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Using the JVLA, we explored the Galactic center (GC) with a resolution of0.05" at 33.0 and 44.6 GHz. We detected 64 hyper-compact radio sources (HCRs)in the central parsec. The dense group of HCRs can be divided into threespectral types: 38 steep-spectrum ($\alpha\le-0.5$) sources; 10 flat-spectrum($-0.5<\alpha\le0.2$) sources; and 17 inverted-spectrum sources having$\alpha>0.2$, assuming $S\propto\nu^\alpha$. The steep-spectrum HCRs are likelyrepresent a population of massive stellar remnants associated with nonthermalcompact radio sources powered by neutron stars and stellar black holes. Thesurface-density distribution of the HCRs as function of radial distance ($R$)from Sgr~A* can be described as a steep power-law $\Sigma (R) \proptoR^{-\Gamma}$, with $\Gamma=1.6\pm0.2$, along with presence of a localizedorder-of-magnitude enhancement in the range 0.1-0.3 pc. The steeper profile ofthe HCRs relative to that of the central cluster might result from theconcentration massive stellar remnants by mass segregation at the GC. The GCmagnetar SGR~J1745-2900 belongs to the inverted-spectrum sub-sample. We findthat two spectral components present in the averaged radio spectrum ofSGR~J1745-2900, separated at $\nu\sim30$ GHz. The centimeter-component isfitted to a power-law with $\alpha_{cm}=-1.5\pm0.6$. The enhancedmillimeter-component shows a rising spectrum $\alpha_{mm}=1.1\pm0.2$. Based onthe ALMA observations at 225 GHz, we find that the GC magnetar is highlyvariable on a day-to-day time scale, showing variations up to a factor of 6.Further JVLA and ALMA observations of the variability, spectrum, andpolarization of the HCRs are critical for determining whether they areassociated with stellar remnants.

Detection of a dense group of hyper-compact radio sources in the central parsec of the Galaxy