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Don Alexander
2011-Dec-12, 01:17 AM
So here's the local GRB dude with the newest on GRBs!!

A few days ago, Swift discovered GRB 111209A. The event initially seemed rather boring (at least to me), it was a faint event, detected in a long image trigger. But then, a few minutes into observing, Swift triggered again, implying a very long event, and indeed the raw BAT light curve showed low-level emission up to at least 1000 seconds after the trigger! This is long but not a complete record. During this time, a powerful X-ray afterglow was detected.

Only after several Swift orbits did it become clear that we were seeing something unprecedented here. This is by quite a margin the longest GRB ever seen!

The Konus-Wind light curve (http://www.ioffe.rssi.ru/LEA/GRBs/GRB111209A/) shows an event duration of ~ 16 ks, with the event beginning about 6 ks before Swift triggered. The Swift X-ray light curve (http://www.swift.ac.uk/xrt_curves/00509336/) shows strong and variable X-ray activity extending over multiple orbits (note the very steep rise at the beginning of the second orbit is a reduction artifact!). At about 20 ks after the Swift trigger, the X-ray afterglow goes into a steep day which is followed by a plateau. This is actually standard behavior, except this sequence of events usually happens in the first 1000 seconds after trigger. The steep decay signals the "turning off" of the central engine. Combining KW and Swift data indicates that the central engine was active for 25 ks!!!! (Observed. The event is at z=0.67, so divide times by 1.67 to get rest-frame times. But it is clear the extreme duration is not due to an extreme redshift.)

I am observing at La Silla right now, and, alas, the GRB was only 13 degrees above the horizon here when Swift triggered. So we could not observe it anymore with GROND. But the robotic REM and TAROT telescopes triggered, also PROMPT at CTIO, Faulkes North on Hawaii, and a team triggered the IRTF there manually and got an early NIR spectrum. The early data (also from UVOT on Swift) shows a moderately bright but strongly variable optical transient, having a baseline at about 18th magnitude but sometimes flaring up to 15th mag.

GROND observations were taken the following night, and instead of a decaying afterglow, it was seen to be rising over the period of 5 hours by over half a magnitude!

The afterglow continues to be bright, and I hope a lot of other people are following it up too!

Anyway, it already seems clear that this event stretches progenitor models to the breaking point. While some long-duration events (we're talking 2000 seconds, not 20,000) are know, they are mostly smooth, single peaks (like the nearby XRF 060218), spectrally soft. These can be explained with the spindown energy from a newly born magnetar, but they have been subluminous, and therefore in easy magnetar range.

GRB 111209A is not really exceptional in most terms. The isotropic energy release, the high-energy spectrum, the optical spectrum, the optical luminosity, all of these are within know bounds. The duration, on the other hand, is truly extreme, as well as the fact that the time-variability of the prompt emission looks quite normal, it's just stretched by a factor of 100!!

And just in case some of you are still thinking it might be at a very high redshift: It's not just the spectral lines, but also detections all the way into the deep ultraviolet that show it to be reasonably nearby, and not, for example, high-z and lensed.

antoniseb
2011-Dec-12, 01:36 AM
Cool! Thanks for posting this. Any papers on this coming in the short term?

Don Alexander
2011-Dec-12, 03:36 AM
If I told you, I'd have to kill you! ;)

But actually, I really don't know yet. We're still at the "Let's see what we've actually got here..." stage.

But I'm pretty ure this one will spawn multiple papers.

And you heard it here first. ;) Just in case the Swift team decide to make a quick press release. :P

Jerry
2011-Dec-12, 04:49 AM
Thanks, Don

Absolutely stunning.


Anyway, it already seems clear that this event stretches progenitor models to the breaking point. While some long-duration events (we're talking 2000 seconds, not 20,000) are know, they are mostly smooth, single peaks (like the nearby XRF 060218), spectrally soft. These can be explained with the spindown energy from a newly born magnetar, but they have been subluminous, and therefore in easy magnetar range.

Where there is smoke, there is fire.


The event is at z=0.67, so divide times by 1.67 to get rest-frame times. But it is clear the extreme duration is not due to an extreme redshift.)
Assuming, of course; that the models that are used to derive the time dilation are not as broken as the spin-down models.

peteshimmon
2011-Dec-12, 04:50 AM
Well fixed sources have to start sometime:)

Actually another recent event had my attention
due to longevity. GRB111129 is one of the few
bursts that the SWIFT UVOT saw as well. And
this afterglow was being looked at some 9 hours
later. Sounds more like a fixed source than
afterglow I thought. The GCNs talked about
field stars being used for accurate positioning.
Little bit of ambiguity whether this object
was a field star. Of course if it IS a fixed
condensed object at about 50-60 lys then I
gotta explanation but I suppose I am mistaken.

