@LBC: Actually, they aren't. The amount of mass available in a neutron star merger is much less than can be achieved in the cora collapse of a massive star. While short GRBs are though to come from NS-NS (or NS-BH) mergers, long GRBs are unequivocally associated with massive stellar death.
Point two: Wrong. The first stars ignited somewhere between z = 50 and z =20. By z = 8, reionization was mostly finished, and since Pop III stars only live a few million years, there will already have been like 100 generations of SNe and ISM metal enrichment. At z = 8, true Pop III stars are actually a dying breed! (Though very new research seems to indicate stars massive enough to produce pair-production instability SNe even exist in the nearby universe).

Also this event occurred 600 My after the big bang during the reionization period. If this GRB was due to the explosion of a star this star was a PopIII star — by definition. It might not have been a monster star, but it was a star with low metalicity (zero metalicity).

LC

Excuse me for my previous error about the size of the TNG scope. Many thanks for your post clarifying and explaining the current observations (and thanks for the link to that 2nd paper). I do realize the difference in spectroscopically derived redshifts and less accurate photometric redshifts used to estimate distances. All these z>8 candidates described in in deep fields (using the photometric dropout method) gives us a rough estimate of the distance to the galaxy, but I have read that photometric redshifts of some extremely distant galaxies/ galaxy clusters may be off up to 20%.

Also thanks for the clarification as to the properties and epochal age of these distant GRBs.

Also, what is the current status regarding the use of GRBs as standard candles. IIRC, there was a push in the late '90s and early '00s to try to establish GRB luminosities as standard candles. Are there too many variables involved that would preclude the use of GRBs as standard candles?

LC

Concerning the last point, I'm pretty sure both papers point out that there is NO evidence for this being a Pop III star. Excepting this extreme distance, it looks just like a normal GRB – with the one difference that it is very short temporally. Check out http://arxiv.org/abs/0902.2419 by Zhang et al. (I'm a co-author) for more on that. This also should answer HeadAroundU – "a monster star" meant a supermassive Pop III, whereas this was due to a more normal (probably still 50 solar masses, but nothing extraordinary) star.

@Aqua: As already more or less stated, the spectra do not allow any analysis beyond the redshift detection. They were taken many hours after the GRB, when the afterglow had already faded by several magnitudes. It just took some time to realize what a special event this GRB is, and by that time it was too late to observe from Hawaii. The TNG (@Jon Hanford: it is 3.6m and proud of it ) was the first to be able to target it, and then came ISAAC at the VLT (already 17 hours after the GRB).

@rudeyd: 600 million years after the Big Bang is a loooong time after the Big Bang. With the exception of the fact that reionization was still going on and metallicity was still low, the Universe was just like today.

@Jon Hanford: We are talking spectroscopically confirmed redshifts here. The WFC3 HUDF observations are fascinating but much less conclusive in terms of distance. Therefore, GRB 090423 rules.

also @Jon Hanford: Spitzer observed about 45 days after the burst at 3.6 microns (warm mission test phase), detecting a faint source in an ultra-deep integration. A follow-up is planned for early 2010. With high probability, this was still the afterglow, and the host will be too faint for – again probably – ANY existing technology. But for sure, JWST and possibly ALMA will target this source.

Hope I wasn't trolling.

LC

I have now realised I mis-read the article and thought that the initial burst was only in infra-red, as well as the afterglow, hence my confusion about how it could be termed a GRB…. :-S
Quick astro-blog catch up sometimes not a good idea!

Now we infer these distances and times by observing more local objects and their redshifts. A galaxy 100 million light years away is observed to have Cepheid variables. These have a luminosity/periodicity relationship and from that the distance can be backed out. This was how Ed Hubble came up with his

V = Hd

relationship, for d = distance H = 71Mpc/(km/sec) and v= velocity.

LC

However, the location (position on the sky; (RA, Dec)) of the IR object is well within the error circle of the Swift GRB localisation, and there's nothing with a light curve that resembles a fading GRB nearby … ergo, the IR source IS the GRB.

(there's a lot more, but it's more indirect; hopefully the above is enough to get you started …)

LC

Btw, Thanks to Salacious B. Crumb for a link to the original paper :0

LC

So an optical ~ 1 micron photon gets expanded into a .1cm photon, which is about right.

where I should have written it gets expanded to .1 meter or 10 cm. So this means for 300nm to 600 nm optical wavelength photons the redshifted photons would be stretched out to 3-6 cm. That is about the measured blackbody peak of the CMB.

My estimate on the z, where I got this to be about double the quoted value probably reflects the limits to which the low redshift approximation works. I would have to work with the more general calcuation from the FLRW cosmology spacetime metric .

Cheers LC

LC

I'm so confused. From where did it come from?

z = a(T)/a(t) – 1,

for a(t) the radius of a region at time T and a(t) the radius much earlier. The Hubble relationship v = Hd indicates an approximate linear relationship with that radius and time. So for a(t) = 13.7 a(t) = .7 this would give z = 18.6, which is rather astounding. Of course out to the CMB with t = 3e5 and T = 1.37e10 one gets a z ~ 10^5. So an optical ~ 1 micron photon gets expanded into a .1cm photon, which is about right.

I would tend to think that a z = 8.1 would put this back to about

z = a(T)/a(t) – 1,

a(t) = a(T)/(z + 1) ~ 13.7e10/9.1 = 1.5e9

or more like twice what the paper states.

LC

And what did the spectra say about what elements were present? Any metals?