Introduction
Gamma ray bursts (GRBs) are the most powerful phenomena in the universe since the Big Bang itself. They emit enough energy to sterilize entire regions of their home galaxies, and are thought to mark the beginning of a supernova. On September 22, 2020, astronomers detected a GRB, dubbed GRB 22 1009a, that was so powerful it temporarily blinded the Fermi Gamma Ray Telescope. This GRB was so powerful that it was estimated to occur only once every 10,000 years, and was dubbed the Brightest of All Time or the BOAT.
Observations
When the Swift Observatory and XMM Newton telescopes imaged the bright X-ray afterglow, they found more than 20 rings of X-ray light, scattering off dust clouds in our galaxy. Follow-up observations were made at all wavelengths to figure out what caused the BOAT, and these findings have called into question our understanding of GRBs. For example, Hubble and the James Webb Space Telescope found no evidence of a supernova, and the GRB was surprisingly faint in the radio spectrum.
Publications
The BOAT was so weird and amazing that a series of papers about it were published in a special issue of the Astrophysical Journal. These papers discussed the implications of the BOAT, and how it challenges our understanding of GRBs.
The brightest gamma ray burst ever seen
Introduction
Gamma ray bursts (GRBs) are highly energetic explosions that are thought to be caused by the collision of two neutron stars or the collapse of a very massive star. GRBs are generally classified by their duration, with short GRBs lasting under two seconds and long GRBs lasting anywhere from two seconds to several hours. Both scenarios produce an initial burst of gamma ray emission, followed by a longer lasting afterglow.
Short GRBs
Short GRBs are thought to be caused when a pair of neutron stars collide. This collision sets off what is called a kill Anova. The shock front produced by the collision produces emission at longer wavelengths, starting from X-rays and going all the way to radio. By studying the afterglow, scientists can learn about the properties of the surrounding medium, the physics of the GRB itself, and piece together the puzzle of what caused the burst in the first place.
Long GRBs
Long GRBs occur when the core of a very massive star collapses to form a black hole. If the GRB came from a black hole inside of a collapsing star, there is a third act to follow. The black holes jet ignites runaway fusion inside the stars interior that explodes the star from the inside out. The result is an extremely energetic supernova, sometimes called a hypernova. These long duration bursts are so energetic that they can easily outshine their host galaxies.
GRB 22 1009a
When GRB 22 1009a was first detected, it was without question the brightest gamma ray burst ever seen.
The Brightest Gamma Ray Burst in Human History
The new record holder for the brightest gamma ray burst in human history was so bright, it actually blinded the instruments on the Fermi gamma ray telescope when its actual brightness was later reconstructed. It blew all of the other bursts out of the water and was even detected by instruments that weren’t designed for this purpose.
The very first detection was picked up a day earlier by Voyager 1, which is now in interstellar space. A day later, the bursts reached the inner solar system and was detected by ISSAs, Gaia, satellite at L2 and then the Integral satellite in CIS lunar space about one second later. It was then detected by Fermi and GRB Alpha in low earth orbit. The burst even irradiated Earth’s ionosphere and continued to L1, where it was detected by the ACE and Wind spacecraft studying the Sun. A few minutes later, it was detected at Mars by Maven and Mars Odyssey.
Once in a Ten Thousand Year Event
Something this bright doesn’t happen very often. In fact, the burst was calculated as being a nearly once in ten thousand year event. Human civilization is only about six thousand years old, so it’s quite possible the burst is literally the brightest gamma ray burst in human history. Luckily for us, we just happen to have telescopes in space that could study it.
Behaving in Unexpected Ways
However, the burst is behaving in ways that really don’t make sense. Bursts like these are understood to be associated with dying, massive stars, but so far the burst hasn’t shown any evidence of a supernova.
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Recently, a bright afterglow was seen at x-ray wavelengths, but it was surprisingly quiet in radio. This has prompted researchers to investigate why it wasn’t brighter at radio wavelengths and why it was so extraordinarily bright to begin with.
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The Brightest Gamma Ray Burst Ever Detected
The boat was the brightest gamma ray burst ever detected, but weirdly the boats, radio, Afterglow wasnt unusually bright at all. It gets even more interesting when you look at how the radio visible and x ray emission faded out over time and thats. What were seeing here in these data points.
Modeling the Radio Visible and X-Ray Emission
Each color corresponds to some time after the burst over the last 50 years of studying grbs, a number of standard models have been developed that describe how the Afterglow Fades across different wavelengths, but when the models were run against the boat, they matched up with the visible And x, ray emission quite well, but largely came up short on the radio.
The Boat Wasn’t As Powerful As It Appeared
The modeling also indicated that, although the boat was the brightest ever seen, it may not have actually been all that powerful in terms of the total energy released. Rather, it may have appeared so bright because all of its energy was concentrated into a very tight beam and that beam happened to be aimed directly at Earth. Its kind of like how a pocket laser is far more intense than a Searchlight, even though it uses far less energy. Now before you get any ideas, no, you should never ever look directly into a gamma ray burst or a laser.
