Magnetic Power Revealed in Gamma-Ray Burst Jet

December 9, 2009 by Francis Reddy
Swift spacecraft
An artist's impression of the Swift spacecraft with a gamma-ray burst going off in the background.

( -- A specialized camera on a telescope operated by U.K. astronomers from Liverpool has made the first measurement of magnetic fields in the afterglow of a gamma-ray burst (GRB). The result is reported in the Dec.10 issue of Nature magazine by the team of Liverpool John Moores University (LJMU) astronomers who built and operate the telescope and its unique scientific camera, named RINGO.

The burst occurred January 2, 2009. NASA's Swift satellite observed its position and immediately notified telescopes all over the world via the Internet. When it received the trigger from Swift, the robotic Liverpool Telescope on the island of La Palma in the Canary Islands automatically swung to observe the burst. Its special camera employs a spinning disk of Polaroid -- similar to the material used in sunglasses.

"By observing how the brightness of the GRB varied as we spun the Polaroid, we could measure the in the burst," explained Iain Steele, Director of the Liverpool Telescope.

"This important result gives us new insight into the physics of these remarkable objects and is a testament to the close collaboration between observers, theoreticians and technologists in the Liverpool and NASA Swift teams," added LMJU team leader Carole Mundell. "It's incredible to think that the GRB discovery and our measurement process - from first detection and notification by NASA's Swift satellite to the polarization measurement using RINGO on the Liverpool Telescope - took place completely automatically within less than three minutes and with no human intervention!"

"This breakthrough observation gives us the first measurement of magnetic fields in the afterglow of a GRB," said Swift lead scientist Neil Gehrels, Swift lead scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

Gamma Ray Bursts form when the core of a massive star collapses or when two neutron stars merge together. The resulting explosions are the brightest events in the universe and vastly outshine entire galaxies containing hundreds of billions of stars. NASA's sees about 100 of these events each year, triggering ground-based follow-up by observations across the globe.

Polarization is one of the least-observed properties in astronomy. This finding opens the door to understanding the role of magnetic fields in some of the most powerful events in the universe.

"These very interesting observations raise the possibility that gamma-ray bursts are not fireballs as usually presumed but are powered and collimated by an organized electromagnetic field," said Roger Blandford, Director of the Kavli Institute of Particle Astrophysics and Cosmology at Stanford University, California, commenting on the result's importance. "It will be very interesting to see if there are similarities in observations of other kinds of cosmic jets."

Source: NASA's Goddard Space Flight Center (news : web)

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1 / 5 (1) Dec 09, 2009
Yes, but what did the observations reveal about the influence of magnetic fields upon this event?
not rated yet Dec 09, 2009
Exactly what do they mean by "collimated", the gamma rays? Does this mean the gamma rays are concentrated or magnified by a magnetic field?
So the fireballs are an illusion? An interesting possiblity.
not rated yet Dec 09, 2009
So how big was the field?
2.8 / 5 (4) Dec 09, 2009
Is the Gamma-Ray Burst coming from a neutron star?

Neutron stars have enormous magnetic fields.

Do black holes?

With kind regards,
Oliver K. Manuel
1 / 5 (1) Dec 10, 2009
Exactly what do they mean by "collimated", the gamma rays? Does this mean the gamma rays are concentrated or magnified by a magnetic field?
So the fireballs are an illusion? An interesting possiblity.

Generally it means that the photons are lasing.

A gamma-ray laser would truly be a sight to behold. A death ray to end all death rays. I have always thought one would need mirrors made of unobtainium to collimate gamma, but there you go.
not rated yet Dec 10, 2009
This breakthrough observation gives us the first measurement of magnetic fields in the afterglow of a GRB

Why measuring polarization of incoming light would constitute a "breakthrough"? And how is the "measurement of magnetic fields in the afterglow of a GRB" extracted from measured polarization?
not rated yet Dec 11, 2009
Well, if someone has and extra $18 they could always buy a reprint from here http://www.nature...728a.pdf and let us all know the scientific details.
not rated yet Dec 16, 2009
Ok, a little clarification.
First, polarization has already been observed in GRB afterglows! So I don't see exactly the breakthrough here.
Second, collimated means that the jet of particles that emit the Xrays is collimated (like a cone) and not isotropic (spherical explosion). But there are till shells of particles that deccalerate to produce the Xray.

The connection with magnetic fields is simple - nobody has a good idea why GRBs are collimated and why they are so powerful. One of the ideas is the so called Blandford-Znajek mechanism, which uses strong magnetic fields to extract energy from a rotating black hole. But this requires extremal magnetic fields, something very hard to acquire. So this study in a way confirms one of the needed conditions for Blandford-Znajek process to work.

Interestingly, the article doesn't imply a BH, but of course magnetic fields are useful for collimation in all kind of objects.

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