EHT Sagittarius A* Polarized Data

We release a calibrated polarimetric data set to accompany tthe First SgrA* Event Horizon Telescope Polarization Results paper series (EHT Collaboration et al. 2024b,c). The data set is derived from the Rev7 Correlation of the Event Horizon Telescope (EHT)'s April 2017 observation campaign (EHT Collaboration et al. 2019c), with further processing and science validation as described in EHT Collaboration et al. 2022b.

This data set contains Sagittarius A* (Sgr A*) data for both low and high bands for two observed days (April 6th and 7th, 2017). This release includes the fringe fitted, a-priori calibrated, and network calibrated data from both the EHT-HOPS and rPICARD (CASA) pipelines, which are used in the First Sgr A* EHT results, with the addition of absolute EVPA calibration from ALMA, parallactic angle rotation, and D-term calibration using the M87-derived leakage solutions (EHT Collaboration et al. 2021a). Independent flux calibration is performed based on estimated station sensitvities during the campaign (Issaoun et al. 2017, Janssen et al. 2019, Wielgus et al. 2022). Data were further calibrated to apply polarimetric gains to remove R-L gain offsets, amplitude gains obtained from calibrators, amplitude gains on LMT for its rapid gain fluctuations, and phase gains on JCMT for its residual phase fluctuations. A description of the data properties, their validation, and estimated systematic errors is given in M87 Paper III and Sgr A* Paper II and Paper III with additional details in Wielgus et al. (2019) and Wielgus et al. (2022). The data are time averaged to 10 seconds and frequency averaged over all 32 intermediate frequencies (IFs). The R/L complex gains have been calibrated assuming the intrinsic Stokes V visibilities are zero.