The brightest GRB ever in the history of ever!

[Don Alexander]

Dear all!



Last night, what is likely the brightest gamma-ray burst (extragalactic) ever detected in the history of mankind occurred. It was a long, highly complex event which triggered the SPI/ACS detector on the INTEGRAL satellite three times:

http://www.isdc.unige.ch/integral/ib...-31363-39824-0
http://www.isdc.unige.ch/integral/ib...-31363-39824-0
http://www.isdc.unige.ch/integral/ib...-31363-39824-0

(click on the image boxes on the left to get a more expanded view of the three episodes)

The third of these episodes also triggered the GBM detector of the Fermi satellite (the first two occurred while the satellite was traversing a space regions where triggers are disabled...). The report from the Fermi team on the GBM observation (http://gcn.gsfc.nasa.gov/gcn3/13377.gcn3) gives a fluence of 9 x 10^-3 erg cm^-2 and a peak photon flux of 850 ph cm^-2 s^-1. The first value is unprecedented, so far, the brightest GRBs ever were GRBs 830801B and 840304, with 2-3 x 10^-3 erg cm^-2 (the famous "naked-eye burst" GRB 080319B reached 6 x 10^-4).

The GRB was also significantly detected by the Large Area Telescope aboard Fermi, which yielded a position RA(J2000) = 170.73 deg, Dec(J2000) = 9.48 deg with an error of 0.45°. (http://gcn.gsfc.nasa.gov/gcn3/13379.gcn3)

This position is observable at the beginning of the night for one or two hours, depending on where you are. Northern observers are disfavored due to the long twilight. Also, it is about 10 degrees from the Moon, but lunar separation is increasing.

If any of you have large amateur telescopes (12" or above) equipped with CCDs and reasonably large FOVs (1° or so), I encourage you to observe this position.

[antoniseb]

Wow! Thanks Don Alexander!

[Don Alexander]

The position has just been improved considerable:

http://gcn.gsfc.nasa.gov/gcn3/13381.gcn3

[slang]

The report from the Fermi team on the GBM observation [...] gives a fluence of 9 x 10^3 erg cm^-2 and a peak photon flux of 850 ph cm^-2 s^-1. The first value is unprecedented, so far, the brightest GRBs ever were GRBs 830801B and 840304, with 2-3 x 10^-3 erg cm^-2

Did a minus drop in the first number? Going over the report, I think there's a typo here. If not, that would be 6 (or 7?) orders of magnitude more energy.

[Don Alexander]

Ah, darn those minuses.

This of course changes nothing about the rest.

If someone needs the BAT position in sexagesimal, it is:

RA = 170.94 = 11:23:46
Dec. = 8.93 = 08:55:48

with 3 arcminutes radius. This may still change a bit, they do not have the entire data set downloaded.

[Don Alexander]

The Konus-Wind team has now reported their detection, and they find a fluence which is about THIRTY times smaller than that reported by GBM.

http://gcn.gsfc.nasa.gov/gcn3/13382.gcn3

A factor of a few can be easily explained, but not an additional factor of 10. This seems to imply something went wrong with the original GBM fluence estimate, and that this is a very bright burst, but not a record holder.

Sorry for that.

[Tensor]

The Konus-Wind team has now reported their detection, and they find a fluence which is about THIRTY times smaller than that reported by GBM.

http://gcn.gsfc.nasa.gov/gcn3/13382.gcn3

A factor of a few can be easily explained, but not an additional factor of 10. This seems to imply something went wrong with the original GBM fluence estimate, and that this is a very bright burst, but not a record holder.

Sorry for that.

Don, don't ever be sorry for bringing things like this to our attention. Even if it wasn't a record holder, it was pretty frigging interesting. Thanks.

[Swift]

Don, don't ever be sorry for bringing things like this to our attention. Even if it wasn't a record holder, it was pretty frigging interesting. Thanks.

