Crosstalk: Mini Workshop on Type I X-ray bursts.

Barry Davids (TRIUMF). Experimental Efforts to Determine the 15O(a,g)19Ne Reaction Rate.
To Astronomers: The 15O(a,g) reaction rate has not been measured, but upper limits are x100 above the theoretical lower limit. With present instrumentation, we can get within x10 the theoretical lower limit; to do better, we will likely need new instrumentation, to produce a high intensity 15O beam, to produce a direct measurement. This would permit pinning down the 15O(a,g)19Ne reaction rate, which is a present choke-point in the rp-process (active in type I x-ray bursts).
To Nuclear Theorists: We need reliable theoretical predictions for reaction rates, benchmarked with observables.

Chris Ruiz (TRIUMF). Nuclear Astrophysics of neutron-deficient nuclei - experimental approaches at ISAC.
To Astrophysicists: We rely on astrophysical modellers to tell us: which reactions are of astrophysical importance? It takes many years (~5 years, say) to develop a specific reaction experimental setup, so the reactions you tell us to measure must be critically important, not merely of some curiosity.


Ed Brown (MSU/JINA). The X-ray Burst-Crust Connection.
For nuclear theorists: Pay attention to all phenomena predicted by your models. It is not enough to see that it produces consistency with one phenomenon; you must also work out the implications for other phenomena as well.


Andrew Cumming (McGill). Constraints on the rp-process from X-ray bursts.
For nuclear experimentalists: There are many possible influences on the phenomena, so nuclear reaction rates are important for understanding them, but there are astronomical influences as well. At present, our uncertainties are not hung up on a single waiting point; however, our level of uncertainty does depend, for example, on
astrophysical causes, such as turbulence or spreading in the burning layer.


Randy Cooper (Harvard/CfA). Nuclear Reactions During the Onset of Type I X-ray Bursts.
The uncertainty in the Hot CNO breakout reaction rates, and in parti15O(a,g)19Ne rate is an important uncertainty in type-I x-ray burst ignition models.

Crosstalk

Zach Medin. Condensed Matter Surfaces of Neutron Stars: Applications and Tangents.
Under certain conditions the atmosphere of a neutron star is negligibly thin and a condensed matter surface forms. This is applicable for neutron stars with large surface magnetic fields and moderate surface temperatures.
For observational astronomers: Condensed matter surfaces could be used, e.g., to explain the featureless spectrum of RX J1856.5-3754, and are also a key ingredient in vacuum gap pulsar emission models.
For nuclear theorists: The strong magnetic fields of neutron stars have an important effect on matter even at low pressure/density.

Crosstalk

O.L. Caballero. Transport Properties of Dense Plasmas. We are calculating transport properties of the ions in the Neutron star crust using MD simulations. In our model the ions interact via a Yukawa potential. We obtained the thermal conductivity, diffusion coefficient and shear viscosity for a density range between 10^9 to 10^13 gm/cm^3. We expect to match results coming from quantum calculations by Prakash and Postnikov for the dilute gas. In the future we expect to generate results for the nuclear pasta phase.

Crosstalk

From Friday, June 29th:

Jean in' t Zand. Observations of Rare and Peculiar X-ray Bursts.
Many of the details of X-ray bursts are not understood, and many of these may have nuclear physics explanations.

Randy Cooper. Generation of Type 1 X-ray Burst Oscillations.
For nuclear theorists: These oscillations are exciting for nuclear theorists, because they can constrain neutron star compactness, and so contain information about the nuclear EOS, in a way which is complementary and independent of methods heard this week.

Erik Kuulkers. INTEGRAL Galactic Bulge Monitoring Program.
For nuclear theorists: the high energy sky changes from time to time.


Fang Peng. Weak Hydrogen-Powered Explosions on Accreting Neutron Stars.
For Nuclear theorists: X-ray burst modeling depends on the heating from the crust.
For Astronomical observers: Observations of the following phenomena would be useful in constraining burst models: X-ray bursts in low-luminosity sources, search for long bursts, weak H flashes, or peculiar bursts, need high resolution light curves.


Andrew Cumming. Nuclear Burning on Accreting Nuetron Stars.
For nuclear theorists: people working the proton rich side, particularly on rp-processes, we need to understand the timescales for the different processes in rp-process burning. Also on the neutron rich side, we need to understand the crustal processes which produce the heat flux at the base of the crust, to help us explain KS 1731-260.


