Astronomers Baffled by Day-Long, Repeating Gamma-Ray Burst
An unprecedented gamma-ray burst (GRB) detected on โขJuly 2, 2024, is challenging existing understanding โof these powerfulโ cosmic explosions. The โburst, designated GRB 250702B, โฃpersisted for an astonishing 24 hours adnโข exhibited repeating activity โ- characteristics never before observed in such events.This discovery, detailed in The โขAstrophysical Journal Letters, has prompted a flurry of observations from leading telescopes worldwide as scientists race to determine its origin and theโ mechanism driving its unusual behavior.Gamma-ray bursts are โthe most luminous electromagnetic events known to occur inโ the universe, typically โฃassociated โฃwith the collapse of massive stars or the merger of neutron stars. Theseโค events usually last only seconds.Though, the Einstein Probe detected initial โขsigns of activity from GRB 250702B a day beforeโ its peak, a phenomenon previously unheard of. Itsโ 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 โthe surprising conclusion that GRB 250702B originated outside theโข Milky Way.Confirmation cameโ with follow-up observations from the Hubble Space Telescope.
“Before these observations, โthe general feeling in the โcommunity 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 โco-lead author ofโข 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 andโฃ repeating nature suggest a novel mechanism at play.Scientists are considering possibilities ranging from the collapse of anโค exceptionally massive star to a star beingโ 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 โขthat 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 โคto 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: Andrewโข J. Levan, Antonioโข Martin-Carrillo, Tanmoy Laskar, โRob A. J. Eyles-Ferris, Albert Sneppen et al.โ The Day-long, Repeating โฃGRB 250702B: A Unique Extragalactic Transient. The Astrophysical โJournal โฃLetters. โDOI 10.3847/2041-8213/adf8e1