A report on the type II X-ray burst from SMC X-1

TL;DR

This study analyzes RXTE PCA data of SMC X-1, revealing frequent type II X-ray bursts, their characteristics, and their impact on the source's spectral and timing properties, with implications for accretion disk behavior.

Contribution

First detailed analysis of type II X-ray bursts in SMC X-1, linking burst properties to accretion disk viscosity and spectral changes.

Findings

272 flares observed with mean FWHM of 21 s

No change in pulse profile shape during flares

Luminosity increases with flaring rate

Abstract

We study RXTE PCA data for the high mass X-ray binary source SMC X-1 between 2003-10 and 2003-12 when the source was in high states. The source is found to be frequently bursting which can be seen as flares in lightcurves on an average of one in every 800 s, with an average of 4-5 X-ray burst per hour of type II. We note that typically burst was short lasting for few tens of seconds in addition few long bursts of more than hundred seconds were also observed. The flares apparently occupied 2.5$\%$ of the total observing time of 225.5 ks. We note a total of 272 flares with mean FWHM of the flare $\backsim$21 s. The rms variability and the aperiodic variability are independent of flares. As observed the pulse profiles of the lightcurves do not change its shape implying that there is no change in the geometry of accretion disk due to burst. The hardness ratio and the rms variability of lightcurves show no correlation with the flares. The flare-fraction shows a positive correlation with the peak-to-peak ratio of the primary and secondary peaks of the pulse profile. The observed hardening or the softening of the spectrum cannot be correlated with the flaring rate but may be due to the interstellar absorption of X-rays as evident from the change in the hydrogen column density ($n_{H}$). It is found that the luminosity of the source increases with the flaring rate. Considering the viscous timescale equal to mean recurrence time of flares we fixed the viscosity parameter $\alpha$ $\backsim$ 0.16.