Additional light in one of the most energetic gamma-ray flashes

Flashes or flashes of gamma rays are the brightest and most energetic explosions in the universe, capable of emitting in a few seconds more energy than our Sun will have emitted during its entire existence. GRB 211106A belongs to a subclass of gamma-ray flashes known as short-duration gamma-ray flashes. Such gamma-ray bursts are generated during explosions that the scientific community attributes to the creation of the heaviest chemical elements in the universe such as platinum and gold. These explosions are the result of a violent merger between members of binary star systems containing a neutron star.

“These mergers occur due to the effect of gravitational wave radiation that strips the orbit of binary stars of their energy. That way, the stars get closer to each other and end up colliding,” explains Tanmoy Laskar, soon to be an assistant professor of physics and astronomy at the University of Utah, United States. “In turn, the resulting explosion emits jets at speeds close to the speed of light. When one of those jets is emitted in the direction of Earth, we observe a short pulse of gamma-ray radiation, known as a short-duration gamma-ray flash.”

These flashes usually last a few tenths of a second. The science team then looked for signs of afterglow, a phenomenon caused by the interaction of the jets with the surrounding gas. Short-lived gamma-ray flashes are difficult to detect, and to date only half a dozen have been observed at radio wavelengths, and none at millimeter wavelengths. Tanmoy Laskar, who led the research while an Excellence Fellow at Radboud University in the Netherlands, explains that the difficulty lies in the great distance that separates us from gamma-ray flashes and the technological capacity of telescopes. “Although the afterglow of short-lived gamma-ray flashes is very bright and energetic, these flashes occur in very distant galaxies, so the light they emit can be quite dim for our ground-based telescopes. Before ALMA, millimeter telescopes were not sensitive enough to detect afterglow.”

ALMA (Atacama Large Millimeter/submillimeter Array) is an international observatory co-managed by the National Radio Astronomical Observatory (NRAO) of the US National Science Foundation.

The gamma-ray flash 211106A, due to the distance from the source that emitted it, poses a challenge. The light emitted is so dim that although NASA’s Neil Gehrels Swift observatory had detected the burst in X-rays, the host galaxy was impossible to detect in that wavelength, and the scientific community was unable to determine exactly where it came from. The explosion. “Afterglow is essential to determine which galaxy a flash is coming from and to better understand the phenomenon itself. At first, when only X-ray observations had been made, the scientific community believed that this flash could come from a nearby galaxy,” says Tanmoy Laskar, who adds that the large amount of dust present in the area also made detection difficult. of the object in optical observations made with the Hubble Space Telescope.

With each new wavelength used, the scientific community gained a little better understanding of gamma-ray flashes, and millimeter-wave observations were particularly important in getting to the heart of the matter. “The observations revealed an unchanging field of galaxies. ALMA’s sensitivity allowed us to pinpoint the location of the gamma-ray flash in that field more precisely, and we discovered that it came from another faint galaxy further away. This means that this flash is even more powerful than we thought, and is among the most luminous and energetic observed to date”, says Tanmoy Laskar.

For the first time in the history of radio astronomy, light at millimeter wavelengths was detected from a short-lived gamma-ray flash. This artist’s rendering shows a neutron star merging with another star (disk-shaped, lower left) causing an explosion that emitted the short-lived gamma-ray flash GRB 211106A (white jet in the center) and that left one of the brightest afterglows observed to date (hemispherical shock wave in the center-right area). While dust from the host galaxy obscured most of the visible light (shown in color), millimeter light from the phenomenon (shown in green) was able to pass through and reach ALMA. In this way, the scientific community obtained an unprecedented view of the cosmic explosion. From this study, it was confirmed that GRB 211106A is one of the most energetic short-lived gamma-ray flashes ever observed. (Image: ALMA (ESO/NAOJ/NRAO), M. Weiss (NRAO/AUI/NSF). CC BY-SA)

Wen-fai Fong, a professor of physics and astronomy at Northwestern University in the United States, adds: “This short-lived gamma-ray flash was the first one we tried to observe with ALMA. The afterglow of this type of flash is very difficult to detect, so seeing this very bright phenomenon was something spectacular. After many years of observing in search of these flashes, this surprising finding opens a new area of ​​study by motivating us to observe many more such phenomena with ALMA and other telescopes in the future.”

There are still many observations to be made at different wavelengths, both for new gamma-ray flashes and in the case of GRB 211106A, and these could bring new surprises. “The study of short-lived gamma-ray flashes requires rapid coordination between telescopes located in different parts of the world and in space to cover all wavelengths,” explains Edo Berger, professor of astronomy at Harvard University in the United States. Joined. “In the case of gamma-ray flash 211106A, we used some of the most advanced telescopes out there: ALMA, the US National Science Foundation’s Karl G. Jansky Very Large Array, NASA’s Chandra X-ray Observatory and the Hubble Space Telescope. With the James Webb Space Telescope now in operation and future 20-40 meter radio and optical telescopes such as the Next Generation VLA (ngVLA), we will be able to get a complete picture of these cataclysmic events and study them at unprecedented distances.”

Tanmoy Laskar adds: “With the James Webb telescope we can now get the full spectrum of the host galaxy and easily calculate its distance, and in the future we could also use it to collect infrared afterglows and study their chemical composition. With the ngVLA, we will be able to study in an unprecedented level of detail the geometric structure of the afterglows and the stellar fuel present in their surroundings. I am very excited about the discoveries that await us in that field.”

The study is titled “The First Short GRB Millimeter Afterglow: The Wide-Angled Jet of the Extremely Energetic SGRB 211106A.” And it has been published in the academic journal The Astrophysical Journal Letters. (Source: NRAO)