  We describe an X-ray source detection method entirely based on the maximum
likelihood analysis, in application to observations with the ART-XC telescope
onboard the Spectrum Roentgen Gamma observatory. The method optimally combines
the data taken at different conditions, a situation commonly found in scanning
surveys or mosaic observations with a telescope with a significant off-axis PSF
distortion. The method can be naturally extended to include additional
information from the X-ray photon energies, detector grades, etc. The
likelihood-based source detection naturally results in a stable and uniform
definition of detection thresholds under different observing conditions (PSF,
background level). This greatly simplifies the statistical calibration of the
survey needed to, e.g., obtain the $\log N - \log S$ distribution of detected
sources or their luminosity function. The method can be applied to the data
from any imaging X-ray telescope.
