Analysis Challenge #2

Welcome to the second ngEHT analysis challenge. The first analysis challenge successfully tested our framework for generating synthetic ngEHT data based on hypothetical array configurations and collecting submitted reconstructions. In our second challenge, we move to a more scientific challenge using dynamical models of SgrA* and M87, while testing the capabilities of ngEHT at making movies of black holes on our primary science targets.

We invite participants to submit image reconstructions from a total of eight synthetic datasets. Additionally, results from any non-imaging analysis are also welcome, as well as an evaluation on the challenge. This challenge includes two dynamical total-intensity source models for SgrA*: one based on GRMHD simulations and one using a sheared hot-spot model on top of a stationary RIAF semi-analytic source. It also includes a dynamical GRMHD model of M87 with simulated observations taken over several months. Simulated observations are taken at two distinct frequencies (230 and 345 GHz) using a hypothetical ngEHT array including the current EHT and 10 additional stations (ngeht_ref1 and eht_2022). Participants are requested to submit results as images or image sequences (for a dynamical model) to the ngEHT challenge website. Submissions before Nov 1st will be able to be considered by the time of the ngEHT November science meeting (Nov 1-5, 2021). Please note that unless otherwise specified, all source models and data products should be kept proprietary among those currently invited to participate in the challenge, which includes all EHT Collaboration members, and any members of ngEHT science and technical working groups.

The information below is (partly) published in our Galaxies paper.

Table of Contents

Communicating with the organizers

The primary way to talk to the challenge organizers is the private analysis-challenge-1 channel on the ngEHT-2021 Slack. If you need an invite to the Slack or to the channel, please contact Greg at glindahl ZAT cfa.harvard.edu. We're also happy to help people with software installation advice.

Schedule

Downloads

Please note that unless otherwise specified, all source models and data products should be kept proprietary among those currently invited to participate in the challenge, which includes all EHT Collaboration members, and any members of ngEHT science and technical working groups.

Downloads are password protected: the username is challenge1 (yes, it's still challenge1 for the second challenge!) and the secret password is available if you ask on Slack, on the analysis-challenge-1 channel on the ngEHT-2021 Slack.

Challenge 2 Downloads

Submit your results

If you have any problems with this upload, please contact Greg Lindahl on slack or email at glindahl ZAT cfa.harvard.edu




Submissions

Images

Please submit your (dynamical) images as FITS files bundled in a zip file as specified below. The images can be reconstructed with any field of view or pixel resolution, as long as this is clear from the FITS header. If you can, submit an image or movie for each source model, frequency, and array. For the M87 datasets and the ngeht_ref1 Sgr A* datasets, you may also analyze the 86, 230 and 345 GHz data jointly. For Sgr A*, please submit your best estimate of the intrinsic source structure (i.e. after any scattering mitigation). You may submit multiple images reconstructed using different methods; please follow the filename conventions as specified below. We will be using eht-imaging to load and evaluate the images, so it may be worth checking if your image loads properly in eht-imaging.

Non-imaging results

If you have performed analysis other than imaging (e.g., fit a geometric model, measured the black hole mass or spin, or constrained plasma parameters), please provide a text file summarizing your method and results. These results will not be formally compared or analyzed, but could certainly provide us with valuable insights.

Evaluation

It would be helpful but not required to add a txt file summarizing your experience with this challenge. Think of questions like:

Filename conventions

For the zip files, use the format challenge2_[firstnamelastname].zip.

Example: challenge2_freekroelofs.zip

For each combination, make a folder challenge2_[source]_[subtype]_[array]_[frequency]_[method]_[firstnamelastname]

Example: challenge2_SGRA_GRMHD_eht2022_230_ehtim_freekroelofs

Within the folder, put the FITS images sorted by frame number, e.g. 0000.fits, 0001.fits, etc. Also provide the start time in hours UT and frame duration in hours in a file timestamps.txt, which for a movie starting at midnight UT with a frame duration of 10 minutes should look like:

0.00 0.16666666666667

For non-imaging results, use the format challenge2_[source]_[subtype]_[array]_[frequency]_nonimaging_[firstnamelastname].txt

Example: challenge2_SGRA_GRMHD_eht2022_230_nonimaging_freekroelofs.txt

For the evaluation, use the format challenge2_evaluation_[firstnamelastname].txt.

Example: challenge2_evaluation_freekroelofs.txt

Source models

SGRA_RIAFSPOT

This Sgr A* model is a RIAF (Broderick et al. 2016) plus shearing hotspot (Tiede et al. 2020) semi-analytical model prepared by Paul Tiede. The hotspot parameters are inspired by Gravity (2018) and the black hole spin was set to 0.1. The pixel resolution is 313x313 px, with a field of view of 315 uas. The frames are spaced ~30 seconds apart and form a 4-hour movie of a hotspot shearing and falling in, which is repeated a few times over the course of the observation. We only use the Stokes I information from the model. The raw and scattered movies are shown below.

SGRA

SGRA

SGRA_GRMHD

This Sgr A* GRMHD model was prepared by Koushik Chatterjee. The GRMHD model is a MAD model with spin 0.5. The images were ray-traced in Stokes I with BHOSS assuming thermal electrons. The 500 frames are spaced 10M (221 s) apart. The pixel resolution is 2048x2048 px, with a FOV of 400 uas. The raw and scattered movies are shown below.

SGRA_GRMHD

SGRA_GRMHD

M87_GRMHD

The M87 model is a GRMHD movie with 20 frames that are spaced 20M (~1 week) apart. The pixel resolution is 2048x2048 px, with a field of view of 1 mas x 1mas. The images were ray-traced from a HAMR simulation (MAD, spin 0.94; K. Chatterjee) using ipole by Razieh Emami. Rhigh was set to 160 and accelerated electron heating was included, setting kappa=3.5. We only use the Stokes I information from the model. The movies are shown below.

M87

Array and data synthesis

Station locations

Two arrays were used to generate the synthetic data. They are labeled eht_2022 and ngeht_ref1. eht_2022 consists of the 11 stations expected to participate in the 2022 EHT observations. In ngeht_ref1, 10 stations are added to this array. The station locations were chosen based on a uv-coverage analysis led by Alex Raymond, investigating which combination of sites from Raymond et al. (2021) provided optimal uv-coverage, folding in weather dropouts. The LMT, SPT, and KP were not included in the 345 GHz observations with eht_2022. The station locations are shown in the image below.

ngEHT ref1

Data properties

Several data corruption and calibration effects were included in the synthetic data generation, for which SYMBA (Roelofs et al. 2020) was used. See the SYMBA antenna files included in the release for detailed antenna and weather parameters.