J. Arons - Academia.edu (original) (raw)

Papers by J. Arons

arXiv (Cornell University), Sep 7, 1999

We report the discovery of kHz fluctuations, including quasi-periodic oscillations (QPO) at ∼ 330... more We report the discovery of kHz fluctuations, including quasi-periodic oscillations (QPO) at ∼ 330 Hz (260−407 Hz) and ∼ 760 Hz (671−849 Hz) and a broadband kHz continuum in the power density spectrum of the high mass X-ray binary pulsar Centaurus X-3 (Jernigan, Klein and Arons 1999). These observations of Cen X-3 were carried out with the Rossi X-ray Timing Explorer (RXTE). The fluctuation spectrum is flat from mHz to a few Hz, then steepens to f −2 behavior between a few Hz and ∼ 100 Hz. Above a hundred Hz, corrections for the observations of Cen X-3, we have also demonstrated that the black hole Cyg X-1 shows clear evidence of variability up to a frequency of ∼ 280 Hz. Also observations of GX 17+2 were used to validate the procedure for deadtime corrections. This analysis of GX 17+2 clearly indicates the presence of a kHz QPO and the absence of any significant simultaneous kHz continuum.

We report here the first polarimetric measurements of the pulsars in the J0737–3039 binary neutro... more We report here the first polarimetric measurements of the pulsars in the J0737–3039 binary neutron star system using the Green Bank Telescope. We conclude both that the primary star (pulsar A) has a wide hollow cone of emission, which is an expected characteristic of the relatively open magnetosphere given its short spin period, and that A has a small angle between its spin and magnetic dipole axes, 4 ± 3 degrees. This near alignment of axes suggests that A’s wind pressure on pulsar B’s magnetosphere will depend on orbital phase. This variable pressure is one mechanism for the variation of flux and profile shape of pulsar B with respect to the orbital phase that has been reported. The response of pulsar B to the A wind pressure will also depend on the particular side of its magnetosphere facing the wind at the spin phase when B is visible. This is a second possible mechanism for variability. We suggest that pulsar B may have its spin axis aligned with the orbital angular momentum ow...

Origin of Cosmic Rays, 1981

The Astrophysical Journal, 2001

The Astrophysical Journal, 2003

$Research paper thumbnail of Wave propagation in pulsar magnetospheres - Refraction of rays in the open flux zone$

The Astrophysical Journal, 1986

The Astrophysical Journal, 2008

We present recent relativistic MHD simulations of the interaction of a magnetized outflow produce... more We present recent relativistic MHD simulations of the interaction of a magnetized outflow produced by a proto-magnetar with a surrounding stellar envelope, in the first ˜ 10 seconds after core collapse. The wind blows inside a cavity created by the outgoing supernova shock. A strong toroidal magnetic field builds up in the wind bubble that is at first inertially confined by the progenitor star. This drives a jet out along the polar axis of the star, even though the star and the magnetar wind are each ``spherically symmetric''. The jet has the properties needed to produce a long-duration gamma-ray burst (GRB). At ˜ 5-10 s after core bounce, the jet has escaped the host star and the Lorentz factor of the material in the jet at large radii ˜ 1011 cm is similar to that in the magnetar wind near the source. Most of the spindown power of the central magnetar escapes via the relativistic jet.

One of the most intriguing results from the gamma-ray instruments in orbit has been the detection... more One of the most intriguing results from the gamma-ray instruments in orbit has been the detection of powerful flares from the Crab Nebula. These flares challenge our understanding of pulsar wind nebulae and models for particle acceleration. We report on the portion of a multiwavelength campaign using Keck, HST, and Chandra concentrating on a small emitting region, the Crab's inner knot, located a fraction of an arcsecond from the pulsar. We find that the knot's radial size, tangential size, peak flux, and the ratio of the flux to that of the pulsar are correlated with the projected distance of the knot from the pulsar. A new approach, using singular value decomposition for analyzing time series of images, was introduced yielding results consistent with the more traditional methods while some uncertainties were substantially reduced. We exploit the characterization of the knot to discuss constraints on standard shock-model parameters that may be inferred from our observations...

ABSTRACT We present results of time-dependent numerical modeling of the internal structure of the... more ABSTRACT We present results of time-dependent numerical modeling of the internal structure of the collisionless reverse shock terminating the pulsar wind in Crab Nebula. We treat the relativistic wind as composed of ions and electron-positron plasma embedded in a toroidal magnetic field, flowing radially outward from the pulsar in a sector around the rotational equator. Relativistic cyclotron instability of the ion ring downstream of the leading shock in the electron-positron pairs is found to launch outward propagating magnetosonic waves. Due to fresh supply of ions crossing the shock, this time-dependent process achieves a limit-cycle pattern, in which the waves are launched with periodicity on the order of the ion Larmor time. Compressions in magnetic field and pair density associated with these waves as well as their propagation speed reproduce the behavior of features observed in the wisps using the Hubble Space Telescope. By selecting the parameters of the ion orbit to fit the spatial separation of the wisps, we predict a period of time variablitiy that is consistent with the current undersampled data, and set constraints on the number and frequency of observations needed in a future observational campaign to quantitatively test the theory. Coupled with non-thermal acceleration of the pairs due to their absorption of the waves generated by the ion cyclotron instability, the compressions in the magnetic field and plasma density associated with the waves naturally account for the location and brightness of X-ray features in the Crab, in particular the recently discovered ``inner ring" observed by the Chandra X-ray Observatory. This work is supported by NASA ATP grant NAG5-3073 and NSF grant AST 9528271

Proceedings of The International Astronomical Union, 1981

A qualitative description is made of the specific mechanisms and general characteristics of pulsa... more A qualitative description is made of the specific mechanisms and general characteristics of pulsar magnetospheres, with specific details of progress toward the development of a slot gap model for the emission regions of a pulsar. Assumptions necessary for the delineation of boundary conditions for the polar current flow are defined, along with conditions which allow a quasi-steady state to exist in the corotating frame with electron inflow and plasma precipitation. The polar cap region is regarded as a flux tube with the plasma precipitating along the auroral field lines. A pair-production front bombards the polar caps and progressively starves the polar flux tube sector which bends toward the rotation axis, creating a slot gap which forms at a calculated height of 2 radii around the pair plasma. Further consideration is given to the emission of soft X rays from the polar caps and subpulse fluctuations, and a ratio is presented for use in correlation studies to measure the total ene...

Arxiv preprint astro-ph/ …, 2004

Abstract: We propose synchrotron absorption in a magnetosheath forming a cocoon around the magnet... more Abstract: We propose synchrotron absorption in a magnetosheath forming a cocoon around the magnetosphere of pulsar B to be the origin of the eclipse phenomena seen in the recently discovered double pulsar system PSRJ07370-3039 A & B. The model predicts ...

The Astrophysical Journal …, 1996

We describe time-dependent, two-dimensional axisymmetric radiation hydrodynamic calculations of l... more We describe time-dependent, two-dimensional axisymmetric radiation hydrodynamic calculations of locally super-Eddington accretion onto highly magnetized neutron stars appropriate to the flow onto the polar caps of high-luminosity X-ray pulsars. Our ...

The Astrophysical Journal, 1988