Astronomers Baffled by Day-Long, Repeating Gamma-Ray Burst
An unprecedented gamma-ray burst (GRB) detected on July 2, 2024, is challenging existing understanding of these powerful cosmic explosions. The burst, designated GRB 250702B, persisted for an astonishing 24 hours adn exhibited repeating activity - characteristics never before observed in such events.This discovery, detailed in The Astrophysical Journal Letters, has prompted a flurry of observations from leading telescopes worldwide as scientists race to determine its origin and the mechanism driving its unusual behavior.Gamma-ray bursts are the most luminous electromagnetic events known to occur in the universe, typically associated with the collapse of massive stars or the merger of neutron stars. These events usually last only seconds.Though, the Einstein Probe detected initial signs of activity from GRB 250702B a day before its peak, a phenomenon previously unheard of. Its location, initially obscured by a star-rich region of our galaxy, further complicated investigations.
Astronomers utilized the European Southern Observatory’s (ESO) Very Large Telescope (VLT) – specifically its HAWK-I infrared camera – to pinpoint the source. The VLT observations revealed a faint glow inconsistent with a galactic origin,leading to the surprising conclusion that GRB 250702B originated outside the Milky Way.Confirmation came with follow-up observations from the Hubble Space Telescope.
“Before these observations, the general feeling in the community was that this GRB must have originated from within our galaxy. The VLT fundamentally changed that paradigm,” explained Andrew Levan, astronomer at Radboud university, The Netherlands, and co-lead author of the study.
The host galaxy appears to be billions of light-years away, though a precise distance remains to be steadfast. The burst’s extended duration and repeating nature suggest a novel mechanism at play.Scientists are considering possibilities ranging from the collapse of an exceptionally massive star to a star being disrupted by a black hole – scenarios that would require unusual conditions.
“What we found was considerably more exciting: the fact that this object is extragalactic means that it is indeed considerably more powerful,” says antonio Martin-Carrillo.
Currently, astronomers are analyzing the fading light from GRB 250702B using the VLT’s X-shooter spectrograph and the james Webb Space Telescope, hoping to unlock the secrets behind this exceptional event.
“We are still not sure what produced this,but with this research,we have made a huge step forward towards understanding this extremely unusual and exciting object,” martin-Carrillo added.
Journal Reference: Andrew J. Levan, Antonio Martin-Carrillo, Tanmoy Laskar, Rob A. J. Eyles-Ferris, Albert Sneppen et al. The Day-long, Repeating GRB 250702B: A Unique Extragalactic Transient. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/adf8e1
