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The Galactic microquasar GRS 1915+105 shows rich variability which iscategorized into different classes. In this paper, we report temporal andspectral analysis of GRS 1915+105 to study the properties of the accretion flowwhen the light curve is showing $\theta$ class variability. For this purpose,we use the LAXPC data from the Target of Opportunity observations of India'sfirst multi-wavelength astronomy satellite AstroSat. The $\theta$ class ismarked by the recurrent appearance of U-shaped regions in the light curve,where the photon count rate first decreases rapidly and then increases slowly.For our analysis, we use U-shaped regions of first two orbits (02345 and 02346)on 2016 March 04. In both of the cases, the dynamic Power Density Spectra (PDS)showed significant power at around $4-5$ Hz, suggesting the presence of alow-frequency Quasi-Periodic Oscillation (QPO) around that frequency interval.The QPO frequency is found to increase with time when the enhancement of theenergy flux also takes place. From the evolution of the spectra, we determinethe evolution of the accretion flow parameters in both of these observations.Fitting the spectra with the transonic flow solution based Two-ComponentAdvective Flow (TCAF) model in $4-25$ keV energy band shows that the Kepleriandisk accretion rate rises with the rise in the radiation intensity, while thelocation of the centrifugal pressure driven shock front decreases. In boththese data, a gradual increment of power-law photon index with intensity isobserved suggesting the progressive softening of the source.

Accretion Flow Properties of GRS 1915+105 During Its $\theta$ Class Using AstroSat Data