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View Full Version : This just in - a GRB at redshift 9???



Don Alexander
2009-Apr-23, 03:26 PM
The following observation report was just posted on the GCN Circulars. This could turn out to be an extremely interesting event!! It was rapidly observed by several large (1.5 - 2m) robotic telescopes in the optical, which yielded no detections down to deep early limits. The X-ray spectrum showed no indications of additional extinction, implying that it's probably not dust-reddened. A probable NIR counterpart was first reported by the United Kingdom InfraRed Telescope on Hawaii, and has now been confirmed by Gemini.

TITLE: GCN CIRCULAR
NUMBER: 9209
SUBJECT: GRB 090423: NIR photometry and evidence for spectral break
DATE: 09/04/23 15:02:30 GMT
FROM: Derek Fox at PSU <dfox@astro.psu.edu>

A. Cucchiara (PSU), D. B. Fox (PSU), and E. Berger (Harvard) report:

"On April 23.33 UT we imaged the field of Swift GRB 090423 (Krimm et al., GCN 9198) with NIRI on the Gemini-North telescope. We obtained 9x60 sec exposures in Y,J,H. In the coadded J and H images we clearly identify the object noted by Tanvir et al. (GCN 9202) and it appears point-like (see also Levan et al., GCN 9206). The object is not detected in Y-band.
We derive the following magnitudes, calibrated using three 2MASS stars in the field:

J mag: 19.29 +- 0.07
H mag: 17.71 +- 0.14

The resulting J-H color of 1.1 AB mag is very red, corresponding to a steep spectral slope of beta=3.8. Taken in conjunction with a flat H-K color (see GCN 9202), our non-detection in Y-band, and a red I-J color of 1.7 AB mag in comparison to P60 limits (GCN 9201), we suggest that there is a likely break in the spectrum at about 1.2 microns, with extinction an unlikely explanation due to the sharpness of the feature and the shallow slope to redder wavelengths. If this is due to Ly-alpha absorption, then the resulting redshift for GRB 090423 is z~9.

Further analysis is in progress and additional observations are planned."


I sure hope someone manages NIR spectroscopy... It's a very faint target for that.

Interestingly enough, the actual GRB is only ten seconds long in the observer frame. Though it shows a large X-ray flare (which is also faintly detected in the lowest energy Swift BAT band) at about 180 seconds, so it's very probably not a "short GRB".

peteshimmon
2009-Apr-23, 05:30 PM
I am never quite sure if these high redshifts
are deduced by precise spacing of at least two
lines or perhaps wishful thinking of the
position of one line!

But then I am sure they know what they are
doing.

peteshimmon
2009-Apr-23, 08:18 PM
Actually I am not sure if I am repeating
myself in my query about redshift measurement
methods so I looked back at the very
informative thread last September about the
record holder then. But still a bit puzzled!
A few words about the nitty gritty stuff
will always be welcome to crude, sceptical
folks rather than bland statements of
redshift values.

Not that everyone here is crude:)

Jerry
2009-Apr-24, 03:15 AM
Interestingly enough, the actual GRB is only ten seconds long in the observer frame. Though it shows a large X-ray flare (which is also faintly detected in the lowest energy Swift BAT band) at about 180 seconds, so it's very probably not a "short GRB".
There is an inverse correlation between gamma ray distance and burst length, but this is incredibly short for a gamma ray picked up that far away.

Don Alexander
2009-Apr-24, 03:52 AM
Note #1: The photometry in this GCN turned out to be wrong.
#2: Revised photometry placed it at a lower redshift.
#3: Further observations (with GROND) give a photo-z of 8 +1.2 -0.5
#4: A very low signal-to-noise spectrum with the 3.6m TNG telescope on La Palma, Canary Islands gives z ~ 7.6

None of these results are based on lines. Not even the TNG spectrum. All use the Lyman alpha line cutoff, with the first results being photometric only.

While this is now pretty sure the most distant object ever spectroscopically confirmed, I'm sincerely hoping larger telescopes will get on it with better spectroscopy.

