NICER and NuSTAR spectra of 4U 1957+115. Top panel: unfolded spectra (i.e. the flux F(E)) for the best-fitting model described by Model 1 during Periods 1, 2, and 3, shown in red, blue, and green, respectively. The total model for each period, the contributions of the kerrbb and the powerlaw models are shown with the solid, dotted and dashed lines, respectively. Bottom panel: model minus data residuals in units of σ.