rp process

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Hydrogen burning under extreme conditions Scenarios: Hot bottom burning in massive AGB stars (> 4 solar masses) (T9 ~ 0.08) Nova explosions on accreting white dwarfs (T9 ~ 0.4) X-ray bursts on accreting neutron stars (T9 ~ 2) accretion disks around low mass black holes ? neutrino driven wind in core collapse supernovae ? further discussion assumes a density of 106 g/cm3 (X-ray burst conditions)

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“Cold” CN(O)-Cycle Hot CN(O)-Cycle Energy production rate: T9 < 0.08 T9 ~ 0.08-0.1 Ne-Na cycle !

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Very Hot CN(O)-Cycle still “beta limited” T9 ~ 0.3 T1/2=1.7s 3a flow

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Temperature (GK) Density (g/cm3) Current 15O(a,g) Rate with X10 variation Multizone Nova model (Starrfield 2001) Breakout No Breakout New lower limit for density from B. Davids et al. (PRC67 (2003) 012801)

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Outline X-ray binaries – nuclear physics at the extremes Observations Model Open Questions Nuclear Physics – the rp process

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X-rays Wilhelm Konrad Roentgen, First Nobel Price 1901 for discovery of X-rays 1895 First X-ray image from 1890 (Goodspeed & Jennings, Philadelphia) Ms Roentgen’s hand, 1895

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0.5-5 keV (T=E/k=6-60 x 106 K) Cosmic X-rays: discovered end of 1960’s: Again Nobel Price in Physics 2002 for Riccardo Giacconi

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Discovery First X-ray pulsar: Cen X-3 (Giacconi et al. 1971) with UHURU First X-ray burst: 3U 1820-30 (Grindlay et al. 1976) with ANS Today: ~50 Today: ~40 Total ~230 X-ray binaries known T~ 5s 10 s

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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)

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X-ray binaries X-ray pulsars Regular pulses with periods of 1- 1000 s X-ray bursters Frequent Outbursts of 10-100s duration with lower, persistent X-ray flux inbetween Type I bursts Burst energy proportional to duration of preceeding inactivity period By far most of the bursters Type II bursts Burst energy proportional to duration of following inactivity period “Rapid burster” and GRO J1744-28 ? (Bursting pulsar: GRO J1744-28) Others (e.g. no bursts found yet)

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The Model Neutron stars: 1.4 Mo, 10 km radius (average density: ~ 1014 g/cm3) 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

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Mass transfer by Roche Lobe Overflow Star expands on main sequence. when it fills its Roche Lobe mass transfer happens through the L1 Lagrangian point

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John Blondin, NC State, http://wonka.physics.ncsu.edu/~blondin/AAS/

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Energy generation: thermonuclear energy Ratio gravitation/thermonuclear ~ 30 - 40 4H 4He 5 4He + 84 H 104Pd 6.7 MeV/u 0.6 MeV/u 6.9 MeV/u Energy generation: gravitational energy (“triple alpha”) (rp process)

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Observation of thermonuclear energy: Unstable, explosive burning in bursts (release over short time) Burst energy thermonuclear Persistent flux gravitational energy

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Ignition and thermonuclear runaway Burst trigger rate is “triple alpha reaction” Ignition: denuc dT decool dT > enuc ecool ~ T4 Ignition < 0.4 GK: unstable runaway (increase in T increases enuc that increases T …) degenerate e-gas helps ! Triple alpha reaction rate BUT: energy release dominated by subsequent reactions ! Nuclear energy generation rate Cooling rate

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Arguments for thermonuclear origin of type I bursts: ratio burst energy/persistent X-ray flux ~ 1/30 – 1/40 (ratio of thermonuclear energy to gravitational energy) type I behavior: the longer the preceeding fuel accumulation the more intense the burst spectral softening during burst decline (cooling of hot layer) Arguments for neutron star as burning site consistent with optical observations (only one star, binary) Stefan-Boltzmann L = sA T4eff gives typical neutron star radii Maximum luminosities consistent with Eddington luminosity for a neutron star (radiation pressure balances gravity) Ledd = 4pcGM/k=2.5 x 1038(M/M )(1+X)-1 erg/s (this is non relativistic – relativistic corrections need to be applied) . k=opacity, X=hydrogen mass fraction

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What happens if “ignition temperature” > 0.4 GK Triple alpha reaction rate at high local accretion rates m > medd (medd generates luminosity Ledd) Stable nuclear burning

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X-ray pulsar > 1012 Gauss ! High local accretion rates due to magnetic funneling of material on small surface area

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Why do we care about X-ray binaries ? Basic model seems to work but many open questions Unique laboratories to probe neutron stars: Over larger mass range as they get heavier Over larger spin range as they get spun up Over larger temperature range as they get heated

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Some current open questions Burst timescale variations why do they vary from ~10 s to ~100 s Superbursts (rare, 1000x stronger and longer bursts) what is their origin ? Contribution of X-ray bursts to galactic nucleosynthesis ? NCO’s (300-600Hz oscillations during bursts, rising by ~Hz) what is their origin ? Crust composition – what is made by nuclear burning ? Magnetic field evolution ? (why are there bursters and pulsars) Thermal structure ? (what does observed thermal radiation tell us ?) Detectable gravitatioal wave emission ? (can crust reactions deform the crust so that the spinning neutron star emits gravitational waves ?)

