Brightest gamma-ray burst ever observed reveals new mysteries of cosmic explosions

Date:
March 28, 2023
Source:
Harvard-Smithsonian Center for Astrophysics
Summary:
Scientists believe the gamma-ray emission, which lasted over 300
seconds, is the birth cry of a black hole, formed as the core of
a massive and rapidly spinning star collapses under its own weight.


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FULL STORY ==========================================================================
On October 9, 2022, an intense pulse of gamma-ray radiation swept through
our solar system, overwhelming gamma-ray detectors on numerous orbiting satellites, and sending astronomers on a chase to study the event using
the most powerful telescopes in the world.


==========================================================================
The new source, dubbed GRB 221009A for its discovery date, turned out
to be the brightest gamma-ray burst (GRB) ever recorded.

In a new study that appears today in the Astrophysical Journal Letters, observations of GRB 221009A spanning from radio waves to gamma-rays,
including critical millimeter-wave observations with the Center for Astrophysics | Harvard & Smithsonian's Submillimeter Array (SMA)
in Hawaii, shed new light on the decades-long quest to understand the
origin of these extreme cosmic explosions.

The gamma-ray emission from GRB 221009A lasted over 300
seconds. Astronomers think that such "long-duration" GRBs are the birth
cry of a black hole, formed as the core of a massive and rapidly spinning
star collapses under its own weight. The newborn black hole launches
powerful jets of plasma at near the speed of light, which pierce through
the collapsing star and shine in gamma- rays.

With GRB 221009A being the brightest burst ever recorded, a real mystery
lay in what would come after the initial burst of gamma-rays. "As the
jets slam into gas surrounding the dying star, they produce a bright `afterglow' of light across the entire spectrum," says Tanmoy Laskar,
assistant professor of physics and astronomy at the University of Utah,
and lead author of the study. "The afterglow fades quite rapidly, which
means we have to be quick and nimble in capturing the light before it disappears, taking its secrets with it." As part of a campaign to use
the world's best radio and millimeter telescopes to study the afterglow
of GRB 221009A, astronomers Edo Berger and Yvette Cendes of the Center
for Astrophysics (CfA) rapidly gathered data with the SMA.

"This burst, being so bright, provided a unique opportunity to explore
the detailed behavior and evolution of an afterglow with unprecedented
detail -- we did not want to miss it!" says Edo Berger, professor of
astronomy at Harvard University and the CfA. "I have been studying these
events for more than twenty years, and this one was as exciting as the
first GRB I ever observed." "Thanks to its rapid-response capability,
we were able to quickly turn the SMA to the location of GRB 221009A,"
says SMA project scientist and CfA researcher Garrett Keating. "The team
was excited to see just how bright the afterglow of this GRB was, which
we were able to continue to monitor for more than 10 days as it faded."
After analyzing and combining the data from the SMA and other telescopes
all over the world, the astronomers were flummoxed: the millimeter and
radio wave measurements were much brighter than expected based on the
visible and X-ray light.

"This is one of the most detailed datasets we have ever collected,
and it is clear that the millimeter and radio data just don't behave
as expected," says CfA research associate Yvette Cendes. "A few GRBs
in the past have shown a brief excess of millimeter and radio emission
that is thought to be the signature of a shockwave in the jet itself,
but in GRB 221009A the excess emission behaves quite differently than
in these past cases." She adds, "It is likely that we have discovered a completely new mechanism to produce excess millimeter and radio waves."
One possibility, says Cendes, is that the powerful jet produced by
GRB 221009A is more complex than in most GRBs. "It is possible that the
visible and X-ray light are produced by one portion of the jet, while the
early millimeter and radio waves are produced by a different component." "Luckily, this afterglow is so bright that we will continue to study its
radio emission for months and maybe years to come," adds Berger. "With
this much longer time span we hope to decipher the mysterious origin
of the early excess emission." Independent of the exact details of
this particular GRB, the ability to respond rapidly to GRBs and similar
events with millimeter-wave telescopes is an essential new capability
for astronomers.

"A key lesson from this GRB is that without fast-acting radio and
millimeter telescopes, such as the SMA, we would miss out on potential discoveries about the most extreme explosions in the universe," says
Berger. "We never know in advance when such events will occur, so we
have to be as responsive as possible if we're going to take advantage
of these gifts from the cosmos."
* RELATED_TOPICS
o Space_&_Time
# Cosmic_Rays # Black_Holes # Space_Telescopes # Astronomy
# Space_Exploration # Astrophysics # Stars # Cosmology
* RELATED_TERMS
o Gamma_ray_burst o Supernova o Blue_supergiant_star
o Spitzer_space_telescope o Black_hole o
Compton_Gamma_Ray_Observatory o Quasar o Holographic_Universe

========================================================================== Story Source: Materials provided by Harvard-Smithsonian_Center_for_Astrophysics. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Tanmoy Laskar, Kate D. Alexander, Raffaella Margutti, Tarraneh
Eftekhari,
Ryan Chornock, Edo Berger, Yvette Cendes, Anne Duerr, Daniel
A. Perley, Maria Edvige Ravasio, Ryo Yamazaki, Eliot H. Ayache,
Thomas Barclay, Rodolfo Barniol Duran, Shivani Bhandari, Daniel
Brethauer, Collin T.

Christy, Deanne L. Coppejans, Paul Duffell, Wen-fai Fong, Andreja
Gomboc, Cristiano Guidorzi, Jamie A. Kennea, Shiho Kobayashi,
Andrew Levan, Andrei P. Lobanov, Brian D. Metzger, Eduardo Ros,
Genevieve Schroeder, P.

K. G. Williams. The Radio to GeV Afterglow of GRB 221009A. The
Astrophysical Journal Letters, 2023; 946 (1): L23 DOI:
10.3847/2041-8213/ acbfad ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/03/230328145539.htm

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