Superburst with Outburst from EXO 1745-248 in Terzan 5 with MAXI

TL;DR

This paper reports the detection of a superburst from EXO 1745-248 in Terzan 5 using MAXI, analyzing its spectral properties, decay, and subsequent outburst, providing insights into superburst phenomena in low-mass X-ray binaries.

Contribution

First detection of a superburst from EXO 1745-248 with detailed spectral and temporal analysis, linking superburst activity to subsequent outburst behavior.

Findings

Superburst characterized by exponential decay with 0.3-day e-folding time.

Spectral analysis shows blackbody radiation with temperatures of 2.2 keV and 1.2 keV.

Follow-up outburst occurred 28 hours after the superburst, lasting 5 days.

Abstract

MAXI/GSC detected a superburst from EXO 1745-248 in the globular cluster Terzan 5 on 2011 October 24. The GSC light curve shows an exponential decay with an e-folding time of 0.3 day. The spectra are consistent with the blackbody radiation, whose temperature is 2.2 keV and 1.2 keV at MJD 55858.56 and 55859.20, respectively. The fluence is $1.4 \times 10^{42}$ erg in 2-20 keV assuming 8.7 kpc distance. The sphere radius of the blackbody and its luminosity are estimated to be 6.2 km and $1.1 \times 10^{38}$ erg s$^{-1}$, respectively, from the spectral fitting at the flux peak. Those e-folding time, temperature, softening, fluence, and radius are typical of superbursts from the low-mass X-ray binaries. The superburst was followed by an outburst 28 hours after the superburst onset. The outburst lasted for 5 days and the fluence was $4.3 \times 10^{42}$ erg. The instability of the accretion disk caused by the superburst would be an explanation for the outburst, whereas the mass accretion of the matter evaporated from surface of the companion star by the superburst would be another possibility.