University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2017 Photometric and Spectroscopic Signatures of Superluminous Supernova Events The puzzling case of ASASSN-15lh Welbanks Camarena, Luis Carlos Welbanks Camarena, L. C. (2017). Photometric and Spectroscopic Signatures of Superluminous Supernova Events The puzzling case of ASASSN-15lh (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/27339 http://hdl.handle.net/11023/3972 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Photometric and Spectroscopic Signatures of Superluminous Supernova Events The puzzling case of ASASSN-15lh by Luis Carlos Welbanks Camarena A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN PHYSICS AND ASTRONOMY CALGARY, ALBERTA JULY, 2017 c Luis Carlos Welbanks Camarena 2017 Abstract Superluminous supernovae are explosions in the sky that far exceed the luminosity of standard supernova events. Their discovery shattered our understanding of stellar evolution and death. Par- ticularly, the discovery of ASASSN-15lh a monstrous event that pushed some of the astrophysical models to the limit and discarded others. In this thesis, I recount the photometric and spectroscopic signatures of superluminous super- novae, while discussing the limitations and advantages of the models brought forward to explain them. I show that a quark nova occurring in the wake of a supernova remnant of an Oxygen-type Wolf-Rayet star can reproduce the light curve, photospheric radius and effective temperature evo- lution of ASASSN-15lh. This model was used to successfully simulate the spectrum of the event using SYNOW. Beyond being a successful explanation for ASASSN-15lh, the quark nova model is an appealing mechanism to power the most luminous events ever seen in the sky. ii Acknowledgements When I heard the learnd astronomer, When the proofs, the figures, were ranged in columns before me, When I was shown the charts and diagrams, to add, divide, and measure them, When I sitting heard the astronomer where he lectured with much applause in the lecture-room, How soon unaccountable I became tired and sick, Till rising and gliding out I wanderd off by myself, In the mystical moist night-air, and from time to time, Lookd up in perfect silence at the stars. -Walt Whitman To my father for his selfless sacrifices, for his advice and his endearing inspiration to pursue my dreams. To my mother for giving me breath. To my grandparents for their care and support towards my career. To Stephanie for her commitment, love, laughter, care and feedback. To my supervisor and mentor, Dr. Rachid Ouyed, for believing in me and pushing me to become the best version of myself. His patience, empathy and thoughtfulness made this work possible. To Dr. Nasser Moazzen-Ahmadi for teaching me that discipline and humour are the virtues of a scholar, and that kindness is the key to success. To Dr. Jo-Anne Brown for teaching me to knock on the doors of opportunity and being a considerate advisor. To the Quark-Nova group, Amir, Nico, Zach and Matt, for being a trustworthy source of knowledge and encouragement. iii Table of Contents Abstract ........................................... ii Acknowledgements .................................... iii Table of Contents . iv List of Tables . v List of Figures . vi List of Symbols . viii 1 Introduction . 1 1.1 Stellar Evolution: The Events Leading up to a Supernova . 2 1.2 A New Piece in the Puzzle: Superluminous Supernova Events . 6 1.3 Powering Mechanisms for Superluminous Supernovae . 9 1.3.1 Nuclear Decay . 10 1.3.2 Circumstellar Material Interaction . 11 1.3.3 Magnetars . 11 1.3.4 Tidal Disruption Events . 12 1.3.5 Advantages and Disadvantages . 12 2 The Quark Nova as a Mechanism Behind Superluminous Supernovae . 14 2.1 The Quark Nova Hypothesis . 14 2.1.1 Nuclear Deconfinement and Seeding . 14 2.1.2 Burning . 17 2.1.3 Energetics . 18 2.1.4 Astrophysical Scenarios and Their Observational Signatures . 19 3 ASASSN-15lh. The Most Luminous Supernova Event Ever Seen . 23 3.1 Detection History: Photometric and Spectroscopic Data . 23 3.2 Standard Powering Mechanisms . 26 4 The Quark Nova Model for ASASSN-15lh . 30 4.1 Quark Novae in Massive Star Binaries . 30 4.1.1 The Quark Nova Luminosity . 30 4.1.2 Spin-Down Interaction . 32 4.1.3 Black Hole Accretion Phase . 33 4.1.4 Light Curve . 33 4.1.5 Obstacles and Challenges . 35 4.2 Dual-shock Quark Nova With a Wolf-Rayet Star Supernova Progenitor . 