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A Deep Chandra Study of Galactic Type Ia Supernova

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A Deep Chandra Study of Galactic Type Ia Supernova A DEEP CHANDRA STUDY OF GALACTIC TYPE IA SUPERNOVA REMNANT G299.2-2.9 by SETH AARON POST Presented to the Faculty of the Graduate School of The University of Texas at Arlington in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY THE UNIVERSITY OF TEXAS AT ARLINGTON December 2017 Copyright c by Seth Aaron Post 2017 All Rights Reserved To my wife and children, whose constant love and support enabled me to reach further and succeed. ACKNOWLEDGEMENTS I would like to thank professor Sangwook Park for his extraordinary and tireless support in this thesis process. I am grateful to my colleagues Doctor Andrew Schenck and Jayant Bhalareo for their wonderful collaboration, many stimulating discussions and overall encour- agement and support. I would also like to thank Doctors Gloria Dubner and Bon-Chul Koo for pro- viding the radio data used within this thesis and for a discussion on the distribution of HI column density towards G299.2-2.9. I also acknowledge the support of my thesis committee including professors Manfred Cuntz, Yue Deng, Zdzisla Musielak and Qiming Zhang. This work has been supported in part by NASA through Chandra grant GO0- 11076X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory. A special mention to my wife and family for their constant love and encourage- ment. TBD iv ABSTRACT A DEEP CHANDRA STUDY OF GALACTIC TYPE IA SUPERNOVA REMNANT G299.2-2.9 Seth Aaron Post, Ph.D. The University of Texas at Arlington, 2017 Supervising Professor: Dr. Sangwook Park In this thesis we perform a comprehensive analysis of Galactic Type Ia super- nova remnant G299.2-2.9. For this study we analyze our deep 628 ks Chandra ob- servation data of G299.2-2.9. G299.2-2.9 has a complex multiple shell-like structure consisting of a bright inner shell, with enhancements (\knots") in the northeastern portion of the shell, and a fainter diffuse outer shell. Our spectral analysis of the outer shells of G299.2-2.9 shows that the bright inner and faint outer shells appear to be emission features from the swept-up ambient medium (by the supernova blast wave) whose density is relatively uniform along the distance from the center of the remnant. We find a density gradient of a factor of ∼3 between the bright inner and faint outer shells. Our analysis of the shell regions suggests that the multiple shell morphology is likely the result of an explosion taking place on the boundary of two regions of interstellar material with differing densities. Based on our equivalent width images and elemental abundance measurements from our spectral analysis throughout the entire remnant we reveal a highly asymmetrical spatial distribution of metal-rich ejecta gas. The metal-rich ejecta gas is present mainly throughout the central regions v (surrounded by the outer shells of swept-up ambient medium). In particular we find an intriguing continuous extension of Fe- and Si-rich gas in the western direction. This asymmetric distribution of metal-rich ejecta gas is likely caused by an asymmet- ric explosion of the progenitor, but non-uniform expansion of the ejecta within the two regions of interstellar material with differing densities cannot be ruled out. We place a new conservative upper limit (8 kpc) on the distance to G299.2-2.9 based on our analysis of HI gas distribution along the line of sight. Based on our new distance upper limit, we place a tight constraint on the distance, d ∼ 5 kpc (with ∼50% errors) 50 to G299.2-2.9, and then we estimate an explosion energy E0 ∼ 1.8 × 10 erg. We estimate a total Fe mass MF e ∼ 0.17 M and a total ejecta mass of Mej ∼ 0.50 M for G299.2-2.9. These estimated values are significantly below those of a canonical Type Ia supernova. Based on these results we propose that G299.2-2.9 may be the result of a double detonation of a sub-Chandrasekhar mass white dwarf or the failed deflagration of a white dwarf. vi TABLE OF CONTENTS ACKNOWLEDGEMENTS . iv ABSTRACT . v LIST OF ILLUSTRATIONS . ix LIST OF TABLES . xi Chapter Page 1. INTRODUCTION . 1 1.1 Type Ia Supernova . 1 1.2 Evolutionary Routes and Explosion Mechanisms of a Type Ia Supernova 4 1.2.1 Single-Degenerate Channel . 6 1.2.2 Double-Degenerate Channel . 8 1.2.3 Core-Degenerate Scenario . 9 1.2.4 Double-Detonation scenario . 10 1.2.5 Direct Collision scenario . 11 1.3 Evolution of Supernova Remnants . 