AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 50. High Angular Resolution Science with the NRAO Very Long Baseline Array
Display, Tuesday, June 1, 1999, 10:00am-7:00pm, Southwest Exhibit Hall

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[50.20] Astrometric Stability of the Radio Continuum Nucleus in the Seyfert~1 Galaxy NGC\,5548

J.M. Wrobel (NRAO), J.E. Conway (OSO), R. Terlevich (RGO)

The NRAO VLA and VLBA were used at 8.4~GHz to monitor the astrometric stability of the radio counterpart to the broad line region (BLR) in the Seyfert galaxy NGC\,5548. The position of the radio continuum nucleus was stable to an accuracy of: [1] 20~mas (6.4~pc) between VLA and VLBA observations separated by 2.4~years, [2] 20~mas (6.4~pc) between VLA and VLBA observations separated by 5.5~years, and [3] 1.8~mas (0.58~pc) between two VLBA observations separated by 3.1~years. This stability is consistent with a black hole being the ultimate energy source for the BLR. Such stability is improbable with star cluster models which treat the BLR as a compact supernova remnant and, for NGC\,5548, require a new supernova event every 1.7~years within a region of diameter 48~pc (150~mas). The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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