Gamma ray bursts are an essential probe in cosmology, not only because they are among the highest redshift observations but also because their causal models (what generate them) and what effect has the InterGallactic Medium on the attenuation of its light. They can also be related to the highest energy phenomena of physics and to ultra high energy cosmic rays.
Despite a limited number of scenarios (with known physics) able to theoretically generates GRBs and their spectrum, the standard models seems to be empirically falsified, leading to either new physics at the emission site and or during the interaction with the IGM. There are other transient explosions than GRBs, such as FRBs, X-ray transients, FBOT and ILOT in the visible spectrum, ?? in infrared and UV? , in microwave, etc Some of those non GRBs explosions might be independent of a GRB, but GRB can have precursor (that precede them) explosions and most importantly are predicted to have afterglow explosions in other parts of the light spectrum. Some time ago I read a paper saying that optical range explosions should be much more frequent than GRBs yet they are empirically very rare, hence this is a big unsolved problem. The study of explosions is part of the wider topic of transient astronomy which is currently booming, one of the least explored light spectrum is transient microwave astronomy. Today was published the largest transient microwave dataset to date and a very surprising result, completely in tension with models of GRBs afterglows is that zero microwave GRB reverse shocks have been detected. https://arxiv.org/abs/2409.08429 So maybe new physics prevents microwave emission during the afterglow of GRBs or there is a reverse shock but the microwave emission would be absorbed in the IGM before it reaches us, such high microwave selective opacification would have large consequences on the nature of the CMB and on the properties of cosmic dust.
There are a few related yet distinct major topics in Gamma ray astronomy than GRBs, one being the polarization of Gamma rays, that just begin to be explored and the other, one of the most major yet ignored tension in astrophysics: The galactic center Gamma ray excess. Basically the center of the Milky Way has an anomalously high level of Gamma ray radiation compared to model and other known Gamma ray sources. The excess of energy is so high that there is only two candidate explanations in standard physics, Either there is a large population of millisecond pulsars concentrated in the center, either the AGN has extremely high activity in the past and this would be a vestigial radiation. The issue with the millisecond pulsars is that they have not been found despite many searches, though it is hard since the nucleus has a lot of obscuration. Most importantly millisecond pulsars can also be probed via gravitational waves detectors and they currently have not detected such a signal in the center. As surveys improve, the millisecond pulsars explanation become more and more unlikely. The second main explanation is that this excess energy is generated via new physics, typically anhiliation of dark matter (but could be neutrinos or gravitons or even gluons) https://arxiv.org/abs/2209.14370 https://arxiv.org/abs/1405.7928
Related is the topic of ULX https://en.m.wikipedia.org/wiki/Ultraluminous_X-ray_source
And The infrared/TeV crisis: Lack of attenuation of very energetic gamma rays from extragalactic sources.[16][17][18]
Related but distinct here are other excesses https://arxiv.org/abs/2203.11236 https://arxiv.org/abs/2211.15077 The UV curve dust polarization excess
related: new record high gamma ray in the milky way https://phys.org/news/2024-10-gamma-rays-milky-core.html https://arxiv.org/abs/2501.10506
New empirical evidence for DM related yet distinct from the 511 kev line https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.101001