Whereas ESA’s satellite tv for pc INTEGRAL was observing the sky, it noticed a burst of gamma-rays — high-energy photons — coming from the close by galaxy M82. Just a few hours later, ESA’s XMM-Newton X-ray area telescope looked for an afterglow from the explosion however discovered none. A global group, together with researchers from the College of Geneva (UNIGE), realised that the burst should have been an extra-galactic flare from a magnetar, a younger neutron star with an exceptionally sturdy magnetic subject. The invention is revealed within the journal Nature.
On 15 November 2023, ESA’s satellite tv for pc INTEGRAL noticed a sudden explosion from a uncommon object. For under a tenth of a second, a brief burst of energetic gamma-rays appeared within the sky. “The satellite tv for pc knowledge had been obtained within the INTEGRAL Science Information Centre (ISDC), based mostly on the Ecogia web site of the UNIGE Astronomy Division, from the place a gamma-ray burst alert was despatched out to astronomers worldwide, solely 13 seconds after its detection,” explains Carlo Ferrigno, senior analysis affiliate within the Astronomy Division at UNIGE College of Science, PI of the ISDC and co-author of the publication.
The IBAS (Integral Burst Alert System) software program gave an computerized localisation coinciding with the galaxy M82, 12 million light-years away. This alert system was developed and is operated by scientists and engineers from the UNIGE in collaboration with worldwide colleagues.
A curious sign from a close-by galaxy?
“We instantly realised that this was a particular alert. Gamma-ray bursts come from far-away and anyplace within the sky, however this burst got here from a brilliant close by galaxy,” explains Sandro Mereghetti of the Nationwide Institute for Astrophysics (INAF-IASF) in Milan, Italy, lead creator of the publication and contributor of IBAS. The group instantly requested ESA’s XMM-Newton area telescope to carry out a follow-up remark of the burst’s location as quickly as doable. If this had been a brief gamma-ray burst, attributable to two colliding neutron stars, the collision would have created gravitational waves and have an afterglow in X-rays and visual gentle.
Nonetheless, XMM-Newton’s observations solely confirmed the new gasoline and stars within the galaxy. Utilizing ground-based optical telescopes, together with the Italian Telescopio Nazionale Galileo and the French Observatoire de Haute-Provence, additionally they regarded for a sign in seen gentle, beginning just a few hours after the explosion, however once more didn’t discover something. With no sign in X-rays and visual gentle, and no gravitational waves measured by detectors on Earth (LIGO/VIRGO/KAGRA), probably the most sure clarification is that the sign got here from a magnetar.
Magnetars: mega-magnetic stars, lately useless
“When stars extra large than eight occasions the Solar die, they explode in a supernova that leaves a black gap or neutron star behind. Neutron stars are very compact stellar remnants with greater than the mass of the Solar packed right into a sphere with the dimensions of the Canton of Geneva. They rotate rapidly and have sturdy magnetic fields.” explains Volodymyr Savchenko, senior analysis affiliate within the Astronomy Division at UNIGE College of Science, and co-author of the publication. Some younger neutron stars have further sturdy magnetic fields, greater than 10,000 occasions that of typical neutron stars. These are referred to as magnetars. They emit vitality away in flares, and infrequently these flares are gigantic.
Nonetheless, up to now 50 years of gamma-ray observations, solely three big flares have been recognized as coming from magnetars in our galaxy. These outbursts are very sturdy: one which was detected in December 2004, got here from 30,000 light-years from us however was nonetheless highly effective sufficient to have an effect on the higher layers of Earth’s ambiance, just like the Photo voltaic flares, coming from a lot nearer to us, do.
The flare detected by INTEGRAL is the primary agency affirmation of a magnetar flare outdoors of the Milky Method. M82 is a brilliant galaxy the place star formation takes place. In these areas, large stars are born, dwell quick turbulent lives and depart behind a neutron star. “The invention of a magnetar on this area confirms that magnetars are doubtless younger neutron stars,” provides Volodymyr Savchenko. The seek for extra magnetars will proceed in different extra-galactic star-forming areas, to?perceive these extraordinary astronomical objects. If astronomers can discover many extra, they’ll begin to perceive how typically these flares occur and the way neutron stars lose vitality within the course of.
INTEGRAL, a key instrument in a race towards time
Outbursts of such quick length can solely be captured serendipitously when an observatory is already pointing in the precise course. This makes INTEGRAL with its massive subject of view, greater than 3000 occasions better than the sky space coated by the Moon, so essential for these detections.
Carlo Ferrigno explains: “Our computerized knowledge processing system is very dependable and permits us to alert the group instantly.” When surprising observations like this are picked up, INTEGRAL and XMM-Newton may be versatile of their schedules, which is crucial in time-crucial discoveries. On this case, had the observations been carried out even only a day later, there wouldn’t have been such sturdy proof that this was certainly a magnetar and never a gamma-ray burst.
