Supernovae and Neutrinos

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Experimental Nuclear Astrophysics Relevant to
Supernovae
Alex Murphy
http//www.ph.ed.ac.uk/nuclear/
http//hepwww.rl.ac.uk/ukdmc/ukdmc.html/
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Nuclear Astrophysics
Interstellar gas
nucleosynthesis
Gravitational collapse
Explosive nucleosynthesis
Triple a HCNO Breakout rp-process p-process r-proc
ess
Rise in T and r
Formation of stars
pp-chains
Nuclear Reactions ? Stellar stability
Thermonuclear runaway
pp-chains CNO cycles s-process
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Nuclear Physics in Stars
The rate at which reactions occur is determined
by the overlap of the thermal energy distribution
and nuclear cross sections

• Thermal energy distribution
• For ions use MB statistics
• Novae up to 2-3 x108 K
• X-ray bursts up to 2-3 x109 K
• Supernovae up to 1010 K

Relevant energies 10keV - 10 MeV

• Cross sections
• Typically below Coulomb barrier
• Low cross sections
• Resonant processes dominate
• Low density of states
• Indirect methods can be useful
• ?Need to know energies, spins, widths

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What we do and how we do it
Coulomb barrier
Ecoul
?
E, J, ltr, G
direct measurements
E, J, ltr, G
non-resonant
resonance
E, J, ltr, G
E, J, ltr, G
Astrophysical region
EG
?(E)
LOG SCALE
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Focus of recent research

• Explosive astrophysical environments
• Novae, X-ray bursters, exotic scenarios
• Typically we have been concentrating on proton
  rich side, Alt30
• This is largely for technical reasons
• (H)CNO cycles
• Breakout from CNO processing
• rp-processing

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Example of what we do Novae

• Masssive star (e.g. Red Giant)
• More massive star expands
• Outer layers transferred to compact object
• movie
• Layer of H builds up on top of evolved material
  (e.g. C/O/)
• Slow accretion rate leads to degeneracy
• Conditions for a thermonuclear runaway
• High temperatures and short timescales
• Ejecta
• Elemental composition
• Gamma ray emission?

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Gamma-ray production in Novae

• Clayton Hoyle Ap. J. 494 (1974)
• direct observation of g-rays in novae ejecta
• Intensity of an observed g-ray flux would provide
  a strong constraint on novae modelling.
• Need to know the relevant reaction rates!
• ? 21Na(p,g)22Mg

Nucleus t Emission Nova type
13N 862 s 511 keV CO ONe
18F 158 m 511 keV CO ONe
7Be 77 d 478 keV CO
22Na 3.75 yr 1275 keV ONe
26Al 1.0x106 yr 1809 keV ONe
Nucleus t Emission Nova type
13N 862 s 511 keV CO ONe
18F 158 m 511 keV CO ONe
7Be 77 d 478 keV CO
22Na 3.75 yr 1275 keV ONe
26Al 1.0x106 yr 1809 keV ONe
INTEGRAL launched Oct 02
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Example Novae

• Why is this reaction important?
• Synthesis of 22Na in ONe novae
• 20Ne(p,g)21Na(p,g)22Mg(b)22Na
• or
• 20Ne(p,g)21Na(b)21Ne(p,g)22Na

24Si
26Si
25Si
27Si
28Si
rp process
23Al
25Al
24Al
26Al
27Al
22Mg
24Mg
23Mg
25Mg
26Mg
MgAl Cycle
21Na
20Na
23Na
22Na
NeNa Cycle
Need to know (p,g) rate compared to b-decay rate
20Ne
19Ne
22Ne
21Ne
18Ne
19F
18F
17F
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Experimental method
Radiative capture and elastic scattering studies
(p,g)
(p,p)
We use radioactive beam facilities such as those
at TRIUMF and Louvain-la-Neuve
DRAGON
TUDA
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Resonant elastic scattering
TUDA
Radioactive Beam 5x107 pps
Target 795 mg/cm2 CH2 foil
LEDA
surface ion source
SiC primary target
192 strips, energy, angle and time of flight from
each
Primary beam 20 mA, 500 MeV, protons
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Particle Identification
Elastically scattered protons 1H(20Na,1H)
20Na beam is radioactive! ? alpha decays
E (MeV) B.R.
5.701 0.0016
5.272 0.036
4.894 0.193
4.683 0.087
4.438 2.94
3.801 0.25
3.210 0.03
2.148 16.4
Time of Flight
Energy
12C(20Na,12C)
20Na _at_ 32 MeV on 795 mg/cm2 CH2, with 12.65 mm
Mylar
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Data

