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Kasliwal Phd Thesis Bridging the Gap: Elusive Explosions in the Local Universe Thesis by Mansi M. Kasliwal Advisor Professor Shri R. Kulkarni In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 2011 (Defended April 26, 2011) ii c 2011 Mansi M. Kasliwal All rights Reserved iii Acknowledgements The first word that comes to my mind to describe my learning experience at Caltech is exhilarating. I have no words to thank my “Guru”, Professor Shri Kulkarni. Shri taught me the “Ps” necessary to Pursue the Profession of a Professor in astroPhysics. In addition to Passion & Perseverance, I am now Prepared for Papers, Proposals, Physics, Presentations, Politics, Priorities, oPPortunity, People-skills, Patience and PJs. Thanks to the awesomely fantastic Palomar Transient Factory team, especially Peter Nugent, Robert Quimby, Eran Ofek and Nick Law for sharing the pains and joys of getting a factory off-the-ground. Thanks to Brad Cenko and Richard Walters for the many hours spent taming the robot on mimir2:9. Thanks to Avishay Gal-Yam and Lars Bildsten for illuminating discussions on different observational and theoretical aspects of transients in the gap. The journey from idea to first light to a factory churning out thousands of transients has been so much fun that I would not trade this experience for any other. Thanks to Marten van Kerkwijk for supporting my “fishing in new waters” project with the Canada France Hawaii Telescope. Thanks to Dale Frail for supporting a “kissing frogs” radio program. Thanks to Sterl Phinney, Linqing Wen and Samaya Nissanke for great discussions on the challenge of finding the light in the gravitational sound wave. Thanks to my thesis committee, Richard Ellis, Sterl Phinney, Fiona Harrison and Tony Readhead for approving a somewhat risky candidacy proposal and for their advice to make it a success. Thanks to the staff of Palomar Observatory, Keck Observatory, Gemini Observatory, CFHT Observatory, Swift Observatory and EVLA for their utmost co-operation with my rapid response campaigns. Thanks to Patrick Shopbell and Anu Mahabal for supporting the large computational needs of this project. Friends are what made Caltech home away from home. Thanks to fellow desi junta, Prabha-Krishna, Uday-Shweta, Sushree-Jayakrishnan, Arundhati-Samir, Mayank, Varun and Anti. Thanks to fellow astronomy grads, Ann Marie, Varun, Anti, Tucker, Laura, Wal- ter, Swarnima, Brian and David. Thanks to my carpool buddy, Beth Harnick-Shapiro, Ana- heim Public Library’s audiobook collection and Sarkis for making the 55,000 mile journey between candidacy and defense manageable. Thanks to my housemate, Nok, for delectable desserts and inspiring Alice demos. Special thanks to Ann Marie, who has been my of- iv ficemate since I came here, from the dungeon to the fridge to the half-window to the rap. Special thanks to Uday for Shweta. Special thanks to Prabha, for being a housemate for the first half and always being there for baatein-chai-khana-neenee during the second half. Special thanks to Varun for patiently listening to many excruciating details of this thesis. And finally, my family, to whom I dedicate this thesis. v Dedication This thesis is dedicated to my family. My grandmother Kaki, Ms. Maltibala Kasliwal, who I miss dearly since she left us on the day Caltech called me to offer admission, My grandfather Kaka, Dr. Sumatikumar Kasliwal, who will always be the sturdy back- bone of our family, All my grandparents, Ms. Maltibala and Dr. Sumatikumar Kasliwal, Ms. Pushpa and Mr. Lalit Bagla, Ms. Rajkumari and Prabhu Narayan Mohta, Ms. Santosh and Bhagirath Prasad Maheshwari, whose blessings are much cherished, My parents, Ms. Sharda Kasliwal and Mr. Manoj Kasliwal, who (in addition to genes) gave me the strength, wisdom and courage to tirelessly pursue my dreams, My parents, Ms. Sudha Maheshwari and Mr. Bhanu Mohta, who have supported my academic pursuits wholeheartedly, My sister and brother-in-law Ji3Ju, Ms. Puja Kasliwal and Mr. Aditya Maheshwari, who helped me survive the transition to a foreign land so far away from home, My brother, Mr. Parth Kasliwal, who always makes me smile and held my hand as we walked to my shaadi-ka-mandap, My niece, Ms. Ananya Maheshwari, who is as old as my thesis and with twinkling eyes taught me the five steps in the scientific method via a raisins in club soda experiment, My nephew, Mr. Aayan Maheshwari, who is an adorable little bundle of joy, and of course, My husband, Mr. Setu Mohta, who discovered the first supernova of the Palomar Transient Factory and has quite literally been the steadfast bridge behind the bridging of the gap between novae and supernovae. vi Prologue I vividly remember the drive to Palomar Mountain on October 5, 2006. Professor Shri Kulkarni was driving his bottlegreen van and bragging about how he knew the mountain roads so well that there was no need to bother using brakes. I had recently passed my qualifying exam in the astrophysics Ph.D. program at Caltech. I had also completed several small