Simulated energy spectra for SRG/eROSITA from the gas at the cores of filaments. Top panel: the spectra are calculated with an overdensity of 30, a temperature of 0.9 keV, and a metallicity of 0.2 Z_⊙. The stacked spectra (red curves) display the expected signal from the brightest N filaments (with N = 10 to 15 165). Energy spectra are also simulated assuming overdensity of 19, temperature of 0.3 keV and metallicity of 0.2 Z_⊙ in the middle panel, and overdensity of 19, temperature of 0.1 keV and metallicity of 0.2 Z_⊙ in the bottom panel. Blue: simulated background energy spectrum of SRG/eROSITA. The optimal energy ranges to maximize the S/N for 15 165 filaments are shown as a light gray area.