First Magnetar Flare: Any high-energy photon with higher energy than an X-ray falls into the wide group of gamma rays. Even though they are often produced by processes like radioactive decay, very few astronomical events generate them in large enough amounts to be identified when radiation from another galaxy is detected.
However, since the list is greater than one, we cannot determine the exact event that created gamma rays just by observing their presence. Neutron stars and the environments around black holes can create them at lower energy. Gamma-ray bursts can also be produced by supernovae and by the merging of compact objects such as neutron stars.
Magnetars are the next in line. These are neutron stars with very powerful magnetic fields—more than 1012 times greater than the Sun’s magnetic field—at least momentarily. Flares and even huge flares, which release massive quantities of energy, including gamma rays, can occur on magnetars.
The only known instances of magnetar large bursts have occurred in our own galaxy or its satellites, and they can be challenging to differentiate from gamma-ray bursts produced by the merging of compact objects. Apparently, up until right now.
Among other instruments, the ESA’s Integral gamma-ray observatory detected the aforementioned burst in November 2023. At various wavelengths, GRB 231115A lasted only around 50 milliseconds. This brief burst is comparable to the gamma-ray bursts predicted to be seen when neutron stars combine, while lengthier bursts can be formed when black holes develop during supernovae.
Gamma-ray Burst
Based on Integral’s observatory data, GRB 231115A was positioned just above M82, often referred to as the Cigar Galaxy, a neighboring galaxy. M82 is classified as a starburst galaxy, indicating that it is rapidly generating stars. Interactions with its neighbors are likely what caused the burst.
The galaxy is star-forming overall at a rate that is more than ten times faster than the Milky Way’s. This indicates a high number of supernovae as well as a sizable population of newborn neutron stars, some of which will develop into magnetars.
That does not, however, rule out the idea that M82 was coincidentally positioned in front of a far-off gamma-ray burst. The most plausible source of the gamma rays, according to the researchers, is anything occurring inside the galaxy, as they demonstrate via two distinct approaches that this is highly unlikely.
Although the estimated total energy of the burst is somewhat less than what we would anticipate from those events, it is still possible that a gamma-ray burst is occurring within M82. Other wavelengths should also show evidence of a supernova, but none was seen here (and these usually create longer bursts anyhow).
We may have detected a signal at this time from a different source, which would have been the merger of two compact objects, such neutron stars, using our gravitational wave observatories. M82 does not appear to have any new sources, however these events also commonly leave behind X-ray sources.
Mechanism of Magnetar
The precise process via which magnetars emit gamma rays is still not well understood. It is believed to entail the neutron star’s crust being rearranged as a result of the powerful forces produced by the incredibly strong magnetic field. Earth’s magnetic field is less than one gauss, while giant flares are expected to require magnetic field intensities of at least 1015 gauss.
The researchers calculate that 1045 ergs, or about 1022 megatons of TNT, of energy were released in total, assuming that the event dispersed radiation instead of focusing it on Earth. Therefore, even if it’s not as energetic as mergers of neutron stars, it’s still a very intense event.
