Thanks to the Bloggers!

The conference ended yesterday, and while there are a few remaining items to be tied up here, the post rate will drop to zero in a few weeks.

I want to thank the bloggers for this conference: Karl Smith, Nathalie Degenaar, Randy Cooper, Liliana Caballero, Nevin Weinberg, and Ed Cackett. They did an outstanding job of communicating the thrust of the conference with their live-blogging the sessions, pointing out goings-on around town and around the conference room. If you see one of them, shake their hand -- they were great.

Rides to Albuquerque Thread

Driving to ALB? Add a comment below on what time you will be going to find riders. Need a ride at a certain time? Add a comment below giving the time you need to leave.

Homework Problems

Chuck began the discussion of homework.

* Multi-dimensional models for X-ray bursts. --> Connects nuclear experiment directly to astrophysical observer, the most distant line this community needs to cross. HS suggests the nuclear physics remains uncertain for multi-dimensional model, and therefore must pinned down.
* Lots of phenomenology from many different angles (define? what's an angle? - crust cooling, X-ray bursts, and code-to-code comparisons of X-ray bursts. BENCHMARK CASES with identical physics. This will be important with phase plots of NS mass and radius, with different constraints from different phenomena, one wants to be sure that the inputs at the microphysical level are identical.
*FYI: At Michael Smith's repository at nucastrodata.org, the whole community has access to the same primary dataset -- this is intended to act as a benchmark.
* FYIDuncan Galloway's X-ray burst lightcurve repository is a resource for the modeling community.
* Modelling the crust: is it amorphous or crystaline, and do magnetic field evolution affect the the crust. A model of the magnetic field evolution with amorphous conductivity, to see if the crust blows up.
* Make magnetic field evolution models a community resource.
* FYI: European Compstar will provide codes for students for neutron structures, NS rotation, supernova hydrodynamical codes.
* FYI: JINA has a series of schools, dedicated to giving away R-matrix code to analyse reaction codes; some network codes; shell model.
* Wiki for this conference.
* Who are all these people? What do they do? How do I know who does what? It seems important to see the expertise in the field in a plainer way.
* The Wasserman Question: Where are the condensed matter people in all this? For example, they have been working with rotation in superfluid 3He for some time, they must be able to inform our understanding of rotation in neutron stars. We need to do outreach to condensed matter physicists, who study superfluidity and strong magnetic fields in matter, because they were not represented at this workshop.
* Gravitational work will continue to grow in importance to neutron stars. We should be embedding them with us, as soon as possible.

At Crust09: X-ray bursters

At Crust09: on the roof

It's near the end of the morning coffee break on Thursday, and the workshop is almost done. Seems we're still enjoying it.

Victoria Kaspi: Anomalous X-ray Pulsars

Vicky kicked off the fourth and final day of the workshop by reviewing the observational properties of anomalous X-ray pulsars (AXPs). AXPs form a class of highly magnetized neutron stars, denoted as magnetars, together with soft gamma repeaters (SGRs).

Vicky showed the results of phase-coherent timing studies of 5 AXPs (SGRs are too faint to detect with RXTE when not bursting or flaring) using a long-term monitoring program with the RXTE satellite.

The AXPs appear to display many glitches; sudden spin-up events that may be explained by a faster rotating crustal superfluid suddenly transferring angular momentum to the crust. Glitch studies can possibly help to constrain the superfluid properties of neutron stars. The AXP glitches are rather peculiar compared to those observed from rotation powered pulsars and sometimes result in a net spin-down rather than an increase in the spin period.

Check out the online magnetar catalog if you are looking for information on one of the AXPs or SGRs.

At CRUST09: Craig Heinke

In Santa Fe: Another night at the pool

Credit: Erik Kuulkers

Gosh, doesn't he play pool like he does science?!

Posters: Jillian Anne Henderson

At Crust09: Dany Page and Jose Pons

Discussion on the balcony.

Posters: Kit Yu Lau

In Santa Fe: Quotations

"Magnetars are hopeless." Anonymous, in response to the question "what did we learn from this workshop?"

"I just don't want to be quoted on any blogs." Erik Kuulkers

"It was accepted? Oh shit!" Andrew Steiner, in reference to his credit card.

"It's almost as contentious as horse jokes." Ed Brown

Coming Talks: Thursday May May 21

Victoria Kaspi	Anomalous X-ray Pulsars	9:00
maxim Lyutikov	Evolution of magnetic fields in magnetars	9:45
Roberto Turolla	Currents in magnetar magnetospheres	10:10
Jose Pons	Thermal Evolution of Magnetars	11:00
Steve Price	Thermo-Resistive Instability in Magnetar Crusts	11:45
Rishi Sharma	Superfluid Heat Conduction in Magnetars	12:10
Bob Rutledge, Hendick Schatz	Getting Organized to make the case for future experiments to studyneutron stars.	2:10

Posters: Will Newton

Posters: Sergey Postnikov

Posters: Gloria Sala

Posters: Karl Smith

Andrew Steiner: Elucidating the properties of dense matter from starquakes in neutron star crusts

Andrew told us about how oscillations detected in magnetar giant flares may quantitatively constrain nuclear physics, in particular the ubiquitous nuclear symmetry energy. The symmetry energy is one of the largest uncertainties of the crust parameters; this uncertainly leads to uncertainties in the shear modulus and shear speed.

