2001/04/18 by J. M. Wrobel, C. D. Fassnacht, L. C. Ho
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #astro-ph
paper · pdf · doi:10.1086/320508
with 3 figures, to appear in the Astrophysical Journal Letters
arxiv created 2001/04/18 · openalex publication_date 2001/05/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
The NRAO Very Long Baseline Array (VLBA) was used at 1.4 GHz to image the inner 550 mas (23 lt-yr) of the nearest known Seyfert 1 nucleus, in the Sm galaxy NGC 4395. One continuum source was detected, with flux density 530 ± 130 μJy, diameter d < 11 mas (0.46 lt-yr), and brightness temperature T b > 2.0 × 10 6 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 T b , 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.