GRBs: A New Era in Gamma-ray Science

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Astronomers have detected the highest-energy light ever seen from celestial sources—100 billion to 1 trillion times more energetic than a photon of visible light.

Almost every day, without warning, gamma-ray bursts (GRBs) wash over Earth from somewhere in the vast depths of the cosmos. Each is thought to signal the cataclysmic birth of a black hole, through either the collapse of a massive star or the merging of neutron stars.

A typical GRB emits, in mere seconds, more energy than a star like our sun will produce across its entire 10-billion-year lifetime, it can be seen across almost the entirety of the visible universe.

Researches suggest that these gamma-ray bursts might generate extraordinarily strong gamma-rays - photons with energies higher than 100 billion electron volts. For comparison, that is about 100 billion times more energetic than the optical light our eyes are sensitive to, or around 100 million times more energetic than X-ray photons, those used when we get an X-ray of our bones.
They are so energetic, in fact, that they rip apart atoms and molecules in Earth’s atmosphere with ruthless efficiency, literally vanishing into thin air before they can reach ground-based telescopes.

A GRB occurs in two stages—an initial, intense flash of almost pure gamma rays, followed by a slowly fading broadband afterglow. The flash lasts for up to a minute, and comes from twin jets of particles shot out at nearly the speed of light from just outside the newborn black hole; the afterglow is the blast wave from the jets slamming into surrounding gas, and can linger for months or even years.

A diagram of a gamma-ray burst’s two stages.
Image credit: NASA’s Goddard Space Flight Center

An initial “prompt emission” of gamma rays arises from particle jets expelled by a newborn black hole; as the jets collide with surrounding material, they create a longer-lived “afterglow” that radiates across the entire electromagnetic spectrum.



The Discovery:

Two international teams of researchers operating ground-based Cherenkov telescopes have independently detected extreme gamma rays from two distinct GRBs.

  • The first observation, occurring in July 2018, came from the High Energy Stereoscopic System (HESS), a 28-meter telescope array in Namibia, which recorded gamma rays in excess of 100 gigaelectronvolts from an event christened GRB 180720b.
  • The second, by the twin 17-meter Major Atmospheric Gamma Imaging Cherenkov telescopes (MAGIC) in La Palma in Spain’s Canary Islands, occurred in January 2019, for an event known as GRB 190114c. 

On Jan. 14, 2019, the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observatory in the Canary Islands captured the highest-energy light every recorded from a gamma-ray burst. MAGIC began observing the fading burst just 50 seconds after it was detected thanks to positions provided by NASA's Fermi and Swift spacecraft (top left and right, respectively, in this illustration). The gamma rays packed energy up to 10 times greater than previously seen.

A visual interpretation of the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observatory measuring the energy of light emitted by a gamma-ray burst on Jan. 14, 2019. 
Image Credit: NASA/Fermi and Aurore Simonnet, Sonoma State University

 

The fading afterglow of GRB 190114C and its home galaxy were imaged by the Hubble Space Telescope on Feb. 11 and March 12, 2019. The difference between these images reveals a faint, short-lived glow located about 800 light-years from the galaxy’s core. Blue colors beyond the core signal the presence of hot, young stars, indicating that this is a spiral galaxy somewhat similar to our own. It is located about 4.5 billion light-years away in the constellation Fornax.

The fading afterglow of GRB 190114c (green circle) within its host spiral galaxy, as seen in two combined images captured by the Hubble Space Telescope in February 11 and March 12, 2019. Found in the constellation of Fornax, the galaxy is some 5.5 billion light-years away from Earth.
Image credit: NASA, ESA, and V. Acciari et al. 2019

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