The rapid proton capture process
(rp-process)
Sites of the rp-process
This lecture
Novae
n-wind in
supernovae ?
X-ray binaries
Nova Cygni 1992
with HST
E0102-73.3
composite
• “r”p-process
(not really a full
rp-process)
• makes maybe
26Al
•makes maybe
45Sc and 49Ti
• if n accelerated
(n interactions)
maybe a major
nucleosynthesis
process?
KS 1731-260
with Chandra
• full rp-process
• unlikely to contribute
to nucleosynthesis
X-rays in the sky
D.A. Smith, M. Muno, A.M. Levine,
R. Remillard, H. Bradt 2002
(RXTE All Sky Monitor)
Cosmic X-rays: discovered end of 1960’s:
0.5-5 keV (T=E/k=6-60 x 106 K)
Nobel Price in Physics 2002
for Riccardo Giacconi
Discovery
Discovery of X-ray bursts and pulsars
H. Schatz
First X-ray pulsar: Cen X-3 (Giacconi et al. 1971) with UHURU
T~ 5s
Today:
~50
First X-ray burst: 3U 1820-30 (Grindlay et al. 1976) with ANS
10 s
Today:
~70 burst sources out of 160 LMXB’s
Total ~230 X-ray binaries known
H. Schatz
Burst characteristics
Typical X-ray bursts:
• 1036-1038 erg/s
• duration 10 s – 100s
• recurrence: hours-days
• regular or irregular
Frequent and very bright
phenomenon !
(stars 1033-1035 erg/s)
Accreting neutron stars
Accreting neutron stars
The Model
H. Schatz
The model
Neutron stars:
1.4 Mo, 10 km radius
(average density: ~ 1014 g/cm3)
Donor Star
(“normal” star)
Neutron Star
Accretion Disk
Typical systems:
• accretion rate 10-8/10-10 Mo/yr (0.5-50 kg/s/cm2)
• orbital periods 0.01-100 days
• orbital separations 0.001-1 AU’s
NASA
H. Schatz
Energy sources
Energy generation: thermonuclear energy
4H
4He
6.7 MeV/u
3 4He
12C
0.6 MeV/u
(“triple alpha”)
5 4He + 84 H
104Pd
6.9 MeV/u
(rp process)
Energy generation: gravitational energy
E=
G M mu
R
= 200 MeV/u
Ratio gravitation/thermonuclear ~ 30 – 40
(called a)
H. Schatz
Observation of thermonuclear energy
Unstable, explosive burning in bursts (release over short time)
Burst energy
thermonuclear
Persistent flux
gravitational energy
H. Schatz
Burst ignition
Burst trigger rate is “triple alpha reaction”
Ignition:
10
-1
2 -1
decool
>
dT
enuc
ecool ~ T4
12C
Nuclear energy generation rate
Cooling rate
Triple alpha reaction rate
-9
reaction rate (cm s mole )
denuc
dT
3 4He
-10
10
Ignition < 0.4 GK:
unstable runaway
(increase in T increases
enuc that increases T …)
-11
10
-12
10
-13
10
-14
10
degenerate e-gas helps !
-15
10
0
1
temperature (GK)
10
BUT: energy release dominated by subsequent reactions !
H. Schatz
At large (local) accretion rates
0.24
at high local
accretion rates m > medd
(medd generates luminosity Ledd)
temperature (GK)
0.23
0.22
0.21
0.2
0.19
0.18
0.17
0.16
-2
10
-1
10
accretion rate (L_edd)
Triple alpha reaction rate
-9
2 -1
-1
reaction rate (cm s mole )
10
-10
10
-11
10
Stable nuclear burning
-12
10
-13
10
-14
10
-15
10
0
1
temperature (GK)
10
0
10
H. Schatz
X-ray pulsar
> 1012 Gauss !
High local accretion rates due to magnetic funneling of material on small surface area
http://www.gsfc.nasa.gov/topstory/2003/0702pulsarspeed.html
Golden Age for X-ray Astronomy ?
XMM Newton
Constellation X
RXTE
XMM
Chandra
RXTE
H. Schatz
Open question I: ms oscillations
4U1728-34
Rossi X-ray Timing Explorer
Picture: T. Strohmeyer, GSFC
Neutron Star spin frequency
Now proof from 2 bursting pulsars
(SAX J1808.4-3658, XTE J1814-338)
(Chakrabarty et al. Nature 424 (2003) 42
Strohmayer et al. ApJ 596 (2003)67)
• Origin of oscillations ?
• Why frequency drift ?
H. Schatz
The bursting pulsar
SAX J1808.4-3658
D. Chakrabarty et al.
Nature 424 (2003) 42
Pulsar
Frequency
Seconds since burst
Origin of frequency drift in normal bursting systems ???
(rotational decoupling ? Surface pulsation modes ?)
H. Schatz
Open question II: ignition and flame propagation
Anatoly Spitkovsky (Berkeley)
H. Schatz
Open question III: burst behavior at large accretion rates
Regular burst duration (s)
Regular burst rate /day
superbursts
a:~40
superbursts
a: 500-5000
Accretion rate (Edd units)
Cornelisse et al. 2003
Accretion rate (Edd units)
H. Schatz
Open question IV: superbursts
X 1000 duration
( can last ½ day)
X 1000 energy
Normal Burst
11 seen in 9 sources
Recurrence ~1 yr ?
4U 1820-30
Often preceeded by
regular burst
H. Schatz
Open question V: abundance observations ?