research projects exploring the optical, infrared and X- ray wavelengths. I was in search of a thesis topic – something fun, something challenging, something simple enough whose jist I could convey to my parents in a few minutes. To me, this was the beauty of astronomy. Even in the 21st century, scientists were seeking answers to very simple questions. Caltech is a fun place and so this was a “problem of choice”. I had talked to several professors about several different ideas. I had walked into their offices with a blank slate and possible questions and walked out with a well-defined plan of which telescopes could answer these and what would be a list of papers suitable for background reading. This evening though was somehow different. We were discussing a rather simple yet age-old conundrum in the venerable field of cosmic explosions – the brightest nova was a thousand times fainter than the faintest supernova leaving a wide gap in-between. Nature abhors gaps, then why hadn’t astronomers found things in-between? It turned out that novae and supernovae were simply the easiest things to find; novae because they are so abundant and supernovae because they are so bright and long-lived. So, what could we do differently to bridge the gap? How could we find these elusive transients that were fainter, faster and rarer than supernovae? Shri told me to suspend all practical concerns and just let my imagination run wild. We discussed a Plan A, B and C. But it was really Plan D that was the most compelling. Plan D was also the craziest to imagine implementing on a graduate thesis timescale. It involved taking over all the telescopes on Palomar mountain and running it like a “factory” systematically churning out transients. I enjoyed thinking about how to find an answer to this simple question. It was definitely something that kept me awake at night. Theoretically, there were several predictions of fundamental stellar physics that should result in transients in the gap. Observationally, vii there appeared to be an opportunity to work on a story from the very beginning and chart unexplored territory. As with roads not taken, one could expect a lot of hard work and the most likely outcome of an upper limit. We should be able to better quantify how hard these transients were to find but the odds of finding anything were very small. As we were driving back, Shri said, “There is no question that this is a high-risk high-gain thesis topic. The decision is now yours.” viii Abstract For centuries, we have known that our dynamic universe is adorned by cosmic fireworks: energetic and ephemeral beacons of light from a single star that are a million (nova) to a billion (supernova) times brighter than our sun. However, it had been an age-old conundrum that the brightest nova is approximately 1000 times fainter than than the faintest supernova; why should nature leave such a wide “gap”? In search of an answer, I undertook three systematic surveys for my thesis. Since I was looking for transients fainter, faster and rarer than supernovae, I focussed my search on galaxies in the local universe. We now have convincing evidence of multiple, distinct popula- tions of rare transients bridging this “gap”. Perhaps, we are witnessing new stellar physics — shell detonations in ultra-compact white dwarf binaries, electron-capture supernovae, white dwarfs collapsing into neutron stars and birth of black-holes. A small number of intensively followed-up discoveries of elusive transients sets the stage for population studies with the upcoming “Large Synoptic Survey Telescope”. This effort works towards building a complete inventory of transients in the local universe (d < 200 Mpc). It better prepares us for the search for potential electromagnetic counterparts to events in the emerging fields of gravitational wave, neutrino and ultra high energy cosmic ray astronomy as these experiments are also limited to the local universe. ix Contents List of Figures xiii List of Tables xvi 1 Introduction 1 1.1 FrameworkofExplosions: 2005 . ... 1 1.2 ThePhysics.................................... 2 1.2.1 CompactBinaries ............................ 3 1.2.2 MassiveStars............................... 4 1.3 ACompleteInventory .............................. 5 1.4 ThesisOutline .................................. 6 2 Understanding Extreme Supernovae: SN2007ax 7 2.1 Introduction.................................... 8 2.2 Observations and Data Reduction . ... 9 2.3 Analysis...................................... 10 2.3.1 OpticalLightCurve ........................... 10 2.3.2 UltravioletLightCurve . 11 2.3.3 SpectralEvolution ............................ 11 2.3.4 NIRImagingandExtinction . 13 2.3.5 Bolometric Luminosity and 56NiMass ................. 14 2.4 Discussion..................................... 15 3 Understanding Extreme Novae: P60-FasTING 24 3.1 Introduction.................................... 25 x 3.2 Observations ................................... 28 3.2.1 ExperimentDesign...........................
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