Magnetars, these neutron stars with an extremely powerful magnetic field, still remain mysterious to astronomers. However, a recent discovery made using ESA’s INTEGRAL and XMM-Newton space telescopes sheds new light on these fascinating objects. For the first time, a giant magnetar eruption has been detected outside our galaxy, in the neighboring galaxy M82.
A sudden explosion detected by INTEGRAL
On November 15, 2023, ESA’s INTEGRAL satellite spotted a sudden explosion coming from a rare object. For just a tenth of a second, a brief burst of energetic gamma rays appeared in the sky.
“ The satellite data was received at the INTEGRAL Scientific Data Center (ISDC), based on the Ecogia site of the UNIGE Department of Astronomy, from where a gamma-ray burst alert was sent to astronomers around the world, only 13 seconds after detection », explains Carlo Ferrigno, senior associate researcher at the Department of Astronomy of the Faculty of Sciences of UNIGE, PI of ISDC and co-author of the publication.
The software IBAS (Integral Burst Alert System) provided an automatic location coinciding with the galaxy M82, located 12 million light years away. This alert system was developed and is operated by scientists and engineers from UNIGE in collaboration with international colleagues.
A curious signal coming from a neighboring galaxy
“We immediately realized that this was a special alert. Gamma-ray bursts come from far away and anywhere in the sky, but this burst came from a bright galaxy nearbysays Sandro Mereghetti of the National Institute of Astrophysics (INAF-IASF) in Milan, Italy, lead author of the publication and IBAS contributor.
The team immediately asked XMM-Newton space telescope of the ESA to carry out a follow-up observation of the location of the burst as soon as possible. If it had been a short gamma-ray burst, caused by two colliding neutron stars, the collision would have created gravitational waves and would have had an afterglow in X-rays and visible light. However, the XMM-Newton observations only showed the galaxy’s hot gas and stars.
Magnetars: mega-magnetic stars, recently dead
“When stars more massive than eight times the Sun die, they explode as a supernova, leaving behind a black hole or neutron star. Neutron stars are very compact stellar remains with more than the mass of the Sun concentrated in a sphere the size of the canton of Geneva. They rotate quickly and have strong magnetic fields», explains Volodymyr Savchenko, senior associate researcher at the Department of Astronomy of the Faculty of Sciences of UNIGE and co-author of the publication.
Some young neutron stars have extremely strong magnetic fields, more than 10,000 times that of typical neutron stars. These are the magnetars. They emit energy in the form of eruptions, and sometimes these eruptions are gigantic.
INTEGRAL, a key instrument in a race against time
Eruptions of such short duration can only be captured by chance when an observatory is already pointing in the right direction. This makes it INTEGRAL with its large field of visionmore than 3000 times greater than the area of the sky covered by the Moon, so important for these detections.
Carlo Ferrigno explains: “Our automatic data processing system is very reliable and allows us to immediately alert the community.»
When unexpected observations like this are noted, INTEGRAL and XMM-Newton can be flexible in their schedules, which is essential for time-critical discoveries. In this case, if the observations had been made even a day later, there would not have been as strong evidence that it was indeed a magnetar and not a gamma-ray burst. .
Illustration caption: Artist’s impression of a magnetar. Magnetars are the cosmic objects with the strongest magnetic fields ever measured in the Universe. © ESA
Article: “A magnetar giant flare in the nearby starburst galaxy M82” – DOI: 10.1038/s41586-024-07285-4
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