An Outer Gap Model of High-Energy Emission from Rotation-Powered Pulsars

We describe a refined calculation of high energy emission from rotation-powered pulsars based on the Outer Gap model of Cheng, Ho \&~Ruderman (1986a,b). We have improved upon previous efforts to model the spectra from these pulsars (e. g. Cheng, et al. 1986b; Ho 1989) by following the variation in particle production and radiation properties with position in the outer gap. Curvature, synchrotron and inverse-Compton scattering fluxes vary significantly over the gap and their interactions {\it via} photon-photon pair production build up the radiating charge populations at varying rates. We have also incorporated an approximate treatment of the transport of particle and photon fluxes between gap emission zones. These effects, along with improved computations of the particle and photon distributions, provide very important modifications of the model gamma-ray flux. In particular, we attempt to make specific predictions of pulse profile shapes and spectral variations as a function of pulse phase and suggest further extensions to the model which may provide accurate computations of the observed high energy emissions.Comment: 13 pages, LaTeX, for figures send request to [email protected]

Echelle Spectroscopy of gamma-ray binary 1FGL J1018.6-5856

We observed the Fermi-discovered gamma-ray binary 1FGL J1018.6-5856 at 20 epochs over 50 days using the CHIRON spectrograph, obtaining spectra at R~25,000 covering 4090-8908A. The average spectrum confirms an O6 V((f)) spectral type and extinction E(B-V) = 1.35+/-0.04. Variable absorption line equivalent widths suggest substantial contamination by wind line features. The limited S/N ratio hindered accurate continuum definition and prevented measurement of a high quality radial velocity curve. Nevertheless, the best data indicate a radial velocity amplitude <40 km/s for the He II lines and substantially lower for H I. We argue that this indicates a most likely compact object mass <2.2Msun. While black hole solutions are not excluded, a neutron star source of the gamma-ray emission seems preferred.Comment: 5 figures. To appear in the Astrophysical Journa

On the X-ray feature associated with the Guitar Nebula

Context: A mysterious X-ray nebula, showing a remarkably linear geometry, was recently discovered close to the Guitar Nebula, the bow-shock nebula associated with B2224+65, which is the fastest pulsar known. The nature of this X-ray feature is unknown, and even its association with pulsar B2224+65 is unclear. Aims: We attempt to develop a self-consistent scenario to explain the complex phenomenology of this object. Methods: We assume that the highest energy electrons accelerated at the termination shock escape from the bow shock and diffuse into the ambient medium, where they emit synchrotron X-rays. The linear geometry should reflect the plane-parallel geometry of its ambient field. Results: We estimate the Lorentz factor of the X-ray emitting electrons and the strength of the magnetic field. The former (~10^8) is close to its maximum possible value, while the latter, at ~45 uG, is higher than typical interstellar values and must have been amplified in some way. The magnetic field must also be turbulent to some degree to trap the electrons sufficiently for synchrotron X-ray emission to occur effectively. We propose a self-consistent scenario in which, by some streaming instability, the electrons themselves generate a turbulent field in which they then diffuse. Some numerical coincidences are explained, and tests are proposed to verify our scenario. Conclusions: Electron leaking may be common in the majority of pulsar bow-shock nebulae, even though the X-ray nebulosity in general is too diffuse to be detectable.Comment: 4 pages. Accepted for publication in A&A, Letters to the Edito

Pequeno manual para escrita de artigos científicos: estrutura textual, dicas e compêndio gramatical.

Introdução. Estrutura textual. Recursos linguísticos. Tópicos gramaticais. relação autor-leitor. Refacção textual.bitstream/CNPTIA/11545/1/doc68.pdfAcesso em: 29 fev. 2008

First Astronomical Application of a Cryogenic TES Spectrophotometer

We report on the first astronomical observations with a photon counting pixel detector that provides arrival time- (delta t = 100ns) and energy- (delta E_gamma < 0.15eV) resolved measurements from the near IR through the near UV. Our test observations were performed by coupling this Transition Edge Sensor (TES) device to a 0.6m telescope; we have obtained the first simultaneous optical near-IR phase-resolved spectra of the Crab pulsar. A varying infrared turnover gives evidence of self-absorption in the pulsar plasma. The potential of such detectors in imaging arrays from a space platform are briefly described.Comment: 4 pages, 5 figure

Agritempo: manual do usuário.

Descrição do sistema. Serviços e produtos disponíveis. Funções do sistema passo-a-passo-produtos. Produtos disponíveis apenas para alguns estados.bitstream/CNPTIA/11984/1/doc73.pd