Supernova Progenitors

As of 2010 over thirty core-collapse SN progenitors have been identified. What do they look like? Generally they are all massive stars (a plus for SN theory); furthermore Type II-P supernova typically have progenitors that are red supergiants at the low-mass end. The question is whether all massive stars result in SN. Kochanek has suggested we look for massive stars vanishing from nearby galaxies. This might be quite feasible and interesting.

arXiv:1011.0203 [pdf, ps, other]

Title: On the Progenitors of Core-Collapse Supernovae Authors: Douglas C. Leonard (San Diego State University) Comments: 7 Pages, invited review accepted for publication by Astrophysics and Space Science (special HEDLA 2010 issue) Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Cosmology and Extragalactic Astrophysics (astro-ph.CO)

No Gamma-Rays from Magnetars

Fermi has looked for gamma-rays from magnetars from 100 MeV to 10 GeV and found none.  This eliminates (or makes things really difficult) for some models of the hard x-ray emission from magnetars such as mine ( http://lanl.arxiv.org/pdf/astro-ph/0502349 ).  Nothing ventured, nothing gained.

arXiv:1011.0091 [pdf, other]

Title: Search for gamma-ray emission from magnetars with the Fermi Large Area Telescope Authors: The Fermi-LAT collaboration Comments: ApJ Letters in press; Corresponding authors: Caliandro G. A., Hadasch D., Rea N., Burnett T Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Galaxy Astrophysics (astro-ph.GA)

Massive Neutron Stars

The Shapiro delay for PSR J1614-2230 indicates that it is the most massive neutron star yet.   The result appears more robust than the last most massive neutron star.  If it is indeed just under two solar mass, this has lots of consequences for the neutron star equation of state.   If in the future additional relativistic effects are measured, this tantalizing result may become even more robust (or go away).

arXiv:1010.5788 [pdf, ps, other] Title: Shapiro delay measurement of a two solar mass neutron star

arXiv:1010.5790 [pdf, ps, other] Title: The Massive Pulsar PSR J1614-2230: Linking Quantum Chromodynamics, Gamma-ray Bursts, and Gravitational Wave Astronomy

Black-Hole Evaporation and BH-NS Binaries

One of the motivations of having larger extra dimensions is to solve the hierarchy problem on physics.  In particular to answer the question of why is gravity so much weaker than the other forces.    The extra dimensions solve this problem by saving that gravity inherently just as strong as the other forces but it leaks into the extra dimensions reducing its efficacy on scales larger than the extra dimensions.    This is either the physical size of the extra dimension (in a Kaluza-Klein picture) or the scale of the warping of the extra dimension in a Randall-Sundrum. picture.  The authors argue that one consequence of this it is that black holes would evaporate much more quickly in this scenario.   As the black hole in a binary loses mass, the size of the binary orbit must increase with the orbital period.  On the other hand, the emission of gravitational radiation causes the orbital period to decrease.   The measurement of the period change in such a system could tell whether evaporation or radiation dominates.

One concern that I have with paper is that they apparently assume that the mass loss is isotropic, so the angular momentum of the system is conserved; however, I think that in reality the mass lost from the black hole will carry the specific angular momentum of the black hole.  This might be what they mean by isotropic, but since they don't derive the change in orbital parameters I'm not sure.    I don't think that this is a major issue because the product of the total mass and the semi-major axis is an adiabatic invariant, so as the total mass decreases, the semi-major axis and the period must increase.  This may change some of the details but not the general conclusions.

arXiv:1010.5245 [pdf, ps, other] Title: A Precision Test for an Extra Spatial Dimension Using Black Hole--Pulsar Binaries

Pulsar Masses

Zhang et al summarize the measurements of neutron-star masses and make inferences from the distribution of millisecond and regular pulsar masses about the formation of millisecond pulsars.  The average mass of the pulsar population has grown since 1999, and the mean mass of fast MSPs is larger than slower ones.    Double neutron-star binaries typically have even lower masses.  However, none of these conclusions are particularly significant in the statistical sense.  On the other hand, the observed masses of MSPs argue that the formation of millisecond pulsars through the accretion-induced collapse of white dwarfs is unlikely because most of the MSPs have masses that exceed the Chandrasekhar limit for white dwarfs.

arXiv:1010.5429 [pdf, ps, other] Title: Study of measured pulsar masses and their possible conclusions

Timing Noise

Shannon and Cordes examine timing noise for millisecond, canonical and magnetar pulsars. They find that the magnetars have an excess of timing noise relative to a model that accounts for the other pulsars. They argue that the timing noise does affect millisecond pulsars although not yet at a detectable level for most of these objects. However, it will affect the construction of PTAs by requiring a larger array of pulsars to reach a given level of sensitivity.

arXiv:1010.4794 [pdf, ps, other] Title: Assessing the Role of Spin Noise in the Precision Timing of Millisecond Pulsars

Deep Underground Astrophysics

This is a neat experiment that up to now I was not familiar.  They measure various astrophysically important reactions at the energies within stars.   Of course the reaction rates are terribly small (otherwise stars wouldn't last very long, would they), so the experiments are performed deep underground in the Gran Sasso tunnel in central Italy to reduce background contamination.

arXiv:1010.4165 (cross-list from nucl-ex) [pdf, ps, other] Title: LUNA: Nuclear Astrophysics Deep Underground