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Exploring Gamma-ray Bursts


Gamma-ray bursts are a great example of how much astronomers have come to understand events in the universe in the decades since the space age began. In the June episode of The Astronomer’s Universe, I talked with Dr. Dale Frail of the U.S. National Radio Astronomy Observatory about these once-mysterious occurrences in the distant cosmos.  They were first discovered during the Cold War, when military satellites detected distant bursts of gamma radiation.  They weren’t coming from nuclear bombs, so they clearly had to be the end point of some huge explosion in space. But what?  Some scientists thought they came from nearby space (such as within our own galaxy). These bursts were observed not just in gamma-ray wavelengths, but in x-ray, ultraviolet, optical, infrared, and radio wavelengths of light. The engine for such powerful outbursts was unknown. Could it be two galaxies colliding? A class of supernova explosion called a hypernova? Or something else? Some were known to be very far away, and that begged the question about what could power an explosion seen from across the universe?

Eventually astronomers devised orbiting telescopes to study these outbursts, and ground-based observers collected data about their optical, radio, x-ray, ultraviolet, and infrared afterglows. In the process,they found out that there are two main classes of gamma-ray bursts: long-burst and short-burst. That finding, along with more observations, led them to a couple of different explanations for these explosions. Most gamma-ray bursts seem to be coming from a narrow beam of radiation that is released as part of a supernova explosion. Those bursts are the long-burst variety. The short-burst events are likely coming from the merger of two massive, energetic objects — most likely a pair of neutron stars.

There is still a lot of data to be gathered about these massive, catastrophic events.  For example, the NASA Swift satellite is the latest in a string of orbiting observatories that have actively studied energetic events in the cosmos, including gamma-ray bursts. Ground-based observatories, such as the Very Large Array in New Mexico, will continuing doing follow-up observations of the explosions, and optical observers (including a number of amateur astronomers) will follow-up with visual confirmation of these distant occurrences. Through a combination of all these observations, in the not-too-distant future astronomers will gain a much better insight into the events that cause these massive explosions in space.

Active Galactic Nuclei and Gamma-Ray Bursts

Last summer (July 2009) there was a conference (Marcel Grossmann conference) held in Paris, France to discuss some of the latest research related to Einstein’s General Theory of Relativity. One session focused on the relationship between active galactic nuclei (AGN) and gamma-ray bursts. Today, astronomers released a summary report covering the current understanding of the nature of active galactic nuclei and their linkage with gamma-ray bursts. Read the summary report about AGNs and gamma-rays online now here.

On the Nature of Dark Gamma Ray Bursts

One of the major questions that remain for the gamma-ray observers, especially those associated with the NASA SWIFT spacecraft, is the nature of the so-called dark gamma-ray bursts (GRB). Usually, after the SWIFT spacecraft detects a GRB, optical telescopes that are part of a network of telescopes supporting the SWIFT mission, take a look in the direction of the GRB and find what is called an optical afterglow. In a number of cases, no optical afterglow is found, and these are the so-called “dark” GRBs. In this paper submitted to the Astrophysical Journal, an international team of astronomers present their searches for the host galaxies of these dark GRBs. The authors conclude that “the host galaxies of dark GRBs seem to have normal optical colors.” So what may be causing this “dark” phenomenon? The problem appears to be dust, and the authors present evidence that “the source of obscuring dust is local to the vicinity of the GRB.” However, in the end, the authors conclude that “the location and nature of this high-redshift dust remains unknown.” Read more about the search for the nature of dark GRBs online now here.

Possible Evolutionary Effects of Gamma Ray Bursts

In a fascinating paper to appear in the journal Astrophysics and Space Science, a group of Brazilian and Cuban scientists consider the effects of gamma ray bursts on Earth’s atmosphere and the life below the atmosphere. Associated with upper atmospheric gamma ray interactions is a phenomenon known as ultraviolet flash. The UV flash can cause mutations in genetic material of life on Earth. This is considered to be “the only important short-term effect on life” caused by such gamma ray bursts. However, the consequences that this team concludes may result from this brief effect, may be very influential in the evolution of certain life forms on Earth. Read more about the possible consequences of gamma ray bursts on life on Earth online now here.

Radio Astronomy’s Future in the Coming Decade

In a white paper released today, a group of American astronomers provide an outline about the future of radio astronomy for the next ten years, given the proper funding. Radio astronomy is expected to bring major advances in the understanding of “orphan gamma-ray burst afterglows, radio supernovae, tidally-disrupted stars, flare stars, magnetars, and transmissions from extraterrestrial civilizations.”

ESA Integral Mission Detects Large Gamma-Ray Burst

The European Space Agency (ESA) utilizing its Integral spacecraft, detected a gamma-ray burst (GRB) in December 2004. After careful analysis of the data, scientists have come to the conclusion that this gamma-ray burst was one of the largest ever detected. This gamma-ray burst, also known as GRB 041219A outputs more energy than 99% of the GRBs ever detected. In a paper to appear in the Astrophysical Journal Letters, astronomers discuss how this very bright GRB allowed astronomers to examine the polarization of light (like with polarizing glasses) in the vicinity of the GRB, which in turn helps them understand the mechanism by which the so-called engine of a GRB (a black hole) produces the associated jets. Learn more about the ESA analysis of GRB 041219A online now here.

November 2014
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