Chandra ACIS-S imaging spectroscopy of anomalously faint X-ray emission from Comet 103P/Hartley 2 during the EPOXI encounter

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2013-02, Vol.222 (2), p.752-765
• Main Authors: Lisse, C.M., Christian, D.J., Wolk, S.J., Dennerl, K., Bodewits, D., Combi, M.R., Lepri, S.T., Zurbuchen, T.H., Li, J.Y., Dello-Russo, N., Belton, M.J.S., Knight, M.M.
• Format: Article
• Language: English
• Subjects: Comets; Solar wind; Spectroscopy
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2012.09.025

► At LX=1.1×1014ergs−1, 103P was the 3rd faintest comet ever detected in the X-ray. ► Its X-ray spectrum varied as the solar wind changed between slow, hot and cold, fast states. ► 103P produced collisionally thin to CXE morphology modulated by cometary rotation. ► The X-ray emission was unusual due to extended coma emission of gas in this hyperactive comet. We present results from the Chandra X-ray Observatory’s characterization of the X-ray emission from Comet 103P/Hartley 2, in support of NASA’s Deep Impact Extended close flyby of the comet on 04 November 2010. The comet was observed 4 times for a total on target time of ∼60ks between the 17th of October and 16th of November 2010, with two of the visits occurring during the EPOXI close approach on 04 November and 05 November 2010. X-ray emission from 103P was qualitatively similar to that observed for collisionally thin Comets 2P/Encke (Lisse, C.M. et al. [2005]. Astrophys. J. 635, 1329–1347) and 9P/Tempel 1 (Lisse, C.M. et al. [2007]. Icarus 190, 391–405). Emission morphology offset sunward but asymmetrical from the nucleus and emission lines produced by charge exchange between highly stripped C, N, and O solar wind minor ions and coma neutral gas species were found. The comet was very under-luminous in the X-ray at all times, representing the 3rd faintest comet ever detected (LX=1.1±0.3×1014ergs−1). The coma was collisionally thin to the solar wind at all times, allowing solar wind ions to flow into the inner coma and interact with the densest neutral coma gas. Localization of the X-ray emission in the regions of the major rotating gas jets was observed, consistent with the major source of cometary neutral gas species being icy coma dust particles. Variable spectral features due to changing solar wind flux densities and charge states were also seen. Modeling of the Chandra observations from the first three visits using observed gas production rates and ACE solar wind ion fluxes with a charge exchange mechanism for the emission is consistent with the temporal and spectral behavior expected for a slow, hot wind typical of low latitude emission from the solar corona interacting with the comet’s neutral coma. The X-ray emission during the 4th visit on 16 November 2010 is similar to the unusual behavior seen for Comet 17P/Holmes in 2007 (Christian, D.J. et al. [2010]. Astrophys. J. Suppl. 187, 447–459) as the solar wind became dominated by a less ionized and faster plasma, more typical of outflow from pola