  We study the charmonium spectral functions at finite momentum and the dispersion relation of $\eta_c$ at finite temperature. For the analysis of the spectral function, we use an extended maximum entropy method (MEM). We perform the MEM analysis for the product space of Euclidean correlators in different channels or momenta to incorporate information encoded in correlations among the Euclidean correlators in MEM. We find that this method can improve the error of the reconstructed spectral images. To study the dispersion relation, we introduce a definition of the peak position in the spectral image in which the associated error can be estimated on the basis of MEM. We find that the dispersion relation of $\eta_c$ at finite temperature follows the Lorentz invariant form even near the dissociation temperature $T\simeq1.7T_c$. 
Charmonium spectra and dispersion relation with improved Bayesian   analysis in lattice QCD