Thermonuclear X-ray bursts detected in Cyg X-2 using AstroSat/LAXPC

Abstract

We report the detection of 5 Type-1 thermonuclear X-ray bursts and one burst-like event in the neutron star LMXB source, Cyg X-2 using X-ray data obtained with the Large Area X-ray Proportional Counter (LAXPC) instrument on board AstroSat. We carry out an energy resolved burst profile analysis as well as time resolved spectral analysis for each of the bursts and characterize their properties. All bursts are weak with burst peak-to-persistent intensity ratios $<$ 3, decay times $\sim$2 s, and with fluences $\sim$1$\times$10${}^{-8}$ ergs/cm${}^2$, indicating that the observed bursts are Helium fuelled flashes. An evolution of the blackbody temperature and radius is also observed during each burst. We carry out a search for Burst Oscillations (BO) and derive upper limits to the rms fractional amplitude for BO (for all the bursts) to be $\sim$1\%. We also carried out search for Quasi Periodic Oscillations (QPOs) in the power density spectra and we obtain upper limits to the fractional rms amplitude as $\sim$3.4\% at frequencies close to $\sim$5.6 Hz. We further carry out spectral and timing analysis of the non-burst persistent emission along with a study of the hardness-intensity and colour-colour diagrams. Using results from our analysis we infer that during this observation in 2016, Cyg X-2 can be characterized as being in the early Flaring Branch (FB) with a puffed up accretion disk and a clumpy coronal structure while undergoing medium-to-high levels of accretion.

arXiv commentAccepted for publication in New Astronomy

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Cited by in corpus (5)

• The study of thermonuclear X-ray bursts in accreting millisecond pulsar MAXI J1816-195 with NuSTAR and NICER
• Spectral and Timing evolution of GX 340+0 along its Z-track
• AstroSat observation of rapid Type-I thermonuclear burst from the low mass X-ray binary GX 3+1
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• Links Between Optical and X-ray Light in Cygnus X-2