V2301Ophiuchi: An X-ray-bright eclipsing AM Herculis object

We present hard X-ray and optical observations of the eclipsing AM Her syst em V2301 Oph. The X-ray data were obtained using the PCA detector of the Ro ssi X-Ray Timing Explorer satellite during 1997 May, and the optical data w ere obtained using the 1 and 1.5 m telescopes of the Cerro Tololo Inter-Ame rican Observatory during 1996 May and 1997 June. V2301 Oph was bright in bo th the optical and hard X-rays during our observations. This, when coupled with its eclipsing nature, makes V2301 Oph an ideal testbed for theories of the large-scale topology of AM Her hows and the radiative shocks in AM Her systems. The X-ray emission from V2301 Oph was modulated strongly on the o rbital period. During the bright orbital phases, the X-ray flux was Fx appr oximate to 3.6 x 10(-11) ergs cm(-2) s(-1) over the energy range E = 2-10 k eV. The X-ray emission did not go to zero during the faint orbital phases; it was similar to 10% of the bright phase level. The X-ray spectrum could b e fitted by (1) optically thin thermal bremsstrahlung (temperature kT(x) ap proximate to 9-19 keV) models with an absorption line at 5.1-5.2 keV or an emission line at similar to 7 keV, and (2) power-law continuum tinder appro ximate to 2) models with an absorption Line at 5.1-5.2 keV or an emission l ine at similar to 7 keV. The absorption columns were large for all fits, n( H) similar to (3-10) x 10(22) Cm-2 The n(H) are model dependent, but their large sizes are secure because they are set by the rollover in the X-ray sp ectrum at 3-4 keV. The hardness of the X-ray spectrum was roughly constant during the bright orbital phases. During the faint orbital phases, the X-ra y spectral properties were not well determined, but it did appear that the spectrum hardened. There were total eclipses in both the X-ray and optical light curves. The X-ray light curves and eclipses were consistent with a do minant hot spot and a secondary hot spot. The dominant hot spot was not a p oint source; it had to cover about 50 degrees in longitude on the surface o f the white dwarf. We argue that the X-ray light curve and eclipse shape al so suggest that the accretion occurs in a sheetlike geometry rather than in a columnar geometry. The optical light curves and eclipses were consistent with emission from the white dwarf photosphere, an extended emission regio n that sat above the surface of the white dwarf, and the X-ray-heated face of the companion star.