Don Alexander
2011-Dec-12, 06:46 AM
I see, the usual suspects. :P

@Jerry: GRBs for sure still have surprises in store for us! But I daresay cosmological redshift and time dilation are on very solid ground.

@Pete: I observed two further epochs of 111129A here last week. It sure looks like a normal GRB afterglow. Furthermore, you're selling UVOT short, it's not that bad in detecting afterglows.

slang
2011-Dec-12, 07:11 AM
Another possible TDE? Or can that be excluded already?

Don Alexander
2011-Dec-12, 07:23 AM
Like I said, except for the duration, it looks like a powerful but normal GRB. The X-ray light curve is very different from SwiftJ1644, and that event had a Gamma-Ray light curve extending over many DAYS.

StupendousMan
2011-Dec-12, 11:57 AM
It seems a bit peculiar that an event of such interesting properties has spawned nary a single entry in http://www.astronomerstelegram.org/, nor on http://grblog.org/grblog.php.

The place to go for news about this event is evidently http://gcn.gsfc.nasa.gov/gcn3_archive.html.

Cougar
2011-Dec-12, 02:04 PM
So the central engine tidally ripped apart some, uh, very massive object and then consumed it in pieces, sort of like Jupiter did comet Shoemaker-Levy 9, only on a hugely more massive scale?

peteshimmon
2011-Dec-12, 07:44 PM
Heh! Just realised your name is on those
GCNs I was reading. Anyhow, hope if you
guys find yourselves looking at an
uncatalogued white dwarf in the position
of a longish, low energy burst, you wont
be shy of posting same in another GCN.
Cheers.

Don Alexander
2011-Dec-13, 03:19 AM
It seems a bit peculiar that an event of such interesting properties has spawned nary a single entry in http://www.astronomerstelegram.org/, nor on http://grblog.org/grblog.php.

The place to go for news about this event is evidently http://gcn.gsfc.nasa.gov/gcn3_archive.html.
Astronomer's Telegram is similar to the GCN, except it's not about GRBs, but mostly supernovae, nova and Galactic high energy sources. This is a GRB event, so no one is cross-posting anything there.

GRBlog is stuck. :( A bit back, someone accidentally submitted a GCN twice. Scott Bathelmy quickly removed the duplicate from the GCN archive before GRBlog updated itself. not it's waiting for the GCN with the number the duplicate had to appear, but of course it will not. Robert Quimby needs to reset it, but he's basically given up the site... :(

@Cougar: Well, in all likelyhood, that "very massive object" was the star surrounding the central core which collapsed. It's just something of a mystery why the rest of the star fell on the black hole so "slowly". Rest assured teams will be looking for supernova signatures in the next weeks. :)

@Pete: Swift has actually detected high energy events from flare stars. I'm not sure if there were white dwarfs amongst them, but I think in all cases, they were known sources.

peteshimmon
2011-Dec-13, 06:07 AM
Interesting! Anyway, dont let us keep you
from GRB111212. No rest etc etc. There may
be another one along today as well.
:)

Don Alexander
2011-Dec-13, 08:33 AM
Oh, no, I hope not. Data reduction and analysis is running out of my ears.

But we discovered the afterglow of 111211A this morning and I am observing it again now! :D

Ara Pacis
2011-Dec-15, 07:33 PM
I'm not sure I follow. Were some components of the event prolonged, or was the entire event prolonged as if it was playing out in slow-motion? Could it be a particularly rare and direct alignment with the star's pole and motion? Or could it be mechanical interactions with deep gravity fields in the vicinity of the star. Could it be time dilation due to deep gravity fields in the vicinity of the star.

Or to really reach, perhaps it's a glitch in the matrix. ;-)

Don Alexander
2011-Dec-15, 10:37 PM
The entire event was prolonged, like in slow-motion. At the same time, the energy released was high but not exceptionally so, so you had a very faint GRB in terms of PEAK flux but a massive ones in terms of fluence.

GRBs are only detectable if we are pretty much looking at the pole of the star, so that's a given.

An extreme motion away from us would cause such a time-dilation, but it would also shift the emitted energy spectrum very strongly into the red, this is not seen. Not to mention to get the factor 100, your exploding star would need to travel ultrarelativistically.

The central engine of GRBs lies in an extremely dense environment and is opaque to pretty much everything except neutrinos. All GRB radiation we see comes at the very least from the surface of the star. The black-hole deep gravity wells are completely cloaked.

So, a glitch in the Matrix sounds like a better idea. ;)

publiusr
2011-Dec-19, 10:52 PM
Now for Hoagland to call it a starship burn.