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We explore the timing and spectral properties of GRS 1915+105 based on X-rayobservations of NICER and Insight-HXMT during the long outburst from 2017 to2021. We find a new class of variability in the rising stage of the outburstthat differs from the formerly reported patterns of light curves. This newvariability pattern, which we name class $\psi$, is characterized by severalperiodic mini pulses superposed on another longer periodic pulse. The periodsare around $\sim$130 seconds and $\sim$10 seconds for the main pulses and minipulses respectively based on the analysis of power spectrum density (PSD) andstep-wise filter correlation (SFC), where the SFC method has an advantage infinding the superimposed periodic components. The mini pulses become weak ordisappear when the luminosity increases and the light curves change into theclassical class $\kappa$. The class $\psi$ shows a softer spectrum with lowercount rates compared to the class $\kappa$ during the main pulse. The new class$\psi$ shows peculiar timing and spectral properties compared to those ofclassic class $\kappa$, which can help us to explore the class transitionmechanism in GRS 1915+105.

A new variability pattern in GRS 1915+105 with NICER and Insight-HXMT observations