• Three resonances observed
• Ex(21Mg) 4.005MeV Primary aim of the
  experiment. Tentative Jp (1/2) ? 3/2
• Ex(21Mg) 4.26 MeV Previously only Ex known (no
  width, spin information) 5/2
• Ex(21Mg) 4.44 MeV Previously unknown Jp
  3/2

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Radiative Capture

• (p,g) or (a,g)
• Use a Recoil mass separator a gamma-ray array
• E.g. DRAGON Detector of Recoils And Gammas of
  Nuclear Reactions
• Windowless gas target
• End detectors silicon strip detector or ion
  chamber

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Measurement of 21Na(p,g)22Mg

• 21Na beam on hydrogen target
• Varied 21Na beam energy in small steps so as to
  scan resonances
• Detected recoils in coincidence with prompt
  gammas
• Determined resonance strengths for seven states
  in 22Mg between 200 and 1103 keV

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Results resonance strengths
22Mg
21Na
22Mg recoils in DSSSD ER740 keV
Yield curves for state at 206 keV (above) and
at 821 keV (left)
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Results Reaction rate

• Results
• The lowest measured state at 5.714 MeV (Ecm 206
  keV) dominates for all novae temperatures and up
  to about 1.1 GK
• Updated nova models showed that 22Na production
  occurs earlier than previously thought while the
  envelope is still hot and dense enough for the
  22Na to be destroyed
• Results explain the low abundance of 22Na

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What about observations?
g-ray emission from several close novae has been
search for

• CGRO/COMPTEL So far no detection upper limits
  only.
• But consistent with current theory incorporating
  new reaction rate data.
• Expectation
• INTEGRAL should see signal from nova lt 1.1 kpc
  away
• (1 ONe nova per 5 yrs)

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Future directions

• Around the world, facilities are advancing
• ISAC-II (Canada), RIA (US), RIPS (Japan),
• Eurisol, REX-Isolde, SPIRAL-II, FAIR (Europe),
• More intense beams, more exotic beams, heavier
  beams
• Opportunities for detector development
• Now is the time to go after new physics!

SUPENOVAE
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Future Directions

• An example relevant to type Ia supernovae

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SN Ia

• Scatter in brightness lt0.3 mags, even without
  extinction correction (which is usually quite
  small). Over 90 have very reproducible light
  curves.
• Thus very useful as a standard candle
• Especially important in light of LCDM
• Non-standard SN Ias
• Effects that can change luminosity (e.g.
  metalicity)

SN1991 D
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Recent atypical observations

• Recently, several atypical SNIas have been
  observed
• SN 1987G - fast decline from maximum
• SN 1986G - anomalies in optical spectra
• SN 1990N - anomalies in optical spectra
• SN 1991T - 'largely deviated' from standard
• SN1991bg - dimmer than usual, some H detected.
• SN1999by - very similar to SN1991bg
• These differences suggest that maybe there really
  are two progenitor types...
• ? He rich accretion on to sub-Chandrasekhar mass
  CO WDs may be responsible for the lt10 of SNIas
  that have peculiar light curves.

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Sub-Chandrasekhar mass models

• The existence of sub-luminous SN Ias interpreted
  as less than 1.4 M? 56Ni powering the light curve
• The Sub-Chandrasekhar mechanism
• A 0.6 0.8 M? CO WD accretes He rich matter.
• 98 4He, 1 12C, 0.5 14N, 0.5 16O
• Existence (but not the exact quantity) of 14N
  critical a product of pop-I burning
• Moderate accretion rate (10-8 M? yr-1) ? He
  ignition at the CO/He interface.
• Competition between 14N(e,n)14C(a,g)18O (NCO)
  Triple-a
• Ignition of He may strongly depend on rate of
  14C(a,g)18O

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LOI XXXV
An indirect study of the 14C(a,g)18O reaction

• Alex Murphy

Alison Laird
Jordi Jose
EEC Meeting, TRIUMF
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Future Directions

• An example relevant to Core Collapse supernovae

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Core Collapse Supernovae

• There is consensus on the basic mechanism
• And yet even the best simulations still dont
  explode!
• Extremely complex
• Need a good diagnostic
• Produced in vicinity of mass cut
• Sensitive diagnostic of models
• Gamma-ray observable nuclide

SN1987A
44Ti!
M1 The Crab
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Core Collapse

• Massive star (gt1012 M?)
• Stellar evolution ? onion-skin-like structure
• At maximum of BE/A, thermal support lost ? Core
  collapses
• After core-bounce, shock wave passes through Si
  layer above core
• Dissociation back to n, p, and a
• Nuclear statistical equilibrium
• Alpha-rich freeze out
• Dominant site for 44Ti production
• Key reactions to be studied
• 40Ca(a,g)
• 44Ti(a,g)
• 44Ti(a,p)
• 45V(p,g)
• Triple a

EPSRC Grant
(The et al ApJ 504 (1998) 500)
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44Ti production as a diagnostic

• Amount ejected sensitively depends on location of
  the mass cut
• Material that falls back is not available for
  detection
• 44Ti yield a sensitive diagnostic of the
  explosion mechanism
• Thus, VERY useful for models to make comparisons
  against
• Whats more, its (relatively) easily observed
• Gamma-Ray observation
• 1.157 MeV
• INTEGRAL other missions
• Meteoritic data
• Enrichment of 44Ca in type X presolar grains

Wilson. (1985)
Timmes et al. (1996)
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Pretty pictures
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Summary

• Nuclear reactions are the power behind most
  astrophysical phenomena
• Astrophysical models require accurate nuclear
  physics inputs
• New facilities (and upgrades) mean we can now
  start looking at reactions important in new
  environments
• Nuclear Astrophysicists need good guidance!

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• The End
• Thank you

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• Spare slides

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Latest development

• Proposed research requires
• Low energy 44Ti and 45V beams
• Refractory elements are hard to extract from
  standard ion sources
• A new approach
• Exotic Radionuclides from Irradiated MAterials
  for Science and Technology
• PSI is looking at reducing the amount of
  radioactive waste it has produced
• Potential users
• Nuclear Medicine
• Geophysics
• Astrophysics
• Could bleed these ions into a non-RNB ion source
  and re-accelerate them
• LLN? Triumf? Other?
• Proposal in to EU FP7 programme

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Typical set-up (from 20Na(p,p) expt)
9.55 or 12.40 mm Mylar
High sensitivity Faraday cup
5.65 or 9.65 mm Mylar
Recoil proton
LEDA
795mg/cm2 CH2
20Na
LEDA

• 1.25 MeV/u
• 1.60 MeV/u

4.6o lt qlab lt 31.2o
60.5 cm
19.5 cm
3.50 lt Ex (21Mg) lt 4.64 MeV
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Astrophysical significance NeMg Novae

• Temperatures achieved are too low for breakout
• NeNa and MgAl cycles thought to provide necessary
  energy production.
• NeNa cycle
• First stage is 20Ne(p,g)21Na.
• Where does the 20Ne come from?
• b-decay of 20Na feeds 20Ne.
• Rate of 20Na(p,g) compared to the b decay of
  20Na (448ms) determines abundance of 20Ne

23Mg
21Mg
22Mg
21Na
22Na
20Na
23Na
20Ne
19Ne
21Ne
NeNa cycle
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Observations
Nuclear Astrophysics
An understanding of the cosmos
Modelling

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Novae and X-ray Bursters

• Binary systems!
• Compact, evolved star (white dwarf or neutron
  star) orbiting a massive star (e.g. Red Giant)
• More massive star expands
• Outer layers transferred to compact object
• Layer of H builds up on top of evolved material
  (e.g. C/O/)
• Slow accretion rate leads to degeneracy
• Conditions for a thermonuclear runaway
• High temperatures and short timescales

• Radioactive nuclei important

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Novae

• White dwarf with companion star
• Temperatures of up to 3 x 108K
• Time 100-1000s to eject layer
• Light curve increases to max in hours but can
  take decades to decline
• Absolute magnitude can increase by up to 11
  magnitudes
• Can be recurrent
• Ejecta
• Elemental composition
• Gamma ray emission?

Nova Herculis 1934 AAT
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Some recent measurements

• p(20Na,p) Indirect study of 20Na(p,g)21Mg
  reaction
• X-ray bursters a crucial link in the
  rp-process
• Novae affects NeNa cycle.
• p( 21Na,p) Indirect study of 21Na(p,g)22Mg
  reaction
• Novae Potential for satellite gamma ray
  observations
• p( 11C,p) Indirect study of 11C(p,g)12N reaction
• High mass stars/Novae
• 18Ne(a,p) Direct study.
• Breakout from HCNO cycle Catalyst for
  rp-process?

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20Na(p,p)20Na Motivation

• Better knowledge of the level structure of 21Mg
  is needed
• Astrophysics
• Nucleosynthesis and energy generation
• X-ray bursts
• Novae
• Reaction rates dominated by resonant
  contributions
• Nuclear Physics
• Proton-rich nuclei far from stability, Large
  level shifts, Comparison of reaction mechanisms,
  Shell model studies

The Experiment Resonant elastic scattering
20Na(p,p)20Na (inverse kinematics, using TUDA at
TRIUMF)
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Astrophysical significance X-ray Bursters

• T 4 x 108K
• Energy generation by HCNO cycles
• Waiting points at 14O, 15O and 18Ne isotopes

18Ne
17F
18F
15O
16O
17O
14O
13N
14N
15N
12C
13C
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The run

• Successful experiment ran at TRIUMF
• 5 days of stable 20Ne calibration beams
• 7 days of radioactive 20Na beams up to 5x107
  pps.
• Thick target method Scan through region of
  excitation in 21Mg to look for resonances
• Detect proton recoils
• Expect Rutherford resonances ( interference).
• Resonance depends on Ex, Gp, J, and ltr
• Twobody kinematics
• For a selected angle ? energy of detected protons
  reflect the energy the reaction occurred at.
• Hence, proton energy spectrum is just an
  excitation function.

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Calibrations etc

• Standard triple alpha source

Pulser walk-through
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Analysis of proton data

• Gate on protons
• Project out energy spectrum
• Subtract alpha background
• R-matrix analysis

• General formalism Lane Thomas
• Inverse level matrix approach
• Based on earlier coding separately developed by
  Lothar Buchman and by Dick Azuma
• Present version courtesy of C. Ruiz.
• ½ integer spin, multi-channel, non-zero ltr,

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X-ray Bursters

• Similar environment to novae, but replace white
  dwarf with a neutron star.
• Much deeper gravitational potential
• Hotter, denser, faster
• Less accreted material/smaller surface area ?
  lower luminosity than novae
• Temperatures up to 2-3 x 109K
• Time 1-10s to lift degeneracy and eject layer
• Ejecta?
• little net ejecta due to gravitational field

X-ray burster in NGC 6624 HST
HEAO light curve of X-ray burst MXB 1728-34
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Simulations

• Helium burning at base of He layer
• Occurs around r106g/cc
• Competition between 14N(e,n)14C(a,g)18O (NCO)
  Triple-a
• Nucleosynthesis (extended network codes Goriely
  et al. A A 388 2002)
• Possible site for generating p-process nuclides.
• Expanding outward shock wave ? T92 3
• Material ejected ?
• Mo and Ru isotopes produced ?
• Such explosions produce 44Ti (contrary to
  standard SN1a)
• Ignition of He may strongly depend on rate of
  14C(a,g)18O
• See also Hoflich, Khokhlov Wheeler 1995,
  Goriely, Jose, Hernanz, Rayet and Arnould 2002

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The 14C(a,g) reaction rate Effect

• This reaction rate is undetermined, with an
  uncertainty factor 100
• Model A Standard reaction rate
• Model B Standard reaction rate x 100
• Model C Standard reaction rate ?100

• Model B
• Shorter accretion duration
• Less mass accreted
• Less 56Ni in explosion
• Ignition density r1.77x106 g/cc?
• Less violent explosion
• Peak (at base of He layer) T9 2.77

• Model c
• Longer accretion duration
• More mass accreted
• More 56Ni in explosion
• Ignition density r3.92x106 g/cc?
• More violent explosion
• Peak T9 (at base of He layer) 3.22

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(No Transcript)
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Current knowledge of reaction rate

• Reaction rate
• See Buchmann, DAuria McCorquodale (1998),
  Funck Langanke (1989), Görres et al. (1992)
• Direct capture component (Tlt3x107 K)
• 177 keV resonant component remains undetermined.
• Dominates rate 0.03 lt T9 lt 0.2
• State of interest
• Er177 keV (6.404 MeV in 18O), Jp3
• No direct measurements
• No spectroscopic factor
• Not calculated in theoretical studies
• (e.g. Descouvemont Baye 1985)
• Proximity to a-threshold
• Resonance strength determined by Ga
• small branching ratio (10-10)
• Indirect methods must be used
• 6Li(14C,d)18O,12C(14C,8Be)18O, 7Li(14C,t)18O

Funck Langanke (1989)
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14C(a,g)18O Experimental details

• Experimental issues
• Can 14C be separated from 14N?
• 5x107 pps for 1 week not likely to be a
  radiological safety hazard
• Rate of FC lt1000 Bq b range 3 cm (in air)
• 6Li(14C,d)18O kinematics drive 2H from
  different states very close together.
• Would require very thin (10mg/cm2) targets
• Target contamination (C/O/F)
• 12C(14C,8Be)18O
• Identify 8Be from 2 alphas Erel92 keV
• Coulomb Barrier

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Spectroscopic factor

• Compare angular distribution to reaction model to
  get spectroscopic factor.
• Alpha transfer below Coulomb barrier
• Need spectroscopic factor measured in transfer
  reaction ? Ga
• Must be careful of model uncertainties
• FRESCO, ZAFRA
• Calibration reaction?
• Compound nucleus contribution
• HF Angular distribution

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Summary

• There are several reasons to believe that He rich
  accretion on to sub-Chandrasekhar mass CO WD SN
  occur.
• They are astrophysically very interesting
• They are consistent with sub-luminous SNIa
• Proposed as a site for p-processing
• Evolution is likely to depend on the currently
  unknown reaction rate of 14C(a,g)18O
• Direct measurement unfeasible
• Indirect methods
• 14C(6Li,d), 14C(12C,8Be)
• Need to develop a 14C beam

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Example Type Ia Supernovae

• For dark energy

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Kinematics
12C(14C,8Be)18O
6Li(14C,d)18O
qcm vs qLab
Elab vs qLab
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States in 18O
State populated strongly in (t,p) stot0.4 mb
(Cobern et al. PRC 23 (1981) 2387) Somewhat
weaker in (7li,p) (d,p), (t,a), (6Li,d), ES
little strength Gamma decay to multiple states.
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Proposed research

• Take advantage of unique future ISAC beams
• 44Ti(a,p)47V direct measurement
• Gas/implanted target
• Trilis, CSB
• LEDA/CD
• Not measured before at astrophysical energies -
  extrapolation of previous results suggests its
  eminently feasible (_at_ 107 pps).
• 45V(p,p)45V resonant elastic scattering
• Knowledge of 46Cr, precursor to 45V(p,g)46Cr
• Trilis, CSB
• CH2 target
• LEDA/CD
• Unmeasured. SM/TES suggests feasible (_at_ 107
  pps).
• 45V(p,g)46Cr
• Trilis, CSB
• DRAGON
• Use (p,p) as guide.

Coordinated approach
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UK Grant application

• A request has been made to EPSRC
• specifically focussed on this work
• Request was for 33 months of PDRA salary Travel
• Panel met 27/7/05
• funded!
• Advertising now
• Deadline 16/09/05
• Can start 1/11/05