How are the distances to the most distant $\gamma$-ray bursts measured?

Question

This question came to my mind when I read on NASA's website that an explosion (gamma ray burst, GRB 080913) took place 12.8 billion light years away from us. How do they measure such large distances?

Possible duplicates: http://physics.stackexchange.com/q/24927/2451 and links therein. — Qmechanic, Jul 18 '14 at 18:57
possible duplicate of How do you measure distance to stars within the galaxy? — John Alexiou, Jul 18 '14 at 20:37
Voting to leave open: certainly not a duplicate of "distances to stars within the galaxy" as the techniques required for this much larger distance are completely different. As to the other possible dup, this measurement uses a technique not mentioned in the answers to that other more general question. Will edit this question a bit to make the distinction more clear. — Kyle Oman, Jul 18 '14 at 22:01
possible duplicate of How is the distance to a $\gamma \mathrm{-ray}$ burst (GRB) measured in just a few days? — , Jul 18 '14 at 22:41
@Kyle but what about the one I linked? Also, if the OP didn't just want GRB's, there's http://physics.stackexchange.com/questions/70400/how-do-we-know-that-these-radio-bursts-are-from-billions-of-light-years-away for radio. — , Jul 18 '14 at 22:42
@ChrisWhite both questions happen to ask about different GRB whose distances were estimated using different techniques (I think the one from this question was from the end of the Ly-$\alpha$ forest, the other one is emission lines from the galaxy). Since they ask about specific objects (though not by name), I'm still leaning not dupe, but your link is certainly arguable. — Kyle Oman, Jul 18 '14 at 22:46
@Kyle then retracted, but perhaps the question should give some hint that photo-z's were involved? Maybe with some quote from the article? — , Jul 18 '14 at 22:49

score 2 · Answer 1 · edited Apr 13 '17 at 12:39

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Did you mean 12.8 billion light years away?

If so, in this case the distance was estimated by measuring a rough spectrum for the GRB. The NASA article I've linked says:

In certain colors, the brightness of a distant object shows a characteristic drop caused by intervening gas clouds. The farther away the object is, the longer the wavelength where this fade-out begins.

This technique is used where it's hard to get a detailed spectrum and calculate the red shift.

If you're asking a more general question then this is covered in the question How is distance measured to far away stars and galaxies? and your question would be a duplicate.

edited Apr 13 '17 at 12:39

Community

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answered Jul 18 '14 at 06:54

John Rennie

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So, in essence, this is a rather fuzzy redshift calculation? – M.Herzkamp Jul 18 '14 at 13:18
@M.Herzkamp: yes, exactly. – John Rennie Jul 18 '14 at 14:00
@JohnRennie: yes sir i meant 12.8 billion light years. sorry for omitting billion there. – syed_ali_mousvi Jul 18 '14 at 18:00
I think that characteristic drop would be the beginning of the "Lyman-$\alpha$ forest". So really this is a lower limit on the distance (which, at 12.8 Gly, still tells you it's pretty darn far away). – Kyle Oman Jul 18 '14 at 18:24

score 0 · Answer 2 · answered Jul 18 '14 at 06:52

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For relatively close objects, the distance can be measured through measurements of parallax (http://en.wikipedia.org/wiki/Parallax ).

answered Jul 18 '14 at 06:52

akhmeteli

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And also using Variable stars in a star cluster. – John Alexiou Jul 18 '14 at 18:09
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Note this was a reasonable answer to the question as stated at the time of the answer (I almost downvoted until I noticed). – Kyle Oman Jul 18 '14 at 22:13

How are the distances to the most distant $\gamma$-ray bursts measured?

2 Answers2