Interestingly, Andrew suggested that the traditional mode assignments to the crust and core modes may be incorrect. If true, this could explain the implied magnetar mass of less than one solar mass: The actual mass could be higher, which would help many at the workshop sleep better.

Nils Andersson: Modeling realistic crust dynamics

Nils convinced us that non-magnetic relativistic model is not good enough to describe torsional oscillations of NS. Improvement could be done by including crust-core coupling. His model uses relativistic multi-fluid equations of motion. He also includes elasticity of the fluids and the effect of magnetic field. His model depends on several aspects. For example, this model requires a detail understanding of the superfluid in the crust. Nils also need to know how smooth is the transition from the crust to the core. Another key ingredient is the vortex dynamics.
One of the main aspects Nils pointed out is the connection between the microphysics and the mesoscopic scale,e.g if you a particular nuclear pasta shape, how this would behave if its dimensions is of the order of cm.

Yuri Levin: MHD aspects of magnetar oscillations

Magnetar quasi-periodic oscillations (QPO's) would be relatively easy to model, and thereby deduce properties of neutron stars, if all we needed to worry about is the crust. If only it were that easy.

There are two types of torsional modes in the neutron star: shear modes in the crust and alfven modes in the core. These two modes have similar frequencies, so we expect coupling between the modes. The timescale for energy exchange is much smaller than the duration of the QPO's, so we expect many exchanges to occur.

Therefore, we need a realistic model of the coupled crust and core to really understand magnetar QPO's.

In Santa Fe: La Plazuela

If you don't want to leave the hotel to go to lunch, the La Plazuela restaurant here in the La Fonda hotel is a good option.

Right: Mark Alford, Craig Heinke and Nathalie Degenaar pose for a picture after discussing the intricacies of strange stars.

Tod Strohmayer: Fast X-ray Oscillations During Magnetar Flares

Tod started the afternoon session with a detailed overview of the fascinating oscillations seen during giant flares on magnetars.  In the two objects where these oscillations have been seen, a wide range of frequencies have been detected.  It is highly suggestive that these are torsional oscillations due to vibrations in the crust.

With further understanding and detections there is the exciting possibility to constrain neutron star properties from these oscillations.  As Tod discussed, there are still a number of theoretical issues, and lots of complexity in the observations.    For example, does the crust fracture (analogy to earthquake fractures)?  And, while what we observe are modulations in X-ray flux - can these actually be produced by crust motions?

At Crust09: Audience

Credit: Erik Kuulkers

The crowd eagerly waiting for the 1st talk after the morning coffee break on May 21.

Achim Schwenk: Neutrinos rates from chiral effective field theory

Achim talked about how to calculate nuclear reaction rates determined by spin relaxation time. This method allows to calculate scattering of neutrinos from one or two nucleons.
The spin response is embedded in the dynamical structure factor of the nucleons. The nucleon interactions are described by chiral effective field theory. I found very interesting his comparison of the chiral EFT and different interactions, including the V- k-low potential, and that they reproduced similar spin relaxation rates at low density. At high density chiral 3n interactions suppresses this rate.

Jorge Piekarewicz: The Nuclear Physics of the Neutron Star Crust

Jorge started with a description of the correlation between neutron skin and pressure of pure neutron matter which then effects the neutron star radius. Then mentioned the PREX experiment wanted to clarify that it is not lead on lead, but a slight tap from an electroweak probe.

Also, mentioned the Garvey-Kelson Mass Relations which has very general assumptions but seems to work extraordinarily well. More general and robust than expected hinges on smoothness of M(N,Z).

Finally, Jorge was trying to understand if nuclear pasta is robust or model dependent. Do we have to go through pasta or is there another possibility? His work showed that there is no pasta formation if there are no long range forces or if neutron skin is large.

At Crust09: Waiting on the couch

Randy Cooper, Ed Brown, and Fang Peng wait for some colleagues to go out to dinner. Ed and Fang smile for the camera, while Randy is distracted by something shiny.

Duncan Galloway: Measuring neutron star parameters from mixed H/He thermonuclear bursts

Duncan discussed a promising approach to constrain the neutron star parameters from type-I X-ray bursts. Comparing observed burst lightcurves with theoretical models allows for an independent distance measurement, whereas the neutron star radius can be constrained from fitting the spectral data and the Eddington flux can be estimated from modeling the temperature profile in the neutron star crust. This combination allows one to put constraints on the neutron star mass and radius. The technique is applied to the bursters GS 1826-24 and KS 1731-26. Eddington limited X-ray bursts have been detected from the latter, which provides additional constraints.

James Lattimer: The Nuclear Equation of State and Properties of the Crust

Jim kicked off the third day of the workshop with a nice discussion of the application of the equation of state (EoS) to properties concerning the crust.

For instance, he discussed how the thickness of the crust has a simple dependence on mass and radius and the chemical potential at core/crust boundary.  He pointed to several types of observations that are dependent on the crust thickness, e.g., crustal cooling and neutron star seismology. 

Jim finished with a summary of measured neutron star masses.  What was particularly exciting is a recent well constrained mass measurement of  1.67 +/- 0.01 M_sun  (Champion et al. 2008).

