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J.M. Wrobel, C.D. Fassnacht (NRAO), L.C. Ho (OCIW)
The NRAO VLBA was used at 1.4~GHz to image the inner 550~mas (23~lt-years) of the nearest known Seyfert~1 nucleus, in the Sm galaxy NGC\,4395. One continuum source was detected, with flux density 530±30~\muJy, diameter d < 11~mas (0.46~lt-year), and brightness temperature T\rm b > 2.0\times106~K. The spectral power P\/ of the VLBA source is intermediate between those of Sagittarius\,A and Sagittarius\,A* in the Galactic Center. For the VLBA source in NGC\,4395, the constraints on Tb, d\/, and P\/ are consistent with an origin from a black hole but exclude an origin from a compact starburst or a supernova remnant like Cassiopeia\,A. Moreover, the spectral powers of NGC\,4395 at 1.4 and 4.9~GHz appear to be too low and too constant to allow analogy with SN\,1988Z, a suggested prototype for models of compact supernova remnants. The variable and warm X-ray absorber in NGC\,4395 has a free-free optical depth much larger than unity at 1.4~GHz and, therefore, cannot fully cover the VLBA source. NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
The author(s) of this abstract have provided an email address for comments about the abstract: jwrobel@nrao.edu