December 2020 saw the "grand conjunction" between Saturn and Jupiter, a rare phenomenon in which the planets could be observed very close together in the same field of sky. This astronomical event aroused the interest of astronomers the world over, and gave rise to numerous observation campaigns.
It was against this backdrop that an international scientific team, led by Oleg Smirnov, professor at the Rhodes Centre for Radio Astronomy Techniques & Technologies (RATT) in South Africa, and including an astronomer from Observatoire de Paris - PSL, pointed the MeerKAT radio telescope of the South African Radio Astronomy Observatory (SARAO) at the area of sky concerned.
And then, surprise : in the field of view, in the vicinity of Saturn, a completely unexpected radio source suddenly came on, lasting for around 45 minutes, before going off again.
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Such sources, known as "transients", are very rare and therefore scientifically interesting.
Over the following months, the intrigued scientists reused MeerKAT several times, succeeding in characterizing the radio emission as the signature of a variable pulsar.
At this stage of the work, it was a method developed at Observatoire de Paris - PSL that provided crucial information about the signal, in particular its polarization state.
A previously unrecorded object
While pulsars are well known and counted by the thousands, this one stands out for its exceptional radio behavior, with signal amplifiers reaching, in just a few minutes, up to 100 times the luminosity usually recorded for this type of object.
This factor of 10 or more has earned it a new name in pulsar nomenclature. The scientific team has christened it "PARROT", an acronym for "pulsar with anomalous refraction recurring on odd timescales".
Pulsars, and other very compact radio objects, often exhibit variations due to scintillation in the solar wind and interstellar medium. This radio scintillation is not very different from the "twinkling" of stars when observed optically through the atmosphere.
But no scintillation effect can make a star brighter by more than a factor of ten ! This phenomenon of extreme radio amplification, known as "lensing", over such short periods, is unprecedented.
The mechanisms underlying this phenomenon are as yet unknown. They could be explained by unusual structures in the solar wind, or by dense plasma in the pulsar’s environment. Research avenues are currently being explored.
Indeed, the discovery of the PARROT pulsar demonstrates MeerKAT’s potential to multiply such discoveries of transient phenomena and other cosmic variables in the future. The scientific community has high hopes and expectations for these new revelations.
Reference
This discovery is detailed in an article entitled "The RATT PARROT : Serendipitous Discovery of a Peculiarly Scintillating Pulsar in MeerKAT Imaging Observations of the Great Saturn-Jupiter Conjunction of 2020", published in the journal MNRAS, February 21, 2024.