EMISSION LINES BETWEEN 1 AND 2 keV IN COMETARY X-RAY SPECTRA

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 Xray 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, andSi 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.

Cometary emissions induced by scattering and fluorescence of solar X-rays

“…The cometary X-ray scattering flux of M-type X-ray solar flares can be 1−3 orders of magnitude higher than the flux observed during quiet solar conditions. In addition, IZ had the highest observed particle production rates of any other comet analyzed (Ewing et al 2013), providing additional atmospheric scatterers. Comparison between the spectral intensities of backgroundcorrected observational data taken from Chandra (×s) and our theorized scattering-fluorescence spectrum model induced exclusively from atmospheric gas (solid line) for Ikeya-Zhang.…”

“…Current interpretation of observed spectra suggest that these hard X-ray peaks are a result of SWCX with abnormal, highly ionized SW ions like Mg 11+ and Si 13+ (Bodewits et al 2007;Ewing et al 2013). However, in situ observations with mass spectrometers have not detected these highly charged ions (Lepri et al 2013;von Steiger et al 2000).…”

“…Recently, comet observations using the Chandra X-ray Observatory have shown emission spectra above 1 keV with unresolved spectral features, or peaks, for several comets (Ewing et al 2013). Current interpretation of observed spectra suggest that these hard X-ray peaks are a result of SWCX with abnormal, highly ionized SW ions like Mg 11+ and Si 13+ (Bodewits et al 2007;Ewing et al 2013).…”

Scattering of Particles and Radiation in Astrophysical Environments

“…These X-ray halos are due to scattering of X-rays from nanoparticles consisting of both ice and dust, common in astrophysical environments [88][89][90][91][92]. Additionally, Xrays have been observed from cometary atmospheres due to both highly ionized solar wind charge exchanging with neutral gases, creating X-rays [93,94], as well as direct scattering and fluorescence of solar X-rays [95].…”

“…These observations were quickly explained through charge exchange (CX) collisions between heavy, highly ionized solar wind (SW) and neutral gases in the cometary atmosphere [111]. Comparison of X-ray spectrum from comet Ikey-Zhang [93] and Jupiter [113], observed during solar X-ray flares. The data sets have been scaled to overlay together in order to better visualize the strong similarity in spectral structure between the two astronomical objects at photon energies above 1 keV.…”