The study of multi-peaked type-I X-ray bursts in the neutron-star low mass X-ray binary 4U 1636$-$536 with RXTE

TL;DR

This study analyzes 16 multi-peaked type-I X-ray bursts from neutron star binary 4U 1636-53, revealing a rare quadruple-peaked burst and correlations suggesting accretion rate influences burst structure.

Contribution

First detailed analysis of multi-peaked X-ray bursts in 4U 1636-53, including a rare quadruple-peaked event and insights into burst morphology related to accretion.

Findings

Discovered a rare quadruple-peaked burst.

Found anti-correlation between second peak flux and peak separation.

Linked burst peak features to accretion rate and neutron star temperature.

Abstract

We have found and analysed 16 multi-peaked type-I bursts from the neutron-star low mass X-ray binary 4U 1636$-$53 with the Rossi X-ray Timing Explorer (RXTE). One of the bursts is a rare quadruple-peaked burst which was not previously reported. All 16 bursts show a multi-peaked structure not only in the X-ray light curves but also in the bolometric light curves. Most of the multi-peaked bursts appear in observations during the transition from the hard to the soft state in the colour-colour diagram. We find an anti-correlation between the second peak flux and the separation time between two peaks. We also find that in the double-peaked bursts the peak-flux ratio and the temperature of the thermal component in the pre-burst spectra are correlated. This indicates that the double-peaked structure in the light curve of the bursts may be affected by enhanced accretion rate in the disc, or increased temperature of the neutron star.