Transcript Burst - Michigan State University

Rp-process Nuclosynthesis
in Type I X-ray Bursts
A.M. Amthor
Church of Christ, Kingdom of Heaven
National Superconducting Cyclotron Laboratory, Michigan State University
Department of Physics and Astronomy, Michigan State University
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Outline
• Quick Review of X-ray bursts
• Delineation of burst types by total accretion rate
• Method of breakout to start the rp-process in a
mixed H/He burst
• Observations – compared to expectations
• Simulations
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X-ray burst basics – mostly review
Accretion – of matter from companion star
GMM
E
R
GMm p
R
 200MeV
Accumulation – of matter on the NS surface
Ignition – near the base of the accreted column
d (cooling ) dreac.

dT
dT
Interesting quantities are:
M - the total mass accretion rate
m - the specific accretion rate
Explosion – runaway fusion chain reactions
through the ap and rp-process
a - the ratio of persistent flux to burst flux
trec - the recurrence time
Also the burst duration and regularity
Burst flux
Persistent flux
Bursts happen for :
M  M Edd.  2 10 8 M sun yr 1
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Burst types
(Assuming accreted material with Z CNO  0.01)
  2 10
For M
10
M sun yr 1 we have T  8107 K which allows unstable CNO H burning.
d (cooling ) dCNO

Burst
dT
dT
  2 10 10 M yr 1 we have T  810 K for which the HCNO cycle leads to
For M
sun
stable H burning.
  2 10 10 M yr 1 and T  8107 K the burst ignition will be by unstable 3a.
So for M
sun
7
d (cooling ) d3a

dT
dT
M  4.4 10 10 M sun yr 1
Burst
M  4.4 10 10 M sun yr 1
trec   H
trec   H
Pure He Burst
Mixed H/He Burst
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Breakout to Rp-process (H/He burst)
Hot CNO cycle below curve a)
Significant boundaries in
temperature vs. density for the
development of the rp-process
O(a ,  )19Ne is dominant
Beyond curve b) 19 Ne( p,  ) 20F is dominant
Beyond curve a)
15
Beyond curve c) the rp-process rate is
limited by decays not by 15O(a ,  )19Ne
18
21
By curve d) Ne(a , p) Na dominates the flow,
then avoiding all decays up to that point
Mg (12)
Na (11)
Ne (10)
F (9)
O (8)
N (7)
C (6)
14
11 1213
9 10
3 4 5 6 7 8
3a flow
Schatz, Phy 983 notes spring 2003.
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Observations
Extended study of GS1826-238
Increased total accretion rate
for the same type of burst
Reduced time to build to critical
column depth
&
Increased temperature in
accreted layer from
gravitational energy release
Reduced recurrence time
Line for t rec  M
1
Measures total
accretion rate
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ms Oscillations
From the neutron star binary 4U 1702-429
Oscillations likely caused by
asymmetric burst ignition.
Frequencies closely related to the
neutron star rotation frequencies.

Frequency drift possibly caused by
expansion of the burning
envelope during the burst.
Contraction recouples the
envelope to the surface resulting
in spin up approaching NS’s
rotation frequency.

R
2

R
Spin up – Spin down ?
Burst rise – Burst tail ?
Strohmayer, T. E. and L. Bildsten, Compact Stellar X-ray sources, astro-ph/0301544 (2003).
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Unexplained observations
• LMXB with accretion rates consistent with steady
bursting which show few or no bursts
• Transition between bursting regimes at total
accretion rates not consistent with theory
• Large frequency drifts in oscillations
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Simulations
Reaction Network Calculations
Given adequate hydrogen
and slow cooling, burning
would continue to a closed
cycle in Sn, Sb, and Te.
Truncated
Network
 1-Zone Model
 Constant temperature
van Wormer et al. ApJ. 432:326 (1994)
 Constant density
 Limited reaction network
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Newer model calculations
Still assumes
spherical symmetry!
 Multi-Zone/1d-Model
 Variable temperature
 Variable density
 1300 isotopes in adaptive network
 Convective and semiconvective
mixing and energy transport
 Compositional inertia in burst trains
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Thank you – any questions?
?
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