XMM-Newton observations of EF Eridani: the textbook example of low-accretion rate polars*
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: email@example.com
2 Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany
Accepted: 28 March 2007
Archival X-ray observations of EF Eridani obtained in a low state revealed distinct X-ray detections at a luminosity 2 1029 erg s-1, three orders of magnitude below its high state value. The plasma temperature was found to be as low as 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 ~10 000 K. Contrary to earlier claims, WD model atmospheres produce sufficient UV flux to reproduce the published GALEX flux and orbital modulation.
Key words: stars: individual: EF Eri / stars: novae, cataclysmic variables / stars: magnetic fields / X-ray: binaries
© ESO, 2007