Coordinated Optical and X‐Ray Observations of the AM Herculis Objects VV Puppis, V834 Centauri, and EF Eridani

We obtained coordinated broadband optical photometry and hard X-ray data on the AM Her objects VV Pup, V834 Cen,and EF Eri. The X-ray data were obtained using the Proportional Counter Array detectors of the Rossi X-Ray Timing Explorer, and the optical data were obtained using the 1 m telescope of the Cerro Tololo Inter-American Observatory. During our observations, VV Pup and V834 Cen were in their high optical luminosity states with average m(V) similar to 17 and 15.1, respectively. EF Eri was in a very low state at the time of our observation: m(V) > 17.7. VV Pup and V834 Cen had average 2-10 keV X-ray fluxes of 1.7 x 10(-12) and 2.13 x 10(-11) ergs cm(-2) s(-1), respectively. EF Eri was not detected in X-rays. The X-ray spectrum of V834 Cen was adequately modeled using an absorbed bremsstrahlung continuum with a Gaussian emission line. The best-fit model had continuum temperature kT(X) = 11.8 +/- 1.0 keV and absorption column n(H) = (1.03 +/- 0.39) x 10(22) cm(-2). The Gaussian emission line had line center energy E = 6.7 +/- 0.1 keV and equivalent width EW = 0.64 keV. VV Pup was too faint to produce reliable spectral fits. The 2-10 keV flux for VV Pup quoted above was based on the best-lit spectral model. Holding kT(X) fixed in the fitting process yielded roughly the same flux for kT(X) = 0.5-30 keV. We detected similar to 1 Hz optical quasi-periodic oscillations (QPOs) with amplitude similar to 2.2% from VV Pup and similar to 1% from V834 Cen. We did, not detect optical QPOs over the range 0.2-1 Hz from EF Eri at a 90% confidence upper limit of 4.5%. The QPO properties are consistent with those found in the literature. None of the targets showed X-ray QPO activity. However, only V834 Cen yielded a meaningful upper limit: similar to 14% at the 90% confidence level over 0.2-1.2 Hz.