Gamma-ray (0.1–300 GeV)-to-X-ray luminosity (0.3–79 keV) ratio in the sub-luminous disc state as a function of the gamma-ray luminosity for known and candidate tMSPs. The green data points represent the two confirmed tMSPs with identified gamma-ray counterparts. The red data points represent candidate tMSPs, including CXOU J110926.4–650224. The gamma-ray luminosity for CXOU J110926.4–650224 was calculated assuming a distance of 4 kpc. X-ray fluxes and distances are taken from Coti Zelati et al. (2019). The gamma-ray fluxes of 4FGL J1023.7+0038 and 4FGL J1227.1–4437 are taken from Torres et al. (2017), while the fluxes for 4FGL J1544.5–1126 and 4FGL J0427.8–6704 are estimated from the latest Fermi-LAT DR4 (Ballet et al. 2023). The gamma-ray flux of CXOU J110926.4–650224 (4FGL J1110.3–6501 in the Fermi-LAT catalogue) is derived in this work.