XMM-Newton observations of EF Eridani: the textbook example of low-accretion rate polars
Abstract
Archival X-ray observations of EF Eridani obtained in a low state revealed distinct X-ray detections at a luminosity LX ≃ 2 × 1029 erg s-1, 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 10 000 K. Contrary to earlier claims, WD model atmospheres produce sufficient UV flux to reproduce the published GALEX flux and orbital modulation.
Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.- Publication:
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Astronomy and Astrophysics
- Pub Date:
- July 2007
- DOI:
- 10.1051/0004-6361:20066928
- arXiv:
- arXiv:astro-ph/0703561
- Bibcode:
- 2007A&A...469.1027S
- Keywords:
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- stars: individual: EF Eri;
- stars: novae;
- cataclysmic;
- variables;
- stars: magnetic fields;
- X-ray: binaries;
- Astrophysics
- E-Print:
- A&