Colloquium Abstract - Natarajan - 2024Dec06

December 6, 2024

11:00am Mountain

Iniyan Natarajan (CfA)

Reference HOPS Calibration Pipeline for the Event Horizon Telescope

Abstract

The Event Horizon Telescope (EHT) is a global network of mm and sub-mm wave radio telescopes that has produced the first resolved images of the supermassive black holes M87 and Sgr A* using VLBI. The EHT-HOPS calibration pipeline extends the capabilities of the Haystack Observatory Postprocessing System (HOPS) with routines specific to the reduction of EHT observations. We present a new version of the EHT-HOPS pipeline which has been refactored with a goal to calibrate multiple years of EHT data and observations from similar VLBI arrays, providing reference calibrated data products under a common automated framework.

The EHT is heterogeneous, consisting of single-dish telescopes and phased arrays of varying designs operating under a wide range of weather conditions, with new telescopes and frequency bands added to the array every year. EHT observes at a frequency of 230 GHz (8 GHz dual-polarization bands) and, more recently, has started observing at 345 GHz, at which the atmospheric phase turbulence and attenuation due to opacity become significant, posing unique calibration challenges. An ongoing effort for a next-generation upgrade to the EHT (ngEHT) will roughly double the number of stations, observe simultaneously at multiple frequencies, and include a mode of routine regular observations with a dedicated VLBI sub-array.

The new reference HOPS calibration pipeline supports python 3.10 and HOPS versions up to 3.26, has improved post-processing performance, and a more intuitive interface between EHT-HOPS and auxiliary libraries improving code integration and reusability. It has a generalized workflow that maintains a clear distinction between code and campaign-specific metadata, updated summary plots and diagnostics and the entire framework can be deployed on SLURM clusters. New calibration features enable the handling of EHT data sans ALMA, disparate frequency configurations, and non-overlapping frequency channels. We have also implemented support for hybrid or arbitrary polarization bases anticipating the inclusion of more linear polarization receivers in the future, and have tested this feature on publicly available 2017 M87 EHT data.

I will also briefly present the plans to incorporate new features into the EHT-HOPS pipeline such as complex bandpass and full polarization calibration capabilities, and a framework for parallel, distributed data processing during calibration. The pipeline will also leverage new data formats, such as the one being developed for HOPS 4.0, to streamline data processing. With these planned improvements, we intend to use the pipeline to produce a collection of standardized HOPS calibrated data products for previous and future EHT campaigns..

Local Host: Preshanth Jagannathan