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(1735-444) 18 18.5 time (days) (rapid burster) (4U 1735-44) Normal type I bursts: duration 10-100 s ~1039 erg Superbursts: (discovered 2001, so far 7 seen in 6 sources) duration … ~1043 erg rare (every 3.5 yr ?) 24 s 3 min 4.8 h

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Spin up of neutron stars in X-ray binaries Unique opportunity to study NS at various stages of spin-up (and mass) Quark matter/Normal matter phase transition ? (Glendenning, Weber 2000) Gravitational wave emission from deformed crust ? (Bildsten, 1998) 331 330 329 Frequency (Hz) 328 327 10 15 20 Time (s) 4U1728-34 Rossi X-ray Timing Explorer Picture: T. Strohmeyer, GSFC F. Weber

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KS 1731-260 (Wijands 2001) Chandra observations of transients Bright X-ray burster from 1988 -early 2001 Accretion shut off early 2001 Detect thermal X-ray flux from cooling crust: Too cold ! (only 3 mio K) Constraints on duration of previous quiescent phase Constraints on neutron star cooling mechanisms

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Nuclear physics overview Accreting Neutron Star Surface fuel ashes ocean Inner crust outer crust H,He gas core n’s X-ray’s ~1 m ~10 m ~100 m ~1 km 10 km Thermonuclear H+He burning (rp process) Deep burning (EC on H, C-flash) Crust processes (EC, pycnonuclear fusion)

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Nuclear reaction networks Mass fraction of nuclear species X Abundance Y = X/A (A=mass number) Number density n = r NAY (r=mass density, NA=Avogadro) (note NA is really 1/mu – works only in CGS units) Temperature T and Density Nuclear energy generation Astrophysical model (hydrodynamics, ….) Network: System of differential equations: 1 body 2 body Ni…: number of nuclei of species I produced (positive) or destroyed (negative) per reaction

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Visualizing reaction network solutions 27Si neutron number 13 Proton number 14 (p,g) (a,p) (a,g) (,b+) Lines = Flow =

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Models: Typical temperatures and densities Temperature (GK) Density (g/cm3) time (s)

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Burst Ignition:

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3a reaction a+a+a 12C ap process: 14O+a 17F+p 17F+p 18Ne 18Ne+a … rp process: 41Sc+p 42Ti +p 43V +p 44Cr 44Cr 44V+e++ne 44V+p … Most calculations (for example Taam 1996) Wallace and Woosley 1981 Hanawa et al. 1981 Koike et al. 1998 Schatz et al. 2001 (M. Ouellette) Phys. Rev. Lett. 68 (2001) 3471 Models: Typical reaction flows Schatz et al. 1998

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3a reaction a+a+a 12C ap process: 14O+a 17F+p 17F+p 18Ne 18Ne+a … In detail: ap process Alternating (a,p) and (p,g) reactions: For each proton capture there is an (a,p) reaction releasing a proton Net effect: pure He burning

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In detail: rp process N=41 38 (Sr) 39 (Y) 40 (Zr) 41 (Nb) 42 (Mo) 43 (Tc) Z Proton number Nuclear lifetimes: (average time between a …) proton capture : t = 1/(Yp r NA <sv>) b decay : t = T1/2/ln2 photodisintegration : t = 1/l(g,p) (for r=106 g/cm3, Yp=0.7)

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Possibilities: Cycling (reactions that go back to lighter nuclei) Coulomb barrier Runs out of fuel Fast cooling The endpoint of the rp process

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Endpoint: Limiting factor I – SnSbTe Cycle

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The endpoint for full hydrogen consumption: Solar H/He ratio ~ 9 90 H per 41Sc available Endpoint varies with conditions: peak temperature amount of H available at ignition He burning: 10 He -> 41Sc if all captured in rp process reaches A=90 + 41 = 131 (but stuck in cycle)

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Production of nuclei in the rp process – waiting points

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Movie X-ray burst

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68 72 76 mass number abundance 64 104 H. Schatz, MSU 80 Final Composition: Mass number slow b decay (waiting point)

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luminosity (erg/g/s) cycle fuel abundance 1H 4He abundance 56Ni 72Kr 104Sn 64Ge time (s) H. Schatz, MSU X-ray burst: Luminosity: Abundances of waiting points H, He abundance

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Nuclear data needs: Masses (proton separation energies) b-decay rates Reaction rates (p-capture and a,p)