R-modes in Neutron Stars

arXiv:1012.4883 [pdf, other]

Title: Viscous damping of r-modes: Small amplitude instability

Authors: Mark Alford, Simin Mahmoodifar, Kai Schwenzer

arXiv:1012.4834 [pdf, other]

Title: Non-linear viscous saturation of r-modes

Authors: Marc Alford, Simin Mahmoodifar, Kai Schwenzer

Looking for Pulsars and Radio Transients

arXiv:1012.4695 [pdf, other]

Title: Blind surveys for radio pulsars and transients

Authors: D.R. Lorimer

Even More Cosmic Rays from Pulsars

arXiv:1012.4562 [pdf, ps, other]

Title: The knee in the cosmic ray energy spectrum: a pulsar/supernova origin?

Authors: Tadeusz Wibig, Arnold W. Wolfendale

Two-Solar-Mass Neutron Star

  arXiv:1012.3208 [pdf, ps, other]

Title: What a Two Solar Mass Neutron Star Really Means

Authors: James M. Lattimer, M. Prakash

ASKAP Pulsars

  arXiv:1012.3507 [pdf, ps, other]

Title: Pulsars with the Australian Square Kilometre Array Pathfinder

New Gamma-Ray Pulsar

arXiv:1012.2121 [pdf, ps, other]

Title: Discovery of an Energetic 38.5 ms Pulsar Powering the Gamma-ray Source IGR J18490-0000/HESS J1849-000

Making heavy neutron stars

arXiv:1012.1877 [pdf, ps, other]

Title: LMXB and IMXB Evolution: I. The Binary Radio Pulsar PSR J1614-2230

Where to Find Pulsar/Black Hole Binaries?

 arXiv:1012.0573 [pdf, other]

Title: Pulsar-Black Hole Binaries in the Galactic Center

Cas A Cooling Part Deux

  arXiv:1011.6142 [pdf, ps, other]

Title: Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter

Authors: Dany Page (1), Madappa Prakash (2), James M. Lattimer (3), Andrew W. Steiner (4

J1718-3718

 arXiv:1011.5697 [pdf, ps, other]

Title: Chandra Observations of the High-Magnetic-Field Radio Pulsar J1718-3718

Authors: W. W. Zhu, V. M. Kaspi, M. A. McLaughlin, G. G. Pavlov, C.-Y. Ng, R. N. Manchester, B. M. Gaensler, P. M. Woods

J1903+0327

arXiv:1011.5809 [pdf, ps, other]

Title: On the nature and evolution of the unique binary pulsar J1903+0327

Authors: P. C. C. Freire, C. G. Bassa, N. Wex, I. H. Stairs, D. J. Champion, S. M. Ransom, P. Lazarus, V. M. Kaspi, J. W. T. Hessels, M. Kramer, J. M. Cordes, J. P. W. Verbiest, P. Podsiadlowski, D.~J. Nice, J. S. Deneva, D. R. Lorimer, B. W. Stappers, M. A. McLaughlin, F. Camilo

Classifying the QPOs of Magnetars

Magnetars after their large flare exhibit quasi-periodic oscillations as they cool.  This paper looks at this modes in GR and includes the effects of the magnetic field with a realistic field geometry.   They find n=0 modes with low l at frequencies of around 10-50 Hz  and n=1 modes at 1 kHz.   The frequencies of course depend on the properties of the underlying star --- wow!

arXiv:1011.5406 [pdf, ps, other]

Title: Magneto-elastic torsional oscillations of magnetars

Authors: Michael Gabler, Pablo Cerdá-Durán, José A. Font, Ewald Müller, Nikolaos Stergioulas

A Bit Far-Fetched But Interesting

The key point is that spacecraft can accurately know the distance to Earth with radio ranging but they don't know their position well perpendicular to the Earth-spacecraft line, so by using x-ray pulsars they could do better.   Some other possibly more realistic ideas:  how about using brighter radio pulsars or other spacecraft.   Spacecraft often use other spacecraft to relay data back to Earth, the timing of the response should be sufficient to determine range if the other systematics could be ironed out.

arXiv:1011.5095 [pdf, ps, other]
Title: Timing X-ray Pulsars with Application to Spacecraft Navigation
Authors: Mike Georg Bernhardt, Tobias Prinz, Werner Becker, Ulrich Walter

Kozai and Compact Objects

This paper dovetails nicely with Yanquin Wu's talk here last week.  Quite a fun idea.

arXiv:1011.4322 [pdf, ps, other]

Title: Accelerating Compact Object Mergers in Triple Systems with the Kozai Resonance: A Mechanism for "Prompt'' Type Ia Supernovae, Gamma-Ray Bursts, and Other Exotica

Authors: Todd A. Thompson

What if you could watch the universe change?

