# Suzaku and XMM-newton observations of the north polar spur

## charge exchange or ISM absorption?

Liyi Gu, Junjie Mao, Elisa Costantini, Jelle Kaastra

Research output: Contribution to journalArticle

7 Citations (Scopus)

### 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.
Original language English A78 8 Astronomy and Astrophysics 594 14 Oct 2016 https://doi.org/10.1051/0004-6361/201628609 E-pub ahead of print - 14 Oct 2016

### Fingerprint

North Polar Spur (astronomy)
XMM-Newton telescope
charge exchange
newton
galactic halos
nitrogen
oxygen
neon
thermal emission
line of sight
magnesium
absorbers
temperature
plasma
iron
stars

### Keywords

• astro-ph.HE
• astro-ph.GA
• physics.atom-ph
• ISM: structure
• north polar spur
• ISM: abundances
• charge exchange

### Cite this

@article{266c075c20f647b9928341bd62705cdb,
title = "Suzaku and XMM-newton observations of the north polar spur: charge exchange or ISM absorption?",
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.",
keywords = "astro-ph.HE, astro-ph.GA, physics.atom-ph, ISM: structure, north polar spur, ISM: abundances, charge exchange",
author = "Liyi Gu and Junjie Mao and Elisa Costantini and Jelle Kaastra",
year = "2016",
month = "10",
day = "14",
doi = "10.1051/0004-6361/201628609",
language = "English",
volume = "594",
journal = "Astronomy and Astrophysics",
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publisher = "EDP Sciences",

}

Suzaku and XMM-newton observations of the north polar spur : charge exchange or ISM absorption? / Gu, Liyi; Mao, Junjie; Costantini, Elisa; Kaastra, Jelle.

In: Astronomy and Astrophysics, Vol. 594, A78, 14.10.2016.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Suzaku and XMM-newton observations of the north polar spur

T2 - charge exchange or ISM absorption?

AU - Gu, Liyi

AU - Mao, Junjie

AU - Costantini, Elisa

AU - Kaastra, Jelle

PY - 2016/10/14

Y1 - 2016/10/14

N2 - 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.

AB - 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.

KW - astro-ph.HE

KW - astro-ph.GA

KW - physics.atom-ph

KW - ISM: structure

KW - north polar spur

KW - ISM: abundances

KW - charge exchange

UR - https://arxiv.org/abs/1607.08334

U2 - 10.1051/0004-6361/201628609

DO - 10.1051/0004-6361/201628609

M3 - Article

VL - 594

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - A78

ER -