Are collapsars responsible for

some r-process elem

ents? How

could it work?

Jason Pruet, N-D

ivision, LLNL

This work w

as performed under the auspices of the U

.S. department of energy by the

University of California Law

rence Livermore N

ational Laboratory under contractW

-7405-ENG

-48.

Overview

•Collapsars, Failed SN

e, and GRBs - an

introduction•

Composition of the central accretion disk and

outflows from

the disk–

Observations

–Speculation on the r-process

•A

n observational test of collapsars as the source ofA

<130 r-process elements

•Sum

mary

e -AÆ

n

9M§ <M

<25 M§

M>25(fallback) - 40(direct) M

§ (Fryer)

Shallow density gradient around Fe

core gives weak or failed shock.

shocknn

viscous diskJET

3•1016 < j < 3•10

17 cm2 (sec) -1 (M

acFadyen)[ 1-5%?]

~50%

~50%nn

blackhole

expl. Ni synthesis

n’s from cooling ns

r-process in a late time w

ind?

Succesful and not-so succesful SNe

Inside a collapsing star(M

acFadyen and Woosley 1999)

Collapsars are most fam

ous as likelypow

ering long duration Gam

ma Ray Bursts

~108cm

Some evidence supporting a

connection between collapsars and

long duration GR

Bs•

GRBs are associated w

ithstar-form

ing galaxies (Bloomet al 2002, D

jorgovski et al.2001, Piro et al. 2001) - justw

here young massive stars

are expected.•

Many - m

aybe all - longbursts are very “SN

-like” inappearance (Price et al. 2002)

shock

~1012cm

the g-raysfromthese eventsoutshine therest ofthe stars in theuniverse for~30 sec

GRB990123

What do collapsars

pollute the galaxy with?

To understand nucleosynthesis in theseevents w

e fist need a closer look at theaccretion disk

BH

Heavy A

dissociatee -pÆ

nne

Ye Æ

Øneutron-rich

T~2-3MeV

; s/kb low

: 7-30convection

Hotter and denser

for the most part

these disks are optically thin to neutrinos

The composition of the inner disk depends

sensitively on the viscosity and accretion rateC

omposition of a slow

ly accreting disk

A disk like this

probablycan’t pow

er a GRB

M=0.01 M

Ä sec -1, a=0.1, a=0

.

a little proton rich

(Pruet, Woosley &

Hoffm

an 2002)

More energetic disks are m

ore neutron richM

=0.1 MÄ

sec -1, a=0.03, a=0.

n/p largeearly on

Are there any outflow

s from the disk?

I) observations“Sn-like” lightcurves associated w

ith GRBs are pow

ered by 56Ni

56Ni

56Co

56FePrice et al. 2003

6 days

77 days

Right now observations are consistent w

ith every GRB

producing a SN-like light curve (Price et al. 2002)

Nickel

•For tw

o bursts there are detailed estimates of N

im

ass and outflow velocity

–v~0.13c and M

Ni ~0.5M

§ for SN

2003dh (Hjorth et al.

2003, Stanek et al. 2003, Woosley &

Heger 2003)

–It’s hard to see how

explosive burning could beresponsible for this m

uch Ni (M

aeda & N

omoto 2003)

•O

bserved Ni probably cam

e in a wind from

thedisk (M

cFadyen & W

oosley 1999; Pruet,Thom

pson & H

offman 2004)

fi n/p < 1 in this w

indfi

the wind is energetically prim

ary (E~4û1052 erg - the

GRB is not so im

portant)

Outflow

s from the disk

II) Calculations

s = low, no e +

viscous and neutrino heatingdrive an outflow

(both contribute about equally)

s = high, lots of e +

†

ln

e

ln e

ª1.2

Everything conspires to drive the outflow proton-rich

Wind-like outflow

s are generically proton richand synthesize 56N

i with m

odest efficiencies

wind from

the outer regions of a mediocre disk

X( 56N

i)~0.5

(Pruet, Thompson &

Hoffm

an 2004)

Wind from

the more n-rich inner regions of

a mediocre disk

X( 56N

i)~0.1

Could r-process elements com

e from the disk?

•N

ot from w

inds - they’re proton rich andhave s/k

b ~30-50.•

Other possibilities

–relativistic outflow

near the hole.–

bubbles.

