[ad_1]
Several billion years ago, a brief gamma-ray burst released more energy in half a second than our Sun will produce during its 10 billion years of life. In May 2020, the light from the event, dubbed GRB 200522A, finally reached Earth and was first detected by NASA’s Neil Gehrels Swift Observatory. NASA / ESA’s Hubble Space Telescope quickly captured the glow within just three days of GRB 200522A and determined that its near-infrared emission was 10 times brighter than expected, challenging conventional models.
This image shows the glow of the GRB 200522A chilonova caused by the merger of two neutron stars. Image credit: NASA / ESA / W. Fong, Northwestern University / T.Laskar, University of Bath.
Lasting less than two seconds, the brief gamma-ray bursts are among the most energetic and explosive events known in the Universe.
Astronomers think these events are caused by the merger of two neutron stars.
Such fusions are very rare and extremely important because scientists think they are one of the main sources of heavy elements in the Universe, such as gold and uranium.
Along with a brief gamma-ray burst, astronomers expect to see a kilonova whose maximum brightness typically reaches 1,000 times that of a classical nova.
Kilonovae are an optical and infrared glow resulting from the radioactive decay of heavy elements and are unique to the merger of two neutron stars or the merger of a neutron star and a black hole.
“It’s surprising to me that after 10 years of studying the same kind of phenomenon, we can discover unprecedented behavior like this,” said Dr. Wen-fai Fong, an astronomer at Northwestern University.
“It just reveals the diversity of explosions the Universe is capable of producing, which is very exciting.”
“These observations don’t fit the traditional explanations for short gamma-ray bursts,” he added.
“Given what we know about the radio and X-rays of this explosion, it just doesn’t match. The near-infrared emission we are seeing with Hubble is too bright. “
This illustration shows the sequence for forming a magnetar-powered kilonova, whose maximum brightness reaches up to 10,000 times that of a classical nova: (i) two orbiting neutron stars spiral closer and closer; (ii) collide and merge, triggering an explosion that releases more energy in half a second than the Sun will produce during its 10 billion years of life; (iii) the merger forms an even more massive neutron star called a magnetar, which has an extraordinarily powerful magnetic field; (iv) the magnetar deposits energy in the ejected material, causing it to glow unexpectedly bright at the infrared wavelengths. Image credit: NASA / ESA / D. Player, STScI.
To pinpoint the precise distance of the host galaxy of GRB 200522A, Dr Fong and colleagues used the Low Resolution Imaging Spectrometer (LRIS) and the DEep Imaging and Multi-Object Spectrograph (DEIMOS) tools installed on the WM Observatory telescopes. Keck.
They determined that the explosion came from a young star-forming galaxy located at a distance of 5.5 billion light years.
They also analyzed the afterglow of GRB 200522A in X-rays with Swift Observatory, optical and near infrared with Las Cumbres Observatory Global Telescope, Hubble, and in radio wavelengths with the Very Large Array.
But what the researchers saw was too bright to even be explained by a traditional kilonova.
“As the data was coming in, we were forming an image of the mechanism that was producing the light we were seeing,” said co-author Dr. Tanmoy Laskar, an astronomer at the University of Bath.
“When we got the Hubble observations, we had to completely change our thinking process, because the information Hubble added made us realize that we needed to discard our conventional thinking and that there was a new phenomenon going on.”
“Then we had to figure out what it meant for the physics behind these extremely energetic explosions.”
Scientists provide a possible explanation for the unusually bright explosion: While most of the brief gamma-ray bursts likely result in a black hole, the merger of neutron stars in this case may have formed a magnetar instead. supermassive neutron with a very powerful magnetic field. ; the magnetar deposited a large amount of energy into the ejected material of the kilonova, making it shine even more.
“What we found exceeds even that of the confirmed kilonova discovered in 2017,” said co-author Jillian Rastinejad, a graduate student at Northwestern University.
“As a first-year graduate student working with real-time data for the first time when this explosion occurred, it is extraordinary to see our discovery motivate an exciting new magnetar-powered model.”
With such an event, the team expects ejection from the burst to produce light at radio wavelengths in the coming years.
“Follow-up radio observations may eventually prove that the source of the burst was indeed a magnetar,” the authors said.
Their article will be published in Astrophysical Journal.
_____
W. Fong et al. 2020. The broadband counterpart of the Short GRB 200522A az = 0.5536: a bright Kilonova or a collimated outflow with a reverse shock? AJ, in print; arXiv: 2008.08593
Source link
