High Forbidden-to-resonance Line Ratio of OVII Discovered in the Cygnus Loop. (arXiv:1812.06616v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Uchida_H/0/1/0/all/0/1">H. Uchida</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Katsuda_S/0/1/0/all/0/1">S. Katsuda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tsunemi_H/0/1/0/all/0/1">H. Tsunemi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mori_K/0/1/0/all/0/1">K. Mori</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gu_L/0/1/0/all/0/1">L. Gu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cumbee_R/0/1/0/all/0/1">R. S. Cumbee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Petre_R/0/1/0/all/0/1">R. Petre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tanaka_T/0/1/0/all/0/1">T. Tanaka</a>
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.
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.
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