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

A. D. Schwope·A. Staude·D. Koester·J. Vogel
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Abstract

Archival X-ray observations of EF Eridani obtained in a low state revealed distinct X-ray detections at a luminosity L_X ~ 2 10^{29} erg/s, three orders of magnitude below its high state value. The plasma temperature was found to be as low as $kT \loa 2$ 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 \~10000K. Contrary to earlier claims, WD model atmospheres produce sufficient UV flux to reproduce the published GALEX flux and orbital modulation.

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A. D. Schwope, A. Staude, D. Koester, J. Vogel. 2007-03-21. XMM-Newton observations of EF Eridani: the textbook example of low-accretion rate polars. https://doi.org/10.1051/0004-6361%3A20066928

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