A cosmic explosion detected in 2022 was still unfolding nearly a month after it began, according to a new analysis.
The event is known as GRB 220706A. It belongs to the family of long gamma-ray bursts, powerful emissions of radiation generally associated with the collapse of massive stars. Their most intense phase usually lasts from a few seconds to a few minutes, although later activity may subsequently appear.
Illustration of a supernova
Here, X-ray observations tell an unusual story. Emission episodes were still detected approximately 51 days after the beginning of the burst as seen from Earth. Because the Universe is expanding, observed durations are stretched. In the frame of the explosion, this activity corresponds to approximately 27 days.
This duration far exceeds previously known cases. According to the researchers, it extends the previous record in the frame of the explosion by approximately 21 days.
GRB 220706A lies at a redshift of 0.8577, meaning that its light traveled for several billion years before reaching us. The researchers gathered observations in X-rays, visible light, and other wavelengths to track its evolution over a long period.
They also identified a signal consistent with a very luminous supernova accompanying the burst. Its exact luminosity remains difficult to determine because dust absorbed some of its light. After correction, it could resemble certain particularly energetic supernovae already associated with very long gamma-ray bursts.
The usual models rely on the collapse of a massive star stripped of its outer layers. Such a star is relatively compact and does not naturally supply matter and energy for several weeks.
Several possibilities are being discussed, including a prolonged supply of matter to the central object. None yet explains all the observations with certainty. GRB 220706A could therefore help determine whether extremely long gamma-ray bursts constitute a distinct population.
These results are currently presented in an arXiv preprint and have not yet been peer-reviewed. Future observations of comparable events will have to establish whether this approximately 27-day activity is an exceptional case or part of a still poorly understood family of bursts.