2025ApJ...994..223A

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 2019 May-June. 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 (R_in) 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 10²³-10²⁴ cm^–2, displaying a strong anticorrelation 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 disk 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.