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Pomona College Professor Helps Discover Primeval Gamma Ray Burst

Bryan Penprase, a professor of physics and astronomy at Pomona College, is part of an international team of astronomers who have discovered the most distant gamma ray burst ever, more than 10 billion light years away. The result is the outcome of several years of collaboration with the Caltech Gamma Ray burst team, led by Dr. Shrinivas Kulkarni. The findings were reported in the October 29 edition of the journal Nature, “A g-ray burst in redshift of z »8.2”.

Penprase joined the team in 2004-05 and his main role has been interpreting the spectra from the gamma ray bursts. This project involved closely monitoring gamma ray burst discoveries with the Swift satellite and rapidly turning optical, and infrared ground-based telescopes onto the location of newly discovered gamma ray bursts.

“By working quickly,” Penprase explains, “it is possible to capture the short burst of optical and infrared energy from a dying massive star before it disappears forever. Gamma ray bursts are like supernovae, but instead of releasing their 100 billion solar luminosities over a year, as supernovae do, they release most of their energy in just a few seconds in gamma ray bursts. Then heat up their surroundings so they glow in x-rays and optical light and, as they cool. in infrared and radio light.

“Because the gamma ray burst is the most luminous source known in astrophysics, it can be seen at great distances,” says Penprase. "But astronomers can only learn more about how far away and how bright the gamma ray burst are if they are ready to follow the burst with a large arsenal of follow-up telescopes. By measuring the spectrum of the gamma ray burst, as in this case, it is possible to find out its redshift and from this the distance. “

“This particular gamma ray burst was seen to have only infrared emission from the ‘afterglow’ which is very unusual. A follow-up spectrum revealed that the gamma ray burst was at such enormous distances that the optical and UV light was redshifted completely into the infrared. The spectrum hinted at the presence of the "Lyman break" which usually occurs near 911 Angstroms, or in the far ultraviolet, at infrared wavelengths, implying a redshift of 8.2, which means that the light was shifted by a factor of 9.2 in wavelength. Another way of looking at it -- the light was emitted when the universe was only 1/9.2 its present size, which means we are looking at something as it was when the universe was about 10% of its present age. By using a model of the universe's expansion, we estimate that the observation is looking back 13.035 billion years into the past. For comparison, the universe is thought to have begun in the Big Bang 13.7 billion years ago!”

“This sort of ‘primeval gamma ray burst’ provides the first ever look at the ancient times of the universe,” explains the clearly excited Penprase. This is just one of the early results of a new field of gamma ray burst afterglow spectroscopy.”

Pomona College, one of the nation’s premier liberal arts institutions, offers a comprehensive program in the arts, humanities, social sciences and natural sciences. Its hallmarks include small classes, close relationships between students and faculty, and a range of opportunities for student research.