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A duty cycle hypothesis for the central engines of LINERsA recent ultraviolet snaphsot 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 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.
Document ID
19950056271
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Eracleous, Michael
(Space Telescope Science Institute, Baltimore, Maryland United States)
Livio, Mario
(Space Telescope Science Institute, Baltimore, Maryland United States)
Binete, Luc
(Space Telescope Science Institute, Baltimore, Maryland United States)
Date Acquired
August 16, 2013
Publication Date
May 20, 1995
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 445
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A87870
Funding Number(s)
CONTRACT_GRANT: NAGW-3268
CONTRACT_GRANT: GO-3724
CONTRACT_GRANT: NAGW-2678
Distribution Limits
Public
Copyright
Other

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