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It has been clear for decades that Type Ia supernovae (SNe Ia) arise from the explosions of carbon/oxygen white dwarfs (WDs) in binaries. These explosions have played a fundamental role probing dark energy. However, the progenitor configuration and the explosion mechanism of SNe Ia remain highly controversial. The traditional scenario involving a Chandrasekhar-mass (~1.4 Msun) WD may have trouble reproducing the observed event rate. The helium-shell double detonation (DDet) scenario, in which a sub-Chandrasekhar-mass WD is ignited by the detonation of a helium shell atop of it, is a promising mechanism to account for a substantial fraction of the SN Ia population. This scenario can lead to both normal, cosmologically useful SNe Ia and peculiar “weirdos”. Observationally, identifying DDet SNe is possible but challenging. In this talk, I will review observers’ efforts in searching for smoking-gun evidence for a DDet. I will present our discovery of SN 2020jgb, a peculiar SN Ia that is indisputably ignited by a helium shell, as well as the first systematic study on these peculiar DDet SNe and their host environments. Then I will move from individual events to the population, discussing what we can learn from the unprecedented legacy of early-time light curves of SNe Ia detected and monitored by Zwicky Transient Facility (ZTF). I will introduce our Gaussian process (GP) model in estimating the intrinsic colors of young SNe Ia, which retain rich information of their progenitor systems and explosion mechanisms. In the future, we will be able to put a tighter constraint on how many SNe Ia actually result from sub-Chandrasekhar-mass WDs.
Chang Liu is a PhD student at Northwestern University, before which he obtained his Bachelor’s degree at Peking University. Chang is broadly interested in time-domain astronomy, and currently focuses on the explosion mechanisms of Type Ia SNe (SNe Ia). His PhD thesis will be based upon building a sample of helium-shell double-detonation (DDet) SNe Ia from sub-Chandrasekhar mass WDs. This will be achieved by (i) following up new peculiar SNe Ia, (ii) datamining the legacy of ongoing surveys such as Zwicky Transient Facility (ZTF), and (iii) updating/designing our survey and follow-up strategies for upcoming facilities (e.g., La Silla Schmidt Southern Survey; LS4). Besides, he also studies tidal disruption events on bound orbits, as well as gravitational microlensing caused by Galactic stellar mass black holes.
Place: N630
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