Finally, Jim's important take away point: observations of crustal properties can have significant ramifications on EoS, not just the crust itself.

At Crust09: PREX

Yesterday, during the general discussion, Chuck Horowitz mentioned that the lead radius experiment (PREX) will become operative in March 2010. This experiment will probe sub-nuclear densities and aims at constraining the symmetry energy term in the nuclear mass, which plays an important role in setting the structure and composition of neutron stars. For example, the symmetry energy term relates to the proton fraction in the core, which sets the threshold mass for the onset of direct Urca neutrino emission. This sounds like an exciting prospect!

Santa Fe morning

breakfast at La Terraza

Confirm Your La Fonda Checkout Date!

There was a programming error at the website which led to confusion regarding checkout dates.

When you selected your dates for Hotel La Fonda at the website, you checked boxes to include your check-in and checkout dates. IF those were the dates you actually planned to check-in and check-out on, then you should experience no difficulties, and need to take no action. Hotel reservations were made to reflect those selections.

After about April 20th, the website stopped taking reservations, and instead displayed your hotel reservations. Unfortunately, a program design error caused the website to display all dates you selected as "Reserved", including your checkout date. This error was not caught (and corrected) until May 14th.

This seems to have caused confusion; in particular, if you relied on the website to tell you the date you intended to check-out on (a completely reasonable proposition), it would have informed you that you had one more night reserved than you actually do.

All attendees were asked to confirm (with a signature) their checkout date at the time of check-in (where you would have caught and the hotel could correct the error). But this may still have slipped past you (it seems to have slipped past more than one attendee). If you have not already done so, please confirm your checkout date with the hotel immediately, and they will extend your stay.

The website programmer apologizes for the confusion; nonetheless, he has been sacked.

In Santa Fe: Quotations

"... one of the many ways he's like a horse." Bob Rutledge, in reference to Erik Kuulkers.

Coming Talks: Wednesday May 20

James Lattimer	The Nuclear Equation of State and Properties of the Crust	8:30
Duncan Galloway	Measuring neutron star parameters from mixed H/He thermonuclear bursts	8:55
William Lynch	Constraining the Nuclear Equation of State with Nucleus-Nucleus Collisions	9:20
Pawel Haensel	Compressible liquid drop model of nuclei in neutron star crust	9:45
Jorge Piekarewicz	The Nuclear Physics of the Neutron Star Crust	10:10
Alexandros Gezerlis	S-wave pairing in neutron matter	11:00
Nicolae Sandulescu	Thermodynamic properties of inner crust matter	11:25
Achim Schwenk	Neutrino Rates in Two-Nucleon Processes from Chiral Effective Field Theory	11:50
Mark Alford	Thickness of the strangelet-crystal crust of a strange star	12:15
Tod Strohmayer	Fast X-ray Oscillations During Magnetar Flares	2:00
yuri levin	MHD aspects of magnetar oscillations	2:45
Nils Andersson	Modelling realistic crust dynamics	3:10
Bennett Link	Dynamics of Quantum Vorticity in the Neutron Star Inner Crust	3:35
Andrew Steiner	Elucidating the Properties of Dense Matter from Starquakes in Neutron Star Crusts	4:00

Issues Raised During Discussion on How to Make Progress on the Crusts of Accreting Neutron Stars

These are issues which were discussed -- all are invited to respond and open new issues in the attached comments.

• Multi-D X-ray bursts models are needed! (And Duncan Galloway, and other observers, would like resulting lightcurves made public).
  
• Next Generation X-ray Observatory (International X-ray Observatory? Launch 2020?) is needed for improved collecting area and spectral resolution of X-ray bursts; timing-capability can also inform inferred properties of X-ray bursts (such as the pulsations, mHz oscillations, etc) and these may occur on a shorter timescale.
  
• An answer to the question, Why is the transition to stable burning occurring at lower accretion rate than predicted?, is needed.
  
• Contined work, critically examining the core cooling rate (from neutrinos?) through quiescent X-ray binary cooling observations are needed.
  
• To accomplish the previous point, a better understanding of low mass accretion rate, as well as the high mass accretion rate, is needed, to derive the total mass accretion rate onto the compact object, and not only the mass loss of the companion (i.e. - how much mass leaves the system, either in outburst, and in quiescence).
  
• Determine the 15O(a,g) rate.
  

Questions for Tuesday Night: Progress for Understanding the Crusts of Accreting Neutron Stars

These questions are posed by Chuck Horowitz, to shape discussion this evening about how to make progress in our understanding of the crusts of accreting neutron stars.

What nuclear measurements to make?
• 12C+12C @1.5 MeV
• Sub-barrier fusion of neutron rich medium light nuclei.
• Masses: which ones? to what accuracy? [Example rp process waiting point
64Ge(1 min half life). Bypass with 65As, 66Se?]
• Masses of n rich nuclei related to symmetry energy.
• PREX: neutron radius of 208Pb.


From Hendrick Schatz:


One way to set this up would be to ask:

- "What do you think are are the most important problems we should try to solve next?"

I think the sense of urgency and importance is where some of the discussion could take place and where it would be interesting to see what different people think.

