by a factor $10^{3}$ at $T\leq 10^9$~K reduces the recurrence and decay times of the superburst, as well as the column depth at ignition. The opposite behavior is observed when the carbon fusion rate is reduced by the same factor. The maximum temperature reached during the explosion is also sensitive to these changes, leading to either an enhancement or a reduction in the synthesis of $α$-nuclides. These changes are comparable to the effect of reducing the amount of base heating at the bottom of the envelope.