A comparison between the X-ray properties of LINERs LLAGNs and normal galaxies

I reviewed recent X-ray observations of LINERs and low luminosity AGNs (LLAGNs) with the Japanese X-ray satellite ASCA. The main purpose of the ASCA observations was to reveal the X-ray properties of these galaxies, especially nuclear activity. ASCA observed 15 LLAGNs and found nuclear X-ray emission for 13 LLAGNs except NGC 1672 and NGC 4501. On the other hand, compact hard X-ray emission probably associated with nuclear activity was found in seven LINERs, and six LINERs among seven have a broad H alpha line. This result suggests that the excitation mechanism of these LINERs is photoionization. Soft X-ray emission from LINERs was found, and the emission can be associated with the starburst phenomenon in LINERs I characterized the variability time scale using the Fourier timing analysis and deduced the lower limit of central black hole mass. The black hole masses are greater than 10(7) solar mass, which are consistent with those of high luminosity AGNs. However, the,X-ray luminosity of LLAGNs and LINERs are only 1/1000 of that of high-luminosity AGNs. This indicates that LLAGNs and LINERs may turn into AGNs if fuel is supplied to the central black hole. (C) 1999 COSPAR. Published by Elsevier Science Ltd.