Hintze Centre for Astrophysical Surveys

Abstract:

Accretion and relativistic jet formation in black holes occur across a wide range of their masses, revealing qualitative and quantitative similarities that connect the entire population of black holes. In March 2026, researchers from all areas across the black hole mass spectrum met in Oxford to educate, explore and forge new research directions.

Abstract:

Interacting supernovae probe the twilight years of massive stars, exhibiting signatures of interaction between the supernova ejecta and surrounding material expelled from the progenitor. We present the peculiar interacting supernova, SN 2025ngs in NGC 5961 (37.8 Mpc). This transient toes the line between strongly interacting supernovae (Type IIn) and Type IIP supernovae. SN 2025ngs presents photometrically as a short-plateau supernova, with a plateau duration t PT≈70 days. Interaction features subside within a week postexplosion, consistent with the growing number of flash supernovae, giving way to a short period where a typical IIP spectrum is exhibited. Towards the drop off the plateau, interaction features re-emerge, exhibiting complex Hα profiles throughout the rest of the transient evolution. We compare with models of early spectra, finding the abundances generally consistent with a supergiant progenitor with a high mass-loss rate (10−3 M⊙ yr−1). Early, high-resolution spectra reveal a double-horned Hα profile, providing strong evidence for shock interaction with a proximate disk-like circumstellar medium. Spectroscopically, SN 2025ngs closely resembles the luminous SN 1998S, despite photometric differences, with SN 2025ngs having a relatively modest peak magnitude of MV = −17.9 mag, adding another member to the surprisingly diverse 98S-like group.

Abstract:

Type Ia supernovae (SNe Ia) are well-known standardisable candles, and are one of the main ways to measure the distance to their host galaxies. However, extinction due to interstellar dust causes objects to appear fainter and redder. Correcting for this requires estimating the amount of intervening material and how the extinction changes as a function of wavelength. We present and analyse optical and near-infrared data of the well-observed SN 2024gy and use these to compare different extinction estimation techniques, making use of photometric, spectroscopic, and polarimetric data. SN 2024gy is a normal SN Ia with high velocity (HV) components in Si  II λ 6355 (phase < −10 days) and a particularly strong HV feature in the Ca  II near-infrared triplet (up to peak). Modelling SN 2024gy with TARDIS shows better matches with a double-detonation scenario compared to a delayed-detonation scenario due to a better match to the Ca  II HV component. A measurement of the stable Ni/Fe ratio, however, favours a delayed-detonation scenario. Host extinction estimates range from E ( B − V ) host = 0.12 ± 0.02 mag (narrow interstellar absorption lines) to E ( B − V ) host = 0.24 ± 0.06 mag (Lira law) with a mean of E ( B − V ) host = 0.22 ± 0.04 mag, assuming R V = 3.1. The spread between different methods highlights the challenge of accurately estimating the amount of extinction light suffers before being observed.