Ditto that. Actually, watching the play-by-play as more is learned is fascinating; science in action.

[ngc3314]

Saw your post in time to send it around to the SARA consortium (because our regular GRB guru seems to have been on a plane at the time); same people were using our telescopes in both hemispheres, as it happened. Didn't see an optical source from either, which fits with other reports from yesterday. (I keep wondering which of the bursts like this might be from Pop III stars).

[peteshimmon]

That "Superbowl" thing must be 20 years ago
now. Can we call this one the Penalties event?

[Don Alexander]

@ngc3314: Likely none of these. A Pop III burst (IF they exist) would be at a very high redshift (10? more?) and therefore not so such rapid variability. also, there are simulations showing that Pop III GRBs might be 10 ks long in the rest frame, implying day-long transients. And your guru, is that Adria??

@pete: it was GRB 930131, so next year. And some penalties should be given for the mess this one was.

No one has reported any afterglow, and hardly anyone has reported any upper limits. I know of at least two groups (one I'm in) that have gotten quite deep data. There's obviously no bright afterglow, but a faint one could not be recognized without a comparison epoch. We'll see what the next days bring.

[ngc3314]

@ngc3314: Likely none of these. A Pop II burst (IF they exist) would be at a very high redshift (10? more?) and therefore not so such rapid variability. also, there are simulations showing that Pop III GRBs might be 10 ks long in the rest frame, implying day-long transients. And your guru, is that Adria??

Oh, yeah, right, I hadn't paid attention to the duration.

The SARA GRB guru is Dieter - Adria is the designated hitter or something.

[Don Alexander]

Pointed Swift observations are in progress.

Now, please give us an X-ray afterglow position.

Then, we'll probably get a bucketload of upper limit GCNs

[Don Alexander]

Well, the formerly brightest GRB of all time is turning into a full-fledged disappointment.

Observations in the near-infrared (Ks band) were obtained with HAWKI on the VLT at two epochs, basically one and two days after the GRB. They reveal one faint possible afterglow candidate, but clearly nothing bright.

Swift itself has identified two X-ray sources in the field. But neither is associated with the HAWKI candidate, and both have counterparts in the SDSS, so they are just X-ray emitting stars or galaxies.

For a GRB this bright, such a faint afterglow is extremely unusual. While that makes it interesting in and of itself, it precludes getting a redshift, which in turn precludes a lot of other analysis...

[Ara Pacis]

If the afterglow is missing, what can you hypothesize about it based on that? Assuming the data is reliable, what phenomenon could result in a bright GRB with an undetectable afterglow?

[Don Alexander]

The most likely solution is a very rapid decay.

If it had had a bright X-ray afterglow but nothing in the optical and NIR, it would have been a "dark GRB", most likely due to very high extinction in the host galaxy (buried deep in a molecular cloud). There is a similar example, GRB 051022, which had a similar high fluence but was not detected in any optical/NIR band, including K.

Instead, we aren't seeing anything really in any band...

[Ara Pacis]

So, I guess I can rule out the "aliens are decelerating towards Earth using a Project Orion-type Nuclear Pulse Propulsion system" possibility then?

[Don Alexander]

I should hope so, otherwise, their engine really stutters...

Anyway, some (non)-news on the GRB:

A follow-up Chandra X-ray space telescope observation revealed that Swift X-ray source S1 had actually faded by a factor of three within several days, implying it to be the afterglow. The extremely precise Chandra position is actually in agreement with a point-source seen in the HAWKI image which is offset by several arcseconds from the bright galaxy (the aforementioned known SDSS source). This is likely the Ks-band afterglow, though it is not seen to fade between the two HAWKI epochs.

Other than this, nothing. No more deep observations reported, no redshift...

Soon, I'll report on Yet Another Extremely Bright GRB that turned out a lot better...

[Ara Pacis]

Are you saying no one was able to determine the redshift, the redshift was indeterminate, or that there was no redshift and it's relatively close?

