The Landscape of Relativistic Stellar Explosions

Description

This thesis reports the discovery of relativistic stellar explosions outside of the gamma ray band, using optical time domain surveys. It is well known that some massive stars end their lives with the formation of a compact object (a neutron star or black hole) that launches a relativistic jet detectable from earth as a burst of gamma rays. It has long been suspected, however, that gamma ray bursts are only the tip of the iceberg in a broad landscape of relativistic explosions, and so the results presented in this thesis represent a major breakthrough. Highlights of this thesis include: characterization of the first major new class of relativistic explosions in a decade; the discovery of abrupt end-of-life mass-loss in a surprisingly diverse range of stars; and the routine discovery of afterglow emission and several events that may represent baryonically dirty jets or jets viewed slightly off axis. These discoveries necessitated the solution of difficult technical challenges such as the identification of rare and fleeting “needles” in a vast haystack of time-varying phenomena in the night sky, and responding to discoveries within hours to obtain data across the electromagnetic spectrum from X-rays to radio wavelengths.  Supervisor's Foreword Acknowledgments Parts of This Thesis Have Been Published in the Following Journal Articles Contents 1 Introduction and Summary 1.1 Landscape Overview The GRB View The Ic-BL SN View Radio Unification Efforts 1.2 Summary of Thesis References Part I Afterglows at Cosmological Distances 2 ZTF20aajnksq (AT2020blt): A Fast Optical Transient at z 2.9 With No Detected Gamma-Ray Burst Counterpart 2.1 Introduction 2.2 Observations ZTF Discovery Follow-up Observations Optical Imaging Optical Spectroscopy X-Ray Observations Radio Observations Search for Associated GRB 2.3 Comparison to GRB Afterglows Optical Light Curve Spectral Energy Distribution Radio Light Curve 2.4 Interpretation A Slightly Off-Axis GRB A Dirty Fireball 2.5 Summary and Conclusions References 3 iPTF Archival Search for Fast Optical Transients 3.1 Introduction 3.2 Data and Candidate Selection 3.3 Properties of the iPTF M-dwarf Flares 3.4 Rate of Relativistic Fast Optical Transients in iPTF 3.5 Conclusions 3.6 Appendix References Part II Low-Luminosity Gamma-Ray Bursts 4 SN2020bvc: A Broad-Lined Type Ic Supernova with a Double-Peaked Optical Light Curve and a Luminous X-ray and Radio Counterpart 4.1 Introduction 4.2 Observations ZTF Detection and Classification Host Galaxy Optical Photometry Spectroscopy UV and X-Ray Observations Submillimeter and Radio Observations Search for a Gamma-Ray Burst 4.3 Light Curve Analysis Comparisons to Other Ic-BL SNe Blackbody Fits 4.4 Spectroscopic Properties Spectroscopic Evolution and Comparisons Velocity Estimates from Fe II Features 4.5 Modeling the Light Curve Nickel Decay Shock-Cooling 4.6 Modeling the Fast Ejecta Radio Emission X-Ray Emission 4.7 Early ZTF Light Curves of Nearby Ic-BL SNe 4.8 Summary and Discussion 4.9 Appendix Photometry Table Details: Mass and Radius of the Extended Material Details: Properties of the Forward Shock Inverse Compton Scattering References Part III Ic-BL Supernovae Reference 5 The Broad-Lined Ic Supernova ZTF18aaqjovh (SN2018bvw): An Optically Discovered Engine-Driven Supernova Candidate with Luminous Radio Emission 5.1 Introduction 5.2 Observations Zwicky Transient Facility Discovery Spectral Classification Radio Observations X-Ray Observations Search for Gamma-Rays 5.3 Analysis and Discussion Modeling the Optical Light Curve Properties of the Fastest (Radio-Emitting) Ejecta Modeling the Radio to X-Ray SED Gamma-Ray Burst 5.4 Summary and Conclusions References 6 Evidence for Late-Stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-Lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient 6.1 Introduction 6.2 Observations Zwicky Transient Facility Discovery Photometry Spectroscopy Search for Pre-discovery Emission Radio Follow-up X-ray Follow-Up Search for Prompt Gamma-Ray Emission Host Galaxy Data 6.3 Basic Properties of the Explosion and Its Host Galaxy Physical Evolution from Blackbody Fits Spectral Evolution and Velocity Measurements Comparisons to Early Spectra in the Literature Origin of the ``W'' Feature Photospheric Velocity from Ic-BL Spectra Properties of the Host Galaxy 6.4 Interpretation Radioactive Decay Interaction with Extended Material 6.5 Comparison to Unclassified Rapidly Evolving Transients at High Redshift 6.6 Summary and Future Work 6.7 Appendix UV and Optical Photometry UV and Optical Spectroscopy Atomic Data for Spectral Modeling Data for Measuring Host Properties References Part IV A New Class of Energetic Stellar Explosions in a Dense Medium 7 AT2018cow: A Luminous Millimeter Transient 7.1 Introduction The Transient Millimeter Sky AT2018cow 7.2 Observations Radio and Submillimeter Observations The Submillimeter Array (SMA) The Australia Telescope Compact Array (ATCA) The Atacama Large Millimeter/Submillimeter Array (ALMA) X-Ray Observations Swift/XRT NuSTAR 7.3 Basic Properties of the Shock Light Curve Modeling the Radio to Submillimeter SED 7.4 Implications of Shock Properties AT2018cow in Velocity–Energy Space and a Discussion of Epsilons A Luminous Millimeter Transient in a Dense Environment Novel Features of the Synchrotron Model Parameters 7.5 Origin of the X-ray Emission and Emergence of a Compact Source 7.6 Conclusions and Outlook 7.7 Appendix ALMA Band 9 Calibration Full SMA Light Curves Selection of Peak Frequency and Peak Luminosity for Other Transients References 8 The Koala: A Fast Blue Optical Transient with Luminous Radio Emission from a Starburst Dwarf Galaxy at z=0.27 8.1 Introduction 8.2 Discovery and Basic Analysis Optical Photometry Spectroscopy and Host-Galaxy Properties Radio Observations 8.3 Comparison with Extragalactic Explosions Optical Light Curve and Spectrum Radio Light Curve A Starburst Host Galaxy 8.4 Interpretation Modeling the Optical Light Curve Modeling the Radio Light Curve Progenitor Systems and a Search for an Associated Gamma-ray Burst 8.5 Rate Estimate 8.6 Prospects for Detecting X-Ray Emission 8.7 Summary and Conclusions 8.8 Appendix Light Curve Measurements References 9 Other Contributions 9.1 ZTF19abvizsw: A Cosmological Afterglow with No Detected Gamma-Ray Burst 9.2 How Much CSM Is Sufficient to Choke a Jet? 9.3 Radio Observations of Ic-BL SNe Discovered by ZTF References 10 Summary and the Future