Free Astronomy Magazine September-October 2021

54 SEPTEMBER-OCTOBER 2021 ASTRO PUBLISHING pernova explosion thanks to the imaging capabilities of the Gemini Multi-Object Spectro- graph on Gemini North in Hawai’i. The researchers used Gemini North to obtain images of the GRB’s host galaxy 28, 45, and 80 days after the GRB was first detected on 26 August 2020 by a network of observa- tories that included NASA’s Fermi Gamma-ray Space Tele- scope. Gemini’s observations allowed the team to spot the tell-tale rise in energy that sig- nifies a supernova, despite the blast’s location in a galaxy 6.6 billion light-years away. “This was a complicated en- deavor as we needed to sepa- rate the light of an already faint galaxy from the light of a supernova,” said Ahumada. “Gemini is the only ground- based telescope that can do follow-up observations like this with a flexible-enough sched- ule to let us squeeze in our obser- vations.” This result shows that classifying GRBs based solely on their duration may not be the best ap- proach, and that additional observa- tions are needed to determine a GRB’s cause. “We were originally hunting for merging neutron stars, which are thought to produce short gamma-ray bursts,” added Ahu- mada. “Once we discovered GRB 200826A, however, we realized that this burst was more likely to be caused by a collapsing star’s super- nova, which was a surprise!” “The Gemini observatories continue to shed new light on the nature of these incredible explosions occur- ring across the distant Universe,” said Martin Still, Gemini Program Officer at NSF. “Dedicated instru- mentation arriving for use over the next decade will maintain Gemini’s leadership in the follow-up of these awe-inspiring cosmic events.” U sing the Gemini North telescope in Hawai’i, astronomers identified the cause of a surprisingly short burst of gamma rays. The source was a supernova explosion, which usually produces a long gamma-ray burst (GRB). Astronomers now think that this and many other short GRBs are actually supernova-produced GRBs in disguise. They suspect these GRBs look shorter because their gamma-ray jets aren’t strong enough to completely escape the collapsing star. [Images and Videos: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/NASA/Goddard Space Flight Cen- ter. Image Processing: M. Zamani (NSF’s NOIRLab). Music: Stellardrone - Airglow] “This discovery represents the short- est gamma-ray emission caused by a supernova during the collapse of a massive star,” commented Tomás Ahumada, who led this research and is a PhD candidate at the Uni- versity of Maryland and astronomer at NASA’s Goddard Space Flight Center. “It lasted for only 0.6 sec- onds, and it sits on the brink be- tween a successful and a failed gamma-ray burst.” The team believes that this and some other supernova-related GRBs are appearing short because the jets of gamma rays that emerge from the collapsing star’s poles aren’t strong enough to completely escape the star — almost failing to produce a GRB — and that other collapsing stars have such weak jets that they don’t produce GRBs at all. This discovery could also help ex- plain an astronomical mystery. Long GRBs are associated with a specific type of supernova (called Type Ic- BL). However, astronomers observe many more of these supernovae than long GRBs. This discovery of the shortest GRB associated with a supernova sug- gests that some of these supernova- caused GRBs are masquerading as short GRBs thought to be created by neutron-star mergers, and are therefore not getting counted as the supernova kind. “Our discovery suggests that, since we observe many more of these su- pernovae than long gamma-ray bursts, most collapsing stars fail to produce a GRB jet that breaks through the outer envelope of the collapsing star,” explained Ahu- mada. “We think this event was ef- fectively a fizzle, one that was close to not happening at all.” The team was able to determine that this GRB — identified as GRB 200826A — originated from a su- !