Doppler-Broadened Iron X-ray Lines from Tychos Supernova Remnant

arXiv:0902.3049v1 [astro-ph.HE] 18 Feb 2009 To appear in The ApJ Letters Doppler-Broadened Iron X-ray Lines from Tycho’s Supernova Remnant Akihiro Furuzawa1, Daisuke Ueno1, Asami Hayato2,3, Midori Ozawa4, Toru Tamagawa2, Aya Bamba5, John P. Hughes6, Hideyo Kunieda1, Kazuo Makishima2,7, Stephen S. Holt8, Una Hwang9, Kenzo Kinugasa10, Robert Petre9, Keisuke Tamura5, Hiroshi Tsunemi11, and Shigeo Yamauchi12 furuzawa@u.phys.nagoya-u.ac.jp ABSTRACT We use Suzaku observations to measure the spatial variation of the Fe Kα line with radius in the Tycho supernova remnant. The Fe line widths show a significant decrease from a FWHM value of 210 eV at the center to 130 eV at the rim. Over the same radial range the line center energy remains nearly constant. These observations are consistent with a scenario in which the shell of Fe-emitting ejecta in Tycho is expanding 1Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Furo-cho, Nagoya 464-8602, Japan 2RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 3Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan 4Department of Physics, Graduate School of Science, Kyoto University, Kita-Shirakawa, Sakyo-ku, Kyoto 606- 8502, Japan 5Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagami- hara, Kanagawa 229-8510, Japan 6Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 USA 7Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 8F. W. Olin College of Engineering, Needham, MA 02492, USA 9NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 10Gunma Astronomical Observatory, 6860-86, Nakayama, Takayama-mura, Agatsuma-gun, Gunma 377-0702, Japan 11Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan 12Faculty of Humanities and Social Sciences, Iwate University, 3-18-34 Ueda, Morioka, Iwate 020-8550, Japan – 2 – at speeds of 2800–3350 km s−1. The minimum line width we measure is still a factor of two larger than expected from a single component plasma emission model. If thermal Doppler broadening is the dominant additional source of broadening, we infer an ion temperature of (1 −−3) × 1010 K. Subject headings: ISM: individual (Tycho, SN 1572) — supernova remnants — X-rays: ISM 1. Introduction Type Ia supernovae (SNe) play an important role in the chemical evolution of the universe by providing a significant fraction of the Fe group elements in stars, the interstellar medium and the intracluster medium. They have also become a prime tool to explore the expansion history of the universe. Yet, in spite of their importance, the physical processes involved in the actual explosions remain unclear. The SN seen by Tycho Brahe in 1572 can be classified with some degree of confidence as Type Ia based on the light curve and color evolution from the historical record (Ruiz-Lapuente 2004). The remnant (hereafter Tycho) is located at Galactic coordinates (l, b) = (120◦.0879, 1◦.4460) and its estimated distance is 1.5–3.1 kpc (Chevalier et al. 1980; Albinson et al. 1986; Smith et al. 1991; Ruiz-Lapuente 2004), but still debated (Schwarz et al. 1995). Tycho is now a young and X-ray bright supernova remnant (SNR) that has been studied extensively for investigations of the SN Ia explosion mechanism. In the radio and X-ray bands, Tycho shows a relatively smooth and regular 8′ diameter limb-brightened shell with several pro- tuberances and indentations notably toward the southeast (SE) and northeast (NE) parts of the shell, possibly driven by fingers of SN ejecta or the consequence of the blast wave interacting with a nonuniform ambient medium. The good angular resolution and photon statistics of Tycho ob- servations by Chandra and XMM-Newton have enabled detailed studies of the spatial structure (Warren et al. 2005) and have set significant constraints on allowed explosion models by compar- ing observed and simulated X-ray spectra (Badenes et al. 2006). Among the results revealed by Chandra is one that finds the region between the forward shock and contact discontinuity to be very narrow and dominated by nonthermal emission, concentrated in geometrically thin filamentary structures (Hwang et al. 2002; Bamba et al. 2005; Warren et al. 2005; Cassam-Chenai et al. 2007). No thermal emission has yet been detected from the forward shock region; all the observed metal lines in the X-ray spectrum are produced predominantly by the ejecta. A direct measurement of the expansion velocity of Tycho has not yet been obtained. Reynoso et al. (1997) reported the expansion rate obtained from the radial displacement of the radio-emitting shell over the course of a decade. Hughes (2000) obtained the rate from a difference of brightness pro- files measured from two ROSAT HRI observations taken in 1990 and 19

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