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The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak radio continuum emission at the galactic center. Quasi-simultaneous multi-frequency observations using the Very Large Array (VLA) from 5 GHz (6 cm) to 22 GHz (1.3 cm) showed inverted spectra in all epochs, which were intra-month variable, as well as complicated spectral features that cannot be represented by a simple power law, indicating multiple blobs in nuclear jets. Using the Nobeyama Millimeter Array (NMA), we discovered a large amplitude variable emission at 100 GHz (3 mm), which had higher flux densities at most epochs than those of the VLA observations. A James Clerk Maxwell Telescope (JCMT) observation at 347 GHz (850 micron) served an upper limit of dust contamination. The inverted radio spectrum of the nucleus NGC 4258 is suggestive of an analogy to our Galactic center Sgr A*, but with three orders of magnitude higher radio luminosity. In addition to the LLAGN M 81, we discuss the nucleus of NGC 4258 as another up-scaled version of Sgr A*.
The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak radio continuum component at the galactic center. We investigate its radio spectral properties on the basis of our new observations using the Nobeyama Millimeter Array at 1
In 2006 June, the obscured low luminosity active galactic nucleus in the nearby Seyfert 1.9 galaxy NGC 4258 was observed with Suzaku for ~ 100 ks. Utilizing the XIS and the HXD, the nucleus emission was detected over 2 to 40 keV range, with an unabso
We present high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; Lbol lesssim 10^42 erg/sec). Infrared (IR) observations may advance
Low-luminosity Active Galactic Nuclei, i.e. L_bol/L_edd ~ 10^-6 - 10^-3, constitute the bulk population of Active Galactic Nuclei (AGNs). Powerful jets, common in these objects, are a crucial source of feedback energy driving mass outflows into the h
Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster mediu