Don Alexander
2009-Apr-24, 05:36 PM
Additional VLT/ISAAC spectroscopy and a refined analysis of the TNG spectroscopy now yield z = 8.1 - 8.2!!!

parejkoj
2009-Apr-24, 07:36 PM
Hoo-Ha! That's a whopper. Please post the preprint when it becomes available, incase I miss it on astro-ph. Is the VLT spectrum also using the lyman break? How well resolved it is? Any lines (emission or absorption)?

Looks like the lyman break galaxies are getting a run for their money!

Lurky
2009-Apr-24, 08:04 PM
:shifty: Sounds fun in here....

Can anyone give a simple version of what this is about...

mahesh
2009-Apr-24, 08:21 PM
Psst. (sotto voce) Hey Lurky, don't blink...you might miss it!

slang
2009-Apr-24, 09:28 PM
:shifty: Sounds fun in here....

Can anyone give a simple version of what this is about...

I'll give it a try, but no guarantees on correctness and/or understandability :)

It is about a Gamma Ray Burst (http://en.wikipedia.org/wiki/Gamma-ray_burst) detected by the Swift (http://en.wikipedia.org/wiki/Swift_Gamma-Ray_Burst_Mission) spacecraft, and the resulting observation of that GRB with other (ground based) telescopes (Gemini north (http://www.gemini.edu/), VLT (http://www.eso.org/projects/vlt/), TNG (http://www.tng.iac.es/)). It was initially thought to be at redshift (http://en.wikipedia.org/wiki/Redshift) z = 9, and that means that it would be very, very far away, and happened a very long time ago, longer than any such object seen before. I think that is still true for the z = 8.1 that Don mentioned. Redshift, or z, is a measure that relates to distance and age, but I don't know what z 9 or 8.1 means in numbers like "x million years since the big bang". It is exciting because the higher redshift items can be detected and studied, the more we learn about the time 'shortly' after the Big Bang.

parejkoj
2009-Apr-24, 09:56 PM
slang's description is a good one.

You can use Ned Wright's Cosmology Calculator (http://www.astro.ucla.edu/~wright/CosmoCalc.html) to turn redshift into distance or lookback time. A redshift of 8 corresponds to a bit over 600 million years after the big bang, or 13.1 billion years ago and about 30 billion light years away from us.

Besides the general science interest (the earlier in the universe, the less we understand about the details of how things form), there is a bit of a race in astronomy to find the highest redshift object. People like setting new records. The previously agreed-upon record was a galaxy with z ~< 7. There is another at z~=10, but I don't think it is as well accepted. There are several quasars (http://en.wikipedia.org/wiki/Quasar) with redshifts between 6 and 7, and the next generation of telescopes should find plenty of sources above z=7.

But finding one now is a pretty big deal.

slang
2009-Apr-24, 10:14 PM
slang's description is a good one.

You can use Ned Wright's Cosmology Calculator (http://www.astro.ucla.edu/~wright/CosmoCalc.html) to turn redshift into distance or lookback time.

Thanks, on both! Bookmarked.

Don Alexander
2009-Apr-25, 12:17 AM
@parejkoj: I don't know more about the spectra than what was posted in the GCNs...

Basically, the redshift is determined via the Lyman alpha line, and under assumption of a stron Gunn-Peterson trough. This means that all light blueward of the red wing of Lyman alpha is absorbed by the neutral intergalactic medium (remember, we are still coming out of the Dark Ages here, so reionization is not complete). The spectrum (from longer to shorter wavelengths) is thus: Continuum --> red wing of Lyman alpha --> nothing.

Actually deterimining a correct redshift from this method is basically not possible. And with "correct", I mean at high precision and confidence. The reason is that unless you have a high S/N which readily maps the red wing, you can't discern a very broad Lyman alpha line (Damped Lyman Alpha system, DLA) at, say, z = 8.1, from a much smaller Lyman alpha line with additional neutral IGM at, say, z = 8.2. This was discussed extensively in Totani et al., PASJ, 2006, on the (high S/N) spectrum of the z = 6.295 GRB 050904.

So, unless the ISAAC spectrum is good enough to show additional lines (I doubt it but don't know), I'd say the redshift will only be known to a precision of +/- 0.1, which is actually pretty unimportant if it's at z > 8 anyway...

