2025/09/23 by Akhter, Shahzada, Boked, Sajad, Maqbool, Bari +2
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2509.19546
We performed a detailed time-resolved spectral study of GRS 1915+105 during its low-flux rebrightening phase using the broadband capabilities of AstroSat and NuSTAR in May-June 2019. The AstroSat light curves revealed erratic X-ray flares with count rates rising by a factor of ∼5. Flares with simultaneous LAXPC and SXT coverage were segmented and fitted using two degenerate but physically motivated spectral models: a reflection-dominated model (hereafter Model A) and an absorption-dominated model (hereafter Model B). In Model A, the inner disk radius (Rin) shows a broken power-law dependence on flux, indicating rapid inward motion of the disk at higher flux levels. In contrast, Model B shows variable column density in the range of 1023 to 1024 cm-2, displaying a strong anti-correlation with flux. Both models exhibit significant variation in the ionization parameter between low- and high-flux segments. The total unabsorbed luminosity in the 0.7--30~keV energy range ranged from 6.64 × 1036 to 6.33 × 1038~erg~s-1. Across both models, several spectral parameters exhibited step-function-like behavior around flux thresholds of 5--10 × 10-9 erg cm-2 s-1, indicating multiple spectral regimes. The disc flux contribution, more evident in Model B, increased with total flux, supporting an intrinsic origin for the variability. These findings point to a complex interplay between intrinsic disk emission, structured winds, and variable local absorption in driving the flare activity.