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Session 20 -- Mergers, Masers and Megamasers

Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[20.05] Periodic Variations of the Water Vapor Maser Source in the Galaxy NGC 4258

The water vapor maser feature at a velocity of 465 km/s in the galaxy NGC 4258 has shown strong variability with a period of 85 days during the time interval 1988 August to 1989 July. During this period the velocity of the spectral features steadily shifted upward at a rate of 6 km /s/yr. Monitoring NGC 4258 from 1986 to the present shows that all individual features shift in velocity at the same rate, while they also vary in strength. We report on the periodicities seen in the NGC 4258 spectral data since July 1989. Besides the NGC 4258 monitoring data, we also present results for IC 10-SE and NGC 3079. Both galaxies have flared recently. During the powerful IC 10-SE flare, a single feature became 16 to 90 times more powerful than Galactic supermaser outbursts. The data for NGC 4258, IC 10, and NGC 3079 support a foreground amplification model of background radio continuum.

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