A duty cycle hypothesis for the central engines of LINERs

Details A duty cycle hypothesis for the central engines of LINERs A duty cycle hypothesis for the central engines of LINERs

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...445l...1e&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 445, no. 1, p. L1-L5

Astronomy and Astrophysics

Astronomy

38

Accretion Disks, Active Galactic Nuclei, Emission Spectra, Line Spectra, Photoionization, Radiation Sources, Ultraviolet Emission, Galactic Evolution, Time Dependence, Ultraviolet Astronomy

Scientific paper

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 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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