092169

We propose an XMM observation of a 12-min-period source detected by the ZTFoptical survey. Initially speculated to be a CV this source exhibits highmodulation and day-long flares in the optical band. It is still unknown whetherthe 12-min period represents its spin or orbital period. The optical and X-rayproperties observed so far including NuSTAR detection of a power-law-like X-rayspectrum up to 30 keV indicate two possible unusual source types. It is eithera massive intermediate polar hosting a WD that exceeds 1 solar mass or anultra-compact X-ray binary with the second shortest orbit ever discovered. Weaim to identify the source by determining whether the X-ray spectrum isnon-thermal exploring the X-ray modulation with the 12-min period and searching for X-ray flares. [truncated! Please see actual data for full text]