Spectra and light curves with M_c = 1 M_⊙ (left panels) and 10 M_⊙ (right panels) in a binary system with P_orb = 10 d. Differently colored lines represent different mechanisms, as indicated in the legends. The blue line shows the persistent preburst radiation for L_w = 9.6 × 10⁴⁴ erg s⁻¹ corresponding to Case I, and the light blue line indicates that for L_w = 5.0 × 10³⁴ erg s⁻¹ corresponding to Case II. In the top panels, we show the light curves. In the bottom panels, we show the spectra for different mechanisms at a distance of d = 100 kpc. The sensitivity curves of Einstein Probe (blue line), Chandra (pink line), and XMM-Newton (black line) are calculated with an exposure time of 10³ s, which can be derived from sensitivity proportional to the −1/2 power of the exposure time (Lucchetta et al. 2022; Yuan et al. 2022), and the r-band sensitivity of the Vera C. Rubin Observatory (purple line) is calculated with a point source exposure time of 30 s (Yuan et al. 2021).