Edited from a release by the National Radio Astronomy Observatory.
Using the U.S. National Science Foundation Very Large Array (NSF VLA) radio telescope, operated by the U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO), the team achieved two firsts: the first detection of polarized radio-wavelength emission from a gamma-ray burst (GRB) afterglow and the first detection of Faraday rotation in a GRB.
Faraday rotation occurs when magnetic fields twist the orientation of polarized light as it travels through space. The effect acts like a magnetic fingerprint, encoding information about the strength and structure of the fields the light passed through. The findings, led by researchers at the University of Arizona and the University of Utah, offer a new window into the extreme physics driving these titanic explosions.
The paper has been submitted to The Astrophysical Journal and is available on arXiv.
What are gamma-ray bursts?
Gamma-ray bursts release in seconds as much energy as the sun will emit over its entire lifetime. They are thought to launch narrow jets of particles traveling at nearly the speed of light, producing a radio “afterglow” that can linger for months. Despite decades of study, the magnetic fields within these jets and their immediate surroundings have remained stubbornly difficult to measure, until now.
“GRBs are the most powerful explosions in the universe, and magnetic fields are thought to play a central role in powering them, but probing those fields has been extraordinarily difficult,” said Tanmoy Laskar, assistant professor of physics and astronomy at the University of Utah. “By detecting polarized radio emission, we can now directly measure the magnetic environment of one of the universe’s most violent events. Our new GRB observations allow us to use the universe as our laboratory to test our understanding of how physics operates in such extreme conditions.”
The burst, GRB 260310A, reveals polarized radio waves
GRB 260310A occurred relatively close to Earth by cosmic standards, giving astronomers an extraordinary opportunity to study one of the brightest radio afterglows seen in decades. By pointing the NSF VLA at the fading explosion, the team found that the radio waves were polarized, meaning the light waves were oscillating in a preferred direction, rather than vibrating randomly. The same property is exploited by polarized sunglasses, which reduce glare by blocking partially polarized light reflected from water and other smooth surfaces.
Faraday rotation in a gamma-ray burst
Detecting polarized radio emission alone would have been an exciting milestone for the NSF VLA. But the team made an even more remarkable discovery: the polarization signal changed across different wavelengths, revealing Faraday rotation for the first time in a gamma-ray burst. Just as a prism bends different colors of visible light by different amounts, magnetized plasma rotates polarized radio waves by different amounts depending on their wavelength. The faster that rotation changes with wavelength, the stronger the magnetic field the light passes through.
The NSF VLA data revealed a magnetic field along the light’s path thousands of times stronger than what could be explained by passage through our Milky Way galaxy or the space between galaxies. Instead, it points to an exceptionally dense, magnetized cloud of gas surrounding the star that exploded to produce GRB 260310A.
Read the full article By Lisa Potter in @ The U