Charge Exchange in Cygnus Loop R. S. Cumbee et al Satoru Katsuda et al Zhang Ningxiao

Charge Exchange “charge (in the form of one or more electrons) is transferred from an atom or molecule to an ion that gets into an excited state, from which it may deexcited by releasing electromagnetic radiation.” (K. Dennerl)

Charge Exchange in SNR SNRs contain interfaces between hot gas and cool clouds. Wise and Sarazin (1989) performed a detailed study of Charge Exchange in SNR. The X-ray is expected to arise between neutral hydrogen and highly ionized heavy ions. But Charge Exchange does not contribute more than 10% of the emission of the shock heated gas within SNR.

Cygnus Loop It is believed that the Cygnus Loop is a remnant from a core-collapse SN and that its forward shock is now hitting the wall of a wind-blown cavity over considerable fraction of the rim. the metal abundances in some of the outermost narrow rim regions are anomalously “enhanced”.

Katsuda et al NE4 “enhanced” VS. NE2 “normal” Significantly enhanced

Fitting result: (tabs*vpshock) Ratios of C/Fe, N/Fe, O/Fe, and Ne/Fe are 2-4 times higher in NE4 than NE2. Post-shock electron densities in NE4 and NE2 to be 1 cm^-3 and 6 cm^-3.

To better understand the spectra, they fit them with an absorbed (3*10^20) bremsstrahlung continuum plus a number of Gaussians (center of lines are allowed to vary freely). Lines (8+9+1)

Fe XVII/XVI or O VII ? Not Fe XVII: keV not (+/ ) keV 2. 3s->2p/3d->2p could be 3.5 (too high) Not Fe XVI: the strongest one is in 0.82 keV Not O VII: The ratio of He (γ+δ) /O Heα is expected to be But 0.7keV /O Heα is 0.06 in nei model.

Charge Exchange Not far from the shell. The neutral hydrogen of Ha filaments. Anti-correlated Radio emission.

Charge Exchange Not far from the shell. The neutral hydrogen of Ha filaments. Anti-correlated Radio emission.

Charge Exchange Not far from the shell. The neutral hydrogen of Ha filaments. Anti-correlated Radio emission.

Detail study Model (thermal+ 22 gauss lines) Thermal model use vpshock as its surrounding. NE2 spectra 22 lines represent C, N, O, Ne, Mg, and Si. Ignore Fe L-shell lines for simple.

discussion The flux of charge-exchange is larger than Wise & Sarazin They explain this is the result of different of physical parameters (shock velocity). O Heα and EM agrees with the theoretical prediction of Lallement (2004b)  0.7 keV originates from CX processes, most likely between neutrals and H-like O.

Cumbee et al Fitting result is not the same. 1.use 35 lines. (lines’ intrinsic widths are much smaller than the instrumental line width.) 2.resolve all multiplets. 3.normalize the Kβ and higher lines to Kα.

0.7 keV Add two unconstrained lines at 0.726keV and 0.822keV. -> 0.726keV is much better.

result 1. charge exchange contributes to the keV 2. lines with unconstrained normalizations may lead to unphysical line ratios 3.O VII + H contribute to the line in 0.7 keV 4.Fe XVII or other lines could also contribute to the line

Other Charge Exchange Stars (stellar winds) ->Later-type dwarf stars, X-ray do not originate in cooling shocks in the acceleration zone. The condition behind the shock is far away from equilibrium. Galaxies ->M82 some lines cannot be fitted well. Excited O VIII ions. (hot gas and cool gas) Clusters of Galaxies

Thanks