As others have mentioned, there's a chase for the highest redshift. The Swift satellite was hoped to get a new record, and GRB are a great tool for ultra-high z observations - and now we have bagged it!

parejkoj, I think you're confusing Lyman break galaxies with Lyman alpha emitting galaxies? (Or I am wrong in thinking the two terms are different...) Anyway, up until now, the (spectroscopically confirmed) record holder was a z = 6.96 galaxy found by the Subaru telescope using a narrow-band filter technique. At this redshift, the night sky has a lot of emission lines (airglow) making spectroscopy extremely hard. There is one "hole" in the airglow, a region with relatively little background, and observing in that region nets you galaxies redshifted to ~ 7. The recently reported giant Lyman Alpha Blob "Himiko" was found by a similar technique in another window at z = 6.6.

Last September, Swift and the GROND detector discovered GRB 080913, wich at z = 6.7 was then a new record-holder for GRBs, and was the second highest spectro-z ever found.

And now we just bypassed the z = 7.X regime and went right to 8! :D

Not knowing the data quality, I can't yet say what these observations are going to tell us. One thing is clear: There are massive stars at z > 8 which are capable of producing GRBs. That in itself is a valuable piece of knowledge.

parejkoj
2009-Apr-25, 01:14 AM
Huh... I might be confusing those, but I thought they were the same: lyman break galaxies are those identified by their Ly-alpha dropout. Lyman Alpha Emitting galaxies are strong emitters of Ly-alpha. Hmm... now that I think about it more, there may be a fine distinction in what things are called (since those Subaru discoveries are looking for just lyman alpha emission, they're just looking at LAEs?).

Hmm... I'll see if I can ask around about the distinction.

Cougar
2009-Apr-25, 03:48 AM
"On April 23.33 UT we imaged the field of Swift GRB 090423 (Krimm et al., GCN 9198) with NIRI on the Gemini-North telescope. We obtained 9x60 sec exposures in Y,J,H.... The object is not detected in Y-band.

So these different letters are... particular ranges (or slices?) of wavelengths in the near-infrared part of the spectrum? And is it the measured distance from gamma radiation to the specific "break" in the infrared that is indicating how distant in space and time is the frame of this GRB?

parejkoj
2009-Apr-25, 03:53 PM
Y,J,H,K are specific filters in the near infrared, yes. Distances to very high redshift sources are estimated through the break in the spectrum blueward of lyman-alpha. It does not require any information about other parts of the spectrum. This page from UC Santa Cruz (http://www.firstgalaxies.org/the-first-galaxies) does a good job of illustrating the technique, though the details are a bit different in this case, since a low resolution spectrum was available.

Don Alexander
2009-Apr-26, 07:14 AM
parejkoj: LAEs are basically visible only in Lyman alpha. You have that one spectral line and no continuum. Lyman-break galaxies are comparable to high-z GRBs - continuum and then dropout.

LAEs, as mentioned, are found via narrowband filters. You see a bright source in the narrow-band image, and nothing in the broadband filters.

Doodler
2009-Apr-26, 05:31 PM
One thing is clear: There are massive stars at z > 8 which are capable of producing GRBs. That in itself is a valuable piece of knowledge.


That's not exactly an Earth-shaking concept. The hypothesized masses of the first generation Pop III stars are in the hundred to several hundred solar mass range.

As a result, I'd expect the number of high z GRBs to be significantly higher anyway, if supernovae/hypernovae are the most common source of them.

ngc3314
2009-Apr-26, 08:39 PM
Huh... I might be confusing those, but I thought they were the same: lyman break galaxies are those identified by their Ly-alpha dropout. Lyman Alpha Emitting galaxies are strong emitters of Ly-alpha. Hmm... now that I think about it more, there may be a fine distinction in what things are called (since those Subaru discoveries are looking for just lyman alpha emission, they're just looking at LAEs?).

Hmm... I'll see if I can ask around about the distinction.

Not all Lyman-break galaxies have net emission at Lyman alpha, and not all Lyman-alpha emitters have strong enough continuum to be picked up via continuum break. Also, at moderate redshifts z<5.5 or so, the break occurs at the Lyman limit rather than Lyman alpha since the confluence of the Lyman-alpha forest and onset of the Gunn-Peterson trough are not yet deep enough to wipe out the 913-1215 A emitted region.

