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


Birth of a Magnetar
This artist’s idea of brief gamma-ray burst 200522A, which produced what scientists have confirmed to be the brightest kilonova ever recorded, 10 instances 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.  Simple arithmetic means that when two neutron stars come collectively on this method, they must have sufficient mass to make a black gap — supplied they don’t lose an excessive amount of materials within the strategy of merging.

Observing the glow that follows these explosive mergers is tough, 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 essential message: Violent as these blasts may be, they’re not essentially cataclysmic. A minimum of 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 research will seem within the Astrophysical Journal later this yr.

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 workforce noticed it once more with Hubble Area Telescope and a large number 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 workforce at first couldn’t make sense of what they have 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. Recognized to astronomers as a kilonova, this emission explains a lot of the afterglow from different GRBs. Nevertheless it didn’t work for this one — the infrared emission was 10 instances brighter than anticipated.

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

A Magnetar Survives

The workforce in reality contemplate 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 pace away from the collision with a surprisingly broad angle.

“In my view, the magnetar state of affairs gives a extra easy clarification for the observations,” says Maria Grazia Bernardini (Astronomical Observatory of Brera, Italy), a GRB professional who was not concerned within the research. It’s unlikely, she provides, {that a} relativistic jet would spray plasma so broadly; such jets are usually fairly slim. A jet additionally wouldn’t make the correct quantity of X-rays, Fong’s workforce notes.

“GRB 200522A is a exceptional 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’s going to nonetheless be round for a very long time to return. Inside a number of years, Fong and his colleagues write, the magnetized remnant ought to produce observable radio emission.

“If detected, this is able to not solely break the degeneracy between the 2 doable explanations on this particular case,” Bernardini says, “however it could present the long-sought smoking gun of the magnetar state of affairs, and the primary direct proof of a steady magnetar related to a GRB.”


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