Spectral and Timing Properties of the Galactic X-ray transient Swift~J1658.2--4242 using Astrosat Observations

Abstract

We present the X-ray timing and spectral analysis of the new Galactic X-ray transient Swift J1658.2-4242 observed with LAXPC and SXT instruments onboard {\it Astrosat}. We detect prominent C-type quasi-periodic oscillations (QPOs) of frequencies varying from $\sim 1.5$ Hz to $\sim 6.6$ Hz along with distinct 2nd harmonics and sub-harmonics. The QPO detected at $\sim 1.56$ Hz drifts to a higher centroid frequency of $\sim 1.74$ in the course of the observation, while the QPO detected at $\sim 6.6$\,Hz disappeared during hard flarings. The fractional rms at the QPO and the sub-harmonic frequencies increases with photon energy, while at the 2nd harmonic frequencies the rms seems to be constant. In addition, we have observed soft time lag at QPO and sub-harmonic frequencies up to a time scale of $\sim 35$ ms, however, at the 2nd harmonic frequencies there is weak/zero time lag. We attempt spectral modeling of the broadband data in the 0.7--25 keV band using the doubly absorbed disk plus thermal Comptonization model. Based on the spectral and timing properties, we identified the source to be in the hard intermediate state of black hole X-ray binaries. To quantitatively fit the energy and frequency-dependent fractional rms and time lag, we use a single zone fluctuation propagation model and discuss our results in the context of that model.

Accepted for Publication in ApJ, 13 Pages, 14 Figures, 3 Tables

References in corpus (6)

• X-ray Properties of Black-Hole Binaries
• Geometrical constraints on the origin of timing signals from black holes
• Large Area X-ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its performance in the orbit
• AstroSat/LAXPC reveals the high energy variability of GRS 1915+105 in the chi class
• A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state
• Broadband X-ray Spectral and Timing Analyses of the Black Hole Binary Candidate Swift J1658.2-4242: Rapid Flux Variation and the Turn-on of a Transient QPO

Cited by in corpus (3)

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• An underlying clock in the extreme flip-flop state transitions of the black hole transient Swift J1658.2-4242
• Evidence for coronal temperature variation in Seyfert 2 ESO 103--035 using NuSTAR observations