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GRS 1915+105 has been in a bright flux state for more than 2 decades, but in2018 a significant drop in flux was observed, partly due to changes in thecentral engine along with increased X-ray absorption. The aim of this work isto explore how X-ray spectro-polarimetry can be used to derive the basicgeometrical properties of the absorbing and reflecting matter. In particular,the expected polarisation of the radiation reflected off the disc and theputative outflow is calculated. We use \textit{NuSTAR} data collected after theflux drop to derive the parameters of the system from hard X-ray spectroscopy.The spectroscopic parameters are then used to derive the expected polarimetricsignal, using results from a MonteCarlo radiative transfer code both in thecase of neutral and fully ionised matter. From the spectral analysis, we findthat the continuum emission becomes softer with increasing flux, and that inall flux levels the obscuring matter is highly ionised. This analysis, on theother hand, confirms that spectroscopy alone is unable to put constraints onthe geometry of the reflectors. Simulations show that X-ray polarimetricobservations, like those that will be provided soon by the Imaging X-rayPolarimetry Explorer (IXPE), will help to determine the geometrical parameterswhich are left unconstrained by the spectroscopic analysis.

Exploring the accretion-ejection geometry of GRS 1915+105 in the obscured state with future X-ray spectro-polarimetry