Broadband X-Ray Spectra of the Persistent Black Hole Candidates LMC X-1 and LMC X-3

We report on observations of the two persistent black hole candidates LMC X-3 and LMC X-1 performed with BeppoSAX in 1997 October. The flux of LMC X-1 was possibly measured up to 60 keV, but there is a possible confusion with PSR 0540-69. Fits with an absorbed multicolor disk blackbody are not satisfactory, while the superposition of this model with a power law is acceptable. The sources showed little variations during the observations. However, in LMC X-1 some X-ray color dependence on intensity is apparent, indicating a hardening of the spectrum in the second half of the observation. The inner disk radius and temperature change, featuring the same (anti)correlation found in RXTE data. QPOs were searched for. In LMC X-3 none was detected; in LMC X-1 a 3 σ upper (≃9% rms) limit is given at 0.07 Hz, the frequency of the QPO discovered with Ginga.