High Forbidden-to-resonance Line Ratio of OVII Discovered in the Cygnus Loop
| Autor: | Uchida, H., Katsuda, S., Tsunemi, H., Mori, K., Gu, L., Cumbee, R. S., Petre, R., Tanaka, T. |
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| Rok vydání: | 2018 |
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| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/1538-4357/aaf8a6 |
| Popis: | Charge exchange (CX) is an important process in shock physics since it indicates an interaction between downstream ions and ambient neutral hydrogen, suggesting a presence of a collisionless shock. We present a high-resolution spectroscopy of an X-ray bright spot in a nearby supernova remnant (SNR), the Cygnus Loop, with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The target is a compact knotty structure called "southwestern knot (SW-K)" located at the outer edge of the shell, where the blast wave is likely interacting with dense surrounding materials. The RGS spectrum of the SW-K shows details of the line features below ~ 1 keV, where we discover a high forbidden-to-resonance line ratio of OVII He$\alpha$. The soft-band (10-35 \AA) spectrum is well explained by a thermal component with a CX X-ray emission obscured by neutral and ionized absorbers. The presence of the CX X-ray emission will provide new insights into the shock physics of SNRs. The high-resolution spectroscopy also reveals that the CNO, Ne and Fe abundances are truly lower than the solar values (0.2-0.4 solar) at the SW-K region . Our result gives a clue to solving the previously known "low-abundance problem" reported from a number of evolved SNRs. Comment: 10 pages, including 4 figures and 2 tables, accepted for publication in ApJ |
| Databáze: | arXiv |
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