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#astronomy Gamma-ray Flash Heralds Start of a Magnetar – Sky & Telescope

November 22, 2020 - Comment

This artist’s idea of brief gamma-ray burst 200522A, which produced what scientists have confirmed to be the brightest kilonova ever recorded, 10 occasions brighter than any others recognized.NASA / ESA / D. Participant (STScI) It seems, two neutron stars don’t essentially make a black gap. Neutron star collisions are probably on the coronary heart of


Birth of a MagnetarThis artist’s idea of brief gamma-ray burst 200522A, which produced what scientists have confirmed to be the brightest kilonova ever recorded, 10 occasions brighter than any others recognized.
NASA / ESA / D. Participant (STScI)

It seems, two neutron stars don’t essentially make a black gap.

Neutron star collisions are probably on the coronary heart of brief gamma-ray bursts (GRBs), flashes of gamma radiation that final lower than two seconds however carry extra energy than the Solar will produce in its lifetime.  Basic math means that when two neutron stars come collectively on this approach, they must have sufficient mass to make a black gap — offered they don’t lose an excessive amount of materials within the means of merging.

Observing the glow that follows these explosive mergers is troublesome, however with the assistance of the Hubble Area Telescope, astronomers have caught the afterglow of 1 such burst, GRB 200522A. Its fading radiation carries an vital message: Violent as these blasts may be, they’re not essentially cataclysmic. Not less than on this case, a extremely magnetized neutron star, or magnetar, seems to have survived the occasion.

Wen-Fai Fong (Northwestern College) and colleagues have posted observations of this GRB on the arXiv preprint server, and the examine will seem within the Astrophysical Journal later this 12 months.

An Odd Burst

NASA’s Neil Gehrels Swift Observatory first detected the burst after the radiation had traveled for five.47 billion years to Earth. Fong’s crew noticed it once more with Hubble Area Telescope and a mess of different ground-based observatories following the preliminary GRB. However when it got here time to grasp the relation between radiation throughout the electromagnetic spectrum — from radio to infrared to X-rays — the crew at first couldn’t make sense of what they had been seeing.

After two neutron stars collide, producing the preliminary burst of gamma-rays, there’s an afterglow of emission that comes from the shock wave that follows. Because the shock wave blasts out, electrons from the exploding plasma spiral across the shock’s magnetic fields. Identified to astronomers as a kilonova, this emission explains many of the afterglow from different GRBs. However it didn’t work for this one — the infrared emission was 10 occasions brighter than anticipated.

“The truth that we see this infrared emission, and that it’s so vibrant, exhibits that brief gamma-ray bursts certainly kind from neutron star collisions,” says crew member Edo Berger (Middle for Astrophysics, Harvard & Smithsonian), “however surprisingly the aftermath of the collision will not be a black gap, however moderately probably a magnetar.”

A Magnetar Survives

The crew in reality think about two eventualities: One is that the neutron star collision birthed a magnetar. The second is that the collision produced a black gap, accompanied by a jet of plasma touring at relativistic velocity away from the collision with a surprisingly huge angle.

“For my part, the magnetar situation offers a extra simple clarification for the observations,” says Maria Grazia Bernardini (Astronomical Observatory of Brera, Italy), a GRB professional who was not concerned within the examine. It’s unlikely, she provides, relativistic jet would spray plasma so broadly; such jets are usually fairly slender. A jet additionally wouldn’t make the correct amount of X-rays, Fong’s crew notes.

“GRB 200522A is a outstanding instance of how brief GRB afterglows can nonetheless shock and puzzle us 15 years after their discovery,” Bernardini says.

If a magnetar survived the collision, it would nonetheless be round for a very long time to return. Inside a couple of years, Fong and his colleagues write, the magnetized remnant ought to produce observable radio emission.

“If detected, this may not solely break the degeneracy between the 2 potential explanations on this particular case,” Bernardini says, “however it might present the long-sought smoking gun of the magnetar situation, and the primary direct proof of a secure magnetar related to a GRB.”

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