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Fraser
2005-May-10, 06:18 PM
SUMMARY: With the launch of NASA's Swift spacecraft, Gamma Ray Bursts - those "most powerful explosions in the Universe" - have been in the news on a regular basis. When a GRB is detected, a worldwide network of instruments tune in and image the afterglow in every possible wavelength, from radio to visible to gamma ray. But some bursts are "dark", causing a brilliant flash in gamma rays, but absolutely nothing in the visible spectrum. The "dark gamma ray bursters" are a mystery to astronomers, but a team of European astronomers think they have a way to narrow down the search for an explanation.

View full article (http://www.universetoday.com/am/publish/shedding_light_dark_grbs.html)

What do you think about this story? Post your comments below.

antoniseb
2005-May-10, 06:42 PM
The word "Dark" makes things sound mysterious. In this case there is a mystery. Hopefully we'll get some interesting examples between Swift and Glast that will give us details.

My understanding is that there is a big overlap between the Dark GRBs and the ultra-short GRBs that last less than a second. That is probably a big clue.

Don Alexander
2005-May-10, 07:46 PM
Congratulations, Palli, you're famous! ;-}

One important thing that does not come out clearly: Next to the GRB itself, GRB 020819 was found in the radio. Now while the gamma-ray error circle is several arcminutes in diameter (the 1/15th of the Moon), the radio position is subarcsecond - the small circle on the outer part of the galaxy is the error region of the radio afterglow. Otherwise, no one could have said where the GRB is within the large field.

Pall Jakobsson has recently implemented a webpage

http://www.astro.ku.dk/~pallja/dark.html

to update another paper on dark GRBs he authored recently. GRB 050412, discovered by Swift, is one of the darkest so far.

Yesterday morning, Swift discovered GRB 050509B (its second discovery for the day, HETE discovered XRF 050509C in the evening), a very short GRB. For the first time in history, the X-ray afterglow of such an event was captured, leading to a small error circle lying at the edge of a large ellptical galaxy within a massive galaxy cluster at z = 0.225.

The GRB community is buzzing like a hornet's nest right now.

If you don't mind a bit of technical language, circulars and images on this burst are collected here:

http://www.mpe.mpg.de/~jcg/grb050509B.html

This is Swift's most important discovery yet!!

antoniseb
2005-May-10, 07:52 PM
Originally posted by Don Alexander@May 10 2005, 07:46 PM
This is Swift's most important discovery yet!!
Thanks for the link. This is great stuff. It is very exciting to have some handle on the afterglow from one of these very short dark GRBs.

The Near-Sighted Astronomer
2005-May-10, 09:04 PM
I've had some excellent input from Palli over the internet (he's been busy following up on another dGRB that happened this weekend) - hopefully we can retrofit this article with some of his input. Even now Fraser should be receiving an email from me...

Don't you just love the internet!

jeff

PS: I just reloaded the original story some of the early changes from Palli are now in - some excellent historical info in fact. Nothing yet on the latest Swift follow up though - w'll see...

om@umr.edu
2005-May-10, 10:19 PM
I agree.

Gamma Ray Bursts are indeed intriguing.

They suggest we still have much to learn.

With kind regards,

Oliver
http://www.umr.edu/~om

Greg
2005-May-11, 05:53 AM
Interesting. I would think that a larger version of a pulsar such as a black hole might be more effective at honing its output to specific frequencies. I would be inclined to think toweards higher frequencies and not lower ones, however. My guess about dark grb sources would be black holes that gobbled up something it wouldn't commonly encounter like another black hole or pulsar.

The Near-Sighted Astronomer
2005-May-11, 10:53 PM
Hi Greg,

This would be the interpretation of such events promulgated in a related article now up on UT.

Cheers,

jeff