@article {1444446, title = {First M87 Event Horizon Telescope Results. II. Array and Instrumentation}, journal = {The Astrophysical Journal Letters}, volume = {875}, year = {2019}, pages = {2}, url = {https://iopscience.iop.org/article/10.3847/2041-8213/ab0c96}, author = {The EHT Collaboration et al.} }