Astronomers have observed the longest-lasting central engine activity ever recorded from a gamma-ray burst. The burst occurred at a redshift of 0.8577, and the activity lasted about 27 days in the burst’s own rest frame—around 20 days longer than the previous record. The paper, posted to the arXiv preprint server on Sept. 18, explores different mechanisms that could be powering this puzzling burst.
Rare, long bursts
Gamma-ray bursts (GRBs) are among the most energetic explosions in the universe, typically linked to the collapse of massive stars into black holes (producing long-duration GRBs, often with an accompanying supernova) or the merger of neutron stars (producing short-duration GRBs).
Ultra-long GRBs are a rare subclass of gamma-ray bursts in which the object driving or powering the explosion stays active longer than in typical bursts. Only a handful of confirmed examples exist, and their cause remains debated. Understanding what powers these rare ultra-long bursts helps explain how massive stars die and what kind of compact object is left behind.
GRB 220706A was first detected on July 6, 2022. The burst kept flaring in X-rays for nearly a month. In this study, the team led by Benjamin P. Gompertz of the University of Birmingham conducted a detailed, multiwavelength study of this mysterious event.
The team used X-ray data from the Swift X-ray Telescope, the Neutron Star Interior Composition Explorer (NICER) and the Chandra X-ray Observatory; optical/infrared imaging from four different ground-based telescopes; and radio/millimeter observations from NOEMA and the Karl G. Jansky Very Large Array (VLA). These follow-up observations across multiple wavelengths spanned the period from around 100 seconds after the initial burst to Oct. 5, 2023.
Eighth-longest of all
The team found that GRB 220706A ranks eighth-longest among 549 GRBs analyzed. Its initial burst lasted about 15.6 hours, exceeding even the previously known “archetypal” ultra-long GRBs.
X-ray observations of GRB 220706A revealed repeated flaring activity that continued for about 51 days after the burst was first detected. Because GRB 220706A is at a redshift of z = 0.8577, the universe would have expanded significantly while its light traveled to us. This expansion stretches the time interval between signals. As a result, after correcting for the redshift, the team found that the X-ray flares remained active until at least 27 rest-frame days after the burst—about 20 days longer than the previous record-holder for delayed flaring.
“Corrected for redshift, this last epoch of flaring suggests that the central engine of GRB 220706A is still active at 27.25 rest-frame days after trigger,” the team writes in the paper. “This is ≈20.6 rest-frame days later than the flares seen in GRB 210204A, which were previously claimed to be the most delayed ever observed.”
Dusty dark burst
Further analysis revealed that the burst’s optical light was much fainter than its X-ray brightness predicted, classifying it as a “dark” burst. “One likely explanation is substantial dust extinction within the host galaxy, which potentially obscures the afterglow emission,” they explain.
About 17 days after the burst, extra optical light appeared, consistent with the predicted emergence of a supernova component. Depending on how much light is assumed to be blocked by dust, this supernova appears to be remarkably luminous, potentially bright enough to qualify as a “superluminous supernova,” a much rarer category of stellar explosion. If confirmed, this would be the first case of both a gamma-ray burst and a superluminous supernova occurring together in the same event.
What could it be?
The team explored several possible explanations for this gamma-ray burst, though none fit perfectly. Black hole accretion from a massive, extended progenitor star is plausible, but this scenario pushed standard models to their limits. A magnetar engine works for some other ultra-long GRBs but may need a lot of parameter adjustment here. “… the typical timescales of such flares are of the order of seconds to minutes, and nascent magnetars are not expected to have fully formed crusts at timescales relevant to GRB 220706A,” they note.
A tidal disruption event, which occurs when a star is torn apart by a black hole, is geometrically possible given the burst’s location at the galaxy’s center, but its X-ray and optical behavior looked more like a standard GRB. The team ultimately favored the death of a star through collapse paired with a supernova, based on similarities to a previously confirmed case.
However, no single proposed mechanism appears to clearly explain every observed detail. The team also notes that the extra light interpreted as a supernova could instead be an unusual optical counterpart to the ongoing X-ray flaring, mimicking a supernova’s brightness and timing by coincidence.
Written for you by our author Shreejaya Karantha, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive.
If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.
Publication details
Benjamin P. Gompertz et al, GRB 220706A: a gamma-ray burst with a month-long engine and a luminous supernova, arXiv (2026). DOI: 10.48550/arxiv.2609.22426
Journal information:
arXiv
© 2026 Science X Network
Citation:
A gamma-ray burst’s engine stayed active for nearly a month, breaking the previous record (2026, October 6)
retrieved 6 October 2026
from https://phys.org/news/2026-10-gamma-ray-stayed-month-previous.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.