Spectral analysis of χ class data of GRS 1915+105 using TCAF solution

Abstract

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency (CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentumKeplerian flow in the form of a radiatively efficient disk and a low angular momentumradiatively inefficient sub-Keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χ subclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the Keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow (TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ 2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ 1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF solution. At the same time, the normalization required by this model along with the variation of photon index and exponential roll-off factor provides us with information on the relative dominance of the outflow in the latter two classes. TCAF fit also supplies us with the size and location of the Compton cloud along with its optical depth. Thus by fitting with TCAF, a physical understanding of the flow geometry in different χ classes of GRS 1915+105 has been obtained.

On the Nature of Jets from a Main Sequence Companion at the Onset of Common Envelope Evolution

“…The flow structure I present here is qualitatively similar to their study. I also note that some observations support the notion that a sub-Keplerian disk can launch jets (e.g., Nandi et al 2018;Banerjee et al 2020;Debnath et al 2020Debnath et al , 2021.…”

Similarities and Differences in Accretion Flow Properties between GRS 1915+105 and IGR J17091-3624: a Case Study

“…The theoretically predicted variation of outflow rate with the shock strength had later been confirmed using extensive hydrodynamic simulations as well (Garain et al 2012). Very recently, the interplay between accretion and ejection under the TCAF paradigm has been successfully applied to understand the spectral and timing features of the non-variable χ class (Banerjee et al 2020a) and the highly variable θ class (Banerjee et al 2020b) of GRS 1915+105.…”

Accretion properties of MAXI J1813-095 during its failed outburst in 2018

“…The CENBOL is also the launch site of the jet. In recent years, the TCAF model has been used successfully used to study the spectral and timing properties of several black holes and active galactic nuclei (Mondal et al 2016;Chatterjee et al 2016;Shang et al 2019;Nandi et al 2019;Chatterjee et al 2020;Banerjee et al 2020).…”