2023/07/09 by M. P. Athulya, Anuj Nandi, P., Athulya M. +1
Earth and Planetary Sciences · Physics and Astronomy · #Astrophysical Phenomena and Observations #Atmospheric Ozone and Climate #FOS: Physical sciences #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · pdf · doi:10.48550/arxiv.2307.04206
openalex publication_date 2023/07/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
GRS 1915+105 is observed in an 'obscured' phase since May 2019, exhibiting steady and low X-ray luminosities, while being intervened by sporadic re-brightenings. In this work, we perform a comprehensive and wide-band analysis of the spectral and timing properties of the source during the period 2019-2021 using AstroSat (SXT: 0.5-8 keV; LAXPC: 3-60 keV), NICER (0.5-12 keV), and NuSTAR (3-60 keV) observations. Spectral analysis reveals the presence of a highly variable obscurer (N_H1∼~1022 - 1024 atoms cm-2) throughout the observation period. Source is detected in the Low/Hard state for most of the time, with the spectra being described by a Comptonised component (Γ∼ 1.16 - 1.79, kTe∼ 2-31 keV). The source spectra steepen (Γ∼2.5) indicating softening of the spectrum during the rise of the re-brightenings. Various emission and absorption lines corresponding to the neutral Fe-Kα, Fe-XXV Kα, Fe-XXVI Kα, and the Ni-XXVIII Kα were detected with equivalent widths varying between 70 eV - 3.5 keV. The column density of the absorbing plasma varied between 1016 - 1018 atoms cm-2 at a distance ≤2×1010 cm. Interestingly, the source is also seen exhibiting various variability classes (ρ, λ, δ, χ) at relatively low luminosities (∼0.01LEdd) during the re-brightening phases. Different variability classes show signature of QPOs (νQPO: 20--180 mHz, rmsQPO: 7.5% - 16%). The source showed a maximum bolometric luminosity (Lbol) of ∼0.01LEdd (Re-brightening phases) and a minimum Lbol of 0.004LEdd (Quiet phase) during the period. We discuss the possible disc dynamics around the black hole during this low-luminosity `obscured' phase.