CGCA Seminar – Reshma Anna Thomas

Low-Frequency Radio Transients

Reshma Anna Thomas
Netherlands Institute for Radio Astronomy, University of Amsterdam

The low-frequency radio sky (<300 MHz) remains comparatively underexplored for fast and slow transients (~ microseconds to minutes), primarily due to strong propagation effects as well as instrumental challenges. However, this regime provides unique leverage on plasma environments and emission physics that are inaccessible at GHz frequencies. Fast radio bursts (FRBs) are extragalactic coherent transients with millisecond durations, often exhibiting sub-millisecond temporal structure. I will present detections of two FRBs at 150 MHz using beamformed searches with LOFAR, which place some of the most stringent constraints to date on free–free absorption in their local environments. In parallel, a new class of Galactic sources, long-period transients (LPTs), has recently emerged, characterized by emission on second-to-minute durations and periodicities spanning minutes to hours. I will discuss two LPTs discovered with LOFAR interferometric imaging searches, highlighting their phenomenology and implications for coherent emission mechanisms in their sources. These results motivate a systematic exploration of the low-frequency transient phase space. Therefore, I will present EuroFlash, a commensal, real-time transient detection system for LOFAR 2.0. Operating on a dedicated compute cluster, EuroFlash performs parallel beamforming and imaging with low latency, enabling both discovery and localization of FRBs, LPTs and previously unrecognized classes of radio transients across a wide range of timescales. I will summarize commissioning progress and discuss how this system opens a new region of parameter space for low-frequency radio transients.