Benjamin Owen: How LIGO can follow up high-energy observations of young neutron stars

Ben discussed LIGO's attempts to do searches for gravitational wave emission from isolated spinning neutron stars, where the position is known but where you have to search over an unknown spin frequency. The poster child source for this type of search is Cas A. LIGO are interested in targeting (a) isolated non-pulsing neutron stars (like some of the CCOs), (b) as yet unseen neutron stars in pulsar wind nebulae/small supernova remnants, (c) massive star-forming regions in which a lot of neutron stars might be born, and (d) globular cluster cores. He also advertised the upcoming LIGO/Neutron Star astronomer meeting to be held in January 2009.

George Pavlov: Central Compact Objects in Supernova Remnants

George reviewed the status of observations of Compact Central Objects (CCOs) - radio and gamma-ray quiet X-ray sources that are found close to the center of supernova remnants. Evidence is emerging that at least two of them are 'antimagnetars' (gamnetars?) - neutron stars that are born spinning slowly but with unusually low magnetic fields compared to most radio pulsars. The youngest of the CCOs (in the Cas A supernova remnant) seems to be different - and could well be a quiescent magnetar. Single temperature blackbody spectral fits for this object suggest a very small radius (which might imply that it is a quark star). More complex spectral fits involving two components with different temperatures, however, can give an acceptable fit to a neutron star equation of state. Ultimately phase-coherent timing analysis (with XMM/Chandra), and the detection and modeling of spectral lines, are the best way to figure out the nature of these objects.

Roberto Turolla: "Surface emission from isolated neutron stars"

Roberto Turolla discussed the various exciting prospects, as well as the complications, in theoretically understanding the surface emission from isolated neutron stars. Whether these have an atmosphere or not is crucial for understanding their emission, but remains unknown.
One would expect there to be an atmosphere, but then why do we see a BB in the X-rays? The seven XDINSs, also known as the "magnificent seven" are still radio quiet (see results/poster by Joshi et al.). Finding more sources is crucial.

David Kaplan: "Optical/IR/UV Observations of Isolated Neutron Stars"

David nicely showed how optical/IR/UV observations are providing unique information about neutron star spectral energy distributions and energetics. These objects are hard to observe (B magnitudes of 25-28), but this is still very worthwhile. So far, 6 isolated neutron stars have optical counterparts. Optical/IR/UV have in fact given very strong evidence that INSs are indeed neutron stars. A major outstanding issue is the "optical excess" (X-ray determined blackbody does not fit well at longer wavelengths). Also, it is still unknown whether the optical or UV is pulsed. Can we constrain atmospheric models using these multi-wavelength data?

Frank Haberl: X-ray observations of Isolated Neutron Stars

The author presented a global view of X-ray observations of neutrons stars and the possible information that one can deduce from them. Evidence of multicomponent Xray spectra and pulsation of the Xray flux are evidence for a non-uniform temperature on the surface of the neutron star. Three middle aged pulsars (The three musketeers) present two thermal components (from the surface and a hot spot) and a power-law component (most probably coming from the magnetosphere). Pulse phase spectroscopy from Chandra and XMM showed that the hot and the cold blackbody components are not in phase.

XMM observations of the 7 known isolated neutron stars showed that they do not have pure blackbody spectra, indicating absorption features (even multiple lines). Several origins for those lines were mentioned, e.g. Cyclotron resonance, atomic lines transitions (Hydrogen). Those isolated neutron stars also provide a unique ways of measuring their magnetic fields using 2 independent method (magnetic dipole breaking and proton cyclotron absorption). Observations of RX J0720.4-3125 put forward the evidence for precession of the neutron star and the evidence of 2 polar caps.

Finally, the author showed with cooling curves analysis the evidence of magnetic field decay. The main conclusion from this presentation is that a NS model with a uniform temperature and a dipolar magnetic field is far too simple.

Valery Suleimanov: Models of magnetized neutron stars atmospheres

New model atmospheres for high magnetic fields (>10^12 G) have been computed for fully ionized hydrogen and helium atmospheres, and for partially ionized hydrogen amospheres. It was found that the inclination of the magnetic field was unimportant, but that vacuum polarization significantly affected the spectra in the case of large fields (polarization is important because magnetic fields introduce angle and polarization dependence in the opacities). Most of the resulting spectra have absobtion features due to proton cyclotron lines.