Hard X-ray Emission and the Ionizing Source in LINERs

We report X-ray fluxes in the 2–10 keV band from LINERs (low-ionization nuclear emission-line regions) and low-luminosity Seyfert galaxies obtained with the ASCA satellite. Observed X-ray luminosities are in the range between 4×10 and 5×10 ergs s, which are significantly smaller than that of the “classical” low-luminosity Seyfert 1 galaxy NGC 4051. We found that X-ray luminosities in 2–10 keV of LINERs with broad Hα emission in their optical spectra (LINER 1s) are proportional to their Hα luminosities. This correlation strongly supports the hypothesis that the dominant ionizing source in LINER 1s is photoionization by hard photons from low-luminosity AGNs. On the other hand, the X-ray luminosities of most LINERs without broad Hα emission (LINER 2s) in our sample are lower than LINER 1s at a given Hα luminosity. The observed X-ray luminosities in these objects are insufficient to power their Hα luminosities, suggesting that their primary ionizing source is other than an AGN, or that an AGN, if present, is obscured even at energies above 2 keV. Subject headings: galaxies: active — galaxies: nuclei — galaxies: Seyfert — X-rays: galaxies