Phy 983 - Spring2005

1

Rp-process Nuclosynthesis in Type I X-ray Bursts

A.M. AmthorChurch of Christ, Kingdom of HeavenNational Superconducting Cyclotron Laboratory, Michigan State UniversityDepartment of Physics and Astronomy, Michigan State University

Phy 983 - Spring2005

2AMA

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

Phy 983 - Spring2005

3AMA

X-ray burst basics – mostly review

                                   

Accretion – of matter from companion star

Accumulation – of matter on the NS surface

Ignition – near the base of the accreted column

Explosion – runaway fusion chain reactions through the p and rp-process

Burst flux

Persistent flux

Interesting quantities are:

- the total mass accretion rate

- the specific accretion rate

- the ratio of persistent flux to burst flux

- the recurrence time

Also the burst duration and regularity

Bursts happen for :

M

m

rect

R

MGME

MeV

R

GMmp 200

dT

d

dT

coolingd reac.)(

18. 102 yrMMM sunEdd

Phy 983 - Spring2005

4AMA

Burst types(Assuming accreted material with )

For we have which allows unstable CNO H burning.

110102 yrMM sun KT 7108

For we have for which the HCNO cycle leads to stable H burning.

110102 yrMM sun KT 7108

BurstBurstdT

d

dT

coolingd CNO

)(

So for and the burst ignition will be by unstable 3

110102 yrMM sun KT 7108

BurstBurstdT

d

dT

coolingd 3)(

01.0CNOZ

110104.4 yrMM sun 110104.4 yrMM sun

Hrect

Pure He Burst

Hrect

Mixed H/He Burst

Phy 983 - Spring2005

5AMA

Breakout to Rp-process (H/He burst)

Significant boundaries in temperature vs. density for the development of the rp-process

3 4 5 6 7 8

9 10

11 12 13

14

C (6) N (7)

O (8) F (9)

N e (10)N a (11)

M g (12)

3 flow

Hot CNO cycle below curve a)

Beyond curve b) is dominantFpNe 2019 ),( Beyond curve a) is dominant

NeO 1915 ),(

By curve d) dominates the flow, then avoiding all decays up to that point

NapNe 2118 ),(

Beyond curve c) the rp-process rate is limited by decays not by

NeO 1915 ),(

Schatz, Phy 983 notes spring 2003.

Phy 983 - Spring2005

6AMA

Observations

Line for 1Mtrec

Extended study of GS1826-238

Measures total accretion rate

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

Phy 983 - Spring2005

7AMA

ms Oscillations

Strohmayer, T. E. and L. Bildsten, Compact Stellar X-ray sources, astro-ph/0301544 (2003).

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.

Spin up – Spin down ?

Burst rise – Burst tail ?

R

R

2

Phy 983 - Spring2005

8AMA

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

Phy 983 - Spring2005

9AMA

Simulations

van Wormer et al. ApJ. 432:326 (1994)

Truncated Network

1-Zone Model

Constant temperature

Constant density

Limited reaction network

Reaction Network Calculations

Given adequate hydrogen and slow cooling, burning would continue to a closed cycle in Sn, Sb, and Te.

Phy 983 - Spring2005

10AMA

Newer model calculations

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

Still assumes spherical symmetry!

Phy 983 - Spring2005

11AMA

Thank you – any questions?

?