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

More Cosmic Rays from Pulsars

Here is yet another paper looking at how cosmic rays (especially leptons) are generated by pulsars. It seems more and more particle physicists are abandoning or at least reconsidering the contrived dark matter models.

arXiv:1010.4200 [pdf, ps, other] Title: Cosmic rays of leptons from Pulsars and Supernova Remnants

Pulsar Timing

Cordes and former UBC undergraduate Ryan Shannon present an error budget for high-precision pulsar timing.  It provides a roadmap for achieving the highest possible precision for pulsar timing through the mitigation of pulsar jitter and interstellar propagation and a careful selection of sources.

arXiv:1010.3785 [pdf, ps, other]  A Measurement Model for Precision Pulsar Timing

Old Cool White Dwarfs

Chen and Hansen argued that the presence of convection complicates the cooling of old WDs with thin layers on hydrogen on their surfaces.   As the white dwarf ages the convective zone grows downward and mixes helium into the photosphere, turning a DA white dwarf into a DB white dwarf.

arXiv:1010.3376 [pdf, ps, other] Title: Old White Dwarf Stars with Some Hydrogen -- Cooling Curves

Gamma-Ray Bursts

Ghisellini gives a great review of what we known about gamma-ray bursts and the puzzles that remain.  He presents the seven pillars of GRB knowledge: GRBs are cosmological, GRBs have relativistic bulk motion, two phases (prompt and afterglow emission), long and short GRBs, spikes have same duration, supernova connection and peak energy.  He also presents some puzzles: the engine, role of magnetic fields,  what makes prompt emission, correlation between SEDs and other features and the high energy emission.

arXiv:1010.3015 [pdf, ps, other] Title: Gamma Ray Bursts: basic facts and ideas

A Low-Magnetic-Field SGR

Rea et al. present the discovery of an SGR with a weak dipole field.  This object emits bursts, has a strong persistent x-ray emission (i.e. it is hot) and exhibits pulsed profile changes -- it acts like a magnetar.   The discovery points out what has been known unconsciously for a long time that the location of a pulsar on the P-Pdot diagram has little to do with its surface and internal fields.   Rea et al. argue that this could mean that any pulsar could turn into a magnetar whenever.  I think that this is a bit of a reach because we also think that magnetars are typically young as demonstrated by their association with supernova remnants and OB associations. Pretty Neat!

arXiv:1010.2781 [pdf, other] Title: A low-magnetic-field Soft Gamma Repeater

A Neat Idea

Could some of the apparent dwarf galaxies orbiting the Milky Way actually be just optical illusions effectively where the projected density of stars diverges?

arXiv:1010.2502 [pdf, ps, other] Are the Ultra-Faint Dwarf Galaxies Just Cusps?

Strongly Magnetized White Dwarfs

Nordhaus et al. present an interesting model in which the accretion and disruption of a binary companion results in a strongly magnetized white dwarf. The key idea is that the evolved red giant can rapidly accreting the companion during a common envelope phase. As the companion is disrupted and forms an accretion disk, a strong magnetic field is generated by the differential rotation of the disk. They argue that it could also happen for magnetars!

arXiv:1010.1529 [pdf, other] Title: The formation of high-field magnetic white dwarfs from common envelopes

Sorry it has been a quiet week!

Cas A cooling

The authors survey the various cooling neutron stars that have been observed including that in Cas-A and compare them with a variety of models to constrain the neutron stars within!

arXiv:1010.1154 [pdf, ps, other] Title: Cooling rates of neutron stars and the young neutron star in the Cassiopeia A supernova remnant

Ambipolar diffusion

Ambipolar diffusion is often invoked in magnetars to account for the energy released by these objects.  Ambipolar diffusion abets the delay of the strong magnetic field within the star whose energy can then power the quiescent and burst emission.   The authors argue that ambipolar diffusion is strongly depressed by superfluidity.  The typical ambipolar diffusion is non-solenoidal.  This means that the density of the material changes as the field evolves; therefore, weak reactions occur to reestablish the equilibria.  These weak reactions are suppressed by superconductivity because pairs must be broken and reformed to convert protons to neutron and vice versa.

arXiv:1010.1153 [pdf, ps, other]
Title: Ambipolar diffusion in superfluid neutron stars

Understanding the RRATs

The high magnetic field pulsar PSR J1119-6127 shows a double-pulse profiles and RRAT-like emission after glitches.  Otherwise, it looks like a normal pulsar.  The RRAT-like emission appears as single pulses outside of the main pulse.  Also the RRAT-like pulses move around in phase so these strong pulses don't show periodicity over the short integration span.

arXiv:1010.0857 [pdf, ps, other]

Title: The glitch-induced identity changes of PSR J1119-6127

How Do Pulsars Get Their Kicks?

Nordhaus et al. perform numerical calculations in which the neutron star forms a couple of kilometers away from the center of the star.   They also have to augment the neutrino luminosity to successfully drive the supernova.   With the proto neutron star off-center, the neutron star naturally gets a velocity kick of 150 km/s and growing at 350 km/s/s by the end of simulation.    It is nice that one's intuition and more rudimentary numerical models are verified by this thorough calculation.

arXiv:1010.0674 [pdf, other]

Title: Theoretical Support for the Hydrodynamic Mechanism of Pulsar Kicks


arXiv:1010.0167
Hydrodynamical Neutron Star Kicks in Three Dimensions

Quantum Vacuum Friction

Dupays et al. have argued in many papers that the magnetization of the vacuum surrounding a neutron star and cause it to spin down more quickly than magnetic dipole emission especially for long spin periods.  The gist of this paper is to argue that the objects that we inferred are magnetars from their values of P and P-dot are actually older analogues to regular radio pulsars but with longer periods of QVF dominates the spin down.   It is a cute argument but it does not address the strange behaviour of the objects that we call magnetars.  This behaviour provides additional support for the magnetar model because the strong B-fields can account for it.   The whole quantum vacuum friction idea seems a bit dodgy too, but I cannot succinctly  explain what is wrong with it.


http://arxiv.org/abs/1010.0597 Quantum Vacuum influence on the evolution of Pulsars

Making pulsars and magnetars

Popov et al. outline the most comprehensive simulations of the production of neutron stars as a function of magnetic field, so far.  They include field decay, accretion, spin evolution and other effects to account for the Log N-Log S relation of pulsars as well as the Log N-Log L relation for magnetars.   I look forward to see an more thorough description of their results than this conference proceeeding.

http://www.arxiv.org/abs/1009.5888 Extensive population synthesis of isolated neutron stars with field decay

Two Bangs for Your Supernova

If the transition to quark matter from neutron matter is strongly first order, a forming quark star will emit to neutrino blasts, one from the newborn neutron star and one from the subsequently formed quark star.  The author argue that the pair of neutrino bursts will be observable with today's neutrino telescopes.
http://arxiv.org/abs/1009.6096 Can a supernova bang twice?