Statistical properties of type-II bursts in Rapid Burster observed with Insight-HXMT

Abstract

We report the detection of type-II X-ray bursts in a neutron star low mass X-ray binary MXB 1730-335 (also known as Rapid Burster) observed with Insight- HXMT satellite. We found significant variations in the burst properties along with the decay phases of its 2017 and 2020 outbursts, such as switches between different burst modes.We investigated the statistical distributions of burst parameters (peak flux $F_{\mathrm{peak}}$, fluence $E$, burst duration $t_{\mathrm{dur}}$, recurrence time $Δt$) and studied their correlations.We confirm the relaxation oscillator behavior ($E \propto Δt^α$), and find that for mode-2 bursts the index $α$ is around 1. For mode-1 bursts, $α$ varies with $Δt$ and the $E-Δt^α$ relation can be described by a broken powerlaw model.We also confirm that $F_{\mathrm{peak}}$ is correlated with $E$ below a critical value and is independent of $Δt$.