When Clusters Collide and Telescopes Misbehave: My Life as a Radio Astronomer

Abstract:
When galaxy clusters collide at thousands of kilometers per second, they create cosmic particle accelerators spanning millions of light years, driving shocks that accelerate particles and amplify magnetic fields to produce diffuse radio emissions revealing the invisible architecture of these extreme environments. I’ll present low-frequency polarization observations of merging galaxy clusters using the upgraded Giant Metrewave Radio Telescope (uGMRT), supported by X-ray and high-frequency radio data from VLA and MeerKAT.

Surprisingly, we found that low-frequency polarization does not follow high-frequency predictions, with depolarization inconsistent with single-component magnetic field models. We present the first linear polarization detection below 1 GHz requiring multicomponent magnetic field distribution, challenging conventional shock compression models in radio relics. However, reliable polarization extraction proved challenging due to mysterious time-variable instrumental effects initially appearing astrophysical. Extensive systematic investigation of the telescope’s signal chain – involving months of debugging, testing individual components from feeds to correlators, and eliminating potential sources one by one – eventually identified an unexpected instrumental culprit responsible for these anomalous signals.

This detective work highlights how instrumental systematics can masquerade as cosmic phenomena and I will walk through this technical adventure. To handle the massive data volumes from modern radio surveys, we developed “Charizard,” a fast radio imaging pipeline using aggressive parallelization strategies that processes terabytes of interferometric data orders of magnitude faster than traditional approaches. This speed enables more iterative analysis, better systematics characterization, and the ability to tackle larger statistical samples of merger systems.

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