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 \pm 130 ~ { } \mu Jy , diameter d < 11 mas ( 0.46 lt-year ) , and brightness temperature T _ { b } > 2.0 \times 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 , can not fully cover the VLBA source .