Speaker
Description
GS 1354-64 is a dynamically confirmed Galactic transient black hole. Recently, it exhibited a bright outburst. We study the temporal, spectral, and polarimetric properties of the source using multi-satellite data. The outburst consists of two short-duration ($\sim 3$-$5$ days) bright X-ray flares, with peak fluxes of 1.4 and 0.8 Crab, respectively. The source exhibits strong signatures of quasi-periodic oscillations (QPOs) and their evolution. The propagating oscillatory shock (POS) model successfully fits the monotonic evolution of the QPO frequency. This provides a clearer understanding of the evolution of the shock wave responsible for the origin of the observed QPOs. A strong signature of relativistic reflection is also observed. From spectral analysis using the relativistic reflection model {\tt RELXILL}, the black hole spin and inclination angle are estimated to be $a = 0.997 \pm 0.002$ and $i \sim (61$--$71)^\circ$, respectively. Strong polarization is detected, with a polarization degree (PD) of $4.1 \pm 0.45$ % ($\sim 10\sigma$ confidence) and a polarization angle (PA) of $(-2.31 \pm 2.8)^\circ$ in the IXPE energy band of $2$-$8$ keV. Both PD and PA are also found to evolve with energy. Detailed spectral analysis suggests that the source was in the softest spectral state during both flares.
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