The rapid proton capture process (rp-process) Sites of the rp-process This lecture
ν-wind in Novae supernovae ? X-ray binaries Nova Cygni 1992 with HST
E0102-73.3 KS 1731-260 composite with Chandra
” • “r p-process • makes maybe • full rp-process (not really a full 45Sc and 49Ti rp-process) • unlikely to contribute • if n accelerated to nucleosynthesis • makes maybe (ν interactions) 26Al maybe a major nucleosynthesis process? 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 H. Schatz Discovery Discovery of X-ray bursts and pulsars 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 H. Schatz The Model The model Neutron stars:
1.4 Mo, 10 km radius 14 3 (average density: ~ 10 g/cm ) Donor Star Neutron Star (“normal” star)
Accretion Disk Typical systems: -8 -10 2 • accretion rate 10 /10 Mo/yr (0.5-50 kg/s/cm ) • orbital periods 0.01-100 days • orbital separations 0.001-1 AU’s 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
G M m E = u = 200 MeV/u R
Ratio gravitation/thermonuclear ~ 30 – 40 (called α) 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” 3 4He 12C
dεnuc dεcool εnuc Nuclear energy generation rate Ignition: > 4 dT dT εcool ~ T Cooling rate
-9 Triple alpha reaction rate 10
) -10
1
-
e 10
l
o -11 Ignition < 0.4 GK:
m
1
- 10
s
2 unstable runaway
m -12
c
( 10
(increase in T increases
e
t
a -13 that increases T …) r εnuc 10
n
o
i t -14 c 10
a
e
r degenerate e-gas helps ! -15 10 0 1 10 te m p e ra tu re (G K) BUT: energy release dominated by subsequent reactions ! H. Schatz At large (local) accretion rates 0.24
0.23
0.22
)
at high local K
G
( 0.21
e
r
accretion rates m > m u edd t 0.2
a
r
e p 0.19
m
e
t (medd generates luminosity Ledd) 0.18 0.17
0.16 -2 -1 0 10 10 10 accretion rate (L_edd) Triple alpha reaction rate -9 10
) -10
1
-
e 10
l
o -11
m
1
- 10
s
2
m -12 Stable nuclear burning
c
( 10
e
t
a -13
r
10
n
o
i t -14 c 10
a
e r -15 10 0 1 10 te m p e ra tu re (G K) 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 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 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
à 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
à Accreted matter is incorporated deeper into the neutron star
à As the density increases interesting things happen Surface of accreting neutron stars
Neutron star surface Hydrogen, Helium
X-ray bursts
1m gas
Ocean (palladium? 10m Zinc?)
Crust of rare isotopes
Inner ashes crust
D. Page H. Schatz Nuclear physics overview Accreting Neutron Star Surface X-ray’s H,He Spallation of heavy nuclei ? ν’s fuel
Thermonuclear H+He burning ~1 m gas (rp process) à X-ray bursts ashes Deep burning ? ~10 m ocean à superbursts outer ~100 m crust Crust processes (EC, pycnonuclear fusion) à crust heating Inner à crust conductivity ~1 km crust
10 km core Step 1: Thermonuclear burning in atmosphere
Neutron star surface
H,He
gas ~ 4m, ρ=106 g/cm3
ocean
outer crust
Inner crust Woosley et al. 2003
Kippenhahn diagram depth
time H. Schatz Conditions during an X-ray burst
Ignition layer ocean
Burst cooling
Ignition J. Fisker Thesis (Basel, 2004) surface H. Schatz Visualizing reaction networks
Proton number (α,γ)
(p, ) γ (α,p) 14 27 Si (,β+)
13 neutron number ⎡dY dY ⎤ Lines = Flow = F i j dt i, j = ∫ ⎢ − ⎥ ⎣ dt i−> j dt j−>i ⎦ Sn (50) In (49) Cd (48) Ag (47) Pd (46) Rh (45) Ru (44) Tc (43) Mo (42) Nb (41) Zr (40) Y (39) Sr (38) 51 52 53 54 Rb (37) Kr (36) Br (35) 47 48 49 50 Se (34) As (33) 45 46 Ge (32) Ga (31) 41 42 43 44 Zn (30) Cu (29) 37 38 39 40 Ni (28) Co (27) 33 34 35 36 Fe (26) Mn (25) 31 32 Cr (24) V (23) 29 30 Ti (22) Sc (21) 25 26 27 28 Ca (20) K (19) 23 24 Ar (18) Cl (17) 21 22 S (16) P (15) 17 18 19 20 Si (14) Burst Ignition: Al (13) 15 16 Mg (12) Na (11) 13 14 Ne (10) F (9) 11 12 O (8) N (7) 9 10 C (6) 8 B (5) 7 Prior to ignition : hot CNO cycle Be (4) 6 ~0.20 GK Ignition : 3α Li (3) : Hot CNO cycle II He (2) 3 4 5 ~ 0.68 GK