1. Presented by Hendrik Schatz Michigan State University
2016 Submitted
Presented by Hendrik Schatz
Michigan State University
National Superconducting Cyclotron Laboratory
Joint Institute for Nuclear Astrophysics – CEE

2. Accreting Neutron Stars as Dense Matter Laboratories
Rare Isotope Facilities
Observe the same nuclei
found inside neutron stars
X-ray Observatories
Observe thermal emission and bursts
Chandra, XMM Newton
NICER
Mass Accretion
Probe response of
neutron star to
mass accretion
(varies!)
Neutron Star
- Thermonuclear explosions on the surface (bursts)
- Cooling in transients
FRIB, NSCL, FAIR, …

3. Burst lightcurve observable affected by nuclear physics
Cyburt et al. 2016
Extract astrophysical parameters from model – observation comparison with accurate nuclear physics
Accreted composition
Neutron star surface temperature
Neutron star mass, radius, compactness
Peak luminosity (distance)
Composition of the neutron star crust
Remove nuclear uncertainties to learn about astrophysical unknowns

4. Burst ashes relates to observables and is affected by nuclear physics
GRS
Possible Cr spectral feature in X-ray burst
(Barriere et al. 2014)  Need nuclear physics to predict expected features and ejected composition
Predicted crustal heating and cooling rate
depending on the mass number of the
burst ashes (Schatz et al. 2014)  Need nuclear physics to predict burst ashes and crustal heating/cooling
NUSTAR Observatory

5. Burst nuclear physics depends strongly on burst system
H/He-bursts:
High accretion rate
Accrete H/He
He-bursts:
Low accretion rate
Accrete He
This is good (sensitivity to astrophysics!)
Must provide nuclear physics for all types of bursts

6. Proposal for Progress ✔ Goals:
Translate rp-process nuclear physics work into an advance in X-ray burst science
Create validation path for burst models
Define 3 “standard” burst sources: GS 1826­‐24, 4U , SAX J
Sensitivity Study GS 1826­‐24 (H/He)
Sensitivity Study 4U
(He accretor)
Sensitivity Study SAX J
(Low accretion rate He) ✔
(This Talk)
New Data Base by Summer 2018
As much experimental data as possible
As much theoretical data as possible
Evaluation effort
Joint publication of all that contributed
This workshop
Benchmark of various group’s models
Extract system parameters from observations
Use as starting point to investigate other systems, time dependent accretion etc

7. Sensitivity Study Approach
Study sensitivity of KEPLER model (Woosley, Heger, Keek, et al.) to reaction rates (not decays or masses) for typical mixed H/He burst
Accreted solar composition
Accretion: 1.75E-9 solar masses/year (about 10% Eddington)
1-zone model to ID potentially important rates
Choose ignition conditions from 1D-KEPLER model
Vary all 1931 rates (+ their inverse) by a factor of 100 up and down
Select 84 top impacts on light curve and composition
1D KEPLER model
Vary top reactions in KEPLER by a factor that is conservatively adapted to the possible uncertainty of the rate
Identify rates that significantly impact light curve or composition

8. 1-Zone Model Approximation
Peak temperature: 1.2GK agrees

9. Sensitivity to Reaction Rates
ap process
(a,p) rates vs p-capture
1-Zone
Light Curve Impact
CNO Breakout
14O(a,p), 15O(a,g), 18Ne(a,p)
Cycles and Major Waiting Points
(p,a) rates vs p-capture; p-capture on WP+p

10. KEPLER

11. KEPLER: Light Curve Impact Use Average Light Curve

12. 15O(a,g) Impact Fisker et al. 2006  Different result
Decreased 15O(a,g) triggers burst later  Increased recurrence time  more He rich bursts
Decreased 15O(a,g) increases CNO  more 3-alpha/HCNO runaway  decreased recurrence time  more He rich bursts

13. KEPLER: Light Curve Impact
 Limited Set of Rates !

14. Comparison with Other Studies
Parikh et al. 2008:
Different bursts
Postprocessing
This work
Conclusions:
Some reactions are of general importance
Sensitivity studies are model dependent and postprocessing has limitations
Important result from Parikh et al.: From Monte Carlo study: Correlations have minor impact on rate selection
In both studies
Also in Parikh et al for composition

15. KEPLER: Definition of final composition

16. Composition Impacts: Global

17. Composition Impacts: Local

18. X-ray Burst Sensitivity to Nuclear Reactions
Sensitivity through 1-by-1 variation
Varied 1931 rates in single zone model  ID 84 key rates
Varied 84 rates in full 1D Model - sequence of ~12 bursts
- variation inspired by possible uncertainty
Composition Impact
Lightcurve Impact
No significant impact
(Impact limited to single zone model)
Never had the ressources for this without JINA-CEE – its truly intersectional work that would fall through the cracks
Significant impact
Identified reaction uncertainties
that may affect:
Light curve (19 reactions)
Composition (47 reactions)
Cyburt et al. 2016

19. Next Steps
Sensitivity study for He accretor, and He bursts for mixed H/He accretor
Expand mixed H/He burst analysis to all reactions
Coordinated experimental and theoretical effort to address nuclear uncertainties as much as possible by summer 2018?
Joint paper (in addition to individual papers) for all contributions before cutoff date
Coordinated evaluation?
Theory – Experiment needs coordination