EXO0748-676
Cottam, Paerels, Mendez 2002
H. Schatz
New era of precision astrophysics
Precision X-ray observations
Uncertain models due to nuclear physics
(NASA’s RXTE)
Galloway et al. 2003
97-98
2000
Burst models with
different nuclear physics
assumptions
 GS 1826-24 burst shape changes !
Woosley et al. 2003 astro/ph 0307425
(Galloway 2003 astro/ph 0308122)
But only with precision nuclear physics
Fate of matter accreted onto a neutron star
accretion rate: ~10 kg/s/cm2
Neutron star surface
Neutron star surface
Neutron star surface
Neutron star surface
Neutron star surface
Accreted matter (ashes)
Neutron star surface
 Accreted matter is incorporated deeper into the neutron star
 As the density increases interesting things happen
H. Schatz
Nuclear physics overview
Accreting Neutron Star Surface
n’s
~1 m
X-ray’s H,He
fuel
Spallation of heavy nuclei ?
Thermonuclear H+He burning
(rp process)  X-ray bursts
gas
ashes
~10 m
ocean
~100 m
outer
crust
~1 km
10 km
Inner
crust
core
Deep burning ?
 superbursts
Crust processes
(EC, pycnonuclear fusion)
crust heating
crust conductivity
Step 1: Thermonuclear burning in atmosphere
Neutron star surface
H,He
gas
ocean
outer
crust
Inner
crust
~ 4m, r=106 g/cm3
Woosley et al. 2003
Kippenhahn
diagram
depth
time
H. Schatz
Conditions during an X-ray burst
Ignition
layer
ocean
Burst cooling
Ignition
surface
J. Fisker
Thesis
(Basel, 2004)
H. Schatz
Visualizing reaction networks
Proton
number
(a,g)
(p,g)
14
27Si
13
(a,p)
(,b+)
neutron number
dY j
 dYi
Lines = Flow = Fi , j  
  dt i  j  dt

 dt
j  i 
Al (13)
Mg (12)
Na (11)
Ne (10)
Burst Ignition:
15 16
13 14
F (9)
O (8)
N (7)
C (6)
B (5)
Be (4)
Li (3)
He (2)
3 4 5
H (1)
n (0)
2
0 1
11 12
9 10
8
7
6
Prior to ignition
~0.20 GK Ignition
: hot CNO cycle
: 3a
: Hot CNO cycle II
~ 0.68 GK breakout 1: 15O(a,g)
~0.77 GK breakout 2: 18Ne(a,p)
(~50 ms after breakout 1)
Leads to rp process and
main energy production
H. Schatz
How the rp-process works
Nuclear lifetimes: (average time between a …)
• A+pB+g proton capture
: t = 1/(Yp r NA <sv>)
• b+ decay
: t = T1/2/ln2
• B+gA+p photodisintegration : t = 1/l(g,p)
Z
43 (Tc)
(for r=106 g/cm3, Yp=0.7, T=1.5 GK)
42 (Mo)
10
10
8
10
41 (Nb)
6
10
4
10
Lifetime (s)
40 (Zr)
39 (Y)
2
10
0
10
-2
10
-4
38 (Sr)
10
-6
10
N=41
-8
10
-10
10
 Endpoint ?
38
39
40
41
neutron number
Proton number
42
43
H. Schatz
The endpoint of the rp-process
Possibilities:
• Cycling (reactions that go back to lighter nuclei)
• Coulomb barrier
• Runs out of fuel
• Fast cooling
Proton capture lifetime of nuclei near the drip line
4
Event
timescale
10
2
10
lifetime (s)
0
10
-2
10
-4
10
-6
10
-8
10
-10
10
0
10
20
30
40
50
charge number Z
60
70
80
H. Schatz
Waiting points
Slow reactions
 extend energy generation
 abundance accumulation
(steady flow approximation lY=const
or Y ~ 1/l)
Critical “wating points” can be easily identified in abundance movie
Endpoint: Limiting factor I – SnSbTe Cycle
The Sn-Sb-Te cycle
Known ground state
a emitter
(g,a)
105Te
106Te
107Te
108Te
104Sb
105Sb
106
107Sb
Sb
Sb (51)
Sn (50)
In (49)
Cd (48)
Ag (47)
Pd (46)
Rh (45)
Ru (44)
(p,g)
103Sn
102In
104Sn
103In
105Sn
104In
106Sn
Xe (54)
I (53)
Te (52)
59
5758
Tc (43)
Mo (42)
Nb (41)
Zr (40)
Y (39)
Sr (38)
b+
56
5455
Rb (37)
Kr (36)
Br (35)
Se (34)
105In
53
5152
4950
As (33)
Ge (32)
Ga (31)
Zn (30)
45464748
424344
41
Cu (29)
37383940
Ni (28)
Co (27)
33343536
Fe (26)
Mn (25)
3132
Cr (24)
V (23)
2930
Ti (22)
Sc (21)
25262728
Ca (20)
K (19)
2324
Ar (18)
Cl (17)
2122
S (16)
P (15)
17181920
Si (14)
Al (13)
1516
Mg (12)
Na (11)
14
Ne (10)
F (9)
11 1213
O (8)
N (7)
9 10
C (6)
B (5)
7 8
Be (4)
(Schatz et al. PRL 86(2001)3471)
Li (3)
He (2)
5 6
H (1)
3 4
0 1 2
Collaborators:
L. Bildsten (UCSB)
A. Cumming (UCSC)
M. Ouellette (MSU)
T. Rauscher (Basel)
F.-K. Thielemann (Basel)
M. Wiescher (Notre Dame)