We present observations of the North Polar Spur ( NPS ) using the X-ray Imaging Spectrometer ( XIS ) aboard the Suzaku X-ray satellite .
The NPS is a large region of enhanced soft X-ray and radio emission projected above the plane of the Galaxy , likely produced by a series of supernovae and stellar winds from the nearby Sco-Cen OB association .
The exceptional sensitivity and spectral resolution of the XIS below 1 keV allow unprecedented probing of low-energy spectral lines , including C vi ( 0.37 keV ) and N vii ( 0.50 keV ) , and we have detected highly-ionized nitrogen toward the NPS for the first time .
For this single pointing toward the brightest 3/4 keV emission ( l = 26.8 \arcdeg , b = +22.0 \arcdeg ) , the best-fit NPS emission model implies a hot ( kT \approx 0.3 keV ) , collisional ionization equilibrium ( CIE ) plasma with depleted C , O , Ne , Mg , and Fe abundances of less than 0.5 solar , but an enhanced N abundance , with N/O = ( 4.0 ^ { +0.4 } _ { -0.5 } ) times solar .
The temperature and total thermal energy of the gas suggest heating by one or more supernovae , while the enhanced nitrogen abundance is best explained by enrichment from stellar material that has been processed by the CNO cycle .
Due to the time required to develop AGB stars , we conclude that this N/O enhancement can not be caused by the Sco-Cen OB association , but may result from a previous enrichment episode in the solar neighborhood .