2025MNRAS.544..866A

X-ray emission is generally believed to be one of the major heating sources for the optical modulation in redback pulsar binaries as we have seen similar phenomena in many low-mass X-ray binaries (LMXBs). While, e.g. MeV/GeV $\gamma$-rays from the neutron stars are also possible heating sources, X-ray observations are currently much more sensitive, and therefore, joint optical-X-ray data are observationally unique on the irradiation mechanism investigation. Using 18 X-ray/B-band simultaneous XMM-Newton observations (717 ks in total) of the redback system PSR J1023+0038 taken during the LMXB state, we find a general trend that the amplitude of the B-band orbital modulation was lower when the observed X-ray flux was higher. Depending on the analysis method adopted, the statistical significance of the anticorrelation can be from 1.7$\sigma$ to 3.1$\sigma$. We also extended the analysis to the GeV $\gamma$-ray band using the Fermi-LAT data, but the result is insignificant to claim any relations. Moreover, another X-ray/optical correlation regarding the low modes of the system was found in some of the XMM-Newton observations, and the astrophysical reason behind is currently unclear yet. These anticorrelations likely suggest that the irradiation is generally stronger when the X-ray flux is in a fainter state, indicating that there is a more dominant irradiation source than the X-ray emission.