Astronomers has observed an optical afterglow of a short gamma-ray burst, thought to be from the merger of two neutron stars, and localized it to a particular host galaxy, which is located 10 billion light-years away in the constellation of Coma Berenices. Dubbed GRB 181123B, the event occurred 3.8 billion years after the Big Bang. It is the second most-distant short gamma-ray burst ever detected and the most distant event with an optical afterglow.
Fig: The afterglow of GRB 181123B (marked with a circle), captured by the Gemini-North telescope. Image credit: Gemini Observatory / NOIRLab / NSF / AURA / K. Paterson & W. Fong, Northwestern University / Travis Rector, University of Alaska Anchorage / Mahdi Zamani / Davide de Martin.
Short gamma-ray bursts (SGRBs) are short-lived, highly-energetic bursts of gamma-ray light.
Tought to result from the merger of two neutron stars, they are cataclysmic events that are almost unfathomable in terms of their basic properties, emitting huge amounts of energy.
The gamma-ray light lasts for less than two seconds, while the optical light can last for a matter of hours before fading.
Therefore, rapid follow-up of the optical afterglow of these intense flashes of gamma-ray radiation is critical.
Astronomers typically only detect 7-8 SGRBs each year that are well-localized enough for further observations.
GRB 181123B was detected on November 23, 2018 by NASA’s Neil Gehrels Swift Observatory.
Within just a few hours after the detection and a worldwide alert, Northwestern University astronomer Kerry Paterson and colleagues quickly pointed the 8.1-m Gemini-North telescope, the 10-m Keck I telescope and the Multi-Mirror Telescope toward the location of GRB 181123B and were able to measure its very faint afterglow.
They were able to obtain deep observations of the burst mere hours after its discovery. The Gemini images were very sharp, allowing them to pinpoint the location to a specific galaxy in the Universe. They certainly did not expect to discover a distant SGRB, as they are extremely rare and very faint.
They perform ‘forensics’ with telescopes to understand its local environment, because what its home galaxy looks like can tell them a lot about the underlying physics of these systems.
Fig: An artist’s impression of how GRB 11823B compares to other short gamma-ray bursts. Except when they are detected by gravitational wave observatories, the gamma ray bursts can only be detected from Earth when their jets of energy are pointed towards us. Image credit: Gemini Observatory / NOIRLab / NSF / AURA / J. Pollard / K. Paterson & W. Fong, Northwestern University / Travis Rector, University of Alaska Anchorage / Mahdi Zamani / Davide de Martin.
After identifying the host galaxy of GRB 181123B and calculating the distance, the astronomers were able to determine key properties of the parent stellar populations within the galaxy that produced the event.
Because GRB 181123B appeared when the Universe was only about 30% of its current age — during an epoch known as ‘Cosmic High Noon’ — it offered a rare opportunity to study the neutron star mergers from when the Universe was a ‘teenager.’
When GRB 181123B occurred, the Universe was incredibly busy, with rapidly forming stars and fast-growing galaxies.
Massive binary stars need time to be born, evolve and die — finally turning into a pair of neutron stars that eventually merge.
References: K. Paterson, W. Fong, A. Nugent, A. Rouco Escorial, J. Leja, T. Laskar, R. Chornock, A. A. Miller, J. Scharwächter, S. B. Cenko, D. Perley, N. R. Tanvir, A. Levan, A. Cucchiara, B. E. Cobb, K. De, E. Berger, G. Terreran, K. D. Alexander, M. Nicholl, P. K. Blanchard, D. Cornish, “Discovery of the optical afterglow and host galaxy of short GRB181123B at z=1.754: Implications for Delay Time Distributions”, astrophysical journal, pp. 1-18, 2020..