35 4.2.1 Light curve . 40 4.2.2 Spectrum . 43 4.3 Discussion . 50 5 Summary and Conclusion . 52 Bibliography . 56 iv List of Tables 1.1 Advantages and disadvantages of models for superluminous supernovae . 13 4.1 Best fit parameters for the ASASSN-15lh light curve in the binary model . 34 4.2 Best fit parameters for the ASASSN-15lh light curve in the dual-shock model . 41 4.3 Elemental species parameter for synthetic spectrum of ASASSN-15lh using SYNOW. The envelope was assumed to be fully mixed giving all elements the same excita- tion temperature . 47 v List of Figures and Illustrations 1.1 Schematic structure of the burning stages of a star. This is the structure of a SN progenitor star. 4 1.2 This Figure shows the light curves of SNe and SLSNe. While common SNe can reach peak luminosities of 2 × 1043 erg s−1(absolute magnitude > −19:5), SLSNe reach luminosities that are greater by a factor of 10. The Figure contains prototypi- cal events for each type of SN and compares them to SLSNe PTF09cnd, SN2006gy and SN2007bi. The specifics of the classification suggested by Gal-Yam are dis- cussed in the source. (Figure 1 from Gal-Yam [19].) . 8 1.3 This Figure shows the early spectra of some SLSNe-I. The absorption lines cor- respond to light elements like O, Mg, Si, and C. Other than the presence of these lines, a characteristic is the absence of H or He lines. Ha has an expected wave- length of 6562.8 A.˚ (Figure 4 from Gal-Yam [19].) . 9 2.1 A massive binary can evolve into a QN. A subsequent BH can accrete matter from the system rebrightening the light curve. The 1x and 10x in Panels g and G corre- spond to 1 and 10 times zoom respectively. (Figure 1 from Ouyed et al. [52].) . 22 3.1 Figure showing the rest-frame absolute magnitude light curve of ASASSN-15lh near peak compared with other type I SLSNe events. The comparison contains the most luminous events previously known showing that ASASSN-15lh is more luminous than the other events by roughly more than 1 magnitude. Dong et al. [16] contains a full description of the corrections performed to obtain this image. (Figure 4 from Dong et al. [16].) . 24 3.2 Multi-band light curve of the rebrightened ASASSN-15lh. The magnitudes are in the Vega system and were not corrected for extinction or contribution from the host. For more information on methods read Godoy-Rivera et al. [21]. (Figure 1 from Godoy-Rivera et al. [21].) . 25 3.3 Top Panel: Spectroscopic evolution of ASASSN-15lh at the rest frame. Differ- ent curves represent different stages of the light curve evolution. (Figure 2 from Godoy-Rivera et al. [21]). Bottom Panel: Spectroscopic evolution of ASASSN- 15lh near Ha. The spectra cover a period of time before and after the fading stage at around 196 days. The green line at 6562.8 A˚ shows the expected position of Ha. For both panels, offsets were added to the spectra for clarity. (Figure 3 from Godoy-Rivera et al. [21].) Godoy-Rivera et al. [21] explain in detail the dates of observation and instruments used for observation. 27 3.4 Top: Effective photospheric temperature of ASASSN-15lh. Bottom: Apparent photospheric radii of ASASSN-15lh. Data obtained from Godoy-Rivera et al. [21]. 28 4.1 Light curve for ASASSN-15lh using the QN model in a binary. Obtained light curve for ASASSN-15lh. The purple stars represent the observations taken from Godoy-Rivera et al. [21]. The red line shows the result of the model while the contributions of each engine are shown separately. In blue the QN, in green the SpD contribution, and in black the BH accretion. 34 vi 4.2 Schematic representation (not to scale) of the sequence of events in our model. The top left panel shows a WO star that later undergoes a SN in the top right panel. The middle left panel shows the two-component configuration of the WO-SNR composed of a dense core and a less dense envelope. The middle right panel shows the QN that results in the birth of a QN and a QN ejecta. The QN ejecta shocks the core and the envelope. The envelope later cools and recedes. The bottom left panel shows the photosphere receding through the envelope resulting in the first hump in the light curve. The bottom right panel shows the photosphere receding through the hot core which rebrightened the light curve resulting in a second hump. 38 4.3 Results for the features of ASASSN-15lh using the dsQN model are shown with solid red lines.