The Boat Originated 1.9 Billion Light Years Away
It also turns out that the boat originated at a redshift of 0.15 and that works out to about 1.9 billion light years away, believe it or not, thats, actually not particularly far for a gamma ray burst.
The Strange Boat
The boat has something strange about it – no Supernova was detected, even though Long bursts are thought to come from dying, massive stars. This is because, as the Afterglow of the burst Fades out, the underlying light from the Supernova Starts to become visible, so the light curve of the burst tends to stabilize and stay bright as the Supernova takes over. However, this time there was no evidence of a supernova as the Afterglow faded.
What Was Going On?
The boat came from a direction that was almost directly in line with the plane of the Milky Way galaxy, and that means its light had to pass through some 60 a thousand light years of our galaxy, which is Laden with dust. If a supernova really happened, then Dust in our galaxy could have blocked up to 99 of its visible light. Fortunately, longer wavelengths, like near infrared, can sidestep much of this dust.
To that end, the James Webb Space Telescope captured Spectra of the boat at both near and mid infrared wavelengths. In fact, this was the first time the mid infrared spectrum of a grb had ever been obtained. But if a supernova were taking place, there should have been some excess submission or changes in web Spectrum over time, but neither of those effects were detected. This might be because there was more dust at work here than just that from our galaxy alone.
Near Infrared Image of Supernova
A near infrared image made with the Hubble Space Telescope reveals an extended feature emerging from the burst. This feature is actually the burst’s home galaxy, and it appears to be a spiral seen edge-on. This suggests that the supernova would have first had to penetrate through its home galaxy’s disk and then through the disk of the Milky Way before arriving at Earth.
No Supernova?
It is possible that there was no supernova at all, because the black hole that formed inside the collapsing star managed to kick off the gamma ray burst, but then swallow its own supernova. In 2015, the mass of star N6946BH1 disappeared without a trace.
Intermediate Case
The event might present us with some new kind of intermediate case, where a massive star’s core collapses to create a black hole which in turn kicks off a gamma ray burst. But then the black hole gets so massive, so quickly, it reverses and consumes the subsequent supernova.
Colliding Neutron Stars?
Alternatively, there may not have been a supernova because the burst was not triggered from a collapsing massive star at all, but rather by a pair of colliding neutron stars. Such events trigger a shorter and less energetic gamma ray burst, but if the burst was confined to an extremely narrow jet and aimed directly toward Earth, it would then make the burst appear bright enough to become the boat. Colliding neutron stars are thought to produce GRBs that are only between a few milliseconds to no more than a couple of seconds long.
The Outburst of Boats
In 2022, Rust and Jod and their collaborators reported the discovery of a kilonova associated with a gamma-ray burst (GRB) that lasted nearly a minute. This was a surprise, as the Outburst of Boats had lasted 600 seconds, leading to the initial assumption that it was a collapsing massive star. To explain the discrepancy, it was suggested that the Outburst of Boats must have been a pair of colliding neutron stars that managed to create a GRB that lasted up to 10 minutes longer, with an ultra-collimated jet aimed directly at Earth.
The Polarization of Light
To explain the ultra-collimated jet, it was suggested that extremely strong magnetic fields were needed in order to collimate the light so tightly. These strong magnetic fields would polarize the emission of the initial burst, with the stronger magnetic fields resulting in more polarized light. To measure this polarization, the Imaging X-ray Polarimetry Explorer (IXPE) was used. The IXPE found that, while the polarization was high, it was not the highest recorded for a burst.
The Effect of Dust
However, the Outburst of Boats was glimpsed through the plane of the Galaxy, with light passing through Galactic clouds scattering and forming the rings surrounding the burst. It was suggested that these dust clouds might have reduced the polarization of the light in some way. To understand the effect of the dust, more observations were needed as the Afterglow faded. In total, 21 rings were counted, indicating that the burst had to pass through no fewer than 21 clouds, ranging from as close as 700 light years from Earth to as many as 61 000 light years.
The Boat GRB: Probing the Structure of Our Galaxy
The Boat GRB, or Gamma-ray burst, is a powerful flash of gamma rays that occurs in distant galaxies. On the other side of the galaxy, however, not all of the light from the burst is passing directly through the geometric plane of the galaxy. The angle of incidence is about 4 degrees, so the most distant Rings were formed above the plane of our galaxy.
Why is There Dust Above the Galactic Plane?
It turns out our galaxy isn’t perfectly flat, but rather has a warp on either end on the far side the warp is lifted upward and that allowed just enough dust present for the boat GRB to pass through. This has allowed astronomers to probe at least a portion of the structure of our galaxy. We now know where the dust clouds lie along the line of sight to the boat and that’ll in turn tell us more about the history of our galaxy’s formation, which includes mergers and collisions with smaller galaxies.
Continued Observations
This past winter, the boat disappeared behind the Sun for a couple of months, but it has since reappeared, and more observations are being conducted now. There are still many questions left to be addressed and much more to be learned.
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