TY - JOUR
T1 - A duty cycle hypothesis for the central engines of LINERs
AU - Eracleous, Michael
AU - Livio, Mario
AU - Binette, Luc
N1 - Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 1995/5/20
Y1 - 1995/5/20
N2 - A recent ultraviolet snapshot imaging survey of the nuclei of nearby galaxies detected a compact nuclear ultraviolet source in only five of the 26 LINERs (low-ionization nuclear emission-line regions) included in the observed sample. Motivated by this observational result, we examine the possibility that all LINERs are powered by photoionization from a nuclear source, which is, however, active only for 20% of the time. We show that the decay times of low-ionization species can be of the order of one to a few centuries, and we demonstrate through time-dependent photoionization calculations that if the nuclear ionizing source is active for only a fraction of the time, this would not be readily noticeable in the emission-line spectrum. We suggest that the activity cycle is related to episodic accretion events which are associated with the tidal disruption of stars by a central black hole. The time interval between tidal disruptions is of the same order as the emission-line decay time, with the accretion episode following each disruption lasting a few decades. These estimates appear to support the duty cycle hypothesis. Some observational consequences of the proposed scenario are also discussed.
AB - A recent ultraviolet snapshot imaging survey of the nuclei of nearby galaxies detected a compact nuclear ultraviolet source in only five of the 26 LINERs (low-ionization nuclear emission-line regions) included in the observed sample. Motivated by this observational result, we examine the possibility that all LINERs are powered by photoionization from a nuclear source, which is, however, active only for 20% of the time. We show that the decay times of low-ionization species can be of the order of one to a few centuries, and we demonstrate through time-dependent photoionization calculations that if the nuclear ionizing source is active for only a fraction of the time, this would not be readily noticeable in the emission-line spectrum. We suggest that the activity cycle is related to episodic accretion events which are associated with the tidal disruption of stars by a central black hole. The time interval between tidal disruptions is of the same order as the emission-line decay time, with the accretion episode following each disruption lasting a few decades. These estimates appear to support the duty cycle hypothesis. Some observational consequences of the proposed scenario are also discussed.
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U2 - 10.1086/187875
DO - 10.1086/187875
M3 - Article
AN - SCOPUS:79960835596
SN - 0004-637X
VL - 445
SP - L1-L5
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1 PART 2
ER -