The plot shows a composite IUE+FUSE spectrum of NGC 604, the brightest star-forming region in M33. The Lyman break is complete at 912 A (with a contribution by gas in the Milky Way, to be sure). Lyman Alpha is in emission at 1215, but again local emission makes it hard to say how much is actually intrinsic. Either way, this shows how the selection criteria for Lyman-break and Lyman alpha emission objects are distinct.

parejkoj
2009-Apr-26, 11:19 PM
Right. Got it. Thanks for clearing that up, both of you.

I should have known that...

Don Alexander
2009-Apr-27, 12:48 AM
@Doodler: It's more than you think. ;) Of course, "out there", you have many massive stars. But it is as yet unclear of Pop III can produce GRBs!

The thing is, mass is just one requirement. You also need a large angular momentum, to power the jets, and you need a mechanism to remove the outer hydrogen envelope, to prevent jet quenching. GRBs come from Wolf-Rayet stars, and those expel their outer envelopes via radiation pressure due to metal line opacities.

Pop III stars have no metals. Also, if they are too massive, they produce pair-production SNe, which can't power GRBs - as no neutron stars or black holes are involved.

slang
2009-Apr-27, 10:36 PM
Universe Today (http://www.universetoday.com/2009/04/27/most-distant-object-ever-seen/) (hey... great site!) story on this GRB. (Who would have guessed that the name Total Science from the comments might end up twice in this forum's banned or suspended users list?)


That's not exactly an Earth-shaking concept. The hypothesized masses of the first generation Pop III stars are in the hundred to several hundred solar mass range.

(bold mine) The concept might not be Earth-shaking.. but the possible actual observation of one would certainly be, IMHO.

peteshimmon
2009-Apr-28, 07:19 PM
I note the SWIFT main webpage is flagging this
event up. When the news gets to the main
media it is set in stone as fact. Yet I still
wonder. If you might let me be the slightly
soggy blanket awhile I would ask the
following. One, hopefully one of the popular
magazines will do a detailed guide to the
evidence and how it is interpreted. Two, would
anyone care to say that the evidence is
watertight...or tenuous..or somewhere
in between?

Lastly, and I think I have put this point
before, given the detected range of energies
in this burst is the range in the original
rest frame of the event comparable to "nearby"
bursts? And I would ask if very high energy
photons traversing great distances have any
interaction with "vacuum energy" that modifies
them.

slang
2009-Apr-28, 10:33 PM
BA (http://blogs.discovermagazine.com/badastronomy/2009/04/28/new-burst-vaporizes-cosmic-distance-record/) weighs in.

Don Alexander
2009-Apr-29, 12:46 AM
UT, BA - all those latecomers...

You read it here first! :D

@Pete:

Point 1: I'm actually not involved in any of this right now, so I can't say anything about the actual quality, I can only go on what I've read in the GCN. From what I have read, the evidence is pretty solid. There are two spectra (though the TNG one, which I have seen, is very low S/N...), and a bunch of good NIR photometric data that alone gives a redshift of ~ 8, with an error of about 0.5. Using the fully calibrated Y-band dropout from Gemini, I expect this to be improvable.

Point 2: The frst assumption that does go in here is of course that the Lyman-dropout + Gunn-Peterson trough causes this spectral break, and not dust extinction. Now, no KNOWN model of dust extinction is able to produce such a sharp spectral break, but who knows about the unknown...

BUT: There is very solid evidence that the X-ray afterglow is not affected by additional extinction. It has been shown often that GRB host galaxies have different so-called dust-to-gas ratios than the Milky Way. Being a very evolved galaxy, there is, per unit hydrogen, a lot of dust in the Milky Way. GRB hosts have much less dust. So they often show strong extinction in the X-rays (which is caused by metal absorption lines, not hydrogen directly, but the metal columns are coupled to the amount of hydrogen) without any strong optical extinction. What you would need here is the OPPOSITE, insanely high optical extinction without almost any gas!!! The explanation that the spectral break is caused by Lyman absorption and the X-ray absorption is simply redshifted into the EUV is much more logical.

