XMM-Newton observations of EF Eridani: the textbook example of low-accretion rate polars

Archival X-ray observations of EF Eridani obtained in a low state revealed distinct X-ray detections at a luminosity L-X similar or equal to 2 x 10(29) erg s(-1), three orders of magnitude below its high state value. The plasma temperature was found to be as low as kT <= 2 keV, a factor 10 below the high state. The X-ray/UV/IR spectral energy distribution suggests faint residual accretion rather than coronal emission as being responsible for the low-state X-ray emission. EF Eri thus showed a clear transition from being shock-dominated in the high state to be cyclotron-dominated in the low state. From the optical/UV spectral energy distribution we re-determine the photospheric temperature of the white dwarf to similar to 10 000K. Contrary to earlier claims, WD model atmospheres produce sufficient UV flux to reproduce the published GALEX flux and orbital modulation.