Suzaku and XMM-newton observations of the north polar spur : charge exchange or ISM absorption?

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Gu, Liyi and Mao, Junjie and Costantini, Elisa and Kaastra, Jelle (2016) Suzaku and XMM-newton observations of the north polar spur : charge exchange or ISM absorption? Astronomy and Astrophysics, 594. A78. ISSN 0004-6361 (https://doi.org/10.1051/0004-6361/201628609)

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Abstract

By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we discovered that the spectra are inconsistent with the traditional model consisting of pure thermal emission and neutral absorption. The most prominent discrepancies are the enhanced O VII and Ne IX forbidden-to-resonance ratios, and a high O VIII Ly$\beta$ line relative to other Lyman series. A collisionally ionized absorption model can naturally explain both features, while a charge exchange component can only account for the former. By including the additional ionized absorption, the plasma in the North Polar Spur can be described by a single-phase CIE component with temperature of 0.25 keV, and nitrogen, oxygen, neon, magnesium, and iron abundances of $0.4-0.8$ solar. The abundance pattern of the North Polar Spur is well in line with those of the Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous studies can be migrated to the large transmission of the O VIII Ly$\alpha$ line. The ionized absorber is characterized by a balance temperature of $0.17-0.20$ keV and a column density of $3-5 \times 10^{19}$ cm$^{-2}$. Based on the derived abundances and absorption, we speculate that the North Polar Spur is a structure in the Galactic halo, so that the emission is mostly absorbed by Galactic ISM in the line of sight.

ORCID iDs

Gu, Liyi, Mao, Junjie ORCID logoORCID: https://orcid.org/0000-0001-7557-9713, Costantini, Elisa and Kaastra, Jelle;
  • Item type:Article
    ID code:70860
    Dates:
    Date
    Event
    14 October 2016
    Published
    14 October 2016
    Published Online
    27 July 2016
    Accepted
    Subjects:Science > Astronomy
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:12 Dec 2019 16:28
    Last modified:20 Nov 2024 01:18
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/70860
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