A report on Type II X-ray bursts from SMC X-1

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 ∽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-topeak 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 α ∽ 0.16.

Timing and spectral properties of Be/Xray pulsar 4U 1901+03 during 2019 outburst

“…We present Be X-ray pulsar 4U 1901+03 analysis which has undergone short bursts of tens to hundreds of seconds. The burst of the X-ray pulsar can be due to instability in accretion disk burst (Taam et al 1988;Lasota & Pelat 1991;Cannizzo 1996) similar to the burst observed in other sources namely, SMC X-1, GRO J1744-28 and MXB 1730-355 (Moon et al 2003;Rai et al 2018;Fishman et al 1995;Lewin et al 1976). Pulse profiles show variation with both time and flux and are similar to that observed by (Lei et al 2009;Reig & Milonaki 2016;Ji et al 2020).…”

Observing the Transient Pulsations of SMC X-1 with NuSTAR

“…One of only a handful of SGXBs known to accrete via Roche lobe overflow, SMC X-1 exhibits persistent emission near or above its isotropic Eddington luminosity of L Edd ∼ 1.3 × 10 38 erg s −1 (for a mass of ∼ 1.1 M , as reported by van der Meer et al 2007) varying between L X (2 − 12 keV) ∼ 10 37 erg s −1 in the low state and luminosities in excess of 5 × 10 38 erg s −1 (2 − 12 keV), more than three times its Eddington luminosity, in the high state (Bonnet-Bidaud & Klis 1981). In addition to this persistent emission, SMC X-1 has been shown to exhibit type II X-ray bursts with durations of tens of seconds (Angelini et al 1991;Rai et al 2018). Its near-to super-Eddington luminosity places the source in a middle ground between less luminous Be/X-ray binaries (BeXB), which exhibit a range of persistent X-ray luminosities from 10 32 erg s −1 (Tomsick et al 2011) up to 10 35 erg s −1 (Reig & Roche 1999), and brighter ultraluminous X-ray pulsars (ULXPs).…”

Microlensing of x-ray pulsars: A method to detect primordial black hole dark matter

“…We take a constant persistent count rate of B = 170 cts/s/pcu [49], though in reality the persistent emission varies with the superorbital period; e.g., the count rate in Fig. 4 is a bit lower, while even higher rates have been observed [50]. Future observations should focus on high points in the superorbital period to obtain the best lensing sensitivity.…”