ROSAT OBSERVATIONS OF SCATTERED X-RAYS FROM LMC-X-4 IN ITS LOW STATE

Observations of the eclipsing accretion-powered high-mass X-ray binary LMC X-4 are described that confirm the idea that the low state of its 30.3 day period cyclical intensity variation is caused by a periodic blockage of the line of sight by a precessing accretion disk that is t ilted with respect to the orbital plane of the binary. The principal e vidence consists of the fact that the intensity and spectrum of scatte red X-rays measured during total eclipse of the neutron star by the pr imary star are approximately the same in both the high and low states of the 30.3 day cycle. Therefore, the low state must be caused not by a decrease in the luminosity of the X-ray source but, rather, by total attenuation in intervening matter. Differences between the spectra ob served in and out of eclipse in the high and in the low states are als o consistent with the precessing disk hypothesis. The brightest of sev eral flares detected in the low state had a peak intensity, which impl ies a source luminosity (0.2-25 keV) of 4 x 10(39) ergs s(-1) if the m easured flux is interpreted as scattered and fluorescent radiation fro m the primary star's surface illuminated by the unblocked X-ray source . This peak luminosity is comparable to that previously reported for a hare observed in the high state. The flare also showed marginal evide nce of the pulsar modulation, which is not inconsistent with the degre e of spread in path lengths of the scattered radiation. The data also show that the column density to LMC X-4, derived by spectrum fits in b oth the low and high states, is about 4 times larger than the interste llar neutral hydrogen column density toward the LMC, possibly as a res ult of a circumstellar accumulation of matter from the wind of the pri mary.