A problem: H and He is clearly burning stably at 0.1-0.2 of the Eddington accretion rate (i.e., at low temperature in the atmosphere); but we expect to only burn stably at accretion rates at the Eddington rate (at a much higher temperature in the atmosphere). How is it able to burn stably at such a low accretion rate?


Sudip Bhattacharyya. Probing Neutron Star Physics Using Thermonuclear X-ray Bursts. For nuclear theorists: produce mass-radius relationships using only up-to-date physics for neutron stars, strange stars and hybrid stars (quark cores, normal matter in the atmosphere/crust). In other words, please specify which models have outlived their assumptions.

Crosstalk

J. Henderson - Solving the Mysteries of Ultra-Magnetized Neutron Stars - Heat Transport inside the Crust.
The addition of a toroidal component to the crustal field can sufficiently reduce the radius of the hot emitting areas on the NS surface to possibly explain some observations (i.e. "The Magnificent Seven").
To Observational Astronomers: Keep doing what you're doing.


Alexandros Gezerlis - Neutron Star Matter Superfluidity: from BCS to QMC.
Microscopic simulations of the 1S0 zero-temperature neutron-matter pairing gap show it to be larger than that calculated within all the previous formalisms.
To Observational Astronomers: to quote Chuck Horowitz, "Astronomers should ask nuclear physicists two questions: (1) Are your results model dependent, and (2) What are your theoretical error bars?"

Crosstalk

E. Cackett: Crustal cooling in accretion heated neutron stars.
Quasi persistent sources provide a rare opportunity to observe crustal cooling ... and we think we've measured the thermal relaxation time of the crust in 2 sources.

A. Steiner: Symmetry energy, crust thickness and KS 1731.
The physics of neutron star crusts is very thorny, the theorist have much work to do, yet we are a vibrant community which is making progress! Keep the observations coming, contact us with questions or concerns anytime. Don't give in to dark energy.

N. Sandulescu: Nuclear Superfluidity and Cooling Time of Neutron Star Crust.
No conclusions but in summary: Pairing in the crust can significantly change the thermal diffusion time.

C. Heinke: Constraints on Neutron Star Physics from Transiently.
Accreting Neutron Stars in Quiescence.
Messages:

• Zero-B hydrogen-atmosphere models are trustworthy.

• M,R constraints from neutron stars in globular clusters are sound and getting interesting
  

• Cooling rates for soft x-ray transients are strictest constraints and disallow minimal cooling.

Questions:

• What range of nuclear EOS are considered reasonable.

K. Levenfish: Thermal steady-states of neutron stars in soft X-ray transients vs deep crustal heating.
Proton superfluidity is strong in the core and neutron superfluidity weak.

E. Brown: Crust electron captures: Implications for superbursts and transient lightcurves.
For the nuclear physicists:
Transport properties: what is the thermal conductivity of pasta (and sauce) - are there reasonable upper and lower limits. Need better understanding of the crust/core interface.

For the astrophysicists
Need larger sample of superburst and burst at low accretion rates. Synthesis of disparate observations: isolated cooling neutron stars, magnetars, X-ray bursters, X-ray transients share the same nuclear physics.

S. Reddy. Weak interactions in superfluids and cooling rates in the inner crust.
Neutrino rates in matter can differ by factors of a few but if larger factors are proposed - be skeptical - ask lots of questions.

Forget about about PBF in the vector channel.

J. Dey: Stellar and terrestial observations from the mean field large colour QCD models.
For astrophysicists: Observations are good.
For nuclear model people: u r doing well.
For phenomenologist like us the message is: look for discrepancies and try simple QCD models.

Crosstalk

Chuck Horowitz: Neutron Rich Matter and Neutron Star Crusts.
To observational astronomers: Astronomers should ask nuclear physicists two questions: (1) Are your results model dependent. and (2) What are your theoretical error bars?


Jorge Piekarewicz:The Impact of Terrestrial Facilities on the Structure of the Neutron Star Crust
To observational astronomers: The new facilities (like RHIB) will constrain the low density EOS. We need nice neutron star M-R measurements to constrain the high-density EOS, and the observational astronomy approaches are the only ones I know which can produce these constraints.


Jim Lattimer: Observational Constraints on the Neutron Star Crust and their Implications for the Dense Matter Equation of State.
We desparately need a radius measurement, even without a mass measurement, because it can provide a reasonable constraint on the EOS.

K. Sato: Nuclear "Pasta" Phases by Quantum Molecular Dynamics.

To observational astronomers: It would be very valuable to have observational constraints on what densities the pasta phase occurs [ed.: it is noted that this will be difficult, since it is not yet clear what observable can provide a unique signature of the pasta phase.]


