Constraining Explosion Physics and Progenitors of Transients via Statistical Inferencing of All Sky Survey Data Streams
Creators: name: Subrayan, Bhagya Madimugar
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 510109
subject: Stellar astronomy and planetary systems

description: Advancements in astronomical imaging all-sky surveys are revolutionising the field of time domain astronomy. However, the immense volume of alert data presents a critical bottleneck in maximizing scientific returns from these surveys. Effectively analyzing alert streams to discover transients in unexplored physical parameter spaces is crucial for enhancing scientific output. Building robust infrastructure to identify, prioritize, and execute efficient follow-up strategies on alert streams from all-sky surveys becomes critical. My thesis confronts this challenge through a multidisciplinary approach, by integrating statistical methods, machine learning algorithms, and hydrodynamical simulations to constrain transient explosion properties and motivate effective follow-up initiatives. I analyze a sample of 45 Type II supernovae from the Zwicky Transient Facility (ZTF) public survey using a grid of hydrodynamical models in order to assess whether theoretically driven forecasts can intelligently guide follow-up observations supporting all-sky survey alert streams. I estimate several progenitor properties and explosion physics parameters, including zero-age main-sequence (ZAMS) mass, mass-loss rate, kinetic energy, <sup>56</sup>Ni mass synthesized, host extinction, and the time of the explosion. This work involves simulations of real-time of evolving incomplete light curves of the sample (∆t &lt; 25 days, ∆t &lt; 50 days, all data) leading to the conclusion that certain physical parameters exhibit greater reliability as indicators of true values during early epochs. This study emphasises the vital role of real-time modeling of transients, supported by multi-band synthetic light curves tailored to survey passbands, for identifying interesting transients based on their progenitor and explosion properties and determining critical epochs for follow-up observations.In my thesis, I report multi wavelength observations and characterization of the ultraluminous transient AT 2021lwx (ZTF20abrbeie; aka“Barbie”) identified in the ZTF alert stream, that was flagged as an anomaly by the Recommender Engine For Intelligent Transient Track-ing (REFITT). From a spectroscopically measured redshift of 0.9945, and slowly fading g and r light curves spanning over 1000 observer-frame days that peak with an absolute magnitude of Mr = −25.7 mag, AT 2021lwx has an extraordinary peak pseudo-bolometric luminosity of log (Lmax/[erg/s]) = 45.7. The total radiative energy is over 10<sup>53</sup> erg, and as of today, the transient continues to decline slowly following a t<sup>−5/3</sup> power-law. Modeling available photometry with MOSFiT suggests that AT 2021lwx is a tidal disruption event (TDE) candidate involving a ≈ 14 or 15 solar mass star accreting onto a supermassive black hole (SMBH) with mass M<sub>BH</sub> ≈ 10<sup>8</sup> solar mass. But, intriguingly, no host galaxy associated with the theorized SMBH is detected yet. The Pan-STARRS non-detections do not definitively exclude the existence of a galaxy hosting AT 2021lwx. Utilizing EzGal, upper limits on the stellar mass for different stellar population models were determined. These upper limits suggest that a 10<sup>10</sup> solar mass host galaxy cannot be ruled out.The enhanced sensitivity of upcoming large-scale all-sky surveys enables the early detection of transients, providing unique insights into their progenitor systems, an example being detection of shock cooling emission (SCE) in light curves of stripped-envelope supernovae(SESNe). Leveraging a statistically significant sample of these events with early detections from all-sky surveys presents an invaluable opportunity to constrain their environments, pro-genitors, and explosion properties. In my final study contributing to this thesis, I analyze a sample of 16 SESNe identified from the ZTF survey, characterised by prominent shock cooling emission features in their light curves. By modeling the SCE and the radioactive peak in these transients, I derive estimates of progenitor radius, mass of the extended envelope and explosion properties of SESNe. This analysis yields upper limits and ranges for the compactness and envelope structures of the SESN progenitors that exhibit SCE in their light curves. I conclude my thesis with a summary of the findings and their future applications.