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The End of the Prolonged Low State of EF Eridani

ATEL # 1562; K. Mukai (NASA/GSFC/CRESST and UMBC), F. Walter (SUNY Stony Brook), A. Schwope (AIP)
on 6 Jun 2008; 14:34 UT
Password Certification: Koji Mukai (mukai@milkyway.gsfc.nasa.gov)

Subjects: X-ray, Cataclysmic Variables

EF Eridani=2A0311-227 was among the first members of the polar (or AM Her type) class of magnetic cataclysmic variables (Griffiths et al. 1979, ApJLett, 232, L27). From the discovery in the mid 1970s until mid 1990s, it was not seen in a low state and was always among the X-ray brightest CVs. However, Wheatley & Ramsay (1998, ASP Conf. Ser. 137, 446) found it in a low state in January 1997. This low state has continued until recently with the exception of a short brightening episode in the spring of 2006 (Howell et al. 2006, ApJ, 652, 709). However, in late March, 2008, it was found in a bright optical state (AAVSO Special Notice #100), just as optical observations were about to become extremely difficult due to the conjunction with the Sun.

We have investigated the X-ray status of EF Eri using Swift/XRT and RXTE/PCA target-of-opportunity observations. It was observed with Swift/XRT for 1.6 ksec on 2008 March 27, when the average 2-10 keV flux was 4.4x10-11 ergs cm-2s-1. EF Eri was observed with RXTE/PCA for 3.4 ksec on 2008 May 22, when the average flux was 3.8x10-11 ergs cm-2s-1 (2-10 keV). Both spectra can be fit with a one component thin-thermal model, with no need for an additional soft component well known in this system. The measured flux values are comparable to the values found in the earlier high state, meaning that EF Eri is once again among the X-ray brightest CVs. It also suggests that the optical brightening observed from March 26 to April 7 (when it was lost behind the Sun) has probably continued at least through May 22, although this cannot be proved. Further optical observations are planned to ascertain how long-lasting the current high state is.


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