Emission lines between 1 and 2 keV in Cometary X-ray Spectra

TL;DR

This study identifies new X-ray emission lines between 1 and 2 keV in cometary spectra, attributed to solar wind charge exchange, expanding understanding of comet-solar wind interactions.

Contribution

The paper reports the detection of specific Mg and Si emission lines in cometary X-ray spectra, enhancing models of solar wind charge exchange processes.

Findings

Detection of Mg XI and Si XIII lines at 1340 and 1850 eV

Identification of weaker Mg XII, Mg XI, and Si XIV lines

Silicon lines detected in all studied comets

Abstract

We present the detection of new cometary X-ray emission lines in the 1.0 to 2.0 keV range using a sample of comets observed with the Chandra X-ray observatory and ACIS spectrometer. We have selected 5 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 (Bodewits et al. 2007). Above 1 keV, we find Ikeya-Zhang to have strong emission lines at 1340 and 1850 eV that we identify as being created by solar wind charge exchange lines of Mg XI and Si XIII, respectively, and weaker emission lines at 1470, 1600, and 1950 eV formed by SWCX of Mg XII, Mg XI, 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 to 2000 eV range are detected for all comets, but with the rising background and decreasing cometary emission, we caution these detections need further confirmation with higher resolution instruments.