# Presentation: 328347

## The North Polar Spur: Detection of Nitrogen Enhancement with Suzaku

- Eric D. Miller (MIT)
- Hiroshi Tsunemi (Osaka. U) Mark Bautz (MIT) Dan McCammon (U. Wisconsin)
*Suzaku* Science Working Group

## North Polar Spur (NPS)

- region of enhanced soft X-ray, radio emission (Loop 1)
- nearby SNR?
- Sco-Cen OB assoc. swept-out bubble?  ~ 170 pccontinuous stellar winds, SN de Geuss 1992, Egger & Aschenbach 1995
- plasma conditions, chemical abundance constrain model
- measure NVII, CVI emission lines with *Suzaku*/XIS

**XIS FOV**

- ROSAT All-Sky Survey

- Snowden et al. (1997)

- Sco-Cen

- Local Bubble & Beyond II

## NPS Emission Model

- line of sight passes through several diffuse emission components
- Local Hot Bubble
- NPSpartly absorbed
- Galactic halo  absorbed
- extragalactic background  absorbed
- power-law_x000b_ = 1.4_x000b__x000b_
- thermal_x000b_kT ~ 0.1 keV, solar
- thermal_x000b_kT ~ ?, abund ~ ?
- _x000b_unabsorbed thermal_x000b_kT ~ 0.1 keV, solar

- Willingale et al. 2003

**XIS**

- Gal. plane

*z*

- NPS

- LHB

- halo

- Local Bubble & Beyond II

## NPS Suzaku Spectrum

- XIS BI

*kT *~ 0.3 keV

- Local Bubble & Beyond II

## NPS Emission from NVII !

- XIS BI

*kT *~ 0.3 keV

- Local Bubble & Beyond II

## NPS Plasma Conditions

*kT *	0.29 ± 0.01 keV
*N**H**	*> 4x1020 cm-2	> 70% LOS value
- Nitrogen enhancement!
- Is it *really* in the NPS?

**RELATIVE ABUNDANCES**
**      **
**Ne/O****	****1.5 ± 0.3****	****solar**
**Mg/O****	****1.4 ± 0.3****	****solar**
**Fe/O****	****1.5 ± 0.2****	****solar**
**N/O****	****4.0 ± 0.4****	****solar**

- Local Bubble & Beyond II

## Other Emission Sources

- two-*kT* galactic halo (0.1 & 0.2 keV) Kuntz & Snowden 2000
*S**X* (GH) ~ 20% *S**X* (NPS)
- Galactic bulge: * kT* ~ 0.2-0.3 keV Snowden et al. 1997
- polytrope model Almy et al. 2000
- contributes < 10% to NVII
- other *kT *~ 0.2 component
- NVII / O line ratio still too large, assuming solar abundance and CIE

- Local Bubble & Beyond II

## Solar Wind Charge Exchange?

- geocoronal SWCX  C,O,Fe emission linesSnowden et al. 1994, Fujimoto et al. 2007
- stable count rate, solar ion flux
- heliospheric?

**NEP**
- Fujimoto et al. 2007

**NPS**

- ACE

- ACE

- Local Bubble & Beyond II

## Scattered Solar X-rays?

- Thomson & fluorescent scattering of solar X-rays  O K lines near 0.53 keV
- flux  sun-lit column of O+O2
- screening  *N*(O+O2) < 51012 cm-2
*F*(solar)	< 10% NVII	< 3% OVII
- NVII is from NPS

- Local Bubble & Beyond II

## NPS - N Enrichment

- O primary production: massive stars, SN
- N primary+secondary production: H shell burning in 4-8 *M*◉ AGB stars
- 14N + p → 15O + limits CNO cycle
- enrichment source
- Sco-Cen OB assoc ~ 106-107 yrs old
- AGB stars form after ~ 108 yrs
- emitting material not from Sco-Cen:  AGB activitywithin Loop I?  SN-heated ISM?

- Local Bubble & Beyond II

## Evidence for N Enrichment

- similar results from abs. studiesN/O > solar in local ISM (*d *< 500 pc)  Knauth et al. 2006
- enhanced recent AGB activity in solar neighborhood?
- large-scale mixing inhomogeneities?
- local infall of primordial material? Koppen and Hensler 2005
- N/O ~ 4 is very large

- Local Bubble & Beyond II

## Summary

*Suzaku *has good low-energy spectral resolution
- NPS plasma conditions
*kT *~ 0.3 keV
*N**H* > 4x1020 cm-2 = 70% line of sight value
- NPS has over-abundance of N compared to O
- enrichment of plasma by AGB activity; not Sco-Cen
- similar result for ISM within 500 pc (absorption)
- heating by recent SN?
- AGB activity in Loop I bubble?

- Local Bubble & Beyond II