If one wanted one could then drill down one level and ask (this could be done in parallel or in series)

- What would you like astrophysicists, observers, nuclear theorists to do [to address these problems]

From Sanjay Reddy:


For x-ray bursts:

1) How can we develop modeling efforts and observations to understand the discrepancies between inferred accretion rate and burning regimes ?
2) Can we securely identify the Eddington Luminosity and thermal emission to extract mass and radius ?
3) Does the light curves (late time) probe the rp process path and weak interaction time scales ?

For Superbursts & Thermal relaxation:

1) We need to pin down the ignition depth - will more detailed models help ? (precursors etc?)
2) Theory and experimental effort to measure the carbon fusion - how can accelerate these efforts ?
3) Heating at shallow depth - need realistic simulations (including accretion) of the thermal relaxation in the crust.


State of the inner crust:

1) The role of electron and neutron capture, proton capture from neutron decay, transfer reactions (as a prelude to pycnonuclear fusion) in getting us closer to the ground state.
2) Role of dripped neutrons in thermal and mechanical properties - need realistic interaction model for neutron-nucleus interaction for neutron rich nuclei.
3) Do we now have unambiguous proof for the existence of a neutron superfluid in the inner crust ?

Craig Heinke: Progress & Problems from Quiescent LMXBs

Craig told us about a possible problem in explaining the quiescent luminosity of the accreting millisecond X-ray pulsar SAX J1808.

X-ray observations of SAXJ1808 in quiescence put tight upper limits on the luminosity of thermal emission from the neutron star surface, indicating that the surface is quite cold.  It has been suggested that this can be explained by having a high mass neutron star (which can give a higher neutrino emissivity).

Recent optical observations of SAXJ1808 have, however, constrained the mass of the neutron star, and it seems to have a low (rather than high) mass.

To complicate things further, another transient, Aql X-1, which seems to have a surface temperature (from quiescent X-ray observations) consistent with standard cooling, may have a high neutron star mass......so it might have been expected to be colder than actually observed.

Craig asked if anyone had any ideas on how to explain this........particularly, can more massive neutron stars emit less neutrinos than lighter neutron stars?

 

Laurens Keek: X-ray bursts with too short recurrence times

Laurens gave a very nice talk discussing the problem of X-ray bursts with short recurrence times. He uses a combined RXTE-PCA and BeppoSAX-WFC archive, containing over 3000 bursts, for his studies. For a large range of mass-accretion rates, bursts are found that are followed up by more bursts minutes later (double and triple bursts). Such time-scales are too short to create a brand new fuel layer through accretion, which suggests that there must be some left-over fuel after the initial burst. It remains a mystery how and where this fuel could be stored.

Jerome Chenevez: The INTEGRAL view of intermediate long X-ray bursts

Jerome shows that the INTEGRAL satellite is an important tool for the detection of intermediately long X-ray bursts. What I find quite impressive is that bursts from different sources can be detected within one detector lightcurve, thanks to the large field-of-view of the instrument. There are several sources for which different types of X-ray bursts are detected at roughly the same mass-accretion rate, so this must be near the transition rate of the different burst types.

Wanpeng Tan: Measurement of alpha-induced nuclear reactions for X-ray bursts

Wanpeng told us about three reactions, alpha captures on waiting points, that are important for type I X-ray bursts: 14O(a,p), 15O(a,g), and 26Si(a,p); such reactions are some of the first that occur at ignition.

15O(a,g) is particularly crucial for burst ignition. Tan's analysis of the measurements result in a rate that is sufficiently precise to constrain the critical accretion rate above which burning is thermally stable to within 10%; the critical rate is roughly the Eddington limit.

However, several workshop participants called the accuracy of his analysis into question. Barry Davids asserted that "it's not a detection at the two sigma level."

At Crust09: Coffee break at La Terraza

Isn't this venue great!?

In Santa Fe: Dinner at Coyote Cafe, and an unexpected tour of the town

It's Monday evening just after the final talk, and I soon join a group of nuclear theorists to go to dinner. Where should we go? How do we get there? Certainly these are difficult questions for Santa Fe neophytes, but luckily our sextet includes Andrew Steiner, a former resident. Excellent! We unanimously decide to follow are intrepid local expert to what certainly will be a great restaurant.

We pass by numerous shops, legal offices, and restaurants. I start to get worried. "Andrew, do you know where we're going?" "No, I'm not really familiar with the area. I just figured we'd walk down this street until we found something good." Having now reached what looks like the end of town, I suspect that won't happen.

Luckily, we run into Sanjay Reddy. Great! He lives here, he must know where we should go! He tells us of a great restaurant, somewhere over that way on a road that probably starts with the letter "G." Oh dear. Thankfully, he mentions the Coyote Cafe as well, which is located on this very street and in the direction of La Fonda. That sounds safe, let's go there.

Coyote Cafe turns out to be an excellent choice: The food is somewhat pricey (~$30 entree), but it's delicious, and the wine list is extensive. Andrew redeems himself with his choice of Chardonnay, and we have a thoroughly enjoyable dinner.

Anuj Parikh: Nuclear Physics Uncertainties in Models of Type I X-Ray Bursts

Anuj started with the quote "Are those original x-ray bursts or RI's" referring to a Gibson guitar. Anuj then continued describing another x-Ray burst sensitivity study.

