Enhanced Imaging of M 87:Simulations with the EHT and Extended-KVN

Abstract

The Event Horizon Telescope (EHT) has successfully revealed the shadow of the supermassive black hole, M 87 & lowast;, with anunprecedented angular resolution of approximately20 mu asat230 GHz. However, because of limited short baseline lengths,the EHT has been constrained in its ability to recover larger-scale jet structures. The extended Korean VLBI Network (eKVN)is committed to joining the EHT from 2024 that can improve short baseline coverage. This study evaluates the impact of theparticipation of eKVN in the EHT on the recovery of the M 87 & lowast;jet. Synthetic data, derived from a simulated M 87 & lowast;model, wereobserved using both the EHT and the combined EHT+eKVN arrays, followed by image reconstructions from both configurations.The results indicate that the inclusion of eKVN significantly improves the recovery of jet structures by reducing residual noise.Furthermore, jackknife tests, in which one or two EHT telescopes were omitted-simulating potential data loss due to poorweather-demonstrate that eKVN effectively compensates for these missing telescopes, particularly in short baseline coverage.Multi-frequency synthesis imaging at86-230 GHzshows that the EHT+eKVN array enhances the recovered spectral indexdistribution compared to the EHT alone and improves image reconstruction at each frequency over single-frequency imaging. Asthe EHT continues to expand its array configuration and observing capabilities to probe black hole physics more in depth, theintegration of eKVN into the EHT will significantly enhance the stability of observational results and improve image fidelity. Thisadvancement will be particularly valuable for future regular monitoring observations, where consistent data quality is essential