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!