A dead star emits a unique mixture of radiations

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Artist’s view of the SGR magnetar 1935+2154. (ESA)
Artist’s view of the SGR magnetar 1935+2154. (ESA)

An international collaboration between ground-based and orbiting telescopes is shedding light on one of the mysteries of the universe. The alert was issued by ESA’s Integral Space Observatory, whose scientific data are processed at the University of Geneva. An international network of telescopes, of which Integral, the high-energy space observatory of ESA (European Space Agency), is a part, has detected a unique mixture of radiation from a dead star in our galaxy. This discovery involves two distinct cosmic phenomena: magnetars and rapid radio bursts. The former are stellar corpses with a mass equivalent to that of the Sun, but concentrated within a radius of about 10 km, and whose magnetic fields are among the strongest in the Universe. When they become active, they can produce short bursts of high-energy radiation that typically last less than a second and are billions of times brighter than the Sun. The latter is one of the main puzzles in astronomy. Discovered for the first time in 2007, fast radio bursts emit very powerful radio waves for only a few milliseconds before fading away.

At the end of April, astronomers discovered that the magnetar SGR 1935+2154 in the constellation Vulpécule had just started to operate and was emitting not only its usual X-rays, but also a brief burst of radio waves at the same time. "Integral’s IBIS imager allowed us to determine precisely the origin of the emission of these X-rays, highlighting their association with magnetar," explains Volodymyr Savchenko, scientific assistant at the Astronomy Department of the Faculty of Science of the University of Geneva (UNIGE), where Integral’s scientific data are processed. "Most of the other satellites involved in the collaborative study of this event were unable to measure its position in the sky - crucial information to confirm that the transmission was indeed from SGR 1935+2154.

A global alert in seconds

"We detected the high-energy X-ray emission of magnetar on April 28, thanks to data from Integral," explains Sandro Mereghetti researcher at INAF IASF-Milano, Italy. A few seconds later, Integral’s monitoring system automatically alerted observatories around the world. In the following hours, further alerts were issued, allowing the scientific community to act quickly and explore this source in more detail". On the same day, the CHIME radio telescope in Canada and the Survey for Transient Astronomical Radio Emission 2 (STARE2) in the United States allowed astronomers on the ground to locate and then confirm a brief and extremely bright radio wave emission in the direction of SGR 1935+2154.

"This is the very first observation connection between magnetars and fast radio bursts," explains Sandro Mereghetti. It’s really a major discovery, and it helps to shed light on the origin of these mysterious phenomena." The true nature of radio bursts remains a mystery. Until now, no such emission has been observed in the Milky Way from an identified source, nor have they been seen to be associated with any other type of radiation beyond radio waves.
This newly observed link supports the idea that rapid radio bursts emanate from magnetars, and demonstrates that emissions from these highly magnetized objects can also be detected at radio wavelengths. Magnetars are becoming increasingly popular with astronomers because they are thought to play a key role in triggering various transient events in the Universe, ranging from supernovae super-bright explosions to gamma-ray bursts.

Four instruments to scan the Universe

Launched in 2002, Integral carries a suite of four instruments capable of observing and taking simultaneous images of cosmic objects in gamma rays, X-rays and visible light. At the time of the explosion, the magnetar was within the field of view of the IBIS instrument, leading to automatic detection by the satellite, immediately alerting observatories around the world. "This type of collaborative, multi-wavelength approach and the resulting discovery underlines the importance of rapid, large-scale coordination of scientific research efforts. Integral has been part of this effort since its launch, thanks to the innovative services of its data centre," says Carlo Ferrigno, Principal Investigator of the UNIGE’s Integral Science Data Centre (ISDC), which distributes and controls Integral satellite data and the software needed to process it.

This research is published in

The Astrophysical Journal Letters
DOI: 10.3847/2041-8213/aba2cf