I hope this is correct?

Please excuse my layman views:)

When I saw the issue of meauring the time valuation of events in our early cosmological history, how could it not be considered in high energy applications?

I think this is the point about our depth of perception.

The “calorimetric views” provide the consistancy and penetration of the cosmological events as tangible realities, in relation too, the expansion of our universe.

Such depths require a consistant view. From the “planck epoch” to now?

Such views are not understood if one did not have some comprehension of “the views” of that early universe. Andrey Kravtsov is very helpful here.:)

I’m not too familiar with the proposed GLAST instrument so someone correct me if I’m wrong, but from what I can tell from their public website they are looking at much higher energies (0.01-100 GeV) than Swift or HETE-2 (2-400 keV). In which case, they would also have a hard time getting spectra for all but the highest energy bursts. Of course, that range of parameter space may also be really interesting for other things.

Would “Glast” determinations fit into this category?

In particular, HETE-2 is particularly adept at detecting the low-energy cousins of GRBs — X-Ray Flashes. XRFs seem to follow this same correlation as GRBs, but are usually seen at lower redshifts. And as Mark pointed out above, having probes of the z less than 2 universe is key to understanding Dark Energy. GRBs are special because they may be standardizable candles that are visible over a redshift range of 0.1 to 6.3 (and possibly higher).

The correlation uncovered by Ghirlanda et al. is also a challenge for theorists to explain. A better understanding of the underlying physics of the GRBs will hopefully allow us to understand and better use these correlations, and thereby improve the cosmological results as well.

Yep, it is quite exciting. The results in the Ghirlanda et al. paper I referenced are pretty much the state-of-the-art right now. There are several other groups working along the same lines, but since everyone is using the same catalog of 40 or so bursts they’re getting similar answers. If we could increase the size of the sample of usable bursts then we could (1) test that the correlation is indeed correct, and (2) shrink the confidence regions for the cosmological parameters.

For a burst to be useful in this project we need 3 quantities:

(1) Burst redshift.
(2) A well-measured afterglow light-curve, which gives us information about the opening-angle of the relativistic jet that causes the GRB, and hence information about its total energy budget.
(3) A measurement of the peak energy of its spectrum.

The Swift satellite is ideally suited to get (1) and (2) and should discover hundreds of bursts over the next few years. But Swift has a narrow spectral bandpass and has a hard time measuring (3). The HETE-2 satellite has a much broader spectral bandpass and can easily measure (3) for a wide range of bursts. So a collaboration between Swift and HETE-2 would greatly expand this dataset. Hopefully these arguments will convince NASA to fund HETE-2 in the coming years (full disclosure: I currently work on the HETE team

In particular, HETE-2 is particularly adept at detecting the low-energy cousins of GRBs — X-Ray Flashes. XRFs seem to follow this same correlation as GRBs, but are usually seen at lower redshifts. And as Mark pointed out above, having probes of the z

To me, the most exciting near term results will be using GRBs to study the intergalactic medium. There is already a great spectrum out there in astro-ph/0508270 from a GRB. The really cool thing is it shows stuff that no one has ever seen before. Frankly, the authors cannot make heads or tails of some of the features, that is just awesome.

Tim D: That is a really exciting prospect! Has there been followup work on that?

-cvj

There are tons of interesting cosmological applications of GRBs. Some of them aren’t quite ready for prime-time, but give us a few years (and a larger dataset) and I bet we can compete! Like Risa said, GRBs are great for studying “later times” cosmology (reionization, first stars, etc), but they also might have something to say about the “5-10 magic numbers”.

In a lot of ways, GRBs are the ideal probe of the reionization epoch in that they are easy to find and some percentage are likely occur and are detectable out to redshifts of 10-20. Check out Lamb & Reichart for a review of the cosmological applications. GRBs are nicer than quasars for measuring the Gunn-Petersen trough because they have a simple intrinsic spectrum and, being transient events, they haven’t completely disrupted the local environment before they explode (no proximity effect). People do want to use them analogously to quasar absorption systems to put constraints on what lies between the burst and us (like Arun suggested). The challenge is ensuring that the afterglow be detected and that high-resolution spectra of the afterglow can be obtained fairly quickly using the new generation of NIR spectrometers. Hopefully, this latest Swift burst is just the tip of the iceberg in this regard.

Probably the cosmology result that’s generating the most excitement right now is the use of GRBs as “standardizable candles” much in the same way that Type Ia supernovae have been used. The breakthrough came last year in a paper by Ghirlanda, Ghisselini & Lazzati, where they discovered a very tight correlation between the total energy emitted in gamma-rays and the peak of the prompt spectrum. Using this correlation they can place GRBs on Hubble diagrams, and they claim that a future large sample of Swift bursts will be competitive with the supernovae results in constraining OmegaM, Omega_Lambda and w.

Cheers,

-cvj

Re early reionization, the first WMAP results indicated z_reionization around 17 (with a *huge* errror bar, which will hopefully go way down with the release of the second third year data) or so, but SDSS quasars now are showing that it seems to be pretty patchy (varies between lines of sight to different quasars) and that it extends in some regions to about z~6 (perhaps later than these GRBs).

Anyhow, I seem to remember early reionization was also in the CMB cards, so I guess my two data points are consistent…

best,

Moshe

-cvj

From the little I’ve read, this event took place above redshift 6, which makes it one of the earliest observable things light sources in the universe (there are now just a handful of galaxies and quasars above z=6). I don’t know the specifics of these new data, or a ton about GRB physics, but even the existance of this event at this redshift tells us probably constrains the formation of the earliest stars in the Universe. Even if all you care about is the 5-10 magic cosmological parameters, and not the evolution of all of the light in the Universe, learning about early star formation can help constrain the reionization era — which is degenerate with a lot of those parameters.