Astrosat view of GX 339-4 during the peak of the recent outburst
Shyam Prakash V. P., Ramadevi M.C., Vivek K. Agrawal

TL;DR
This study analyzes AstroSat observations of GX 339-4 during its 2024 outburst peak, revealing spectral and timing features characteristic of the steep power law state, including a high black hole spin and a compact corona.
Contribution
First detailed AstroSat spectral and timing analysis of GX 339-4 during the 2024 outburst peak, estimating black hole spin and coronal geometry.
Findings
Black hole spin estimated at a = 0.99 ± 0.003
Detected strong QPOs at ~4.6 Hz with harmonic features
Coronal height estimated at about 2.5 Rg
Abstract
We present the spectral and timing analyses of \textit{AstroSat} observations of the Black Hole X-ray Binary GX 339-4 when the source was close the peak of the outburst in 2024. We find that both the spectral and timing variability of the source is indicative of it in its steep power law (SPL) state during the observations. We used phenomenological and physical models to understand the physics and geometry of accretion during this spectral state of the source. Spectral fits indicate the presence of an accretion disc with a temperature of 0.82 keV and a hot corona with a spectral index of 2.2 along with a significant contribution from iron line emission from the accretion disc. Strong QPOs were detected at 4.6 Hz in the Power Density Spectra of the source along with a harmonics feature. Time and phase lag at the QPO frequency are studied and we find a hard lag at the…
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Taxonomy
TopicsEarthquake Detection and Analysis · Astronomical Observations and Instrumentation · Advanced Research in Science and Engineering
