ESA’s Integral Detect The Gasp Of a Dead Star

In November 2023, thanks to the Integral space observatory of the European Space Agency (ESA), astronomers detected a burst of gamma-rays coming from the Galaxy M82.

Now, thanks to further studies and the use of various ground-based and space observatories to analyze the source of the powerful energy emissions, it has been confirmed that the burst was an extragalactic flare from a magnetar.

A magnetar is a particular type of neutron star, the collapsed core of a massive supergiant star, with an extremely powerful magnetic field. Some young neutron stars can have strong magnetic fields, more than 10 000 times that of a typical neutron star. These are called magnetar.

The research results have been published today in the journal Nature. The paper titled “A magnetar giant flare in the nearby starburst galaxy” was authored by Sandro Mereghetti of the Italian National Institute of Astrophysics (INAF).

The discovery

For only a tenth of a second, ESA’s Integral detected a short burst of energetic gamma-rays coming from Messier 82, a starburst galaxy 12 million light-years away in the constellation Ursa Major. The data, collected by the Integral Science Data Centre, was sent to astronomers worldwide in just 13 seconds. The Integral Burst Alert System (IBAS) software provided an automatic location of the explosion zone.

If the gamma-ray burst had been caused by the collision of two neutron stars, it would have generated gravitational waves and an afterglow in X-rays and visible light. Therefore, astronomers rapidly used the ESA’s XMM-Newton space telescope to conduct a follow-up observation of the relevant area. However, no X-rays emission was detected.

Subsequently, observations were conducted with ground-based telescopes, including the Italian Telescopio Nazionale Galileo and the French Observatoire de Haute-Provence, to detect a signal in visible light. But again nothing was found. 

Gravitational waves were also not detected by ground-based detectors such as LIGO in the USA, VIRGO in Italy, and the Japanese KAGRA. Thus, it was understood that the rare gamma-ray burst was most likely caused by a magnetar.

So far, only a few dozen magnetars have been discovered. Furthermore, in the last 50 years, only three giant flares have been detected from magnetars in our galaxy. This is the first time one has been spotted outside of the Milky Way.

Key assets for important discoveries

This discovery, in addition to the rarity of the astronomical phenomenon, provided evidence of the great flexibility of Integral and XMM-Newton. The speed of reprogramming the use of these instruments is crucial when such unexpected observations occur.

“In this case, if the observations had been performed even just a day later, we would not have such strong proof that this was indeed a magnetar and not a gamma-ray burst.”

—  Jan-Uwe Ness, ESA’s Integral Project Scientist

Launched in 2002, ESA’s Integral is the first space observatory to simultaneously observe objects in gamma rays, X-rays, and visible light. It is still today one of the most sensitive telescopes to x-rays, and it is currently the most sensitive gamma-ray observatory. Integral’s observations are mainly focused on gamma-ray bursts, black holes, and supernova explosions. The spacecraft is tarìgeted to reenter Earth’s atmosphere in 2029.

ESA’s XMM-Newton continues to provide scientists with important data and help to solve many cosmic mysteries since the 90s. Its objective is to study the most violent phenomena in the universe through the observation of X-ray sources. XMM-Newton is focused on observing active black holes, neutron stars, supernova remnants, and galaxy clusters. Designed to operate for nearly a decade, the telescope continued its operational life for much longer.