The diffuse soft X-ray sky

Tanaka, Yasuo; Bleeker, J. A. M.

doi:10.1007/bf02431836

Cited by 82 publications

(31 citation statements)

References 89 publications

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“…Galactic emissions from a thermal plasma within the Local Hot Bubble (e.g., Tanaka and Bleeker 1977;Sanders et al 1977;Snowden et al 1990Snowden 2002), a low density (0.05 cm −3 ), high temperature (10 6 K), region extending from ∼ 30 to ∼ 150 parsecs from the Sun depending on direction, dominate the flux of soft X-rays at lower (∼ 1 4 keV) energies. High neutral H column densities within the Milky Way disk absorb emissions from greater distances.…”

Section: Cosmic Soft X-ray Emissionsmentioning

confidence: 99%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

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Both heliophysics and planetary physics seek to understand the complex nature of the solar wind's interaction with solar system obstacles like Earth's magnetosphere, the ionospheres of Venus and Mars, and comets. Studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in con- text by observations from far and extreme ultraviolet (FUV, EUV), hard X-ray, and energetic neutral atom imagers (ENA). Each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the KelvinHelmholtz instability) generates diagnostic plasma density structures. The significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, Venus, and Mars or global magnetospheric/ionospheric convection at Earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. This paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1-2.0 keV) X-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles. The introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. In situ measurements confirm the existence of time-and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at Venus, Mars, comets, and the Earth. However, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. Remote sensing observations provide global information about auroral ovals (FUV and hard X-ray), the terrestrial plasmasphere (EUV), and the terrestrial ring current (ENA). ENA instruments with low energy thresholds (∼ 1 keV) have recently been used to obtain important information concerning the magnetosheaths of Venus, Mars, and the Earth. Recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft X-ray imagers.Section 2 describes proposed dayside interaction mechanisms, including reconnection, the Kelvin-Helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. It focuses upon the questions that remain as yet unanswered, such as the significanc...

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Section: Cosmic Soft X-ray Emissionsmentioning

confidence: 99%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

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“…The LHB surrounds the Sun with an extent of ∼ 100 pc (Tanaka & Bleeker 1977;Sanders et al 1977;Snowden et al 1990) and a spatially constant temperature of kT = 0.10±0.01 keV (Liu et al , 2016, in prep. ).…”

Section: Local Hot Bubblementioning

confidence: 99%

Discovery of Galactic O iv and O v X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum

Nevalainen

Wakker

Kaastra

et al. 2017

A&A

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FUV observations have revealed the transition temperature gas (TTG; log T (K) ∼5), located in the lower Galactic halo and in the High Velocity Clouds. However, the corresponding X-ray absorption has so far remained mostly undetected. In order to make an improvement in this respect in Galactic X-ray absorption studies, we accumulated very deep (∼ 3 Ms) spectra of the blazar PKS 2155-304 obtained with the spectrometers RGS1, RGS2, LETG/HRC and LETG/ACIS-S and studied the absorption lines due to the intervening Galactic components. The very high quality of the data and the coverage of important wavelengths with at least two independent instruments allowed us to reliably detect ten Galactic lines with better than 99.95% confidence. We discovered significant absorption from blended O iv transitions 1s-2p 2 S (22.571 Å), 1s-2p 2 P (22.741 Å) and 1s-2p 2 D (22.777 Å), and from the O v transition 1s-2p (22.370 Å) from TTG at log T (K) = 5.2 ± 0.1. A joint X-ray and FUV analysis indicated that photoionisation is negligible for this component and that the gas is in a cooling transition phase. However, the temperature is high enough that the column density ratio N(O iv)/N(O v) is not significantly different from that in collisional ionisation equilibrium (CIE). Under CIE we obtained N OIV = 3.6±2.0 × 10 15 cm −2 , corresponding to N H = 1.0±0.5 × 10 19 Z Z TTG cm −2 .

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“…Most of them were soft X-ray observations. The results were summarized in a review by Tanaka & Bleeker (1977). A highlight of the results was that a large volume surrounding the Solar System appeared to be ionized and filled with plasma exceeding 1 million K. Soft X-rays with the same spectral shape came from every direction.…”

Section: Rocket Observations Of Soft X-raysmentioning

confidence: 99%

An Unscheduled Journey: From Cosmic Rays into Cosmic X-Rays

Tanaka

2013

Annu. Rev. Astron. Astrophys.

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My research career began with cosmic-ray physics. Invited to the Netherlands, I was engaged in the measurement of cosmic-ray electrons. In parallel, we began balloon observations of the cosmic X-ray background. Coming back to Nagoya, we carried out rocket observations of soft X-rays with a thin polypropylene window. Since moving to the Institute of Space and Aeronautical Science (ISAS: later reorganized to the Institute of Space and Astronautical Science), I have been involved in several astronomical satellite programs, in particular X-ray astronomy missions. The main features and major results of those programs are mentioned. Features characteristic of the Japanese space program and the specific roles of ISAS are explained.

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The diffuse soft X-ray sky

Cited by 82 publications

References 89 publications

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Discovery of Galactic O iv and O v X-ray absorption due to transition temperature gas in the PKS 2155-304 spectrum

An Unscheduled Journey: From Cosmic Rays into Cosmic X-Rays

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