An investigation into one of the current great mysteries of astronomy
has come to the fore thanks to a four-year observing campaign conducted at the
Jodrell Bank Observatory.
Using the
long-term monitoring capabilities of the iconic Lovell Telescope, an
international team led by Jodrell Bank astronomers has been studying an object
known as a repeating Fast Radio Burst (FRB), which emits very short duration
bright radio pulses.
Using the 32
bursts discovered during the campaign, in conjunction with data from previously
published observations, the team has discovered that emission from the FRB
known as 121102 follows a cyclic pattern, with radio bursts observed in a
window lasting approximately 90 days followed by a silent period of 67 days.
The same behaviour then repeats every 157 days.
This discovery
provides an important clue to identifying the origin of these enigmatic fast
radio bursts. The presence of a regular sequence in the burst activity could
imply that the powerful bursts are linked to the orbital motion of a massive
star, a neutron star or a black hole.
Dr Kaustubh
Rajwade of The University of Manchester, who led the new research, said: “This
is an exciting result as it is only the second system where we believe we see
this modulation in burst activity. Detecting a periodicity provides an
important constraint on the origin of the bursts and the activity cycles could
argue against a precessing neutron star.”
Repeating FRBs
could be explained by the precession, like a wobbling top, of the magnetic axis
of a highly magnetized neutron star but with current data scientists believe it
may be hard to explain a 157-day precession period given the large magnetic
fields expected in these stars.
The existence of
FRBs was only discovered as recently as 2007 and they were initially thought to
be one-off events related to a cataclysmic event such as an exploding star.
This picture partly changed once FRB 121102, originally discovered with the
Arecibo radio telescope on November 2 2012, was seen to repeat in 2016.
However, until now, no one recognised that these bursts were in fact organised
in a regular pattern.
Professor
Benjamin Stappers, who leads the MeerTRAP project to hunt for FRBs using the
MeerKAT telescope in South Africa said: “This result relied on the regular
monitoring possible with the Lovell Telescope, and non-detections were just as
important as the detections.”
In a new paper published in Monthly Notices of the Royal Astronomical
Society, the team confirm that FRB 121102 is only the second
repeating source of FRBs to display such periodic activity. To their surprise,
the timescale for this cycle is almost 10 times longer than the 16-day
periodicity exhibited by the first repeating source, FRB 180916.J10158+56,
which was recently discovered by the CHIME telescope in Canada.
“This exciting
discovery highlights how little we know about the origin of FRBs,” says Duncan
Lorimer who serves as Associate Dean for Research at West Virginia University
and, along with PhD student Devansh Agarwal, helped develop the data analysis
technique that led to the discovery. “Further observations of a larger number
of FRBs will be needed in order to obtain a clearer picture about these
periodic sources and elucidate their origin,” he added.
Journal article: https://academic.oup.com/mnras/article/495/4/3551/5840547
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