Maunakea Observatories Capture Fleeting Gamma-Ray Burst

PC: International Gemini Observatory/NOIRLab/NSF/AURA/K. Paterson & W. Fong, Northwestern University. Image Processing: Travis Rector (University of Alaska Anchorage), Mahdi Zamani & Davide de Martin

Astronomers have discovered the second-most distant confirmed short gamma-ray burst (SGRB) ever studied using two Maunakea Observatories, the W. M. Keck Observatory and the international Gemini Observatory.

Since these highly-energetic bursts of gamma-ray light last for less than two seconds and their optical afterglow last for only hours before fading, swiftly pointing telescopes toward these short-lived powerful explosions is critical.

Observations confirm the object’s distance at 10 billion light-years away, placing it squarely in the epoch of cosmic high noon when the universe was in its “teenage years” and rapidly forming stars, according to a press release from W.M. Keck Observatory.

The appearance of an SGRB at such an early time could alter theories about their origins, particularly the length of time it takes two neutron stars to merge and produce these powerful explosions, as well as the rate of neutron star mergers in the young universe, the release explains.

“This was a very exciting object to study,” said Kerry Paterson, a postdoctoral associate at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and lead author of the study. “Our research now suggests neutron star mergers could occur surprisingly quickly for some systems — with neutron star binaries spiraling together in less than a billion years to create an SGRB.”

The study has been accepted in The Astrophysical Journal Letters and is available in preprint format on arXiv.org.

The SGRB was initially detected by NASA’s Neil Gehrels Swift Observatory. Within just a few hours, a worldwide alert was broadcasted and Paterson’s team quickly pointed the Gemini North and Keck I telescopes toward the location of the SGRB.

Using the Gemini Multi-Object Spectrograph followed by Keck Observatory’s Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) instrument, the researchers were able to measure the very faint afterglow of the object, which is named GRB181123B because it was the second burst discovered on Nov. 23, 2018 – Thanksgiving night.

“It was such an adrenaline rush to be at Keck when the SGRB alert went off and personally move the telescope towards the object to capture data mere hours after the burst,” said Paterson.

Precisely-localized SGRBs are rare, typically only seven to eight are detected per year, the release states. To pinpoint the distance of GRB181123B, the team obtained spectra of its host galaxy through follow-up observations using Keck Observatory’s DEep Imaging and Multi-Object Spectrograph (DEIMOS).

“Once we obtained the optical spectrum from DEIMOS, it was clear this event was one of the most distant SGRBs measured, which further fueled our investigation to determine its precise distance,” said Paterson.

Additional data was collected from the Gemini South telescope in Chile and Multi-Mirror Telescope in Arizona. The data confirmed the object is the most distant high-confidence SGRB with an optical afterglow detection ever found.

“The identification of certain patterns in the spectrum, together with the colors of the galaxy from the three observatories, allowed us to precisely constrain the distance and solidify it as one of the most distant SGRBs to date in 16 years of Swift operations,” said Paterson.

Once the team identified the host galaxy, they were able to determine key properties of the parent stellar population within the galaxy that produced the SGRB.