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 x 10(39) and 5 x 10(41) ergs s(-1), 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 H alpha emission in their optical spectra (LINER Is) are proportional to their H alpha luminosities. This correlation strongly supports the hypothesis that the dominant ionizing source in LINER Is is photoionization by hard photons from low-luminosity active galactic nuclei (AGNs). On the other hand, the X-ray luminosities of most LINERs without broad H alpha emission (LINER 2s) in our sample are lower than LINER is 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 other than an AGN, or that an AGN, if present, is obscured even at energies above 2 keV.