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      Detection of a Dense Group of Hypercompact Radio Sources in the Central Parsec of the Galaxy

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      The Astrophysical Journal Letters
      American Astronomical Society

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          Abstract

          Using the JVLA, we explored the Galactic center (GC) with a resolution of 0.″05 at 33.0 and 44.6 GHz. We detected 64 hypercompact radio sources (HCRs) in the central parsec. The dense group of HCRs can be divided into three spectral types: 38 steep-spectrum ( α ≤ −0.5) sources, 10 flat-spectrum (−0.5 < α ≤ 0.2) sources, and 17 inverted-spectrum sources having α > 0.2, assuming Sν α . The steep-spectrum HCRs are likely to represent a population of massive stellar remnants associated with nonthermal compact radio sources powered by neutron stars and stellar black holes. The surface-density distribution of the HCRs as a function of radial distance ( R) from Sgr A* can be described as a steep power law Σ( R) ∝ R −Γ, with Γ = 1.6 ± 0.2, along with the presence of a localized order-of-magnitude enhancement in the range 0.1–0.3 pc. The steeper profile of the HCRs relative to that of the central cluster might result from the concentration of massive stellar remnants by mass segregation at the GC. The GC magnetar SGR J1745−2900 belongs to the inverted-spectrum subsample. We find two spectral components present in the averaged radio spectrum of SGR J1745−2900, separated at ν ∼ 30 GHz. The centimeter component is fitted to a power law with α cm = −1.5 ± 0.6. The enhanced millimeter component shows a rising spectrum α mm = 1.1 ± 0.2. Based on the ALMA observations at 225 GHz, we find that the GC magnetar is highly variable on a day-to-day timescale, showing variations up to a factor of 6. Further JVLA and ALMA observations of the variability, spectrum, and polarization of the HCRs are critical for determining whether they are associated with stellar remnants.

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          ChandraX‐Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy

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                Author and article information

                Contributors
                Journal
                The Astrophysical Journal Letters
                ApJL
                American Astronomical Society
                2041-8205
                2041-8213
                March 01 2022
                March 01 2022
                March 01 2022
                March 01 2022
                : 927
                : 1
                : L6
                Article
                10.3847/2041-8213/ac54be
                e3a3c482-f116-40a9-9843-7a091e32fd03
                © 2022

                http://creativecommons.org/licenses/by/4.0/

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