EPISODE · Jun 10, 2026 · 20 MIN
FRB 20191221A or "the telescope that hallucinated in the rain"
from Multi-messenger astrophysics · host Astro-COLIBRI
In 2022, the astronomy community was buzzing about FRB 20191221A, an unusual Fast Radio Burst that made headlines for exhibiting a highly significant 217-millisecond periodicity. But what if this groundbreaking extragalactic signal actually originated from our own cosmic backyard? In today's episode, we dive into a fascinating course-correction by the CHIME/FRB Collaboration. We explore how a "series of unfortunate events" led the team to misclassify what turned out to be a known Galactic pulsar, PSR J0248+6021. The true culprit behind the mix-up was the weather: heavy rain on December 21, 2019, caused water to pool in the telescope's electronics, which corrupted the calibration data. This error generated a massive 20-degree pointing offset in the declination. Because the telescope assigned the bursts to the wrong location, the pulsar's high Dispersion Measure (DM) made it artificially appear as though it was an extragalactic FRB. Join us as we discuss how the team unraveled the mystery after discovering "twin bursts" at different coordinates, how the pulsar's unusual emission pattern disguised its true identity, and the new diagnostic checks CHIME has implemented to guarantee the accuracy of their wider FRB catalog. Article Reference:- A series of unfortunate events: CHIME/FRB misclassification of a Galactic pulsar as a periodic fast radio burst by The CHIME/FRB Collaboration (Bridget C. Andersen, Mohit Bhardwaj, P. J. Boyle, et al.).Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Danielle Futselaar
What this episode covers
In 2022, the astronomy community was buzzing about FRB 20191221A, an unusual Fast Radio Burst that made headlines for exhibiting a highly significant 217-millisecond periodicity. But what if this groundbreaking extragalactic signal actually originated from our own cosmic backyard? In today's episode, we dive into a fascinating course-correction by the CHIME/FRB Collaboration. We explore how a "series of unfortunate events" led the team to misclassify what turned out to be a known Galactic pulsar, PSR J0248+6021. The true culprit behind the mix-up was the weather: heavy rain on December 21, 2019, caused water to pool in the telescope's electronics, which corrupted the calibration data. This error generated a massive 20-degree pointing offset in the declination. Because the telescope assigned the bursts to the wrong location, the pulsar's high Dispersion Measure (DM) made it artificially appear as though it was an extragalactic FRB. Join us as we discuss how the team unraveled the mystery after discovering "twin bursts" at different coordinates, how the pulsar's unusual emission pattern disguised its true identity, and the new diagnostic checks CHIME has implemented to guarantee the accuracy of their wider FRB catalog. Article Reference:- A series of unfortunate events: CHIME/FRB misclassification of a Galactic pulsar as a periodic fast radio burst by The CHIME/FRB Collaboration (Bridget C. Andersen, Mohit Bhardwaj, P. J. Boyle, et al.).Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: Danielle Futselaar
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FRB 20191221A or "the telescope that hallucinated in the rain"
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