12 1.4 Galactic Type Ia Supernova Remnant G299.2-2.9 . 14 1.5 Chandra X-Ray Observatory . 18 1.6 Software Tools . 19 1.7 Spectral Modeling of X-Ray Emission from Supernova Remnants . 20 1.8 Thesis Composition . 21 2. Data Analysis . 28 2.1 Observations . 28 2.2 Imaging Analysis . 28 vii 2.2.1 Three Color Image . 28 2.2.2 Line Equivalent Width Images and Line Flux Ratio Distributions 29 2.3 Spectral Analysis . 31 2.3.1 Ambient Medium . 31 2.3.2 Metal-Rich Ejecta Material . 33 2.4 Radial Structure . 34 2.4.1 Structure of the Ambient Medium . 34 2.4.2 Structure of the Metal-Rich Ejecta Material . 36 2.5 Ejecta Distribution throughout the Entire Remnant . 38 3. Discussion . 62 3.1 Constraining The Distance To G299.2-2.9 . 62 3.2 Stellar Ejecta Material . 65 3.2.1 Ejecta Mass . 65 3.2.2 Spatial Structure of the Ejecta . 70 3.3 Nature Of The Ambient Gas . 74 3.4 Binary Companion Search . 81 3.5 Progenitor Scenarios . 82 4. Summary & Conclusions . 93 REFERENCES . 95 viii LIST OF ILLUSTRATIONS Figure Page 1.1 Lightcurves of Supernovae . 22 1.2 Structure of the shock front in a supernova remnant . 23 1.3 ASCA image of G299.2-2.9 . 24 1.4 Chandra ACIS Image ofG299.2-2.9 . 25 1.5 Chandra X-Ray Mirror . 26 1.6 Advanced CCD Imaging Spectrometer(ACIS) . 27 2.1 Three-color image of G299.2-2.9 . 47 2.2 Spectrum of G299.2-2.9 . 48 2.3 Equivalant width images . 49 2.4 Regions selected for ISM analysis . 50 2.5 Spectra of the bright and faint shells . 51 2.6 Regions selected for Ejecta analysis . 52 2.7 Spectra of the ejecta . 53 2.8 Regions selected for shell radial profile . 54 2.9 Shell temperature and Emission measure radial profiles . 55 2.10 Regions selected for Ejecta radial profile . 56 2 2.11 χν radial profile . 57 2.12 Radial profiles of Si and Fe abundances . 58 2.13 Radial profiles of O and Ne abundances . 59 2.14 Adaptive mesh distribution of Ejecta . 60 2.15 Outer ejecta spectra . 61 ix 3.1 Neutral atomic hydrogen line profile . 89 3.2 Regions selected for Ejecta mass calculations . 90 3.3 Hydrodynamical blast wave models . 91 3.4 Asymmetric Outflow . 92 x LIST OF TABLES Table Page 2.1 Our Chandra Observations of Galactic Supernova Remnant G299.2-2.9. 41 2.2 Best-fit Spectral Parameters for the Bright and Faint Shell Regions. 42 2.3 Average Values of Spectral Parameters for the Bright and Faint Shells. 43 2.4 Best-fit Parameters for Characteristic Ejecta Regions. 44 2.5 Best-fit Parameters for the Bright and Faint Radial Shell Regions. 45 2.6 Best-fit Parameters for Outer Ejecta Regions. 46 3.1 Mass estimates for various elements at 5 kpc. 86 3.2 Candidate Ex-Companion Stars for the Progenitor of G299.2-2.9 . 87 3.2 Candidate Ex-Companion Stars for the Progenitor of G299.2-2.9 . 88 xi CHAPTER 1 INTRODUCTION 1.1 Type Ia Supernova Supernovae are among the brightest and most energetic events to occur within the universe and as such, they have captivated the imaginations of scientists for gener- ations. Our knowledge and understanding into the nature of these unique phenomena have greatly expanded over the last few decades. These violent and explosive events are due to the gravitational collapse (core-collapse supernova) of massive stars or by the thermonuclear explosion of a white dwarf (Type Ia supernova). They shine with the brightness of several billion suns, typically outshining their host galaxy for many months thus, allowing them to be observed at great distances. These explo- sions expel stellar debris at velocities of up to ∼30000 km s−1 (∼10% the speed of light). These stellar ejecta debris play a significant role in shaping and enriching the interstellar medium (ISM) with the heavy chemical elements (e.g, Whittet 2003, pp. 45-46) produced by nucleosynthesis throughout the lifetime of the star and also produced during the explosion itself. This enriched material then later gives birth to the next generation of stars and planets. Supernovae may potentially be sources of strong gravitational waves (Ott et al. 2012). Their remnants are expected to accel- erate a large fraction of cosmic rays (Baade & Zwicky 1934). Because these events produce a wide range of astrophysical consequences they are important to many areas of investigation across a wide range of fields of study. The Type Ia supernova is a subclass of supernovae that occurs in all types of galaxies. They have been detected both in star forming regions as well as areas with 1 little to no star formation activity. They are believed to occur at a rate of a few 10−3 yr−1 within our Galaxy (e.g., Maoz et al.
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