The Zwicky Transient Facility Census of the Local Universe I: Systematic search for Calcium rich gap transients reveal three related spectroscopic sub-classes
Creators: name: De, Kishalay
name: Kasliwal, Mansi M.
name: Tzanidakis, Anastasios
name: Fremling, U. Christoffer
name: Adams, Scott
name: Andreoni, Igor
name: Bagdasaryan, Ashot
name: Bellm, Eric C.
name: Bildsten, Lars
name: Cannella, Christopher
name: Cook, David O.
name: Delacroix, Alexandre
name: Drake, Andrew
name: Duev, Dmitry
name: Dugas, Alison
name: Frederick, Sara
name: Gal-Yam, Avishay
name: Goldstein, Daniel
name: Golkhou, V. Zach
name: Graham, Matthew J.
name: Hale, David
name: Hankins, Matthew
name: Helou, George
name: Ho, Anna Y. Q.
name: Irani, Ido
name: Jencson, Jacob E.
name: Kaye, Stephen
name: Kulkarni, S. R.
name: Kupfer, Thomas
name: Laher, Russ R.
name: Leadbeater, Robin
name: Lunnan, Ragnhild
name: Masci, Frank J.
name: Miller, Adam A.
name: Neill, James D.
name: Ofek, Eran O.
name: Perley, Daniel A.
name: Polin, Abigail
name: Prince, Thomas A.
name: Quataert, Eliot
name: Reiley, Dan
name: Riddle, Reed L.
name: Rusholme, Ben
name: Sharma, Yashvi
name: Shupe, David L.
name: Sollerman, Jesper
name: Tartaglia, Leonardo
name: Walters, Richard
name: Yan, Lin
name: Yao, Yuhan
Publisher: name: arXiv
Year: 2020
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: (Abridged) Using the Zwicky Transient Facility alert stream, we are conducting a large campaign to spectroscopically classify all transients occurring in galaxies in the Census of the Local Universe (CLU) catalog. The aim of the experiment is to construct a spectroscopically complete, volume-limited sample of transients coincident within 100" of CLU galaxies out to 200 Mpc, and to a depth of 20 mag. We describe the survey design and spectroscopic completeness from the first 16 months of operations. We present results from a systematic search for Calcium rich gap transients in the sample of 22 low luminosity (peak absolute magnitude $M &gt; -17$), hydrogen poor events found in the experiment (out of 754 spectroscopically classified SNe). We report the detection of eight Calcium rich gap transients, and constrain their volumetric rate to be at least $\approx 15\pm5$% of the SN Ia rate. Combining this sample with ten events from the literature, we find a likely continuum of spectroscopic properties ranging from events with SN Ia-like features (Ca-Ia objects) to SN Ib/c-like features (Ca-Ib/c objects) at peak light. Within the Ca-Ib/c events, we find two populations of events distinguished by their red ($g - r \approx 1.5$ mag) or green ($g - r \approx 0.5$ mag) spectral colors at $r$-band peak, wherein redder events show strong line blanketing signatures, slower light curves, weaker He lines and lower [Ca II]/[O I] in the nebular phase. Together, we find that the spectroscopic continuum, volumetric rates and striking old environments are consistent with the explosive burning of He shells on low mass white dwarfs. We posit that Ca-Ia and red Ca-Ib/c objects are consistent with the double detonation of He shells with high He burning efficiency, while green Ca-Ib/c objects could arise from less efficient He burning scenarios such as detonations in low density He shells or He shell deflagrations.
description: 30 figures, 6 tables. Submitted to ApJ