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We propose that the ring structure found by the Event Horizon Telescope Collaboration (EHTC) as the black hole shadow of Sgr A*is an artifact by the bumpy PSF (Point Spread Function) of the EHT2017. The imaging using sparse u-v data requires detailed scrutiny of the PSF. The estimated shadow diameter (48.7 +- 7 muas) is equal to the spacing between the main beam and the first sidelobe of the PSF (49.09 muas), which immediately suggests a potential problem in the deconvolution of the PSF. We show that the ring image can be derived from non-ring simulated datasets (noise only; point source) with a narrow Field-of-View (FOV) and an assumed self-calibration suggesting the EHT2017's u-v coverage is insufficient for reliable imaging. The EHTC analysis, based on calibrations with assumptions about the source's size and properties, selected the final image by prioritizing appearance rate of the similar structure from a large imaging parameter space over data consistency. Our independent analysis with the conventional hybrid mapping reveals an elongated east-west structure, consistent with previous observations. We believe it to be more reliable than the EHTC image, due to half the residuals in normalized visibility amplitude. The eastern half is brighter, possibly due to a Doppler boost from the rapid rotating disk. We hypothesize our image shows a portion of the accretion disk about 2 to a few Rs away from the black hole, rotating with nearly 60 % of the speed of light viewed from an angle of 40 -45 degrees., Comment: 28 pages, 19 figures

JASMINE is a Japanese planned space mission that aims to reveal the formation history of our Galaxy and discover habitable exoEarths. For these objectives, the JASMINE satellite performs high-precision astrometric observations of the Galactic bulge and high-precision transit monitoring of M-dwarfs in the near-infrared (1.0-1.6 microns in wavelength). For feasibility studies, we develop an image simulation software named JASMINE-imagesim, which produces realistic observation images. This software takes into account various factors such as the optical point spread function (PSF), telescope jitter caused by the satellite's attitude control error (ACE), detector flat patterns, exposure timing differences between detector pixels, and various noise factors. As an example, we report a simulation for the feasibility study of astrometric observations using JASMINE-imagesim. The simulation confirms that the required position measurement accuracy of 4 mas for a single exposure of 12.5-mag objects is achievable if the telescope pointing jitter uniformly dilutes the PSF across all stars in the field of view. On the other hand, the simulation also demonstrates that the combination of realistic pointing jitter and exposure timing differences in the detector can significantly degrade accuracy and prevent achieving the requirement. This means that certain countermeasures against this issue must be developed. This result implies that this kind of simulation is important for mission planning and advanced developments to realize more realistic simulations help us to identify critical issues and also devise effective solutions., Comment: 13 pages, 7 figures, 1 table

Two critical aspects of radio interferometric imaging analysis are data calibration and deconvolution of the point spread function (PSF) structure. Both of these are particularly important for high-frequency observations using a VLBI network consisting of a small number of stations, such as those conducted by the Event Horizon Telescope (EHT). The Event Horizon Telescope Collaboration (EHTC) has presented images of ring-shaped black holes from observations of M 87 (d = 42 +- 3 muas)(EHTC2019a) and the Galactic Center (d = 51.8 +- 2.3 muas)(EHTC2022a). The ring structures seen in the EHTC images are consistent with the estimated shadow diameter of the black hole based on its mass and distance. However, these black hole ring sizes are also the same with the typical up and down spacings (e.g., the intervals between the main beam and nearby 1st-sidelobes) seen in the point spread function (PSF; dirty beam) for each observation. These facts suggest that the EHTC ring structures are artifacts derived from the shape of the PSFs rather than the intrinsic structure of the SMBHs in M 87 and the Galactic Center. The EHTC utilizes novel imaging techniques in addition to the standard CLEAN algorithm. The CLEAN method was designed for PSF shape deconvolution in mind, yet in practice, it may not always be able to completely remove the PSF shape. In the imaging analysis of data from interferometers with a small number of antennas like the EHT, it is crucial to assess the PSF shape and compare it with the imaging results. The novel imaging methods employed by the EHTC have not yet been fully evaluated for PSF deconvolution performance, and it is highly recommended that their performance in this regard be thoroughly examined. It is also important to investigate the data calibration capability, i.e., the ability to separate error noise from the observed data., Comment: 5 pages, 4 figures, Manuscript for the Proceedings of the 13th IVS General Meeting & 25th Anniversary held at Tsukuba, Japan, March 2024

M 87 is the best target for studying black hole accretion and jet formation. Reanalysis of the EHT public data at 230 GHz shows a core-knots structure at the center and jet features (Miyoshi et al. 2022a). We here compare this with the new results of GMVA at 86 GHz showing a spatially resolved central core (Lu et al. 2023a). There are similarities and differences between the two. At 86 GHz,"two bright regions" are seen on the ring in the core."Core-Knot-Westknot", triple structure in the 230 GHz image shows apparent appearance of two peaks similar to the "two bright regions" when convolved with the GMVA beam. This similarity suggests that both frequencies reveal the same objects in the core area. Protrusions are observed on both the south and north sides of the core at both frequencies, becoming prominent and wing-like at 230 GHz. The 86 GHz image shows a triple ridge jet structure, while the 230 GHz image shows only a bright central ridge with two roots. Both frequencies show a shade between the core and the central ridge. To detect the faint features from the EHT2017 data, we found that the use of all baseline data is essential. Using all including the ultrashort baseline data, revealed the jet and faint structures. Without the ultrashort baselines, these structures were not detectable. The lack of detection of any faint structures other than the ring in the M 87 data by the EHTC is presumably due to the exclusion of ultrashort baselines from their analysis., Comment: 17 pages, 4 figures, ApJL, Accepted 27, January, 2024