The study explored sensitivity of model to peak temperature, duration, and initial composition. Then, using one-zone post processing models the study varied individual reactions (>2000), simultaneous varied multiple reaction rates, and individual variation of Q-values (<1MeV).

Varying individual rates identified as65(p,g) and ga61(p,g) as having the strongest effect on the models used.

Anuj also showed that Q-values are important for calculating forward reactions from theory and for detailed balance in reverse rate calculation. Q-value uncertainty is most important when the Q-value is small. The sensitivity study identified the Q-value from ge64(p,g) as having the most significant impact.

In Santa Fe: Tomasitas

If you are thinking about (affordable) dinner for tonight, I would suggest Tomasitas. This is a Mexican restaurant (not surprising in NM). I have enjoyed the food but overall I like to go there on Tuesday nights because they have Mariachi at 8 p.m (no cover). Siting can be limited at that time so I recommend to arrive early. Here is a link with the address and more information.

http://local.yahoo.com/info-20219154-tomasitas-santa-fe

At Crust09: Bob's Take Away

Something for the observers: still wondering what exactly Bob's famous quest is?

Since June 2007 Bob's quest is available for download. Try it out, and prepare your answer, before Bob asks!

Many thanks to Erik Kuulkers for the mp3.

Richard Cyburt: X-ray burst reaction flows and ash composition

Richard compared results for XRB lightcurves coming from two different methods: Multizone and single zone calculations. Overall the two methods agree quite well, both for composition and light curves. Both compositions peak in the interval A =60,80.
Richard shared us a very useful piece of information about the JINA REACLIB project. REACLIB is a huge data base with nuclear reaction rates. Users can create their own libraries there too.

Jordi Jose: Hydrodynamic simulations of type I X-ray bursts: metallicity effects

Jordi described his groups simulations of type I X-ray bursts using the 1D SHIBA hydro code coupled to a large network. In models with solar abundance of metals he finds very little 12C in the ashes (~1% by mass), peak nuclei with A~60, and, in general, results that approximately match those found by Heger et al. Sub-solar models (Z=0.001) had less energetic but longer bursts, lower alpha (alpha~30), synthesized heavier species (A~100), and smaller 12C mass fractions (~0.1%). More runs are in progress. Among the take home points (better constraints on Mdot, L, reaction rates), Jordi suggested we take home some local jewelry and handmade artwork :).

Jeff Blackmon: Nuclear Physics on Accreting Neutron Stars

Jeff Blackmon stressed the importance of experimental measurements of (p,g) and (a,p) reactions to accreting neutron stars. Current experiments are using indirect techniques to locate important resonances for these reactions. Specifically mentioned two direct measurements, the first was performed at Oak Ridge studying f17(p,g). Important resonance was measured, but direct capture rate still needs to be constrained. Secondly, he mentioned o14(a,p) measured at CRIB (RIKEN) which is 50-80% different from the recommended REACLIB rate.

To measure many of these reactions more low energy rare isotope beams are needed. Combined with new high resolution detectors such as ANASEN these important X-ray burst ignition rates can be better constrained.

Andrew Melatos: Crustal magnetic field in an accreting neutron star

Andrew gave us a lucid discussion of magnetic field evolution and its consequences in accreting neutron stars.  

Magnetic field burial and flux freezing together distort the initial dipole and decrease the magnetic moment; however, the local field strength may increase!  ZEUS says that the magnetic structures are Parker unstable but the instability is suppressed: In the end, the substrate exhibits global MHD oscillations.  The interesting claim is that the end state could be a 10^15 G (!!!) magnetic field "wall" that could affect type I X-ray bursts, for example.  The idea is exciting because there are severe discrepancies between observations and X-ray burst models that are difficult to explain through nuclear physics uncertainties alone, but the presence of such a structure, particularly at the ignition pressures of X-ray bursts (which are << B^2/8pi for B = 10^15 G), are difficult to believe.

A more plausible, yet no less exciting, idea is that asymmetric field burial could produce a quadrupole; the resultant gravitational radiation would limit the possible neutron star spin frequency.  This could explain why all neutron stars have spin frequencies <~ 700 Hz, well below the break-up spin.

Alexander Heger: An Overview of X-Ray Burst Simulations

Alex began with an overview of type I X-ray bursts and their various accretion rate regimes. He then described his numerical simulations of bursts using the 1D Kepler hydro code which he coupled to a large reaction network. Runs with H/He accreting at high Mdot with low Z show long (~200s) tails due to rp-process burning and little 12C in the ashes of burning (X12~0.001). In runs with low Mdot and high Z, the ignition takes place in a pure He layer, leading to a very quick burst rise (~1 ms) and near Eddington luminosity at peak. Runs with very low Mdot undergo weak hydrogen flashes.

Some of the results may be sensitive to uncertainties in the nuclear physics and reaction rates and are a subject of future study.

At Crust09: Alex Heger Opens the Tuesday Session

In Santa Fe...

Bob Rutledge performs a delicate scattering experiment.

