Tag Archives: GammaRay

Unexpected forms of gamma-ray emissions observed in tropical thunderstorms

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Thunderclouds include more than just rain and lightning. In addition to visible light radiation, thunderclouds can produce powerful bursts of gamma rays that last one millionth of a second. Clouds can also glow steadily with gamma rays for seconds to minutes at a time. Using a battery of detectors onboard NASA’s ER-2 research aircraft, scientists have discovered a new type of gamma-ray radiation whose duration is shorter than steady light but longer than microsecond bursts. They call it a flickering gamma ray flash.

NASA’s high-flying ER-2 plane is equipped with the Fly’s Eye Stationary Lightning Mapper Simulator, which records gamma rays (purple in the illustration) from thunderclouds, and instruments in this artist’s impression of the Airborne Lightning Observatory for the Ground Gamma Ray Flash (ALOFT) mission. is installed. Image credit: NASA/ALOFT team.

Previous studies have reported two types of gamma-ray emissions from thunderclouds. One is a high-intensity burst known as a terrestrial gamma-ray flash, and the other is a moderate-intensity, long-duration gamma-ray glow.

However, the characteristics of these emissions and how they are produced are not completely understood.

Researchers used data collected by the aircraft during 10 flights in July 2023 to investigate gamma-ray emissions that occurred during marine and coastal thunderstorms in the Caribbean and Central America.

“The ER-2 aircraft will be the ultimate platform for observing gamma rays from thunderclouds,” said Professor Nikolai Ostgaard of the University of Bergen.

“Flying at 20 km (12.4 miles) allows us to fly directly above the clouds, as close as possible to the gamma-ray source.”

“There’s a lot more going on in thunderstorms than we imagined,” added Professor Steve Comer of Duke University.

“At the end of the day, basically all large thunderstorms produce gamma rays in different forms throughout the day.”

“Several aircraft operations have attempted to determine whether these phenomena are common, but results have been mixed, and some operations over the United States have not found gamma rays at all.”

“This project was designed to answer these questions once and for all.”

Professor Ostgaard, Professor Comer and their colleagues. identified Another type of gamma-ray radiation, called flicker gamma-ray flashes, consists of pulses of longer duration than terrestrial gamma-ray flashes.

A total of 24 flickering gamma-ray flashes were observed as the spacecraft passed over gamma-ray thunderclouds on five of its 10 flights. Seventeen of these flickering gamma-ray flashes resulted in lightning.

The researchers suggested that flickering gamma-ray flashes, which can begin as the emission of gamma rays and then suddenly increase in intensity into a series of pulses, may also be involved in the formation of lightning. are.

Because flickering gamma-ray flashes share similar characteristics with gamma-ray glows and terrestrial gamma-ray flashes, they propose that flickering gamma-ray flashes could provide evidence of a link between the two phenomena.

In another study, Dr. Martino Marisardi from the University of Bergen and colleagues investigated Characteristics of gamma ray glow detected by aircraft.

These included thundercloud systems covering an area of ​​more than 9,000 km.2 Luminescence was observed for at least 3 hours.

They found that the emission was general and not uniform across the emission region.

During nine of the 10 flights, more than 500 individual gamma-ray glows were observed across the study area, each lasting between 1 and 10 seconds.

These findings contradict the results of previous studies that reported that the gamma-ray glow can last up to several hundred seconds and is emitted uniformly over a range of up to 20 km.

Taken together, these findings improve our understanding of gamma-ray emissions from thunderclouds and suggest a causal relationship between glows and flashes and the possible role of these emissions in the subsequent development of lightning.

“These two new forms of gamma rays are what I find most interesting,” Professor Comer said.

“They don’t seem to be related to the occurrence of lightning. They somehow appear naturally.”

“There are hints in the data that they may actually be related to the process that causes lightning, but it’s still a mystery to scientists.”

The results are published in two papers: journal nature.

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N. Ostgard others. 2024. Gamma ray flashing, the missing link between gamma rays and TGF. nature 634, 53-56; doi: 10.1038/s41586-024-07893-0

M. Marisardi others. 2024. Highly dynamic gamma-ray emissions are common in tropical thunderclouds. nature 634, 57-60; doi: 10.1038/s41586-024-07936-6

Source: www.sci.news

Fermi’s Time-Lapse Tour: A One-of-a-Kind View of the Gamma-Ray Sky

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new movies from NASA's Fermi mission shows the intensity of gamma rays, the highest energy form of light, with energies of over 200 million electron volts (MeV), detected by Fermi's Large Area Telescope between August 2008 and August 2022 . For comparison, visible light has an energy of 2 to 3 electrons. bolt. Lighter colors indicate the location of more intense gamma ray sources.

“The Milky Way's bright, steady gamma-ray glow is punctuated by intense flares of near-light-speed jets that last for days, powered by the supermassive black hole at the center of the distant galaxy.” Dr. Digel said. Staff Scientist at SLAC National Accelerator Laboratory.

“These dramatic eruptions can appear anywhere in the sky, occurred millions to billions of years ago, and their light is just reaching Fermi as we see it. ”

“The first thing you see in a movie is a steady arc of light across the screen,” said Dr. Judy Racusin, a research scientist at NASA's Goddard Space Flight Center.

“It's our sun, and its apparent motion reflects the Earth's annual orbital motion.”

Most of the time, Fermi's Large Area Telescope (LAT) picks up faint glimpses of the Sun due to the influence of accelerated particles called cosmic rays. When they come into contact with the sun's gases or the light it emits, gamma rays are produced.

But sometimes, the sun suddenly brightens up in a powerful eruption called a solar flare, temporarily making our star one of the brightest sources of gamma rays in the sky.

The Fermi team created an all-sky time-lapse movie using 14 years of data acquired by Fermi's large-area telescope. Image credit: NASA Goddard Space Flight Center/DOE/LAT Collaboration.

“The new film depicts the sky from two different perspectives,” the astronomers said.

“The rectangular view shows the entire sky with the galaxy's center in the middle.”

“This highlights the central plane of the Milky Way, which glows with gamma rays produced from cosmic rays striking interstellar gas and starlight.”

“Many other sources are also scattered, such as neutron stars and supernova remnants.”

“Above and beyond this central band, we look out beyond our galaxy and into a wider universe studded with bright, rapidly changing light sources.”

“Most of these are actually distant galaxies that are better seen from a different perspective, centered around our galaxy's north and south poles.”

“Each of these galaxies, called blazars, has a central black hole with the mass of more than a million suns.”

“Somehow, black holes produce jets of matter that move at very high speeds. Using a blazar, we can see one of these jets almost directly below us, enhancing their brightness and variability. Masu.”

“This fluctuation indicates that something has changed in these jets,” Dr. Raksin said.

“We monitor these sources regularly and alert other telescopes, both in space and on the ground, when something interesting is happening.”

“We need to catch these flares quickly before they disappear, and the more observations we can collect, the better we can understand these events.”

Fermi plays a key role in a growing network of missions working together to capture these changes as they unfold in space.

“Many of these galaxies are very distant,” the researchers said.

“For example, the light from the blazar known as 4C +21.35 has been traveling for 4.6 billion years. This means that the flare-ups we see today actually happened when the sun and solar system began to form. means.”

“Other bright blazars are more than twice as far away, providing an impressive snapshot of black hole activity across cosmic time.”

“Many short-lived events that Fermi studies, such as gamma-ray bursts, the most powerful cosmic explosions, cannot be seen in time-lapse.”

“This is the result of processing data over several days to sharpen the image.”

Source: www.sci.news