The authors propose an experiment where you actually measure the redshifts of objects changing with time (almost achievable now) and how the CMD changes with time (more fantastical).

 arXiv:1011.2646 [pdf, ps, other] Real-time Cosmology

Claudia Quercellini, Luca Amendola, Amedeo Balbi, Paolo Cabella, Miguel Quartin

Three Generations

The actual argument for three generations is a bit weak; however, this paper is definitely an interesting read with a quick history of the need for three generations to explain the experiments in the sixties and to account for baryogenesis.   As for why not more than three, is it just too unlikely.

 arXiv:1011.2761 (cross-list from hep-ph) [pdf, ps, other]

Anthropic Argument for Three Generations

Andrew Gould

Is the universe isotropic?

I reckoned that it is a good idea to check this out.  Ralston outlines how to quantify the anisotropy of various observations and of course finds it.   The quantification and potential observations are useful, the finding it is a lot harder to believe.

arXiv:1011.2240 [pdf, ps, other] Question Isotropy John P. Ralston

The Chameleon and the Giant

A Chameleon scalar field in scalar-tensor gravity is a field that modifies the strength of gravity at low densities and large length scales.  It disappears below a thin layer of high density material, so it would affect the structure of most stars.   However, the outer layers of giant stars especially supergiants like Betelgeuse are essentially hot vacuums, so the chameleon would not be fully shielded here and would change the structure of these stars.

arXiv:1011.4107 [pdf, ps, other]

Stellar Structure and Tests of Modified Gravity

Philip Chang, Lam Hui

Neutron-Star Optics

Researchers have generally assumed that the spacetime surrounding a neutron star is well approximated by Schwarschild or Kerr to calculate ray tracing because of the high degree of symmetry of these spacetimes.  Psaltis and Jonahannsen present a new algorithm that goes beyond these toy models and use a metric with an arbitrary quadrupole moment.  This requires integrating 2nd-order ODES (rather than the 1st-order in the case of Kerr).  They outline some systems where this technique provides potentially important diagnostics.

 arXiv:1011.4078 [pdf, ps, other]

A Ray-Tracing Algorithm for Spinning Compact Object Spacetimes with Arbitrary Quadrupole Moments. I. Quasi-Kerr Black Holes

Dimitrios Psaltis, Tim Johannsen (Arizona)

Modelling MSXP Disk

The authors present a model of a radiation pressure dominated accretion disk around a millisecond x-ray pulsar including the interaction of the stellar magnetic field with the disk.

[277]  arXiv:1011.2621 [pdf, ps, other]

Thin accretion discs around millisecond X-ray pulsars

Solomon Belay Tessema, Ulf Torkelsson

Mount Ararat

Two astronomer-mountainers obtained permission to climb Mt Ararat in 2004.  They took a rarely travelled route and discovered a much of interesting things including a possible meteor crater and an ancient fortress.

 arXiv:1011.3715 [pdf] A meteorite crater on Mt. Ararat? V.G.Gurzadyan, S.Aarseth

Fermionic Molecular Dynamics

The authors present a technique better to account for the antisymmetry of fermionic wavefunctions in molecular dynamic simulations.

arXiv:1011.2928 (cross-list from nucl-th) [pdf, other] Title: Towards a quantal dynamical simulation of the neutron-star crust Authors: Klaas Vantournhout, Thomas Neff, Hans Feldmeier, Natalie Jachowicz,Jan Ryckebusch

SGR Bursts from Kes 73

Yet another AXP is found to emit gamma-ray bursts further cementing the common heritage of AXPs and SGRs.

 arXiv:1011.3537 [pdf, ps, other] Title: SWIFT study of the first SGR-like burst from AXP 1E 1841-045 in SNR Kes 73

Faraday Rotation

Whenever I see papers about asymmetries in Faraday rotation or other polarization stuff, I am reminded of a bunch of wacky papers from about five to ten years ago about quasar polarizations. This paper on the other hand argues that the observed Faraday rotation correlations come not from extra physics nor the Galactic magnetic field but from a nearby bubble of HI about 100 pc away toward the Galactic center. The bubble supposedly has compressed the magnetic field on either side of it, increasing its strength and therefore the Faraday rotation. These observations were performed at DRAO in Penticton in the beautiful Okanagan valley of BC.

arXiv:1011.0341 [pdf, ps, other]

Title: Antisymmetry in the Faraday Rotation Sky Caused by a Nearby Magnetized Bubble Authors: M. Wolleben, A. Fletcher, T. L. Landecker, E. Carretti, J. M. Dickey, B. M. Gaensler, M. Haverkorn, N. McClure-Griffiths, W. Reich, A. R. Taylor Comments: Published in Astrophysical Journal Letters 724 (2010) L48-L52 Subjects: Galaxy Astrophysics (astro-ph.GA)

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

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?

