Among the neutron stars, objects that can contain half a million times the mass of Earth in a diameter of about twenty kilometers, stands a small group with the most intense magnetic field known: the magnetars.
These rare objects – barely thirty were detected – suffer violent eruptions, of which little is known, due to their unexpected nature and their short duration, of only tenths of a second.
A scientific group led by the Andalusia Institute of Astrophysics (IAA-CSIC) publishes today in the magazine Nature the study of an eruption in detail, as they were able to measure different oscillations (or pulses) in your glow that occur during moments of greatest energy. These oscillations are a crucial component in understanding giant magnetar explosions.
“Even in an inactive state, magnetars can be a hundred thousand times more luminous than our Sun”, he emphasizes. Alberto J. Castro-Tirado, IAA researcher who heads the work. “In the case of the flash we studied, GRB200415, which took place on April 15, 2020 and lasted only about a tenth of a second, the energy released is equivalent to the energy radiated by our Sun in a hundred thousand years”, emphasizes the researcher.
The observations revealed multiple pulses, with the first appearing only about tens of microseconds, much faster than other extreme transients, the authors note.
In the case of the flash we studied, GRB200415, which occurred on April 15, 2020 and lasted only about a tenth of a second, the energy that was released is equivalent to the energy that our Sun radiates in a hundred thousand years.
Alberto J. Castro-Tirado (IAA-CSIC)
It is believed that eruptions in magnetars may be due to instabilities in their magnetosphere or to a kind of earthquake produced in its crust, a layer of a rigid and elastic character about a kilometer thick.
“Regardless of the trigger, a type of waves will be created in the star’s magnetosphere, the Alfvén waves, which are well known in the Sun and which, as they bounce back and forth between points at the base of their magnetic field lines, interact with each other, dissipating energy”, explains Castro-Tirado.
ASIM instrument with which the event was detected. / NASA
The oscillations detected in the eruption are consistent with the emission produced by the interaction between the Alfvén waves, whose energy is quickly absorbed by the crust. So, in a few milliseconds, the process of magnetic reconnection and therefore also the pulses detected in GRB200415, which disappeared just 3.5 milliseconds after the main burst.
The analysis of the phenomenon allowed us to estimate that the volume of the flare was similar or even greater than that of the neutron star itself.
One year studying the sign
The eruption was detected by the instrument AH YES, on board the International Space Station, which was the only one of a total of seven able to record the main phase of the eruption in its entire energy range without suffering saturation.
ASIM is a mission of the European Space Agency, with strong Spanish participation, led by Valencia University it’s him National Institute of Aerospace Technology (INTA)
The scientific team managed to solve the temporal structure of the event, a truly complex task that involved more than a year of analysis for one second of data.
The scientific team managed to solve the temporal structure of the event, a truly complex task that involved more than a year of analysis for one second of data.
“The detection of quasi-periodic oscillations in the GRB200415 has been a challenge from a signal analysis point of view. The difficulty lies in the brevity of the signal, whose amplitude decays quickly and is embedded in the background noise. Correlated noise, it is difficult to distinguish the signal from the noise “indicates Javier Pascual, IAA-CSIC researcher who participated in the work.
“We therefore owe this achievement to the sophisticated data analysis techniques that were applied independently by the various team members, but it is also, without a doubt, a technological achievement due to the excellent quality of the data provided by the ASIM instrument aboard the Station. International Space, “adds Pascual.
The most distant magnetar ever observed
These flames were detected in two of the thirty known magnetars in our galaxy, the Milky Way, but also in two others located in other galaxies. GRB2001415 would be the eruption in a magnetar Further captured so far, being in the group of sculptor galaxies about thirteen million light years away.
“This eruption provided a crucial component to understanding how magnetic stresses are produced in and around a neutron star. The continuous monitoring of magnetars in nearby galaxies will help to understand this phenomenon and will also open the way to learn more about fast radio bursts, one of the most enigmatic phenomena in astronomy today”, concludes the researcher.
In addition to researchers from the IAA and the University of Valencia, scientists from the universities of Cádiz and Malaga participated in this work, also using data from the robotic telescope network BOOTES and the Gran Telescopio Canarias.
Reference:
castro-drawn et al. “Very high frequency oscillations at the main peak of a giant magnetar flame”. Nature, 2021.
Rights: Creative Commons.
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