GRBs, colliding neutron stars and fast physics
Good news article on scienceNow, and associated press put out a very short teaser.
The official NASA press conference is cancelled, and "scientists are cleared to discuss the results".
Since I am unaffiliated with either Swift or the ground based followups, I was free to comment, but was promptly co-opted as a "outside commentator" and therefore under a "no-comment" embargo until release.
NASA has a reason for this, they like co-ordinated, well spaced and timed blitzed on specific news, and preferably stuff that has been published in a refereed paper (and there were high energy astrophysics press events today [on COUP] and another on thursday on GRB041209a (not a NASA event I believe).
But, what do you do when the data and citable telegrams on followups are published immediately on the web?
Journalists aren't stupid, and many good science journalists know where to look for breaking news; they follow the GCN, IAUC and MPEC circulars, and religiously read arXiv every evening. And good for them.
Now, how they're getting my cell number I don't know. Our secretary is not handing it out...
Still, no press is bad press. And it made slashdot - total geek streed cred, d00d.
Oh, science. Its still there; though whether the faint, possibly variable optical counterpart is real or background is very uncertain. The x-ray counterpart is quite well localised and is right next to a whopping big elliptical galaxy at z=0.22.
Those are relatively rare beasts, and this is highly suggestive, but not conclusive, evidence for physical association.
(I guesstimate less than 1:100 chance of a short GRB being that close to a galaxy like this.. post hoc ergo...)
But, deeper Keck imaging reveals "shitloads" of faint blue crap all over the XRT error circle. Which could be high redshift star forming galaxies, which could be the real hosts of the GRBs, which would kinda blow the theory of a delayed offset neutron star merger right out of the water, and incidentally scupper the beautiful model of Bloom, Sigurdsson & Pols (1999).
So what could it be? It fits the NS merger model well, almost scarily well; like coincidence well.
If it is higher z, it is faster (to compensate for (1+z) time dilations, so true time scale of less than 10 millisec (?!) and higher energy. That points to neutron star-black hole merger, with dynamically unstable disruption of the neutron star and a ballistic accretion flow (as opposed to an angular momentum limited disruption with viscous evolution).
That's interesting too. (and thanks to Prof Cole Miller for illuminating discussion on this!) But I still lean to the neutron star merger theory.
Ultimate proof will come when several of these are seen. If they are seen in statistical association with L* galaxies at low redshift, and not ones undergoing a lot of recent star formation; then the NS-NS merger model is likely right.
Interesting possible implications - gravitational radiation sources for ALIGO; tests of extreme nuclear physics, sites for rare nucleosynthetic processes, possible extreme magnetic field evolution, tracer of past star formation, and relativistic physics.
Need lots more, hope Swift picks them up. They're x-ray faint, which is consistent with a relativistic blast wave in low densityh intergalactic medium, but that makes them harder to localise.
Knowing what the beaming fraction is would be very valuable.