The intrinsic structure of Sagittarius A* at 1.3 cm and 7 mm
Creators: name: Cho, Ilje
name: Zhao, Guang-Yao
name: Kawashima, Tomohisa
name: Kino, Motoki
name: Akiyama, Kazunori
name: Johnson, Michael D.
name: Issaoun, Sara
name: Moriyama, Kotaro
name: Cheng, Xiaopeng
name: Algaba, Juan-Carlos
name: Jung, Taehyun
name: Sohn, Bong Won
name: Krichbaum, Thomas P.
name: Wielgus, Maciek
name: Hada, Kazuhiro
name: Lu, Ru-Sen
name: Cui, Yuzhu
name: Sawada-Satoh, Satoko
name: Shen, Zhiqiang
name: Park, Jongho
name: Jiang, Wu
name: Ro, Hyunwook
name: Yi, Kunwoo
name: Wajima, Kiyoaki
name: Lee, Jee Won
name: Hodgson, Jeffrey
name: Tazaki, Fumie
name: Honma, Mareki
name: Niinuma, Kotaro
name: Trippe, Sascha
name: An, Tao
name: Zhang, Yingkang
name: Lee, Jeong Ae
name: Oh, Se-Jin
name: Byun, Do-Young
name: Lee, Sang-Sung
name: Kim, Jae-Young
name: Oh, Junghwan
name: Koyama, Shoko
name: Asada, Keiichi
name: Wang, Xuezheng
name: Cui, Lang
name: Hagiwara, Yoshiaki
name: Nakamura, Masanori
name: Takamura, Mieko
name: Hirota, Tomoya
name: Sugiyama, Koichiro
name: Kawaguchi, Noriyuki
name: Kobayashi, Hideyuki
name: Oyama, Tomoaki
name: Yonekura, Yoshinori
name: Kim, Jongsoo
name: Hwang, Ju-Yeon
name: Jung, Dong-Kyu
name: Kim, Hyo-Ryoung
name: Kim, Jeong-Sook
name: Oh, Chung-Sik
name: Roh, Duk-Gyoo
name: Yeom, Jae-Hwan
name: Xia, Bo
name: Zhong, Weiye
name: Li, Bin
name: Zhao, Rongbing
name: Wang, Jinqing
name: Liu, Qinghui
name: Chen, Zhong
Publisher: name: arXiv
Year: 2021
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Sagittarius A* (Sgr A*), the Galactic Center supermassive black hole (SMBH), is one of the best targets to resolve the innermost region of SMBH with very long baseline interferometry (VLBI). In this study, we have carried out observations toward Sgr A* at 1.349 cm (22.223 GHz) and 6.950 mm (43.135 GHz) with the East Asian VLBI Network, as a part of the multi-wavelength campaign of the Event Horizon Telescope (EHT) in 2017 April. To mitigate scattering effects, the physically motivated scattering kernel model from Psaltis et al. (2018) and the scattering parameters from Johnson et al. (2018) have been applied. As a result, a single, symmetric Gaussian model well describes the intrinsic structure of Sgr A* at both wavelengths. From closure amplitudes, the major-axis sizes are ~704$\pm$102 $μ$as (axial ratio $\sim$1.19$^{+0.24}_{-0.19}$) and $\sim$300$\pm$25 $μ$as (axial ratio $\sim$1.28$\pm$0.2) at 1.349 cm and 6.95 mm respectively. Together with a quasi-simultaneous observation at 3.5 mm (86 GHz) by Issaoun et al. (2019), we show that the intrinsic size scales with observing wavelength as a power-law, with an index $\sim$1.2$\pm$0.2. Our results also provide estimates of the size and compact flux density at 1.3 mm, which can be incorporated into the analysis of the EHT observations. In terms of the origin of radio emission, we have compared the intrinsic structures with the accretion flow scenario, especially the radiatively inefficient accretion flow based on the Keplerian shell model. With this, we show that a nonthermal electron population is necessary to reproduce the source sizes.
description: accepted to ApJ