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Y. Terashima (NASA/GSFC), L.C. Ho (OCIW), A.F. Ptak (Carnegie Mellon University)
We report X-ray luminosities of 21 LINERs (low-ionization nuclear emission-line regions) and 17 low-luminosity Seyferts obtained with ASCA and discuss the ionizing source in LINERs. Most LINERs with broad H\alpha emission in their optical spectra (LINER 1s) have a compact hard X-ray source and their 2--10 keV X-ray luminosities (LX) are proportional to their H\alpha luminosities (LH\alpha). This correlation strongly supports the hypothesis that the dominant ionizing source in LINER 1s is photoionization by hard photons from low-luminosity AGNs. Although some LINERs without broad H\alpha emission (LINER 2s) have X-ray properties similar to LINER 1s, the X-ray luminosities of many LINER 2s in our sample are lower than LINER 1s at a given H\alpha luminosity. The observed X-ray luminosities in these objects are insufficient to power their H\alpha luminosities, suggesting that their primary ionizing source is something other than an AGN, or that an AGN, if present, is obscured even at energies above 2 keV. LINER 2s having small LX/LH\alpha occupy a localized region with small [OI]/H\alpha on the excitation diagram. Such LINER spectra can be reproduced by photoionization by very hot stars.