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Your search keyword '"Ona Wilhelmi, E"' showing total 3 results
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3 results on '"Ona Wilhelmi, E"'

1. Unveiling the Magnetic Structure of VHE SNRs/PWNe with XIPE, the X-ray Imaging-Polarimetry Explorer.

Author

de Ona Wilhelmi, E., Vink, J., Bykov, A., Zanin, R., Bucciantini, N., Amato, E., Bandiera, R., Olmi, B., and Uvarov, Yu.

Subjects
*X-ray imaging, *POLARIMETRY, *MAGNETIC structure, *PULSARS, *NEBULAE
Abstract

The dynamics, energetics and evolution of pulsar wind nebulae (PWNe) and supernova remnants (SNRs), are strongly affected by their magnetic field strength and distribution. They are usually strong, extended, sources of non-thermal X-ray radiation, producing intrinsically polarised radiation. The energetic wind around pulsars produces a highly-magnetised, structured flow, often displaying a jet and a torus and different features (i.e. wisps, knots). This magnetic-dominant wind evolves as it moves away from the pulsar magnetosphere to the surrounding large-scale nebula, becoming kinetic-dominant. Basic aspects such how this conversion is produced, or how the jets and torus are formed, as well as the level of turbulence in the nebula are still unknown. Likewise, the processes ruling the acceleration of particles in shell-like SNRs up to 1015 eV, including the amplification of the magnetic field, are not clear yet. Imaging polarimetry in this regard is crucial to localise the regions of shock acceleration and to measure the strength and the orientation of the magnetic field at these emission sites. X-ray polarimetry with the X-ray Imaging Polarimetry Explorer (XIPE) will allow the understanding of the magnetic field structure and intensity on different regions in SNRs and PWNe, helping to unveil long-standing questions such as i.e. acceleration of cosmic rays in SNRs or magnetic-to-kinetic energy transfer. SNRs and PWNe also represent the largest population of Galactic very-high energy gamma-ray sources, therefore the study of their magnetic distribution with XIPE will provide fundamental ingredients on the investigation of those sources at very high energies. We will discuss the physics case related to SNRs and PWNe and the expectations of the XIPE observations of some of the most prominent SNRs and PWNe. [ABSTRACT FROM AUTHOR]

Published
2017
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2. Deep observation of the giant radio lobes of Centaurus A with the Fermi Large Area Telescope.

Author

Yang, R.-Z., Sahakyan, N., De Ona Wilhelmi, E., Aharonian, F., and Rieger, F.

Subjects
*ASTRONOMICAL observations, *SPECTRAL energy distribution, *CENTAURUS (Constellation), *RADIO sources (Astronomy), *RADIO galaxies, *ASTROPHYSICS
Abstract

The detection of high-energy (HE) γ-ray emission up to ∼3 GeV from the giant lobes of the radio galaxy Centaurus A has been recently reported by the Fermi-LAT Collaboration based on ten months of all-sky survey observations. A data set more than three times larger is used here to study the morphology and photon spectrum of the lobes with higher statistics. The larger data set results in the detection of HE γ-ray emission (up to ∼6 Gev) from the lobes with a significance of more than 10 and 20σ for the north and the south lobe, respectively. Based on a detailed spatial analysis and comparison with the associated radio lobes, we report evidence for a substantial extension of the HE γ-ray emission beyond the WMAP radio image for the northern lobe of Cen A. We reconstructed the spectral energy distribution (SED) of the lobes using radio (WMAP) and Fermi-LAT data from the same integration region. The implications are discussed in the context of hadronic and time-dependent leptonic scenarios. [ABSTRACT FROM AUTHOR]

Published
2012
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3. Multiwavelength observations of the transitional millisecond pulsar binary XSS J12270-4859.

Author

de Martino, D., Papitto, A., Belloni, T., Burgay, M., De Ona Wilhelmi, E., Li, J., Pellizzoni, A., Possenti, A., Rea, N., and Torres, D. F.

Subjects
*PULSARS, *ASTRONOMICAL observations, *WAVELENGTHS, *NEUTRON stars, *ACCRETION (Astrophysics)
Abstract

We present an analysis of X-ray, ultraviolet and optical/near-IR photometric data of the transitional millisecond pulsar binary XSS J12270-4859, obtained at different epochs after the transition to a rotation-powered radio pulsar state. The observations, while confirming the large-amplitude orbital modulation found in previous studies after the state change, also reveal an energy dependence of the amplitudes as well as variations on time-scale of months. The amplitude variations are anticorrelated in the X-ray and the UV/optical bands. The average X-ray spectrum is described by a power law with Γ index of 1.07(8) without requiring an additional thermal component. The power-law index Γ varies from ~1.2 to ~1.0 between superior and inferior conjunction of the neutron star.We interpret the observed X-ray behaviour in terms of synchrotron radiation emitted in an extended intrabinary shock, located between the pulsar and the donor star, which is eclipsed due to the companion orbital motion. The G5-type donor dominates the UV/optical and near-IR emission and is similarly found to be heated up to ~6500 K as in the disc state. The analysis of optical light curves gives a binary inclination 46 ≲ i ≲ 65 and a mass ratio 0.11 ≲ q ≲ 0.26. The donor mass is found to be 0.15 ≲ M² ≲ 0.36M๏ for a neutron star mass of 1.4 M๏. The variations in the amplitude of the orbital modulation are interpreted in terms of small changes in the mass-flow rate from the donor star. The spectral energy distribution from radio to gamma-rays is composed by multiple contributions that are different from those observed during the accretion-powered state. [ABSTRACT FROM AUTHOR]

Published
2015
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