Dr Shubham Srivastav

Abstract:

We present the photometric and spectroscopic analysis of five Type Ibn supernovae (SNe): SN 2020nxt, SN 2020taz, SN 2021bbv, SN 2023utc, and SN 2024aej. These events share key observational features and belong to a family of objects similar to the prototypical Type Ibn SN 2006jc. The SNe exhibit rise times of approximately 10 days and peak absolute magnitudes ranging from −16.5 to −19 mag. Notably, SN 2023utc is the faintest Type Ibn SN discovered to date, with an exceptionally low r -band absolute magnitude of −16.4 mag. The pseudo-bolometric light curves peak at (1 − 10)×10 42 erg s −1 , with total radiated energies on the order of (1 − 10)×10 48 erg. Spectroscopically, these SNe display a relatively slow spectral evolution. The early spectra are characterised by a hot blue continuum and prominent He  I emission lines. The early spectra also show blackbody temperatures exceeding 10 000 K, with a subsequent decline in temperature during later phases. Narrow He  I lines, which are indicative of unshocked circumstellar material (CSM), show velocities of approximately 1000 km s −1 . The spectra suggest that the progenitors of these SNe underwent significant mass loss prior to the explosion, resulting in a He-rich CSM. Our light curve modelling yielded estimates for the ejecta mass ( M ej ) in the range 1 − 3 M ⊙ with kinetic energies ( E Kin ) of (0.1 − 1)×10 50 erg. The inferred CSM mass ranges from 0.2 to 1 M ⊙ . These findings are consistent with expectations for core collapse events arising from relatively massive envelope-stripped progenitors.

Abstract:

We present results from the Pan-STARRS optical search for kilonovae without the aid of gravitational wave and gamma-ray burst triggers. The search was conducted from 2019 October 26 to 2022 December 15. During this time, we reported 29 740 transients observed by Pan-STARRS to the IAU Transient Name Server. Of these, 175 were Pan-STARRS credited discoveries that had a host galaxy within 200 Mpc and had discovery absolute magnitudes . A subset of 11 transients was plausibly identified as kilonova candidates by our kilonova prediction algorithm. Through a combination of historical forced photometry, extensive follow-up, and aggregating observations from multiple sky surveys, we eliminated all as kilonova candidates. Rapidly evolving outbursts from massive stars (likely to be Luminous Blue Variable eruptions) accounted for 55 per cent of the subset’s contaminating sources. We estimate the rate of such eruptions using the Asteroid Terrestrial-impact Last Alert System 100 Mpc volume-limited survey data. As these outbursts appear to be significant contaminants in kilonova searches, we estimate contaminating numbers when searching gravitational wave skymaps produced by the LIGO-Virgo-Kagra science collaboration during the Rubin era. The Legacy Survey of Space and time, reaching limiting magnitudes of , could detect 2–6 massive stellar outbursts per 500 deg within a 4-d observing window, within the skymaps and volumes typical for binary neutron star mergers projected for Ligo-Virgo-Kagra Observing run 5. We conclude that while they may be a contaminant, they can be photometrically identified.