There is also tentative evidence from high-energy correlations. Using the deduced high-energy (gamma-band) spectral parameters and the redshift, the GRB agrees well with these correlations. Redhifts lower than about 1 are strongly ruled out.

Point 3: Now, if one were to start off like "Total Science" on the first UT report and immediately doubt any correlation between redshift and actual distance, and spout Halton Arp... Well... Can't help there anymore. ;)

Jerry
2009-Apr-29, 01:58 AM
Even if one is of the Halton Arp camp, this is a record redshift for a gamma ray burst as redshifts of gamma ray bursts are determined. So mainstream or not, this highly significant.

It is certainly either extremely distant and luminous, or extremely unusual.

Cougar
2009-Apr-29, 02:16 AM
Science@NASA (http://science.nasa.gov/headlines/y2009/28apr_grbsmash.htm?list108750), headline news. 8.2.

Jerry
2009-Apr-29, 03:16 AM
Science@NASA (http://science.nasa.gov/headlines/y2009/28apr_grbsmash.htm?list108750), headline news. 8.2.

Thanks, Cougar.


It was 8.2, smashing the previous record of 6.7 set by an explosion in September 2008. A redshift of 8.2 corresponds to a distance of 13.035 billion light years.

"We're seeing the demise of a star -- and probably the birth of a black hole -- in one of the universe's earliest stellar generations," says Derek Fox at Pennsylvania State University.

Gamma-ray bursts are the most luminous explosions in the Universe. Most occur when massive stars run out of nuclear fuel. As their cores collapse into a black hole or neutron star, jets of matter punch through the star and blast into space. There, they strike gas previously shed by the star and heat it, which generates short-lived afterglows in many wavelengths.

For years, astronomers have been hunting for gamma-ray bursts from the earliest generations of stars--and mysteriously failing to find them...
A couple of comments:

If you read the balance of this thread, it is clear that determining the EXACT redshift of a gamma ray event is much more problematic than depicted in the NASA article.

Also, no one is even close to certain about what happens when a gamma ray burst appears. Sheesh.

peteshimmon
2009-May-05, 09:04 PM
A bit late but thanks Don (or David) for the
reply. I suppose the increasing series of
redshifts deduced by the same method gives
confidence in this extreme example. But
another part of me thinks the extreme
energy requirements suggest a completely
wrong track.

I know...beam away there:)

Don Alexander
2009-May-06, 06:10 PM
@Jerry: Actually, we are pretty sure what happens when a GRB appears... There are still a lot of details to be researched (How are the jets launched exactly? Are the magnetic fields intrinsic or from turbulence? Stuff like that...), but basic questions such as the distance scale, beaming properties and progenitors are widely accepted... in mainstream science.

@Pete: Actually, this burst wasn't that energetic. The isotropic energy release is at least a factor 50 less than the largest values detected so far.

Jerry
2009-May-07, 06:12 PM
@Jerry: Actually, we are pretty sure what happens when a GRB appears... There are still a lot of details to be researched (How are the jetzt launched exactly? Are the magnetic fields intrinsic or from turbulence? Stuff like that...), but basic questions such as the distance scale, beaming properties and progenitors are widely accepted... in mainstream science.

Agreement is subjective to change:

http://arxiv.org/abs/0905.0690


...Measuring this opening angle, typically inferred from an achromatic steepening in the afterglow light curve (a "jet" break), has proven exceedingly difficult in the Swift era...

However, the opening angles for the events in our sample are larger than would be expected if all GRBs had a canonical energy release of ~ 10e51 erg. The total energy release we measure for those "hyper-energetic" (E(total) >~ 10e52 erg) events in our sample is large enough to start challenging models with a magnetar as the compact central remnant.

slang
2009-May-07, 10:05 PM
http://arxiv.org/abs/0905.0690

Please correct me if I'm wrong, I'm really out of my depth on this one...

I thought that most GRB's were thought to be caused by a black hole doing some fancy acceleration with matter and magnetic fields 'n stuff. So this study may "start challenging models with a magnetar". Since a black hole isn't a magnetar, is this finding a surprise?

From the same abstract: "we find evidence [...] strongly supporting the canonical picture of GRBs as collimated explosions.". From the conclusion in the paper: " [..] we demonstrate all five events are consistent with our understanding of relativistic, collimated explosions."