Coming Talks: Tuesday May 19

Alexander Heger	An Overview of X-Ray Burst Simulations	8:45
Andrew Melatos	Crustal magnetic field in an accreting neutron star	9:30
Jeff Blackmon	Nuclear Physics on Accreting Neutron Stars	9:55
Jordi Jose	Hydrodynamic simulations of type I X-ray bursts: metallicity effects	11:00
Richard Cyburt	X-ray burst reaction flows and ash composition	11:25
Livius Trache	Nuclear reaction rates for explosive H-burning from experiments with rare nuclear beams. Indirect methods	11:50
K. Ernst Rehm	Recent Results for (p,g) and (a,p) Reactions on the rp-Procerss Path	12:15
Uwe Greife	Proton Capture Measurements with Radioactive Ion Beams	2:00
Anuj Parikh	Nuclear Physics Uncertainties in Models of Type I X-Ray Bursts	2:25
Giuseppe Lorusso	beta deay study in the Sn100 region	2:50
Wanpeng Tan	measurement of alpha-induced nuclear reactions for X-ray Bursts	3:15
Jerome Chenevez	The INTEGRAL view of intermediate long X-ray bursts	4:10
Laurens Keek	X-ray bursts with too short recurrence times	4:35
Craig Heinke	Progress & Problems from Quiescent LMXBs	5:00
Schatz, Brown, Haensel, Horowitz	Discussion, Accreting Neutron Stars	5:30

In Santa Fe: The Shed

Ed Brown discusses burning models with Nevin Weinberg and Andrew
Cumming. The Shed is a "new Mexican" restaurant, one block from La
Fonda. Map.

Milan Matos: Mass Measurements of Exotic Nuclei

Milan gave a nice summary of mass measurement techniques. Milan mentioned the importance of masses to neutron star modeling. He then summarized current techniques including direct measurements such as Penning traps, Schottky method, time-of-flight, and indirect measurements done with transfer reactions. Milan also mentioned capabilities of different facilities producing isotopes in different regions of the chart of nuclides.

Dmitry Yakovlev: Pyconuclear reactions in the crust

Dmitry Yakovlev gives an interesting and entertaining overview of pyconuclear reactions. These density sensitive nuclear fusion processes are manifestations of the QED vacuum, which involves Kindergarten physics and the problem is therefore explained by a young Russian girl. The reaction rate of pyconuclear reactions is independent of temperature, but increases exponentially with increasing density. These processes are thought to allow for the formation of large nuclei in the neutron star crust.

(The image shows George Gamow at young age).

Dany Page: Crust cooling of strange stars vs neutron stars

Dany described how as cooling depends on the thickness of the crust it should be possible to distinguish between neutron stars and strange stars - a strange star has a much thinner crust (a few hundred metres as opposed to km).  So, relaxation of the crust should be a good test.  However, he hasn't yet had the chance to do the calculations.......answers may be coming in the near future.

Sanjib Gupta: Nuclear reactions in the crust and implications for superburst ignition and cooling

Some talked about nuclear reactions near the stellar surface; others talked about those in the core.   Sanjib talked about reactions in between.  Such reactions in the crust are a figurative bridge between surface heating and core neutrino cooling.

These nuclear reactions, electron captures, neutron emissions, and pycnonuclear reactions, are of utmost importance because they set both the heating and compositional profile.

In the outer crust, electrons can capture into excited states of nuclei; the subsequent radiative de-excitation can release ~4 times more energy than previous models predicted, which assumed electron capture into the ground state.  Interestingly, Daligault & Gupta (2009) find that the outer crust is amorphous, i.e. it does not form a lattice!  This result is exciting, but conflicts with previous calculations (like Chuck Horowitz's simulations).  Does it conflict with observations?  Unclear right now, but it would be useful to find out (hint, hint...).

A multi-component inner crust may form a lattice, as some leaked, free neutrons redistribute themselves among the other nuclei and thereby "homogenize" the plasma.  This neutron rearrangement can affect pycnonuclear heating as well.

Nathalie Degenaar: Crust cooling of EXO 0748-676.

Nathalie shows us new observations of crustal cooling for the source EXO 0748-676. This source just turned to be in quiescence. It would be interesting to compare the cooling behavior of KS 1731 and MXB 1659. Data are just coming out. I find this very promising.  Theorists have now more data to compare with current models (see Ed Brown and Cackett talks). This of course if the source is really in quiescence.

Nevin Weinberg: Carbon detonation and shock-triggered helium burning in neutron star superbursts

Nevin told us about the physics of the superburst rise.  This is relevant because the rise both (1) determines the energy released during the superburst and thereby the light curve morphology and (2) sets the composition of the deep ocean and crust. 

The burning during the rise eventually occurs on such a small timescale that it becomes hydrodynamic; Nevin convincingly argues that a detonation ensues.  The detonation-induced shock triggers rapid heating of the overlying H/He layer and thus an X-ray burst-like event.  Such events are likely the detonation's observational signature.

The existence of the burst-like events may set an upper limit on the superburst ignition depth independently of other methods.

Randall Cooper: The 12C + 12C Reaction Rate and Superburst Ignition

Thermal properties of crust  and core sets ocean temperature and thereby the superburst ignition depth, so superbursts are probes of NS interiors.  But there is a problem......observationally inferred ignition depths are shallower than all theoretical superburst models predict (in models ocean is too cold)

Randy's proposed solution: 12C +12C rate is unmeasured at relevant energies and the rate used in models assumes reaction rate is nonresonant.  But, 12C + 12C rate may be much higher if a resonance exists......if a resonance exists observations agree with a range of NS models.

