jason pruet- are collapsars responsible for some r-process elements? how could it work?
TRANSCRIPT
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.