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Based on XMM--Newton X-ray observations IGR J19552+0044 appears to be eithera pre-polar or an asynchronous polar. We conducted follow-up opticalobservations to identify the sources and periods of variability precisely andto classify this X-ray source correctly. Extensive multicolor photometric andmedium- to high-resolution spectroscopy observations were performed and periodsearch codes were applied to sort out the complex variability of the object. Wefound firm evidence of discording spectroscopic (81.29+/-0.01m) and photometric(83.599+/-0.002m) periods that we ascribe to the white dwarf (WD)\ spin periodand binary orbital period, respectively. This confirms that IGR J19552+0044 isan asynchronous polar. Wavelength-dependent variability and its continuouslychanging shape point at a cyclotron emission from a magnetic WD with arelatively low magnetic field below 20 MG.  The difference between the WD spin period and the binary orbital periodproves that IGR J19552+0044 is a polar with the largest known degree ofasynchronism (0.97 or 3%).

IGR J19552+0044: A new asynchronous short period polar: "Filling the gap between intermediate and ordinary polars"