Gamma-Ray Burst Exceeds All Others

by Paul Gilster on February 24, 2009

Adam Goldstein must be living right. Here’s a grad student (University of Alabama, Huntsville) who’s on his first day on the job working with the Fermi Gamma-ray Space Telescope. He’s given the task of monitoring the Gamma-ray Burst Monitor (GBM) instrument, which routinely detects bursts, about one a day. This time, though, when the phone rings, it is to flag a burst like no other, 700 times longer in duration than the average.

grb_080916c_a

We already knew that GRBs were exotic events. Many astronomers believe that they occur when, out of its nuclear fuel, a massive star collapses into a black hole, creating jets of material that interact with gaseous debris previously shed by the star. But this one, detected in mid-September last year, was a true behemoth, with a red shift pegging its point of origin as twelve billion light years from Earth, in the constellation Carina. GRB 080916C turns out to be the most powerful gamma-ray event ever detected.

Image: GRB 080916C’s X-ray afterglow appears orange and yellow in this view that merges images from Swift’s UltraViolet/Optical and X-ray telescopes. Credit: NASA/Swift/Stefan Immler.

Valerie Connaughton (UAH), a member of the GBM team, says this about the burst:

“This is the most spectacular burst ever seen at high energy. If the event that caused this blew out in every direction instead of being a focused beam, it would be equivalent to 4.9 times the mass of the sun being converted to gamma rays in a matter of minutes.”

But it’s not just the power of the burst that is worth noting. GRB 080916C lasted for 23 minutes, implying (at the specified distance) that the actual event was four minutes in duration when it occurred. What processes produce this kind of gamma-ray activity? Moreover, rather than starting with high-energy gamma rays, the early detection here was on the low-energy side, with the high-energy gamma rays not showing up until five seconds into the event. The cooler gamma rays faded out early on but the high-energy rays persisted for an additional twenty minutes. Why?

“This one burst raises all sorts of questions,” says Peter Michelson (Stanford). “In a few years, we’ll have a fairly good sample of bursts, and may have some answers.”

Those answers could give us insights into the environment around gamma-ray bursts, which includes stellar debris, a black hole and massive amounts of radiation. They might also give us a read on theories of quantum gravity that suggest empty space is actually a froth of quantum foam, one that would allow lighter, lower-energy gamma rays to move more quickly than their higher-energy cousins. Future observations to study unusual time lags like these should help us pin down a plausible explanation.

The paper is Abdo et al., “Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C,” Science Express February 19, 2009 (abstract). A news release from the SLAC National Accelerator Laboratory is also available.

{ 5 comments }

ad February 24, 2009 at 14:48

They might also give us a read on theories of quantum gravity that suggest empty space is actually a froth of quantum foam, one that would allow lighter, lower-energy gamma rays to move more quickly than their higher-energy cousins.

Shouldn’t that be the other way around: “allow higher-energy gamma rays to move more quickly than their lower-energy cousins”?

Administrator February 24, 2009 at 15:39

ad, this is from the SLAC news release:

“If the theorized idea of quantum gravity is correct, then at its smallest scale space is not a smooth medium but a tumultuous, boiling froth of “quantum foam.” Lower-energy (and thus lighter) gamma rays would travel faster through this foam than higher-energy (and thus heavier) gamma rays. Over the course of 12.2 billion light years, this very small effect could add up to a significant delay.”

Note that it was the lower-energy gamma rays that provided the earliest detection; they seem to have gotten here first.

James M. Essig February 24, 2009 at 15:40

Hi Folks;

It may indeed be the case that 13 GeV range gamma rays travel at a lower velocity than do visible light photons. The observed 5 second delay would amount to a velocity difference of C{5/{[1.22 x 10 EXP 10][3.1 x 10 EXP 7]}} or (2.998 x 10 EXP 8){5/{[1.22 x 10 EXP 10][3.1 x 10 EXP 7]}} meters per second.

However, if such a quantum gravity effect exists of C dependence on photon energy, we might still find an effect whereby photons that approach the Planck Energy or perhaps of even higher energies, if such is possible without such photons becoming a black hole due to self gravitational effects, would travel much faster than ordinary values of C due to effects proposed by the theory of doubly special relativity. The curve of photon energy in a vacuum along the x axis verses photon velocity along the y-axis might dip ever so slightly at x ray and GeV to TeV range gamma ray energies, but afterward begin to rise perhaps taking the form of an assymptote as the photon energy approaches the Planck Energy or perhaps some other greater yet limiting energy.

There might exist other inflection points along any such curve for extreme photon energies due to other spatial effects that have not yet be theoretically formulated.

Regardless, I am reasonably sure there is more to learn about the transport effects of any fine grained structure to space and/or time and other spatial-temporal aspects on photon propagation velocities.

Thanks;

Jim

ljk September 9, 2009 at 9:12

Gamma Ray Bursts – Maybe not so old after all

Authors: Enrico Ramirez-Ruiz, William Lee

(Submitted on 8 Sep 2009)

Abstract: The discovery of a short-lived gamma-ray burst at a surprisingly early epoch in the history of the Universe shows how much is still unknown about the evolution of the parent systems of such bursts.

Comments: Published in Nature News and Views

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Journal reference: Nature, 460, 1091 (2009)

Cite as: arXiv:0909.1368v1 [astro-ph.HE]

Submission history

From: William H. Lee [view email]

[v1] Tue, 8 Sep 2009 01:22:40 GMT (548kb,X)

http://arxiv.org/abs/0909.1368

ljk October 29, 2009 at 17:21

October 28, 2009

Einstein Still Rules, Says Fermi Telescope Team

Written by Nancy Atkinson

While the Fermi Space Telescope has mapped the gamma ray sky with unprecedented resolution and sensitivity, it now has been able to take a measurement that has provided rare experimental evidence about the very structure of space and time, unified as space-time.

Einstein’s theory of relativity states that all electromagnetic radiation travels through a vacuum at the same speed. Fermi detected two gamma ray photons which varied widely in energy; yet even after traveling 7 billion years, the two different photons arrived almost simultaneously.

On May 10, 2009, Fermi and other satellites detected a so-called short gamma ray burst, designated GRB 090510. Astronomers think this type of explosion happens when neutron stars collide. Ground-based studies show the event took place in a galaxy 7.3 billion light-years away.

Of the many gamma ray photons Fermi’s LAT detected from the 2.1-second burst, two possessed energies differing by a million times. Yet after traveling some seven billion years, the pair arrived just nine-tenths of a second apart.

“This measurement eliminates any approach to a new theory of gravity that predicts a strong energy dependent change in the speed of light,” Michelson said. “To one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules.”

Full article here:

http://www.universetoday.com/2009/10/28/einstein-still-rules-says-fermi-telescope-team/

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