breakout 1: 15O(α,γ) ~0.77 GK breakout 2: 18Ne( ,p) H (1) α (~50 ms after breakout 1) n (0) 2 Leads to rp process and 0 1 main energy production Sn (50) In (49) Cd (48) Ag (47) Pd (46) Rh (45) Ru (44) Tc (43) Mo (42) Nb (41) Zr (40) Y (39) Sr (38) 51 52 53 54 Rb (37) Kr (36) Br (35) 47 48 49 50 Se (34) As (33) 45 46 Ge (32) Ga (31) 41 42 43 44 Zn (30) Cu (29) 37 38 39 40 Ni (28) Co (27) 33 34 35 36 Fe (26) Mn (25) 31 32 Cr (24) V (23) 29 30 Ti (22) Sc (21) 25 26 27 28 Burst Ignition: Ca (20) K (19) 23 24 Ar (18) Cl (17) 21 22 S (16) P (15) 17 18 19 20 Si (14) Al (13) 15 16 Mg (12) Na (11) 13 14 Ne (10) F (9) 11 12 O (8) N (7) 9 10 C (6) 8 B (5) 7 Prior to ignition : hot CNO cycle Be (4) 6 ~0.77 GK breakout 2: 18Ne(α,p) Li (3) : Hot CNO cycle II (~50 ms after breakout 1) He (2) 3 4 5 Leads to rp process and ~0.77 GK breakout 2: 18Ne(α,p) H (1) main energy production (~50 ms after breakout 1) n (0) 2 Leads to rp process and 0 1 main energy production
Competition between αp- & rp- processes
l 22Mg is branching point 24Si 25Si 26Si l (p,γ) and (α,p) compete
23 24 25 Al Al Al l rp-process eats p’s
lα p-process eats α’s 22Mg 22Mg(α,p)25Al vs 23Al(p,γ)24Si Branch points also appear at 26Si, 30S & 34Ar 21Na 26Si(α,p)29P vs 27P(p,γ)28S 30S(α,p)33Cl vs 31Cl(p,γ)32Ar 34Ar(α,p)37K vs 35K(p,γ)36Ca H. Schatz How the rp-process works Nuclear lifetimes: (average time between a …)
• A+pàB+γ proton capture : τ = 1/(Yp ρ NA <σv>) Z + • β decay : τ = T1/2/ln2 • B+γàA+p photodisintegration : τ = 1/λ 43 (Tc) (γ,p) (for ρ=106 g/cm3, Yp=0.7, T=1.5 GK) 10 42 (Mo) 10 8 10 6 41 (Nb) 10 4 10
40 (Zr) ) 2
s
(
10 e 0
m
i 10
t
39 (Y) e
f
i -2
L 10 -4 38 (Sr) 10 -6 10 -8 N=41 10 -10 10 38 39 40 41 42 43 Protonneutron number number à Endpoint ? 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 10 Event 2 timescale 10 0 10
)
s
( -2 e 10
m
i
t
e
f -4
i l 10
-6 10
-8 10
-10 10 0 10 20 30 40 50 60 70 80 charge number Z Development of Cycles l 56Ni is doubly magic
58Zn 59Zn 60Zn l 59Cu is branch point
l Either rp-continues 57Cu 58Cu 59Cu l or (p,α) back to 56Ni 56Ni Cycle 1 rxns • 57Cu(p, )58Zn This is the NiCu cycle γ • 59Cu(p,γ)60Zn 55 59 56 Co Cycle pattern repeats for 60Zn • Cu(p,α) Ni Cycle 2 rxns This is the ZnGa cycle • 61Ga(p,γ)62Ge • 63Ga(p,γ)64Ge • 63Ga(p,α)60Zn H. Schatz Waiting points
Slow reactions à extend energy generation à abundance accumulation (steady flow approximation λY=const or Y ~ 1/λ)
Critical “wating points” can be easily identified in abundance movie Endpoint: Limiting factor I – SnSbTe Cycle The Sn-Sb-Te cycle Known ground state (γ,a) Xe (54) I (53) 105 106 107 108 emitter Te (52) Te Te Te Te α Sb (51) Sn (50) In (49) Cd (48) Ag (47) 104 105 106 107 Pd (46) 59 Sb Sb Sb Sb Rh (45) Ru (44) 5758 (p, ) Tc (43) γ Mo (42) 103 104 105 106 Nb (41) Sn Sn Sn Sn + Zr (40) 56 β Y (39) Sr (38) 5455 Rb (37) 53 Kr (36) 5152 102 103 104 105 Br (35) 4950 In In In In Se (34) As (33) 45464748 Ge (32) Ga (31) 424344 Zn (30) 41 Cu (29) 37383940 Ni (28) Co (27) 33343536 Fe (26) Mn (25) 3132 (Schatz et al. PRL 86(2001)3471) Cr (24) V (23) 2930 Ti (22) Sc (21) 25262728 Ca (20) K (19) 2324 Ar (18) Cl (17) 2122 S (16) Collaborators: P (15) 17181920 Si (14) Al (13) 1516 L. Bildsten (UCSB) Mg (12) Na (11) 14 A. Cumming (UCSC) Ne (10) F (9) 11 1213 M. Ouellette (MSU) O (8) N (7) 9 10 C (6) T. Rauscher (Basel) B (5) 7 8 Be (4) F.-K. Thielemann (Basel) Li (3) He (2) 5 6 M. Wiescher (Notre Dame) H (1) 3 4 0 1 2 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 α:∼40
superbursts superbursts α: 500-5000 Accretion rate (Edd units)
Accretion rate (Edd units) Cornelisse et al. 2003 H. Schatz Open question IV: superbursts
X 1000 duration ( can last ½ day)
Normal Burst X 1000 energy
11 seen in 9 sources
Recurrence ~1 yr ?
Often preceeded by regular burst 4U 1820-30 H. Schatz Open question V: abundance observations ?
EXO0748-676
Cottam, Paerels, Mendez 2002