EHT M87 Polarized Data

We release a calibrated polarimetric data set to accompany the First M87 Event Horizon Telescope Polarization Results paper series (EHT Collaboration et al. 2021a,b, 2023, see the README.md file for full references). It consists of 24 data sets covering the 4 observing days (April 5,6,10,11), two frequency bands (high and low) and two calibration pipelines (HOPS and CASA). All datasets include absolute EVPA calibration from ALMA and parallactic angle rotation. We provide two versions of the HOPS calibrated data. The base version ("\*_hops_ALMArot.uvfits") has no D-term calibration applied. The second version ("\*_hops_zbl-dtcal+selfcal") has zero-baseline-derived D-terms (covering ALMA, APEX, SMA, and JCMT) corrected, but the remaining stations are not corrected. In addition, this version has all visibility amplitudes and phases self-calibrated to fiducial images Stokes I images of M87 from the SMILI pipeline (EHTC+ Paper IV, 2019). Both versions of the HOPS data have had the relative R/L complex gains calibrated with a global, multi-source fit (Steel+ 2019). The CASA data has had all​ D-terms corrected to their reported values in EHTC+ Paper VII, 2021. It has not been self-calibrated. The R/L complex gains have been calibrated assuming the intrinsic Stokes V visibilities are zero.