Bennet Link. The Dynamics of Vortex Pinning in the Neutron Star Crust.
To observational astronomers: Please identify rotational and seismic modes (observationally!).
To Nuclear Theorists: fully solve the vortex/nucleus interaction problem.

Steve Price. Time-correlated Structure in Spin Fluctuations of an Isolated Neutron Star.
To nuclear theorists: In the future, we will assume some physical value for the torque, and be able to constrain the value of the reduce the moment of inertia. This should constrain the ratio of the core moment of inertia to that of the crust.

Alex Turbiner. One-Two Electrons Atomic-Molecular Systems in a Strong Magnetic Field.
To observational astronomers: At B-fields between 1e12 and 4.4e13 G of two-electron systems, all basic transitions, dissociations and ionization energies have energies between 100-1000 eV.


Marcello Baldo. Microscopic Theory of the Neutron Star Inner Crust.
To observational astronomers: We can calculate in a reliable way the Equation of State of the crust (pressure vs. density); however, the more detailed physics (such as the shear modulus) is still not well known.


Jerome Margueron. Equation of State in the Inner Crust of Neutron Matter: Discussion of the Finite Size Effects. What is interesting in thisese models is the impact on predictions regarding cooling processes (see talk by N. Sandulecu).

Chris Fryer. After the Shock, Magnetic Fields and Fallback on Newly Formed Neutron Stars.
To observational astronomers: Anything you can tell me about Cas A (is it a magnetar?) will help me constrain SNe models. To nuclear physicists: are there any effects of fallback on nucleosynthetic yields?


Aimee Hungerford. Neutrino Scattering in Proto-Neutron Stars.
To observational astronomers: Self-regulation was a bit of surprise to us, but it seems one cannot learn very much about the interior equation of state from neutrino observations.

Crosstalk

Throughout the conference, I am asking all observational astronomers, "What single most important fact do you want our nuclear theorist colleagues to take away from your talk?". Also, I am asking all nuclear theorists the similar question, what observational astronomers should take away from their talks.

This is the compendium of responses from the first day.

David Kaplan:
To nuclear theorists: Things are a lot more complicated than we thought five or ten years ago, but we are making progress and learning a lot.

Slava Zavlin: X-ray emission from the young pulsar J1357-6429 and similar objects.
To nuclear theorists: Be cautious in interpreting numbers from observations. There are many systematic uncertainties.

Dong Lai: Surfaces of Magnetic Neutron Stars.
To nuclear theorists: There is a lot of interesting physics to be explored regarding the condensed surfaces of neutron stars.

Eric Gotthelf: CCO pulsars as anti-magnetars: Evidence of Neutron stars Weakly Magnetized at Birth.
To nuclear physicists: Emission mechanisms for CCOs, magnetars and INSs are something which we don't understand, and what we need to know, to explain these classes of NSs jointly.

H.-J. Schulze: Pairing Gaps in Neutron Star Matter.
To observational astronomers:
Polarization effects suppress the BCS gaps. This will impact cooling, and observations of glitches.

Achim Schwenk: Superfluidity in neutron stars.
To observational astronomers:
1. There are many developments attempting S-wave pairing.
2. Neutrons may not be superfluid in the core.
3. Nuclear Theory is now trying to do calculations without model dependence, but including systematic uncertainties.
4. I would like to know what observational constraints exist on pairing in superfluid neutrons.

Enrico Vigezzi. Pairing Calculations Beyond Mean Field in the Inner Crust.
To observational astronomers:
1. Listen to the next talk (Barranco).
2. The specific heat in superfluid neutrons can be influenced due to the presence of nuclear clusters, by 1-2 orders of magnitude.
3. Be cautious about the local density approximation.

F. Barranco: Microscopic Calculations of Vortex-Nucleus Interaction.
To observational astronomers:
1. The pinning energy is not negative at > 0.03 fm-3 as previously thought; it is apparently positive.
2. Consequences in terms of glitch properties will be discussed by Bennet Link tomorrow. But, pinning is simply much less likely, only very weakly, and in a much smaller volume. Bennet will argue that pinning is very difficult to ever occur in this scenario. In other words, pinning would have nothing to do with glitches in the crust.

Joe Carlson. Pairing gaps in low-density neutron matter and cold atoms
To observational astronomers:
A question: The laboratory experiments using cold atoms will solve the problem of low density s-wave pairing caps -- is that useful in an astrophysical setting?