Randy's task for nuclear experimentalists - measure 12C + 12C reaction rate at astrophysically relevant energy.

Ed Brown relayed a new experimental result from the CLAUS2009 workshop.....recent experimental efforts suggest a large resonance.

Jean in 't Zand: New phenomena in thermonuclear X-ray bursts and Superbursts

Jean described two newly discovered X-ray burst phenomena: (1) long burst tails, (2) superexpansion bursts.

Long burst tails:
-- by stacking bursts from the clocked burster GS 1826-24, can now detect ~hour long tails in its ~100 sec. long type I X-ray bursts. These tails are due to heat propagating out on long time scales and match tails seen in the Heger et al. 2007 burst calculations.
-- puzzle: some bursts show tails with a fluence that is larger than the fluence of the flash itself, suggesting that more heat goes down than goes out. Is this due to strange variations in the surface conduction properties?

Superexpansion bursts:
-- found 32 bursts in data catalog that show a very large photospheric radius expansion (>1000 km) just after burst onset. These superexpansions always lasts for a few seconds and are followed by a moderate expansion phase (10 < r_ph < 100 km) which lasts on a time of order the burst duration (10-1000 s).
-- puzzle: why is the superexpansion duration independent of burst duration? It's probably not due to variations in early time luminosity. Maybe due to ejection of a thin shell that becomes optically thin after a few seconds?

Introducing: Karl Smith

Hi,
I am currently a graduate student at Michigan State Univ. where I have been working on sensitivities of X-ray burst models to nuclear uncertainties. I will be blogging about the interesting talks during the workshop.

Introducing: Nathalie Degenaar

Hi all,

I am currently a phd student at the University of Amsterdam where I work on (X-ray) observations of accreting neutron stars. I will be one of your dedicated bloggers at this conference in Santa Fe.

Chuck Horowitz: Physics of the neutron star crust and its breaking strain

In accreting Neutron Stars the new crust formed is a perfect crystal with some impurities, which could increase pycnocuclear reactions. Perhaps this provides the heat needed to explain superburst ignition (see Cumming talk).

NS shear modulus seems to be independent of impurities.

NS nuclear pasta shear viscosity does not depend on the pasta shape.

NS crust does not fracture.

Liliana asks: If NS does not break, where are the star faults (star quake sources) located? 

Andrew Cumming: Long thermonuclear flashes and the heating and composition of neutron star crusts

Andrew Cumming kicked off the workshop with a germane review of type I X-ray bursts, thermonuclear flashes on accreting neutron stars.  X-ray bursts are of great interest because some bursts, specifically those for which hot CNO cycle burning does not set the temperature of the ignition region, can be useful probes of the interior temperature and thereby the crust and core properties.

There are both great successes and failures in comparisons between observations and model results of "normal" H- and He-triggered bursts.  Generally, models of individual bursts agree well with observations (e.g., GS 1826-24), whereas models of global bursting behavior disagree.

Superbursts, extremely energetic flashes thought to be triggered by carbon burning, may be particularly useful probes of crust physics.  Models predict that all crust & core parameters "must be turned to hot," to match observations, but the same predictions are inconsistent with complementary observations of other phenomena.  What's the solution: More exothermic electron captures? a resonance in the carbon fusion reaction rate? strange stars? a new source of shallow heating?

We'll more about these possibilities in the next couple of days.  Stay tuned!

Posting your talk or poster at the conference website

Presenters can post their talks or posters from the online talk schedule. Just log in (so the system can figure out which presentation is yours), then upload a PDF file.

Coming Talks: Monday May 18

The talks for Monday May 18 (full schedule):

Andrew Cumming	Long thermonuclear flashes and the heating and composition of neutron star crusts	9:00
C. J. Horowitz	The Breaking Strain (Strength) of Neutron Star Crust	9:45
Jean in 't Zand	New phenomena in thermonuclear X-ray bursts	11:00
Randall Cooper	The 12C + 12C Reaction Rate and Superburst Ignition	11:25
Nevin Weinberg	Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts	11:50
Edward Cackett	Crustal cooling in MXB 1659-29 and KS 1731-260	1:30
Edward Brown	Mapping neutron star crusts with the cooling lightcurves of quasi-persistent transients	1:55
N. Degenaar	Crust cooling of EXO 0748-676	2:20
Sanjib Gupta	New results in neutron star crust nucleosynthesis and implications for X-ray Superburst ignition	2:45
Dany Page	Cooling of the crust of strange stars vs neutron stars	3:30
D.G. Yakovlev	Pychnonuclear reactions in the neutron star crust	4:25
Milan Matoš	Nuclear Masses and their Importance for the Cooling of the Neutron Star Crust	5:10
Peter Moller	GLOBAL CALCULATIONS OF NUCLEAR STRUCTURE PROPERTIES.	5:55

Ed Cackett: Crustal cooling in MXB 1659-29 and KS 1731-260.

