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
Credential Certification: Koji Mukai (mukai@milkyway.gsfc.nasa.gov)
Subjects: X-ray, Cataclysmic Variable
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.
