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View Full Version : Here's a New Way to Explode: Hybrid Gamma-Ray Burst



Fraser
2006-Dec-20, 07:02 PM
Just when you thought you'd figured out all the ways to blow up, nature reveals a new way. This latest class of explosion is called a hybrid gamma-ray burst, and it was discovered by NASA's Swift satellite. ...

Read the full blog entry (http://www.universetoday.com/2006/12/20/heres-a-new-way-to-explode-hybrid-gamma-ray-burst/)

antoniseb
2006-Dec-20, 07:58 PM
Here (http://gcn.gsfc.nasa.gov/other/060614.gcn3) is what is online from the Swift team about this GRB.

It really isn't clear from this data what the press release meant by characteristics of the short burst, but it is clear that this one was unusual. I'll be curious to see any good modeling that explains these spectra and light curves from any starting point.

John Mendenhall
2006-Dec-20, 08:50 PM
How about a heavy object with a long light tail, like a superheated gas giant? Although I'd think you'd get a whump of gamma rays and a trail of light, rather than the other way round.

Circumstellar disc around a neutron star?

This is a puzzler, alright. Maybe another one will turn up eventually.

Dr Nothing
2006-Dec-20, 09:51 PM
Perhaps this was an object on the very brink of collapsing, that merged with a companion already there... thus causing the first one to collapse as they merged? :whistle:

antoniseb
2006-Dec-20, 09:53 PM
Circumstellar disc around a neutron star?
How about a white dwarf (a less compact object than a neutron star) getting consumed by a black hole? That would take longer, and potentially be a multi-peak flash.

John Mendenhall
2006-Dec-20, 10:04 PM
How about a white dwarf (a less compact object than a neutron star) getting consumed by a black hole? That would take longer, and potentially be a multi-peak flash.

Neutron star with dwarf companion! Whump, then fizzle, fizzle, fizzle.

Don Alexander
2006-Dec-20, 10:14 PM
First off, an error in Fraser's short article: A merger of two black holes will not produce a GRB. Gamma-rays are emitted by matter, either because it is extremely hot, or because of nuclear reactions, or because of relativistic particles spiralling in magnetic fields etc.
Black holes are not baryonic matter. Two merging black holes will create a pulse and train of gravitational radiation, but that's it. (ignoring any accretion discs around them)

Secondly, here's the official Swift press release:
http://swift.gsfc.nasa.gov/docs/swift/news/2006/06-373.html

Then, the preprints of the four Nature papers:

http://arxiv.org/abs/astro-ph/0610635
http://arxiv.org/abs/astro-ph/0608322
http://arxiv.org/abs/astro-ph/0608313
http://arxiv.org/abs/astro-ph/0608257

Here's the best explanation I've found so far - exactly what antoniseb suggests!!
http://arxiv.org/abs/astro-ph/0610452

Finally, an interesting paper showing that if GRB 060614 had been fainter and a bit further away, it would have resembled another "true" short burst strongly:
http://arxiv.org/abs/astro-ph/0612238

Concerning antoniseb's first question: In the last year, one of the main characterstics of merger-induced GRBs that has been recognized is negligible spectral lag. This means: Take your gamma-ray light curve and split it into, say, four channels. Imagine these as colors, from low energy red to high energy blue. Look at the light curve in each channel. Short GRBs are normally just spikes - in other words, you can very easily measure the exact time when the spike peaks. Measure this for all four channels. Negligible spectral lag means: The spike happens at the same time in all channels. Long GRBs do not have this feature, there, the light curve at longer wavelengths is broader and peaks later.

The Swift team found that both the few second long multi-spiked burst which started GRB 060614 and the softer, trailing tail had negligible lag, a charactersitic very untypical for collapsar GRBs.

Alex

Fraser
2006-Dec-20, 10:27 PM
Thanks for the fix, I've updated my article.

John Mendenhall
2006-Dec-20, 10:30 PM
Here's the best explanation I've found so far - exactly what antoniseb suggests!!

http://arxiv.org/abs/astro-ph/0610452

Alex

Great links, thanks. Good luck with your work!

gnomus
2006-Dec-21, 12:09 AM
It seems the problem with most merger-type events is that there are already GRB events fitted to the possible models. It also seems all long GRB events involve non-compact objects or involve normal matter and have a optical flash or supernova associated.

But what if GRB 060614 is not a merger event? What if you had a very compact object with mass sufficient for collapse, but with a high rotation rate that prevented collapse. With this compact object, you had something that was stealing angular momentum - another companion, or other phenomena without the infalling matter to "flash" during the collapse. The object trips over into a collapse without any type of infalling matter.

Plausible?

Cougar
2006-Dec-21, 02:34 AM
Here's the best explanation I've found so far - exactly what antoniseb suggests!!
http://arxiv.org/abs/astro-ph/0610452
Yes, that article from October seems to have been prescient with respect to this burst, which as yet appears to have no associated supernova.

Edit to add: Oops! Not so prescient... since this burst occurred in June! I guess that's relatively quick to get publications into Nature.

John Mendenhall
2006-Dec-21, 01:32 PM
What if you had a very compact object with mass sufficient for collapse, but with a high rotation rate that prevented collapse.
Plausible?

Good question. Objects that are teetering on the verge of black hole collapse must have several possible mechanisms to send them over the edge. A large meteor could produce the ultimate impact; everything disappears!

pantzov
2006-Dec-22, 06:32 AM
this is very cool. we all love thinking about superpowers in the universe. now we have a new one to ponder.