84 research outputs found
Resonant Compton Upscattering in High Field Neutron Stars
The extremely efficient process of resonant Compton upscattering by
relativistic electrons in high magnetic fields is believed to be a leading
emission mechanism of high field pulsars and magnetars in the production of
intense X-ray radiation. New analytic developments for the Compton scattering
cross section using Sokolov & Ternov (S&T) states with spin-dependent resonant
widths are presented. These new results display significant numerical
departures from both the traditional cross section using spin-averaged widths,
and also from the spin-dependent cross section that employs the Johnson &
Lippmann (J&L) basis states, thereby motivating the astrophysical deployment of
this updated resonant Compton formulation. Useful approximate analytic forms
for the cross section in the cyclotron resonance are developed for S&T basis
states. These calculations are applied to an inner magnetospheric model of the
hard X-ray spectral tails in magnetars, recently detected by RXTE and INTEGRAL.
Relativistic electrons cool rapidly near the stellar surface in the presence of
intense baths of thermal X-ray photons. We present resonant Compton cooling
rates for electrons, and the resulting photon spectra at various magnetospheric
locales, for magnetic fields above the quantum critical value. These
demonstrate how this scattering mechanism has the potential to produce the
characteristically flat spectral tails observed in magnetars.Comment: 2 pages, no figures, The proceedings from the Pulsar Conference:
Electromagnetic Radiation from Pulsars and Magnetars will be published in the
Astronomical Society of the Pacific Conference Serie
Constraining Relativistic Bow Shock Properties in Rotation-Powered Millisecond Pulsar Binaries
Multiwavelength followup of unidentified Fermi sources has vastly expanded
the number of known galactic-field "black widow" and "redback" millisecond
pulsar binaries. Focusing on their rotation-powered state, we interpret the
radio to X-ray phenomenology in a consistent framework. We advocate the
existence of two distinct modes differing in their intrabinary shock
orientation, distinguished by the phase-centering of the double-peaked X-ray
orbital modulation originating from mildly-relativistic Doppler boosting. By
constructing a geometric model for radio eclipses, we constrain the shock
geometry as functions of binary inclination and shock stand-off . We
develop synthetic X-ray synchrotron orbital light curves and explore the model
parameter space allowed by radio eclipse constraints applied on archetypal
systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the
stand-off is -- fraction of binary separation from the
companion center, depending on the orbit inclination. Constructed X-ray light
curves for B1957+20 using these values are qualitatively consistent with those
observed, and we find occultation of the shock by the companion as a minor
influence, demanding significant Doppler factors to yield double peaks. For
J1023+0038, radio eclipses imply while X-ray light curves
suggest (from the pulsar). Degeneracies in the
model parameter space encourage further development to include transport
considerations. Generically, the spatial variation along the shock of the
underlying electron power-law index should yield energy-dependence in the shape
of light curves motivating future X-ray phase-resolved spectroscopic studies to
probe the unknown physics of pulsar winds and relativistic shock acceleration
therein.Comment: Accepted to ApJ, 36 pages, 15 figures; comments welcom
Resonant Inverse Compton Scattering Spectra from Highly-magnetized Neutron Stars
Hard, non-thermal, persistent pulsed X-ray emission extending between 10 keV
and keV has been observed in nearly ten magnetars. For
inner-magnetospheric models of such emission, resonant inverse Compton
scattering of soft thermal photons by ultra-relativistic charges is the most
efficient production mechanism. We present angle-dependent upscattering spectra
and pulsed intensity maps for uncooled, relativistic electrons injected in
inner regions of magnetar magnetospheres, calculated using collisional
integrals over field loops. Our computations employ a new formulation of the
QED Compton scattering cross section in strong magnetic fields that is
physically correct for treating important spin-dependent effects in the
cyclotron resonance, thereby producing correct photon spectra. The spectral
cut-off energies are sensitive to the choices of observer viewing geometry,
electron Lorentz factor, and scattering kinematics. We find that electrons with
energies MeV will emit most of their radiation below 250 keV,
consistent with inferred turnovers for magnetar hard X-ray tails. More
energetic electrons still emit mostly below 1 MeV, except for viewing
perspectives sampling field line tangents. Pulse profiles may be singly- or
doubly-peaked dependent upon viewing geometry, emission locale, and observed
energy band. Magnetic pair production and photon splitting will attenuate
spectra to hard X-ray energies, suppressing signals in the Fermi-LAT band. The
resonant Compton spectra are strongly polarized, suggesting that hard X-ray
polarimetry instruments such as X-Calibur, or a future Compton telescope, can
prove central to constraining model geometry and physics.Comment: 43 pages, 12 figures; accepted for publication in ApJ; v3 fixes typos
and updates some reference
Standard supersymmetry from a Planck-scale statistical theory
We outline three new ideas in a program to obtain standard physics, including
standard supersymmetry, from a Planck-scale statistical theory: (1) The initial
spin 1/2 bosonic fields are transformed to spin 0 fields together with their
auxiliary fields. (2) Time is defined by the progression of 3-geometries, just
as originally proposed by DeWitt. (3) The initial (D-1)-dimensional "path
integral" is converted from Euclidean to Lorentzian form by transformation of
the fields in the integrand.Comment: 8 pages, to be published in the proceedings of DARK2007, Sixth
International Heidelberg Conference on Dark Matter (Sydney, Australia,
September 24-28, 2007
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