Properties of Hard X-ray Bright Polars

Polars are a subclass of magnetic cataclysmic variables (CVs) in which a strongly magnetic white dwarf accretes matter from a late-type, Roche-lobe filling mass donor. They are usually soft X-ray bright and hard X-ray dim, due to either buried shocks or strong cyclotron cooling, depending on system parameters. Indeed, the majority of the 100 currently-known polars were detected in the ROSAT all-sky survey. However, a small subset of polars have been detected as bright hard X-ray sources in INTEGRAL and Swift BAT surveys, and they make up a small, but increasingly non-negligible, fraction of INTEGRAL and BAT-detected CVs. I will present the current sample of polars detected in the BAT 105-month survey, as well as results of pointed X-ray observations of a subset of them. I will then summarize the current status towards understanding why a subset of polars are hard X-ray bright.