They do say: "However, the inferred opening angles for several events are larger than would be expected if GRBs were truly standard candles.". Don (or anyone..), are GRBs considered truly standard candles? Or is this just confirmation that they are correctly considered not to be?

Don Alexander
2009-May-12, 12:17 AM
Ach, Jerry, talk about cherry-picking quotes... ;)

First off, slang has pointed out several things already.

The magnetar model has been used to explain things like the "plateau phase" seen in X-ray afterglows, as the rapid spindown of a millisecond magnetar offers a natural solution to power such shallow decays through constant energy injection. The sub(!)luminous XRF 060218 has been explained quite well in the magnetar model.

Cenko et al. offer evidence that not all GRBs can be powered by magnetars, which no one really thought anyway. Black holes have always been more viable candidates. Anyway... Independent of what the remnant is. You start with a Wolf-Rayet star, and you end with relativistic jets. So far, no observations challenge this picture.

As slang pointed out, one of the main findings is actually that all events showed the jet break associated with collimation!

Furthermore, the "canonical energy release" of "one foe" (10^FiftyOne Erg), originally posited by Frail et al. in 2001 with a very limited data set has been shown to be wrong, especially due to subluminous events which seem close to isotropic anyway.

And, no, so far there are no indications that GRBs are standard candles. This would be surprising anyway, as GRB progenitors can be much more diverse than Type Ia SN progenitors (and even there, you have the Super-Chandrasekhar cases...).

So far, people are trying to somehow make them standard candles, because, as we see, they can be detected to distances further than anything else.

PS.: Another interesting event has occured. GRB 090510 was an extremely energetic short/hard GRB which was not only localized and immediately followed up by Swift, but has an excellent detection from Fermi GBM and LAT. The peak energy in the gamma-ray spectrum lies at 4.4 MeV, which is an incredibly high value (about twice as high as anything I've ever heard of), and the GRB is significantly detected by the LAT up to GeV energies, and shows a long tail (at least a minute) at GeV energies, compared to the ~ 0.5 seconds of emission at MeV energies. This promises to be an extremely interesting test case for high-energy emission. Swift discovered an afterglow, but it is quite faint, and no word on spectroscopy yet.

slang
2009-May-12, 10:50 PM
Thanks for the confirmation and explanations, Don Alexander. Jerry, I'm curious, why did you post a paper that strengthens the mainstream view, with the ominous words that "Agreement is subjective to change", and some quotemines?

GRB 090510 sounds interesting. Please keep us updated as you've been doing, I enjoy the reads.

Jerry
2009-May-13, 02:46 AM
Thanks for the confirmation and explanations, Don Alexander. Jerry, I'm curious, why did you post a paper that strengthens the mainstream view, with the ominous words that "Agreement is subjective to change", and some quotemines?

GRB 090510 sounds interesting. Please keep us updated as you've been doing, I enjoy the reads.
As Don said, Frail 2001 put upper-limits on energy and then pinched down the beaming angle to keep the energy levels within this 'canonical' constraint. It doesn't sound like anyone agrees with Frail any more.

Don Alexander
2009-May-14, 02:54 PM
I sure have an update on GRB 090510.

The Very Large Telescope of the European Southern Observatory has nailed the GRBs redshift!!! :D

Probably due to very strong collimation (something which will give the theoreticians extreme headaches) the afterglow became faint very rapidly, and had about 23rd magnitude in the R band when it became visible from the VLT - just a few hours after the GRB.

So there was not much afterglow light to go on, but the VLT detection emission from the underlying host galaxy! In this case, thanks to the very precise optical afterglow localization, there is basically no doubt the two objects are associated (the offset from the galaxy core is just 0.7 arcseconds).

And the redshift is...

z = 0.903!!!!

This is pretty nearby in terms of long GRBs, but just a bit closer than the most distant high-confidence short GRBs.