A Stable Analytic Magnetic Equilibrium

Duez et al. have verified that they can generate stable, non-force-free, equilibria for regions of stars. It is well known that purely poloidal or toroidal fields are unstable; however, mixed states are generally difficult to express analytically. Duez et al. generate a self-consistent mixed state and verify that it is stable. Such states will provide useful realistic models for stellar magnetic fields.

http://arxiv.org/abs/1009.5384 On the Stability of Non Force-Free Magnetic Equilibria in Stars

Black-Hole Inspiral Resonances

Flanagan and Hinderer have discovered a resonance phenomenon that ruins the adiabatic evolution of inspiral orbits around Kerr blackholes.   Orbits around Kerr black holes are characterized by a polar and azimuthal frequency, generally these two frequencies are not comeasureable.    This allows one to assume that the orbit completely fills the surface of a torus around the black hole, so one can average the various dissipative terms that cause the inspiral and accurately calculate the gravitational waveform.  However, when these two frequencies near the ratio of two small integers, this ergodic assumption fails and so does the averaging.   If the ratio is of two large integers, the duration of non-ergodicity is short so little phase error accumulates; however, for small integers the error in phase is of order unity.

http://arxiv.org/abs/1009.4923 Transient resonances in the inspirals of point particles into black holes

A Heavyweight Pulsar! Oh No, Maybe not!

The Black Widow millisecond pulsar is slowly vaporizing its companion star.  Van Kerkwijk obtained spectra of the companion and measured how much its velocity changes during its orbit about 325 km/s.  Because the star is illuminated by the pulsar the centre of light is closer to the centre of mass of the system than the centre of mass of the star does.  With atmospheric modelling and modelling the light curve, the authors address this issue and the question of the orbital inclination, yielding a really heavy pulsar at 2.4 +/- 0.1 solar masses.  Unfortunately once they account for the various systematic errors they get a quite modest and svelte neutron star whose mass is likely to be greater than 1.66 solar masses.  The observations are exquisite; unfortunately the models are not yet up to providing strong constraints.

http://arxiv.org/abs/1009.5427 Evidence for a Massive Neutron Star from a Radial-Velocity Study of the Companion to the Black Widow Pulsar PSR B1957+20

The Millisecond Pulsar Unveiling

Millisecond pulsars are believed to be form in binary systems comprised of a low-mass star and a neutron star, an LMXB.   As matter flows from the low-mass star onto the neutron star through an accretion disk, angular momentum flows as well.   Millisecond radio pulsars are especially common in globular clusters where such LMXBs are also common and the number of LMXBs in such systems agreed well with the numbers of millisecond pulsars in globular clusters and elsewhere.  Finally, several accreting neutron stars have been discovered with millisecond spin periods.   A final piece in the puzzle was the discovery of radio pulsations from PSR J102347.67+003841.2 in 2007.   This object spends sometime as an accreting neutron star from observations as late as 2000 and 2001 (from x-ray and optical measurement), and by 2007 the accretion disk had all but disappeared.   The first paper outlines a mechanism where gamma-rays produced near the light cylinder of the millisecond pulsar are sufficient to ablate the accretion disk entirely within such a short time.  The second paper provides a recent observational update on this really cool pulsar.

http://arxiv.org/abs/1009.4781 On the Transition from Accretion Powered to Rotation Powered Millisecond Pulsars

http://arxiv.org/abs/1008.1068 X-ray Variability and Evidence for Pulsations from the Unique Radio Pulsar/X-ray Binary Transition Object FIRST J102347.6+003841

The Fermi Pulsar Revolution

Arguably the most exciting result from the Fermi mission is the discovery of gamma-ray emission from many neutron stars.   A class of seven has grown to number nearly fifty in the first Fermi pulsar catalogue.  A large fraction of these objects are radio quiet and only a few lie in supernova remnants, so the identity of these objects would have remained unknown if it weren't for the outstanding sensitivity of Fermi and the development of blind search algorithms for the gamma-ray telescope.  Check out the following articles for more:

http://arxiv.org/abs/1009.2421 Fermi pulsar revolution by Patrizia A. Caraveo

http://arxiv.org/abs/1007.2183 Pulsar Results with the Fermi Large Area Telescope by Paul S. Ray, Pablo M. Saz Parkinson

http://arxiv.org/abs/1007.1381 New Neighbours: Modelling the Growing Population of Gamma-ray Millisecond Pulsars by C. Venter, A.K. Harding, T.J. Johnson