Are there advection-dominated accretion flows in nearby giant elliptical galaxies?

Recently, it has been suggested that the hard X-ray power-law tails exhibit ed in the ASCA spectra of several nearby giant elliptical galaxies are caus ed by low radiative efficiency accretion flows (advection-dominated accreti on flows [ADAFs]) onto a massive black hole in the centers of the galaxies. The estimated fluxes from these central ADAFs as derived from the ASCA X-r ay spectral analyses indicate that they may be visible as X-ray point sourc es. We analyze archival ROSAT HRI images of three such galaxies, NGC 1399, 4636, and 4696, to determine whether X-ray point sources consistent with AS CA-derived fluxes are present in the centers of the galaxies. We find that the upper limit for the flux of a central X-ray point source in each of the se galaxies, as determined by the ROSAT HRI data, is only marginally consis tent with the predicted flux inferred from the ASCA spectra. We suggest tha t although a central point source, such as an ADAF associated with a massiv e black hole, cannot be completely ruled out, they can only account for a f raction of the flux of the observed hard X-ray power-law components.