This extreme redshift means that the isotropic energy release in those about 0.2 seconds rest-frame time are comparable to a typical long GRB which is at least 100 times longer!! What is even more astonishing is that the peak energy becomes 8.4 MeV, which is a simply ridonkulous value. It's like finding Godzilla.... o_O

Basically, this even is a paradigm shift, nothing less. Whatever is creating short GRBs (very probably the coalescence of compact objects - neutron stars and/or black holes - but we have no smoking gun evidence yet) seems to either be capable of unleashing much vaster energies than suspected before, or is able to focus that energy much better than suspected.

My suspicion (you heard it here first!) is that in this case, similar to GRB 080319B, we were right on the axis of the jet, which may have been less than a degree wide.

StupendousMan
2009-May-14, 05:31 PM
I sure have an update on GRB 090510.

The Very Large Telescope of the European Southern Observatory has nailed the GRBs redshift!!! :D
...

And the redshift is...

z = 0.903!!!!


Has this been published anywhere? I'd like to see the spectrum ...

Don Alexander
2009-May-14, 09:45 PM
Well, no image, either 1D or 2D, has been released of the spectrum yet.

The report is here: http://gcn.gsfc.nasa.gov/gcn3/9353.gcn3

TITLE: GCN CIRCULAR
NUMBER: 9353
SUBJECT: GRB090510: VLT/FORS2 spectroscopic redshift
DATE: 09/05/12 17:42:34 GMT
FROM: Arne Rau at MPE <arau@mpe.mpg.de>

Arne Rau (MPE Garching), Sheila McBreen (UCD/MPE Garching), Thomas Kruehler, and Jochen Greiner (both MPE Garching) report:

We present follow-up optical spectroscopy of the short Swift/Fermi GRB 090510 (Hoversten et al., GCN 9331; Ohno & Pelassa, GCN 9334; Guiriec et al., GCN 9336) using VLT/FORS2 (PI McBreen). Observations of the optical source consistent with position of the afterglow (Marshall & Hoversten, GCN 9332; Olofsson et al., GCN 9338; Olivares et al., GCN 9352) started on May 12 08:17UT. A total of three 30min exposures with the 300I grism were obtained, covering an approximate wavelength range of 6000-10000 Angstroms.

Preliminary analysis of the spectra reveals two emission lines at 7093 and 9250 Angstroms, which we identify as [OII] and Hbeta at a common redshift of z=0.903 +/- 0.003. Furthermore, there are indications of a spectral break in the continuum around 7600 Angstroms, suggesting a possible 4000A break at the same redshift.

The detection of emission lines and the possible 4000A break suggest the dominance of the underlying host galaxy over the afterglow at the time of our observations. It also confirms that host galaxies of short GRBs are not all old and dead ellipticals but instead drawn from the underlying field galaxy distribution (e.g., Berger 2009, ApJ, 690, 231).

In the acquisition image the center of the host is 0.7" offset with respect to the NOT refined afterglow position, which corresponds to 5.5 kpc at a z=0.903.

At a redshift of z=0.903, the isotropic equivalent energy of the burst is 3.8E52 erg in the 1 keV - 10 MeV rest frame (using the Fermi/GBM spectral parameters of Guiriec et al., GCN 9336). The peak energy of the best fit GBM Band function model is 8.4 +/- 0.8 MeV in the rest frame.

We acknowledge excellent support from the ESO staff, in particular F. Selman and I. Condor.

Jerry
2009-May-18, 08:15 PM
http://arxiv.org/PS_cache/arxiv/pdf/0905/0905.2417v1.pdf

On the generation of high energy photons detected by the Fermi Satellite from gamma-ray bursts


It is widely assumed that photons of energy larger than 100 MeV are produced by the same source that generated lower energy photons – at least whenever the shape of the spectrum is a Band function. We report here a surprising discovery – the Fermi data for a bright burst, GRB 080916C, unambiguously shows that the high energy photons ( >~ 102MeV) were generated in the external shock via the synchrotron process, and the lower energy photons had a distinctly different source.

Don Alexander
2009-May-19, 07:10 AM
Heh, I just read that an hour ago. This explanation is either complete rubbish or, actually, glaringly obvious. One wonders why the Fermi team didn't think of that.

The one thing I haven't quite understood is the shape of the broadband spectrum...

It would be great to finally get a massive GRB that has simultaneous optical, X-ray, keV/MeV and GeV observations. So far, only GRB 090510 has been both detected/localized/immediately followed up by Swift as well as Fermi GBM/LAT - and in that case, it seems the LAT emission sank under threshold even before Swift had completed it's slew.

