Published: Monday, 27 December 2021 23:15
The giant gamma-ray flare event, designated GRB 2001415, was emitted by a powerful magnetar in NGC 253, an active starburst galaxy approximately 11 million light-years away in the constellation of Sculptor.
“Magnetars are strongly magnetized, isolated neutron stars with magnetic fields up to around 1015 gauss, luminosities of approximately 1031-1036 ergs per second and rotation periods of about 0.3-12 seconds,” said Dr. Alberto Castro-Tirado, an astrophysicist with the Instituto de Astrofísica de Andalucía del Consejo Superior de Investigaciones Científicas (IAA-CSIC) and the Universidad de Málaga, and his colleagues.
“Very energetic giant flares from Galactic magnetars have been detected in hard X-rays and soft gamma-rays, and only one has been detected from outside our Milky Way Galaxy.”
“During such giant flares, quasi-periodic oscillations with low and high frequencies have been observed.”
Using with the Atmosphere-Space Interactions Monitor (ASIM) aboard the International Space Station, the astrophysicists detected two quasi-periodic pulsations in the main peak of the GRB 2001415 event.
During the approximately 160-ms duration of the flare, around 1046 erg equivalent energy was released, roughly the energy the Sun radiates in about 100,000 years.
“Even in an inactive state, magnetars can be one hundred thousand times more luminous than our Sun, but in the case of GRB 2001415, the energy that was released is equivalent to that which our Sun radiates in 100,000 years,” Dr. Castro-Tirado said.
“The explosion of the magnetar, which lasted approximately a tenth of a second, was discovered on April 15, 2020,” said Professor Víctor Reglero, an astrophysicist at the Universitat de València.
“Since then we have developed very intense data analysis work, since it was a 1016 Gauss neutron star and located in another galaxy. A true cosmic monster!”
According to the team, eruptions in magnetars may be due to instabilities in their magnetosphere or to a kind of ‘earthquakes’ produced in their crust, a rigid and elastic layer about a kilometer thick.
“Regardless of the trigger, a type of waves is created in the star’s magnetosphere — the Alfvén waves — which are well known in the Sun and which interact with each other, dissipating energy,” Dr. Castro-Tirado said.
“The oscillations detected GRB 2001415 are consistent with the emission produced by the interaction between Alfvén waves, whose energy is rapidly absorbed by the crust,” the authors said.
“Thus, in a few milliseconds the magnetic reconnection process ends and therefore also the pulses detected in the event, which disappeared 3.5 milliseconds after the main burst.”
“The analysis of the phenomenon has made it possible to estimate that the volume of the eruption was similar or even greater than that of the neutron star itself.”
“Although these eruptions had already been detected in two of the thirty known magnetars in our Galaxy and in some other nearby galaxies, GRB 2001415 would be the most distant magnetar eruption captured to date, being in the Sculptor group of galaxies about 11 million light years,” Professor Reglero.
“Seen in perspective, it has been as if the magnetar wanted to indicate its existence to us from its cosmic solitude, singing in the kHz with the force of a Pavarotti of a billion suns.”
The team’s paper was published in the Nature.
A.J. Castro-Tirado et al. 2021. Very-high-frequency oscillations in the main peak of a magnetar giant flare. Nature 600, 621-624; doi: 10.1038/s41586-021-04101-1
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