Simultaneous [ITAL]EXTREME ULTRAVIOLET EXPLORER[/ITAL][ITAL]Extreme Ultraviolet Explorer[/ITAL] and [ITAL]ROSSI X-RAY TIMING EXPLORER[/ITAL][ITAL]Rossi X-Ray Timing Explorer[/ITAL] Observations of AM Herculis

Abstract

We present coordinated Extreme Ultraviolet Explorer (EUVE) and Rossi X-Ray Timing Explorer (RXTE) target of opportunity observations of the 1998 August high state of AM Herculis. The EUVE light curve sampled phases ~0.0–0.3 and ~0.5–0.8 and showed AM Her to be uncharacteristically bright during these phases but lacking the expected counts at phase ≈0.5, possibly because of absorption. The RXTE proportional counter array (PCA) 2–20 keV and HEXTE 15–60 keV light curves clearly show the 3.09 hr orbital modulation. No correlations between the soft and hard bands predicted in the simple one-pole accretion model were detected in the ≈1600 s of true, simultaneous EUVE and RXTE data. Quasi-periodic oscillations (QPOs) of 1–3 s found in optical data for several magnetic cataclysmic variables were not detected in PCA high time resolution data of AM Her with a 90% confidence upper limit for the rms amplitude of 3%. No significant QPOs were detected in the 10s–100s of seconds range with EUVE or RXTE. The EUVE spectrum was well fitted with a 19 eV blackbody. The phase-averaged PCA spectrum was well fitted with a 17.6 keV thermal bremsstrahlung (TB) continuum plus a broad iron line centered at 6.5 keV and absorption edge at 9.2 keV. HEXTE detections extended to 100 keV and preferred a highly absorbed TB continuum with temperature of 37 keV. The thermal bremsstrahlung plus emission-line (Eline = 6.7 keV) and edge model fit to PCA spectra as a function of phase could be described as a single TB temperature of 18.9 ± 0.2 keV with a variable column density of 7.1–53.5 × 1021 cm-2 and did not require more complex continuum models. The ratio of EUV to X-ray luminosity showed no soft excess and was more in accord with the simple one-pole model than previous observations.