"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
Wednesday, May 20, 2009
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 |
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.
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.
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.
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.
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.
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!
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.
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.
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