X-ray Emission from Charge Exchange in the Cygnus Loop SNR

Abstract

The Cygnus Loop has been the focus of substantial debate concerning the contribution of charge exchange (CX) to supernova remnant (SNR) X-ray emission. We take advantage of a distinct feature of CX, enhanced Kα forbidden line emission, and employ the energy centroid of the OVII Kα triplet as a diagnostic. Based on X-ray spectra extracted from an extensive set of Suzaku observations, we measure the energy centroid shifts of the triplet on and off the shock rim of the remnant. We find that enhanced forbidden to resonance line emission exists throughout much of the rim and this enhancement azimuthally correlates with non-radiative Hα filaments, a tracer of strong neutral-plasma interaction in the optical. We also show that alternative mechanisms cannot explain the enhancement observed. These results demonstrate the need to model the CX contribution to the X-ray emission of SNRs, particularly for shocks propagating in a partially neutral medium. Such modeling may be critically important to the correct measurements of the ionization, thermal, and chemical properties of SNRs.

arXiv comment8 pages, 5 figures, MNRAS accepted

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• Charge Exchange X-ray Emission Detected in Multiple Shells of Supernova Remnant G296.1-0.5
• High-resolution Charge Exchange Spectra with L-shell Nickel Show Striking Differences from Models
• Charge exchange, from the sky to the laboratory: A method to determine state-selective cross-sections for improved modeling
• Unusual X-ray Oxygen Line Ratios of SN 1987A Arising From the Absorption of Galactic Hot Interstellar Medium