Response of circumnuclear water masers to luminosity changes in an active galactic nucleus

Abstract

Circumnuclear water masers can respond in two ways to changes in the luminosity of an active galactic nucleus. First, an increase in the X-ray luminosity can lead to an increase in the maser emissivity; and second, an increase in the intrinsic bolometric luminosity may result in a temporary decrease in the difference between the gas and dust temperature and a consequent decrease in the maser output. Whilst the latter effect can occur over a period shorter than the thermal timescale, the former effect cannot. Quantitative estimates of the response of the water maser emissivity to changes in either the X-ray or bolometric luminosity are presented, together with estimates of the relevant timescales. Either mechanism could account for recent observations by Gallimore et al. which suggest that the water maser variability in two widely separated regions of the circumnuclear gas in NGC 1068 have been coordinated by a signal from the active nucleus. For either mechanism, a minimum H2 density ~ 1.E+8 cm-3 is needed to explain the observed variability timescale.

12 pages (AASTeX), including 4 figures. Accepted for publication in ApJ Letters

References in corpus (1)

• Observational Evidence for Massive Black Holes in the Centers of Active Galaxies

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• Enhancing the H2O Megamaser Detection Rate Using Optical and Mid-infrared Photometry
• Water masers in dusty environments
• High Sensitivity Observations of the Water Megamasers of NGC 1068: Precise Astrometry and Detailed Kinematics
• Theory and Extragalactic Masers