Don Alexander
2009-Jun-11, 08:19 AM
Grab them here:

Tanvir et al. (http://arxiv.org/abs/0906.1577)
Salvaterra et al. (http://arxiv.org/abs/0906.1578)

The final redshift measurement is 8.26.

cbacba
2009-Jun-22, 06:45 PM
I note the SWIFT main webpage is flagging this
event up. When the news gets to the main
media it is set in stone as fact. Yet I still
wonder. If you might let me be the slightly
soggy blanket awhile I would ask the
following. One, hopefully one of the popular
magazines will do a detailed guide to the
evidence and how it is interpreted. Two, would
anyone care to say that the evidence is
watertight...or tenuous..or somewhere
in between?

Lastly, and I think I have put this point
before, given the detected range of energies
in this burst is the range in the original
rest frame of the event comparable to "nearby"
bursts? And I would ask if very high energy
photons traversing great distances have any
interaction with "vacuum energy" that modifies
them.

vacuum energy?

there is an interaction with the cosmic background radiation photons. Both gamma rays and ultra high energy cosmic rays can interact as I understand it. The cosmic ray interaction comes into play around the ultra top end of 10^19 eV and puts a limit to the distance traveled for a CR of such high energy.

peteshimmon
2009-Jun-22, 07:14 PM
Well Zero Point Energy, polarisation of the
vacuum or whatever. I remember reading that
very fast particles in the universe would
interact and be slowed down but it was
theoretical. And are very high energy photons
akin to particles? I am not sure.
The original redshift of 9 announced was
convenient as you just move the decimal
point one place to have the original
rest frame energies. I just wondered if the
value was reasonable.

But I leave them to it, my angle is to
obtain clear physical facts away from
what seems like hype sometimes. And they
dont do so bad!

Don Alexander
2009-Oct-29, 01:41 AM
Tanvir et al. and Salvaterra et al. have been published in Nature today.

Alas, no update to astro-ph yet, and I do not have access to Nature, not even at our institute.

StupendousMan
2009-Oct-29, 02:08 AM
Tanvir et al. and Salvaterra et al. have been published in Nature today.

Alas, no update to astro-ph yet, and I do not have access to Nature, not even at our institute.

Here's the abstract from the paper:




Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars1, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology2, 3, 4. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy5. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approx630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

dgavin
2009-Oct-29, 03:22 AM
At 500milyear after big bang, wouldn;t this object be more likely the signiture of a galatic core SMBH being formed?

RussT
2009-Oct-29, 11:16 AM
At 500milyear after big bang, wouldn;t this object be more likely the signiture of a galatic core SMBH being formed?

I think that you are correct, But part of your statement is actually irrelevent.:think:

Don Alexander
2009-Oct-29, 01:38 PM
Whyyyyy does it have to be something so complicated when the simple explosion of a massive star perfectly explains it? :confused:

Not to mention the burst was less than two seconds long in the rest frame. Anything involving an event horizon in solar system dimensions is immediately ruled out by light travel time arguments, thank you very much. :P

Finally, by 600 Mio years after the BB, any supermassive BHs should long since have existed.

@StupendousMan: That's actually the abstract of Tanvir et al.

Here we also have Salvaterra et al:


Gamma-ray bursts (GRBs) are produced by rare types of massive stellar explosion. Their rapidly fading afterglows are often bright enough at optical wavelengths that they are detectable at cosmological distances. Hitherto, the highest known redshift for a GRB was z = 6.7 (ref. 1), for GRB 080913, and for a galaxy was z = 6.96 (ref. 2). Here we report observations of GRB 090423 and the near-infrared spectroscopic measurement of its redshift, z = 8.1 +0.1 -0.3. This burst happened when the Universe was only about 4 per cent of its current age3. Its properties are similar to those of GRBs observed at low/intermediate redshifts, suggesting that the mechanisms and progenitors that gave rise to this burst about 600,000,000 years after the Big Bang are not markedly different from those producing GRBs about 10,000,000,000 years later.

Way to go, Nature, making people write a lot of zeros...:doh: