depth

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Woosley et al. 2003
Kippenhahndiagram
depth
time
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Conditions during an X-ray burst
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The endpoint of the rp-process

• Possibilities
• Cycling (reactions that go back to lighter
  nuclei)
• Coulomb barrier
• Runs out of fuel
• Fast cooling

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Golden Age for X-ray Astronomy ?
XMM Newton
Con X/IXO
RXTE XMM
Chandra
RXTE
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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 ?

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The bursting pulsar
SAX J1808.4-3658
D. Chakrabarty et al. Nature 424 (2003) 42
PulsarFrequency
Seconds since burst
Origin of frequency drift in normal bursting
systems ???
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Open question II ignition and flame propagation
Anatoly Spitkovsky (Berkeley)
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Open question III burst behavior at large
accretion rates
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Open question IV superbursts
X 1000 duration ( can last ½ day) X 1000
energy dozen seen in 10 sources Recurrence
1 yr ? Often preceeded by regular burst
Superburst
Normal Burst
4U 1820-30
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Open question V abundance observations ?
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Open question VI
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Nuclear input

• we are just at the beginning!
• ReA3 at NSCL (reaccelerated beams) (new
  accelerator and hall being built)
• HELIOS at ANL
• FRIB, FAIR, RIKEN,

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LEBIT mass measurements (Bollen, Morrissey,
Savory (thesis), Schury (thesis)
X-ray bursts mass uncertaintieswithin
AME95 (Brown et al. 2002)
After precision mass measurements at LEBIT of
64Ge, 65Ge, 68Se, 69Se(plus ISOLTRAP data on
72Kr,73Kr)
Schury et al. Phys. Rev. C 75 (2007)
055801 Savory et al. accepted for PRL
Luminosity (erg/g/s)
Time (s)
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Using experimental data to improve burst models
Experiments
R. Cyburt et al.
(100 unique visits/ month)
Sensitivity studies 1-zone/multizone(Cyburt,
Amthor, Heger, Smith, Meisel)
Energy radiated (erg/g/s)
100
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Time(s)
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Constraining hydrogen abundance with X-ray bursts?
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Constraining neutron star properties from X-ray
bursts?
(Ozel, Nature 441 (2006) 1115)
Observables
Fedd Eddington Luminosity (peak flux in radius
expansion bursts) Z gravitational surface
redshift (lobserevd lemitted)/lemitted
(EXO 0748-676)
Color temperature(Temperature inferredfrom
spectral shape)
f00Tc/Teff
Emitted Flux
Stefan Bolzmann F s T4eff
Converges to fixed number for constant surface
area towards the end of the burst
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Galloway 2003
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Need to know H abundance of atmosphere (accreted
composition)
1) Electron scattering opacity kes 0.2 (X1)
cm2/g
2) Correction for color temperature effective
temperature
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Constraints for neutron star mass and radius (and
distance)
(3 equations, 3 unknowns)
This is for hypothetical case of 1.8 Mo star with
R10 km, 10 uncertainty In each measuremeny
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(EXO 0748-676)
No condensates
Condensates
Strange stars
BUT uncertainties are large(see spectral fits
etc)
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Fate of matter accreted onto a neutron star
accretion rate 10 kg/s/cm2
Burst
Neutron star surface

• An accreted fluid element experiences
  continueosly increasing pressure and density
  (after a day 106 g/cm3 surface gravity is
  earth x1011)
• is incorporated deeper and deeper into the
  neutron star travels through neutron star
  crust
• on the way undergoes compositional changes
  through nuclear reactions

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Surface of accreting neutron stars

• All processes are connected
• composition (ashes seed for next process)
• heat release ? thermal conditions everywhere

D. Page
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Step 2 Deep ocean burning Superbursts
Neutron star surface
H,He
superburst
gas
ashes
ocean
20m, r109 g/cm3
outer crust
Innercrust
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Ashes to ashes the origin of superbursts ?

• Consequences
• heavy ashes important fuel
• crust made of Fe/Ni

• Problems
• need x10 more carbon than made in bursts
• ignition depth x10 too deep (the ocean is too
  cold !)

(Schatz, Bildsten, Cumming, ApJ Lett. 583(2003)L87
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Step 3 Crust burning
Neutron star surface
H,He
gas
ashes
ocean
outer crust
ashes
25 70 m r109-13 g/cm3
Innercrust
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Crustal heating by pairing
Z-2,N2 even-even
Z-1,N1 odd-odd

• Need
• Masses (threshold difference)
• Daughter states (neutrino loss)
• Rates in some cases?

Z,N even-even
Gupta et al. 2006
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Crust processes
Known mass
superbursts

• Each reaction is a heat source
• Masses (EC thresholds) determine depth of
  reaction
• Masses (Pairing) determine amount of heat
• Structure matters capture in excited states x5
  heating (Gupta et al. 2006)

Haensel Zdunik 1990, 2003, 2008 Gupta et al.
2006
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Crust processes
Recent massmeasurementsat GSI (Scheidenberger
et al.,Matos et al.)
Recent massmeasurementsat Jyvaskyla (Hager et.
al. 2006)
Q-valuemeasurementat ORNL (Thomas et al. 2005)
Recent massmeasurementsat ISOLTRAP (Blaum et.
al.)
Recent TOF massmeasurementsat MSU (Matos et al.)
Reach of next generation Rare Isotope Facility
FRIB_at_MSU
Recent discovery of 40Mg and 42Al at
NSCL(Baumann et al.)
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Observables of crustal heating processes
Transients
KS 1731-260
Bright X-ray burster for 12 yr Accretion shut
off early 2001
NASA/Chandra/Wijnands et al.
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Observables transients in quiescence
Crust heating and surface radiation
Depth into crust
(Ouellette Brown 2005, 2006)(Rutledge 2002)
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Observations probe heat sources and crust
properties
Unknown shallowheat source ??
KS 1731-260 (Chandra)
MXB 1659-29

• Thermal crust conductivity high
• n superfluid in inner crust (do not contribute
  to heat capacity)
• shallow heat source of 0.5 MeV/u dM/dt for
  superbursts?