If the burst was offset from the near galaxy, does that mean it may be farther away in a galaxy not visible, extragalactic (flung out from a galactic merger of that galaxy or another near the axis of our line of site?), or from a dim cloud of stars orbiting a distant galaxy?

Or am I missing something?

[antoniseb]

Are you saying no one was able to determine the redshift...

No observations were made that collected spectra that could have given us the red shift.

[Don Alexander]

a) No one was able to determine the redshift. This is usually done via one of two methods. If you have a bright afterglow, you get absorption-line spectroscopy of the afterglow, it will show lines of elements in the interstellar medium surrounding the GRB. Or you get deep spectroscopy of the host galaxy and hope for typical emission lines of star-forming regions to stick out, like H alpha, [O III] and [O II]. The first could not be done (no afterglow except a faiiint K-band fizzle), and the second may be done one day, but right now, the GRB is rapidly moving out of visibility. And if there is a host, it must be pretty faint.

b) Yes, the first possibility is probably the solution. The middle one probably not, since these stars which produce GRBs probably do not live long enough to become real runaway stars. The final one is distinctly possible too. There is a very faint splotch to the south-east of the bright galaxy, which may represent an interacting system (or may be totally unrelated). In that case, the GRB could have detonated in a star cluster in a bridge between the two galaxies (think of the Tadpole or the Antennae). One thing speaking against this, though, is the very faint and seemingly highly extinguished afterglow, unless the GRB progenitor was still buried deep in its birth cocoon, there should not be much matter in the way. Such star clusters, having relatively small gravitational potentials, usually can't keep dense molecular gas once the OB stars blaze on, their extreme stellar winds and UV radiation quickly clear the fogs of nascent dawn...

All in all, you have the bases covered well, I'd say.

[Ara Pacis]

Thanks, I always like to learn something new.

[peteshimmon]

A small point from the above, if a redshift
cannot be determined it does not mean there
has to be a redshift!

Two GRBs lately have my interest, one on the
12th and today. I wonder if there is a field
star in the error circles. And are such stars
regularly discounted? I let them get on with
it but I am starting to get an itch to have
them swear on Astrophysical Quantities that
the redshifts announced are the best possible
interpretations of the spectra

[Don Alexander]

The burst from the 12th shows a clear Damped Lyman absorber line as well as multiple metal absorption lines at a redshift 4.17, which was first roughly determined by my team (I am on the GCN) photometrically.

There is absolutely no way that this is a "field star", especially a field star in a very uncrowded field right in the middle of the very small error circle of a decaying X-ray source, both of which were not there before.

You read "the redshift was not determined" and you immediately go on wild tangents. The redshift (of 120624B) was not determined because the source was so faint it was hardly detected in any (optical/NIR) band and so far no one has tried to do spectroscopy of this position, especially since the chance is high nothing will be measurable for sheer lack of photons.

[peteshimmon]

OK I accept that, thanks. Sometimes I
wonder about the X-ray source not being
there before, it suggests a complete
catalogue of very faint sources.

Field stars do show up in the error
circles sometimes surely. The GCNs
talk about "credible" sources for
the bursts. Gets me going!

[Don Alexander]

Yes, in crowded fields, it happens often enough that stars in the X-ray error circle, even if it is clear the X-ray source is the GRB afterglow. It's just a chance superposition. But in such cases, these three things almost always happen:

a) Someone does take a spectrum, and reports it is a star (has happened several times).
b) Someone does multi-color photometry and cleary the source is not a power-law spectral energy distribution.
c) Data over a longer time-span is taken and the source is seen to not be variable.

Also, such a complete catalog of faint sources does exist, ever heard of ROSAT? GRB afterglows are usually pretty bright initially, and a lot brighter than the limits of the ROSAT catalog. Therefore, in most cases it is easy to verify that no X-ray source this bright was there before.