Emission lines between 1 and 2 keV in cometary X-ray spectra

We present the detection of new cometary X-ray emission lines in the 1.0�2.0 keV range using a sample of comets observed with the Chandra X-Ray Observatory and ACIS spectrometer. We have selected five comets from the Chandra sample with good signal-to-noise spectra. The surveyed comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught�Hartley), 153P/2002 (Ikeya�Zhang), 2P/2003 (Encke), and C/2008 8P (Tuttle). We modeled the spectra with an extended version of our solar wind charge exchange (SWCX) emission model. Above 1 keV, we find Ikeya�Zhang to have strong emission lines at 1340 and 1850 eV which we identify as being created by SWCX lines of Mgxi and Si xiii, respectively, and weaker emission lines at 1470, 1600, and 1950 eV formed by SWCX of Mgxii, Mgxi, and Si xiv, respectively. The Mg xi and xii and Si xiii and xiv lines are detected at a significant level for the other comets in our sample (LS4, MH, Encke, 8P), and these lines promise additional diagnostics to be included in SWCX models. The silicon lines in the 1700�2000 eV range are detected for all comets, but with the rising background and decreasing cometary emission, we caution that these detections need further confirmation with higher resolution instruments.

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