XRT image of GRB 080319B (courtesy Swift team)

GRB 080319B

Nature's Brightest Explosion

Bursting onto the scene – In the seconds after it first pointed at GRB 080319B, the infrared telescope PAIRITEL was blinded by the brilliant explosion (a). As the burst began to fade, PAIRITEL was able to track the light from the explosion for many hours (b and c).
PAIRITEL evolution of GRB 080319B, from blinding to barely visible.

Astronomers are used to counting the passage of time in millions of years, not seconds – but the moment of March 19, 2008, at precisely 06:12:49 GMT, was a second to remember. Having travelled through intergalactic space for 7.5 billion years after being released by the explosion of a gigantic star in the most distant reaches of the known universe, a brilliant pulse of gamma-ray and X-ray radiation, accompanied by a bright flash of optical light, finally reached Earth.

This flash of light would have been bright enough that under the right conditions, a person staring at the sky with the naked eye would have been able to see this explosion in spite of its distance of 7.5 billion light years – a factor of two thousand times further away than what is normally the record-holder for the most distant object the human eye can see (the galaxy M32, at a comparatively nearby 3 million light years.)

But as far as we know, no person noticed the explosion. Instead, the news was broken by a humble robot – the Swift telescope, a NASA satellite launched in 2004 to study explosions like this one, known to astronomers as "gamma-ray bursts". Within seconds, the instrument's gamma-ray telescope was swamped with signal as thousands of high-energy gamma-rays pelted the detector at once. The robotic telescope, which carries on-board software to quickly re-point itself to quickly stare at the source with its more sensitive X-ray and optical telescopes, rapidly turned and began observations – and was nearly blinded by the accompanying optical flash, which was so bright that the detector was briefly overwhelmed, unable to accurately track the evolution of the event until several minutes later when the explosion began to quickly fade.

Ordinary optical telescopes on the ground, such as the infrared telescope PAIRITEL (images shown at right), met a similar fate – saturated by the initial burst, these telescopes were only able to begin to study the event until several minutes after. Luckily, a few specialized telescopes – small intstruments no larger than a backyard scope, but specially designed to be able to monitor large portions of the sky at once – were small enough to avoid being swamped by the brightness of the event, but still able to track it from its beginning for several minutes, when the larger telescopes took over. These telescopes, including Pi of the Sky, REM/TORTORA, and RAPTOR, allowed scientists to study for the first time exactly what a gamma-ray burst looks like in optical light all the way from beginning to end.

Space can be a violent place – racked by explosions from magnetic storms on neutron stars to supernovae. Yet even among this trigger-happy assortment of rogues, March's gamma-ray burst – catalogued as GRB 080319B – stands out. Since the first recored supernova was discovered in 386 C.E. by Chinese astronomers, it is the brightest (after taking into account the vast distance of this event) explosion ever discovered. In the moments after the explosion, the gamma-ray burst was so bright that it outshone the light from the galaxy it occurred in by a factor of 200,000,000. It took several months for the explosion to fade enough for the galaxy in which it occurred to even be visible again.

The implications of this may be profound. The fact that an event was visible to the naked eye at a distance of 7.5 billion light years implies that if similar explosions occur even further away – at a distance from Earth of 13 billion light years or more, meaning that they occurred in the very earliest phases of the universe, which is 13.7 billion light years old – current and upcoming telescopes would be able to study them in great detail, potentially informing us in great detail about this earliest era in cosmic history.

Image Gallery

Two months later – Thirty seconds after GRB 080319B first exploded, it may have been visible to the naked eye. It took several months for the burst to fade sufficiently for the galaxy it occurred in to be visible to the biggest telescopes on Earth. At lower right is an image from Gemini-North showing the field around the gamma-ray burst, filled with stars and galaxies unrelated to the event. An arrow shows the location where the burst once occurred, barely visible in this image. At bottom right is an image from the Hubble Space Telescope (credit N. Tanvir) showing the fading ember left behind by the burst - which, two months later, is still dominating the light from the galaxy in which it occurred. The top three images, from the Sloan Digital Sky Survey (via Google Earth), show a progression of zooming from the constellation Bootes (top right), to the field shown in the Pi-of-the-Sky images (top middle, compare to image below), and progressively to the Gemini and Hubble images.
GRB 080319B zoom-in tiled image SDSS: zoom 1 SDSS: zoom 2 SDSS: zoom 3 Gemini-North zoom image Gemini-North deep image Hubble Space Telescope

Rise and fall of a GRB – This sequence of images, courtesy of the Pi-of-the-Sky collaboration, shows the flash of visible light from GRB080319B (center of image) as it rose and faded during the first minute of the explosion. The time sequence goes from left to right.
GRB 080319B from Pi-of-the-sky

Fade to black – Comparison of the same field, with the GRB at the center, at two minutes (imaged by PAIRITEL) and two months (imaged by Gemini-North). The burst has faded by a factor of over a million.
PAIRITEL vs. Gemini

Links and Resources

GRB 080319B

General gamma-ray bursts

Page authored by D. Perley (University of California, Berkeley)
Images shown on this page are credit D. Perley, A. Miller, and J. Bloom unless otherwise mentioned. The X-ray image in the title line is courtesy the Swift team. Copying and reuse of the images and text contained in this article is strongly encouraged. Contact dperley@astro.berkeley.edu for more information.