KITP: grb II

yesterday I missed the post-Newtonian discussion, which is a bummer, but I was busy explaining to a hoard of pre-Ks why Mars looked green...
so now we go back to blowing things up

yes, it turns out that not all whites are the same, and trying to project onto that shade of white which has just a tint of blue in it, is not the same as your eggwhite screen, when using an RGB projector.

I should have riffed on Kim Stanley Robinson, I guess, but I didn't.

Look!
Hubble Space Telescope! Astronauts! Rockets! Aliens!

Today, we return to massive binaries and long GRBs in particular, which lets me recoup my Total Loss of Notes from last week...

Ed is on deck, and has resummarised nicely.

Long GRBs

duration: 2-hundreds of secs

Lorentz factors: Γ ~ 300-1000

Jets: opening angles of ~ 5 degrees, total energies of 10^51-52 ergs

Related to peculiar type Ic supernovae. Which have explosive energies of order 10⁵² ergs.

No H, He
C/O core greater than 6 solar masses.
Outflow velocities of 30,000-50,000 km/sec

Typical redshifts of 1-3
Maximum observed redshift 6.7 - many with no known redshift.
Lowest redshift 0.0008

1998 bw

Model: collapsar - relativistic jet from a forming black hole with a hyperaccreting torus,

Requires: specific core angular momentum of 3-20 * 10¹⁰ cm²/s

Rate of type GRBs is about 0.0001 that of core-collpase supernovae.

I Zw 18 - low Z blue irregular

Host galaxies

(cf Fruchter et al 2006)

41 out of 42 : Irregular dwarf galaxies - dwarf starbursts (blue)

Long GRBs fall on brightest unresolves spots within galaxies - clumps of massive O and WR stars - superstar clusters

=> LGRBs originate from most massive stars: O/WR progenitors

- Never seen in ULIRGs (Ultra Luminous InfraRed Galaxies)
- something like > 50% of all star formation appears to take place in ULIRGs at intermediate redshifts (z ~ 1-3) [ed. need a cite on this]
-- basically at these redshift the L* galaxies are dominant
-- NB extinction of optical counterparts must be an issue to some extent
-- is XRB localization adequate and seen for enough of sample that we know that the "dark" bursts aren't just all obscured LGRBs in ULIRGs? - yes, apparently we have enough X-ray burst localizations that have no optical counterparts to know that most of the dark bursts can't by in ULIRGs. Interesting.

-- ULIRGs have metallicities of about solar,

So we infer that Long GRBs are related to star formation at sub-solar metallicity
the blue dwarf irregular have metallicities of more like 0.1 solar

Signs of low Z
All hosts have Ly α emission
- very low extinction of afterglows (but; dark bursts???)
- Z up to 1/3 of solar (1998 bw)

Are all metals equal? We don't really mean scaled solar abundance when we talk
about low Z, nor do we probably care that much about Fe as it happens.
So are we talking O? CNO? Alphas? All s-process?
We gots to knows.

Models: single star -> fully mixed evolution -> He4

binary -> H/He envelope removed by mass transfer
rapid rotation due to tidal coupling

Need a low mass companion?
High mass helium core with short orbital period companion?
Narrow range of orbital periods and masses that works, but that is ok.
Need only 1/10,000 of big stars to do this.
But is this channel too rare?
Hard to get a handle on our local population because we don't know the duty cycle of the activity of the descendant black hole binary, assuming that is the channel.

Go through something like Cyg X-3?

Where does low Z come in?
Probably in J coupling to envelope - need to lose H/He either by blowing off envelope, which needs some metals, or by rotational mixing, which may need Z below some critical.
This is a hard problem...

Lo Z so that we have low enough envelope mass loss that the He core is massive enough?
Yet again we are then reduced to rotation and magnetic fields...

In the other room, I just missed Juan Maldacena's talk on Fundamental Aspects of String Theory, or some such. I'll put a link to the video tonight or tomorrow.