Relativistic outflow from

near the hole

JET

The jet proper -G~200, s/k

b ~105,

very little mass,

only makes 2H

,a’s, etc. (Pruet,G

uiles & Fuller

2002)

continuum?

G~2?

• relativistic outflows expand on a hole light crossing

(~10-5 sec) and can rem

ain neutron rich - nw

eak ~10-6 T

n 5

for n-driven outflows (Pruet, Fuller &

Cardall 2001)• G~2 outflow

s synthesize r-process elements

abundantly, though in proportions quite different fromsolar (Inoue et al. 2003).

BubblesM

agnetic instabilities are thought to give rise to the viscosity allow

ing accretion. In this case, localized magnetic instabilites

are expected.

Bouyant magnetic filam

ent

reconnection deposits entropy

The rise time of the filam

ents is not a wind

hydrodynamic tim

e, but ~W-1k - w

hich is very fast. The neutron richness of the disk is preserved in bubbles (DY

e £ 0.1-0.2).

g

Properties of the bubbles•

s/kb : For a bubble to survive until T

9 ~2 the entropy of the bubble must be greater than

the entropy of the background wind (~30-50)

•Y

e : ~0.2-0.4 depending on the kind of disk and where in the disk the bubble originates.

•t- the expansion tim

escale: since the background wind and the bubbles are

approximately radiation dom

inated they both have similar t’s.

•Som

e bubbles must break at T

9 >1 and mix w

ith the proton rich background. This canroughly be approxim

ated by stopping all strong interactions.

As a rough approxim

ation:( r a random

number in [0,1] )

s = 50 + 50 rY

e = 0.15 + 0.25 r t = 0.03(1+ 4 r) secT

9,mix = 1 + 2 r

Nucleosynthesis in 100 bubbles

Fair agreement w

ith solar abundance pattern.Choice of bubble properties not so im

portant.

Does the idea of collapsars as the source of

A<130 r-elem

ents make any sense?

•Even though collapsars are relatively rare (~1/10 -1/100 the SN

rate), very little mass in bubbles is

needed (~10-3M

§ if collapsars are as frequent as

GRBs). This is only 0.1%

as much as the w

indm

ass.•

The kinetic energy of the collapsar ejecta is about10 tim

es greater than that of typical SNe, so they

sweep up about 10 tim

es more m

ass. This implies

a Ag refreshm

ent rate consistent with that

predicted by Qian, Q

ian and Wasserburg, .... .

Can the idea be tested?

Yes. O

bservations of Ni associated w

ith GRBs im

ply thatthese are unique nucleosynthetic events.

•A

very energetic shock within the collapsar

synthesizes a peculiar abundance pattern quitedifferent from

regular SNe (M

aeda & N

omoto

2003).•

Disk w

inds synthesize even more peculiar

abundance patterns (Pruet, Surman &

McLaughlin

2004).fi

Association of the peculiar abundance pattern

(explosive or wind) w

ith A<130 elem

ents couldconfirm

collapsars as the site of A<130 r-

elements.

Nuclei accom

panying Ni in a disk w

indO

bservations of Ni tell us alm

ost everything we need to calculate

nucleosynthesis in the wind. H

owever, w

e don’t know if

Ye is very close to 0.5 or if Y

e >0.51. To a first approxim

ation:Y

e =0.5 winds m

ake only 64Zn Y

e >0.51 winds m

ake only 45Sc.

A test

If collapsars are responsible for Ag synthesis, then in

the collapsar ejecta

†

AgFeÈ Î Í

˘ ˚ ˙ ~1.5

depending on the collapsar rate.

†

ScFeÈ Î Í

˘ ˚ ˙ or

†

ZnFeÈ Î Í

˘ ˚ ˙ ~ 1-1.5, depending on details of the wind.

while

So, large Ag overabundances in m

etal poor stars should be accompanied by large

Sc or Zn overabundances.

Summ

ary•

Collapsars or collapsar-like disks are neutron rich(n/p ~ 10). Bubble-like or sem

i-relativistic wind-

like outflows from

these regions may synthesize

some r-process nuclei.

•O

bservations of GRBs im

ply correlations between

Sc and/or Zn abundances and these r-processelem

ents.•

So far, the data on Ag abundances is not

conclusive.