Ed Cackett reviewed the existing data, and described the coming data, regarding observed cooling of the long-duration transients MXB 1659-29 and KS 1731-260. These are two post-outburst low mass X-ray binaries of great interest to observers and theorists, because the total magnitude of accretion over their outbursts is high enough to cause an energy deposit in the crust (due to Deep Crustal Heating) of such magnitude that it will heat the crust out of thermal equilibrium out of the core. Seven observations of the cooling crust have taken place; more have been approved, and will be made in the near future -- so stay tuned for new observational results. Up to now, these objects have continued a monotonic decrease in their emission temperature, consistent with the expectations of neutron star crustal cooling theory -- although interestingly different from the simple, early calculations of such cooling.

This talk informed the talk which followed, given by Ed Brown, in which Ed presented his (with Andrew Cumming) analysis of the observed cooling curves of these two objects, using more detailed cooling calculations.

Opening Reception

Mark Alford, Pawel Haensel, Nils Andersson.

Introducing: Liliana Caballero

Hi! Currently I’m a postdoc at North Carolina State University and I’m studying neutrino scattering from accretion disks formed during the coalescence of a neutron star and a black hole. I’m also interested in the transport properties of the neutron star crust such as the viscosity and the thermal conductivity – topics I examined during my PhD with Chuck Horowitz at Indiana University.

I will be contributing to the CRUST09 blog. If you have any comments, questions and/or suggestions and you are too busy these days to post them, share them with me. I will be happy to help! 

Introducing: Nevin Weinberg

Hi, I'm Nevin Weinberg, one of the bloggers at the Crust09 conference. I'm a postdoctoral fellow at University of California, Berkeley. At the workshop I'll be talking about my work on explosive carbon burning during superbursts. Let's see, my interests outside of science... hockey, music, nytimes. I'm excited about the meeting and looking forward to sharing what I hear & see!

Introducing: Randy Cooper

Hi everyone!   I'm Randy Cooper, an official blogger for the Crust09 conference.  I graduated from Harvard last May and am now a postdoctoral fellow at the Kavli Institute for Theoretical Physics.  My research interests include type I X-ray bursts and superbursts; you'll learn about my most recent work on superburst ignition on Monday morning.  My non-scientific interests are fitness, reading nonfiction books, listening to jazz and metal, and playing drums.

By the way, I encourage all speakers to be prepared for Bob's inexorable question: "What one thing would you like astronomers/nuclear theorists to take away from your talk?"

Introducing: Ed Cackett

Hi, I'm Ed Cackett, a Chandra Fellow at the University of Michigan, and one of your intrepid bloggers for the rapidly approaching Crust09 workshop. You'll hear about my research interest in quiescent low-mass X-ray binaries during the workshop. Outside of astronomy, I have a keen interest in music (mostly jazz & blues), eating, and trying to avoid changing diapers. Come say 'hello' to me in Santa Fe (I'm the guy in the picture not in red!).

Questions from Chuck Horowitz

Chuck Horowitz posed a set of questions recently to the organizers, which he thought would be useful to consider in the context of the "Defining the Neutron Star Crust" workshop:


I] Neutron star geology
A) Are neutron stars planets?
B) Are NS geologically active?
C) Do NS have plate tectonics?
a. Faults?
b. Volcanoes?
c. Mountains?
d. Other surface features?
D) What minerals/ kinds of rock are present?

II] Star quakes
A) Are giant flares triggered by star quakes? If so, must the crust be very strong to explain the large energy of the 2004 giant flare in SGR 1806-20?
B) Are flares and microflares also related to star quakes? If so, how are quakes, that correspond to flares of different energy, related?
C) How does the crust break?
a. Catastrophically or more gradually?
b. In which direction and over what volume?
c. Does the crust melt during a quake?
d. At what depth?
e. Which oscillation modes are excited and with what amplitudes?
f. What is the role of magnetic fields?
D) How do quakes change the properties of future quakes?

III] Composition of accreting star crust
A) What is the value of the impurity parameter Q=-^2 (dispersion in ion charge Z) and how does it vary with density?
B) Do we have an “impurity problem” where theoretical Q is too large to agree with limits from crust cooling observations?
a. Are limits robust?
b. If so, how might the impurity problem be solved? [During nucleosyn?, phase separation?, nuclear reactions?]
C) Does the composition relax to cold catalyzed matter soon after neutron drip? If so how much heat is released?

IV] Pasta
A) How do we “smell the pasta”? What observables demonstrate the presence of pasta? [I think this is hard]
B) How does the microphysics change in going from crust to pasta to core? Does it change abruptly, or is there a more smooth transition?
C) How does pasta change the shear modulus, shear mode frequencies, and breaking strain?
D) Is there large damping of collective modes at the crust / core interface, or is the damping muted by the pasta?

Welcome!

Welcome to the blog for "Defining the Neutron Star Crust: X-ray Bursts, Superbursts and Giant Flares", a conference sponsored by Los Alamos National Observatory, the Joint Institute for Nuclear Astrophysics, and the CompStar collaboration, to be held in Santa Fe, New Mexico May 18-21 2009.

In the run-up to the meeting, we'll be introducing your intrepid bloggers, who will be posting brief summaries of the talks as they happen, giving you an insider's ear to the discussions around the conference room, and a view outside to what is going on around Santa Fe. We'll also be posting any last-minute or additional information for those who are traveling to the conference. Postings will have comments sections, and we hope to hear from those who are physically present with us in Santa Fe, and those who are following the proceedings from a distance.

We're looking forward to see you.