HEAPOW: Metal Poor Burst? (2014 Jul 14)

[bystander]

HEAPOW: Metal Poor Burst? (2014 Jul 14)

Massive stars die in tremendous explosions called supernovae. In the most massive stars, the loss of thermonuclear fuel at the center of the star can cause the collapse of the star's core and the formation of a black hole inside the star. As the newly-formed black hole begins to swallow the star from the inside out, a powerful jet of particles and radiation forms inside the star, blowing the star apart as the jet surges towards the stellar surface. If these beams are directed towards earth, we can detect this event as a bright burst of high energy gamma rays. Roughly one such gamma-ray burst is detected by modern gamma-rays observatories each day. These types of gamma-ray bursts typically last less than a few minutes. But on September 25, 2013, a gamma-ray burst was detected by the Swift Gamma-ray Burst space telescope which lasted neary 2 hours, an "ultra-long" burst. The duration of this burst, and its subsequent X-ray and radio emission, suggests to astronomers that this event must have occured in a very large star, a so-called "blue supergiant". An artist's rendition of a jet bursting through the surface of a blue supergiant star is shown above. Since massive stars shrink over time due to mass-loss from their strong stellar winds, the explosion of a star as a blue supergiant suggests that this star must have had a very weak wind. Since the stellar wind is created by the absorption of the star's intense ultraviolet radiation by iron and other heavy elements, it's believed that the star that gave rise to this gamma-ray burst may have had very few of these metals. Because the first stars which formed in the Universe had no heavy elements, astronomers think that this long gamma-ray burst may provide a glimpse into the deaths of the very first generation of stars.

NASA/GSFC/Swift: Out of an Hours-Long Explosion, a Stand-In for the First Stars
ESA/XMM-Newton: Bizarre Nearby Blast Mimics Universe's Most Ancient Stars

A hot cocoon in the ultralong GRB 130925A: hints of a Pop III-like progenitor in a low density wind environment - Luigi Piro et al

• Astrophysical Journal Letters 790(2) L15 (2014 Aug 01) DOI: 10.1088/2041-8205/790/2/L15
  arXiv.org > astro-ph > arXiv:1405.2897 > 12 May 2014 (v1), 21 Jun 2014 (v3)

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Author: Dr. Michael F. Corcoran

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Mystery of rare 5-hour space explosion explained
Penn State University | 2014 Sep 17

The X-ray image from the Swift X-ray Telescope of the gamma-ray burst GRB 130925.
The white object in the center is the gamma-ray burst. The large diffuse region to the
right is a cluster of galaxies. The other objects are X-ray-emitting celestial objects,
most likely supermassive black holes at the centers of distant galaxies. The full image
is approximately the size of the full moon. Credit: Phil Evans/ University of Leicester

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray bursts -- a very rare form of the most powerful explosions in the universe.

"The recent discovery of ultra-long gamma-ray bursts raised questions about whether some new physics is required to explain them, but our work suggests a much simpler explanation," said David Burrows, a Penn State professor of astronomy and astrophysics. "Our analysis reveals that these rare gamma-ray bursts, which can last for hours, can be explained as standard explosions occurring in a region with a low density of matter that is located behind a cloud of dust when viewed from Earth."

Dick Willingale, an astronomer at the University of Leicester and a co-author of the study, said, "Not only is this result significant scientifically, but it shows the importance of international collaborations to build observatories, and of sharing information between those observatories." ...

Scientists probe the mystery of hours-long celestial explosions
University of Leicester | 2014 Sep 17

GRB 130925A: an ultra-long Gamma Ray Burst with a dust-echo afterglow,
and implications for the origin of the ultra-long GRBs - P. A. Evans et al

• Monthly Notices of the RAS 444(1) 250 (2014 Oct 11) DOI: 10.1093/mnras/stu1459
  arXiv.org > astro-ph > arXiv:1403.4079 > 17 Mar 2014 (v1), 21 Jul 2014 (v2)