Authors: The Event Horizon Telescope Collaboration et al.
Date: May 12, 2022
Primary Reference: The Event Horizon Telescope Collaboration, et al. 2022b, ApJL, 930, L13 (Sgr A* Paper II)
Data Product Code: 2022-D02-01
Brief Description:
We release a data set to accompany the First Sagittarius A* Event Horizon Telescope Results paper series (EHT Collaboration et al. 2022a,b,c,d,e,f). 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). It is made public simultaneously with four imaging pipelines (2022-D02-02, EHT Collaboration et al. 2022c).
This data set contains Sagittarius A* (Sgr A*) data for both low and high bands for two observed days (April 6th and 7th, 2017). Data from the 2017 observations were processed through two independent reduction pipelines (Blackburn et al. 2019, Janssen et al. 2019, M87 Paper III, and Sgr A* Paper II, Paper III). This release includes the fringe fitted, a-priori calibrated, network calibrated data from both the EHT-HOPS and rPICARD (CASA) pipelines, which are used in the First Sgr A* EHT results. 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). All polarization information
is explicitly removed. To make the resulting uvfits files
compatible with popular very-long-baseline interferometry (VLBI)
software packages, the circularly polarized cross-hand visibilities
RL and LR are set to zero along with their errors, while
parallel-hands RR and LL are both set to an estimated Stokes I
value. Measurement errors for RR and LL are each set to sqrt(2)
times the statistical errors for Stokes I.
All uvfits files are located in the "uvfits*/" subdirectory.
Easy-to-read csv and txt files are derived from the uvfits files
and provided in "csv*/" and "txt*/", respectively. Scripts that
generate these files from the processed ER6 data are also included.
Finally, the run.sh script in the top directory will convert
uvfits files into csv and txt files.
In addition to the visibility data sets after the above calibrations
in uvfits/*, csv/*, and text/* directories, we have prepared two
additional data sets. The first additional data set is
lightcurve-normalized data in the uvfits_norm/*, csv_norm/* and
text_norm/* directories, where each of visibility amplitudes is
normalized by the total flux density from the Sgr A*'s light curve
at the corresponding time (Wielgus et al. 2022). These are the data
files used by all Sgr A* static imaging pipelines in Paper III.
The second additional data set consists of am 100-minute interval of
visibility data cropped from the original (unnormalized) full-night
visibilities. During this 100-minute interval of time the EHT array
has the best snapshot uv-coverages (see Farah et al. 2022 and Paper
III). This data set is used in the analysis of short-time-scale
dynamic properties of Sgr A* in Paper III.
The three tgz files are gzipped tarballs that contains uvfits,
txt, and csv files, respectively. They are included in this
repository for convenience.
File Name Convention:
The data files are named in the following convention:
[Data-Release-Tag]_[Source]_[year]_[day-of-year]_[band]_[pipeline]_[stage]_StokesI.[format]
Station Code Table:
| UVFITS Code | Station Name | Location |
|---|---|---|
| AA | ALMA | Chile |
| AP | APEX | Chile |
| AZ | Submillimeter Telescope | Arizona |
| JC | James Clerk Maxwell Telescope | Hawai'i |
| LM | Large Millimeter Telescope | Mexico |
| PV | IRAM | Spain |
| SM | Submillimeter Array | Hawai'i |
| SP | South Pole Telescope | Antarctica |
References:
- EHT Collaboration Data Portal Website
- The Event Horizon Telescope Collaboration, et al. 2019a, ApJL, 875, L1 (M87 Paper I)
- The Event Horizon Telescope Collaboration, et al. 2019b, ApJL, 875, L2 (M87 Paper II)
- The Event Horizon Telescope Collaboration, et al. 2019c, ApJL, 875, L3 (M87 Paper III)
- The Event Horizon Telescope Collaboration, et al. 2019d, ApJL, 875, L4 (M87 Paper IV)
- The Event Horizon Telescope Collaboration, et al. 2019e, ApJL, 875, L5 (M87 Paper V)
- The Event Horizon Telescope Collaboration, et al. 2019f, ApJL, 875, L6 (M87 Paper VI)
- Blackburn, L., Chan, C.-k., Crew, G., et al. 2019, ApJ, 882, 23
- Janssen, M., Goddi, C., van Bemmel, I., et al. 2019, A&A, 626A, 75
- Issaoun, S., Folkers, T., Blackburn, L., et al. 2017, EHT Memo 2017-CE-02
- Janssen, M., Blackburn, L., Issaoun, S., et al. 2019, EHT Memo 2019-CE-01
- Wielgus, M., Blackburn, L., Issaoun, S., et al. 2019, EHT Memo 2019-CE-02
- The Event Horizon Telescope Collaboration, et al. 2022a, ApJL, 930, L12 (Sgr A* Paper I)
- The Event Horizon Telescope Collaboration, et al. 2022b, ApJL, 930, L13 (Sgr A* Paper II)
- The Event Horizon Telescope Collaboration, et al. 2022c, ApJL, 930, L14 (Sgr A* Paper III)
- The Event Horizon Telescope Collaboration, et al. 2022d, ApJL, 930, L15 (Sgr A* Paper IV)
- The Event Horizon Telescope Collaboration, et al. 2022e, ApJL, 930, L16 (Sgr A* Paper V)
- The Event Horizon Telescope Collaboration, et al. 2022f, ApJL, 930, L17 (Sgr A* Paper VI)
- Wielgus, M., Marchili, N., Marti-Vidal, I., Keating, G.K., Ramakrishnan, V., et al. 2022, ApJL, 930, L19