Time-Lag properties associated with LFQPO in X-ray variability classes of GRS 1915+105: Findings from AstroSat
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| Format: | Preprint |
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2026
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| _version_ | 1866908893380083712 |
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| author | Majumder, Prajjwal Dutta, Broja G. Nandi, Anuj |
| author_facet | Majumder, Prajjwal Dutta, Broja G. Nandi, Anuj |
| contents | We present a comprehensive analysis of Low Frequency Quasi-periodic Oscillation (LFQPO) associated time-lags in the persistently variable black hole binary GRS 1915+105 using 441 ks of \textit{AstroSat} observations from March 2016 to March 2019. LFQPO frequency ($1.38-7.38$ Hz) are detected across the $θ$, $β$, $ρ$, and $χ$ classes, with the $χ$ class further subdivided into $χ_1$, $χ_2$, $χ_3$, and $χ_4$ based on spectro-temporal characteristics. Class transitions occur on timescales of a few hours, appearing either as a simultaneous increase in X-ray count rate and QPO frequency, or vice versa, indicating rapid changes in the accretion flow geometry. The $\text{rms}_{\rm QPO}$ increases with QPO frequency up to $\sim 3.4$ Hz and declines at higher frequencies, a trend similar to \textit{RXTE} observations, where peak occurred at $\sim 2$ Hz. Spectro-temporal correlations reveal that increasing $F_{\rm Comp}$ drives higher $\text{rms}_{\rm QPO}$ and decreases the soft-lag magnitude, while $ν_{\rm QPO}$ and $Γ$ also decline, suggesting that the observed time lag may result from the combined effects of multiple physical mechanisms. The consistent increase of $\text{rms}_{\rm QPO}$ with $F_{\rm Comp}$ provides clear evidence that modulated Comptonized photons enhance the rms power ($\text{rms}_{\rm QPO}$). Moreover, the soft-lag ($1.59-13.49$ ms) observed across all QPO frequencies, without the sign reversal at $\sim$ 2 Hz observed in \textit{RXTE} observations, is interpreted within the framework of a dynamical accretion disk model around the black hole. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_16305 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Time-Lag properties associated with LFQPO in X-ray variability classes of GRS 1915+105: Findings from AstroSat Majumder, Prajjwal Dutta, Broja G. Nandi, Anuj High Energy Astrophysical Phenomena We present a comprehensive analysis of Low Frequency Quasi-periodic Oscillation (LFQPO) associated time-lags in the persistently variable black hole binary GRS 1915+105 using 441 ks of \textit{AstroSat} observations from March 2016 to March 2019. LFQPO frequency ($1.38-7.38$ Hz) are detected across the $θ$, $β$, $ρ$, and $χ$ classes, with the $χ$ class further subdivided into $χ_1$, $χ_2$, $χ_3$, and $χ_4$ based on spectro-temporal characteristics. Class transitions occur on timescales of a few hours, appearing either as a simultaneous increase in X-ray count rate and QPO frequency, or vice versa, indicating rapid changes in the accretion flow geometry. The $\text{rms}_{\rm QPO}$ increases with QPO frequency up to $\sim 3.4$ Hz and declines at higher frequencies, a trend similar to \textit{RXTE} observations, where peak occurred at $\sim 2$ Hz. Spectro-temporal correlations reveal that increasing $F_{\rm Comp}$ drives higher $\text{rms}_{\rm QPO}$ and decreases the soft-lag magnitude, while $ν_{\rm QPO}$ and $Γ$ also decline, suggesting that the observed time lag may result from the combined effects of multiple physical mechanisms. The consistent increase of $\text{rms}_{\rm QPO}$ with $F_{\rm Comp}$ provides clear evidence that modulated Comptonized photons enhance the rms power ($\text{rms}_{\rm QPO}$). Moreover, the soft-lag ($1.59-13.49$ ms) observed across all QPO frequencies, without the sign reversal at $\sim$ 2 Hz observed in \textit{RXTE} observations, is interpreted within the framework of a dynamical accretion disk model around the black hole. |
| title | Time-Lag properties associated with LFQPO in X-ray variability classes of GRS 1915+105: Findings from AstroSat |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2603.16305 |