Les observations étudient la nature d'une supernova particulière

Astronomers have conducted detailed follow-up observations of a rare and unusual Type Ia supernova named SN 2023vjh, offering new insights into the nature of such cosmic events. Discovered on October 17, 2023, by the Zwicky Transient Facility (ZTF), the explosion occurred in the elliptical galaxy MCG+04-10-013, located approximately 271 million light-years away from Earth. The supernova itself was situated roughly 22,000 light-years from the galaxy's core. These observations were part of a broader effort to understand the unique characteristics of this celestial phenomenon. The study, led by Maria Kopsacheili of the Institute of Space Sciences in Barcelona, Spain, focused on both photometric and spectroscopic data collected using multiple ground-based telescopes around the world. The research team analyzed the light curve and spectral features of SN 2023vjh over a period extending from −8.6 to +47.3 days relative to its peak brightness in the B band. Their findings suggest that the supernova displays traits similar to the well-known 91bg-like subclass of Type Ia supernovae, which are marked by strong silicon absorption and the presence of intermediate-mass element features. Additionally, the explosion exhibited relatively low ejecta velocities, a defining characteristic of this subgroup. One of the key discoveries from the analysis was the unusually long rise time of SN 2023vjh, which lasted 11.6 days before reaching its peak luminosity. This is longer than the typical rise times observed in standard Type Ia supernovae. Furthermore, the optical spectra revealed a cool photosphere, indicating that the explosion produced less energy than usual. The reddening of the supernova was also notably high, ranging from 0.2 to 0.35 magnitudes, which suggests either intrinsic factors or external influences affecting the light we observe. In addition to optical data, late-phase near-infrared spectra captured at three different points in time showed absorption features corresponding to calcium, iron, and cobalt. These findings complement the optical data and provide further evidence of the unique composition of the ejected material. Notably, the absence of the H-band break, a sharp decline in flux typically associated with the formation of iron-peak elements, adds another layer of complexity to the understanding of this particular supernova. The researchers noted that while SN 2023vjh shares many similarities with other known 91bg-like events, it stands out due to its extreme dimness and rapid decline in brightness. Despite the lack of clear signs of host-galaxy extinction, the supernova’s light curve is significantly fainter than average for its class. The team proposed that the observed reddening could potentially be influenced by circumstellar material surrounding the progenitor star, which might have interacted with the expanding debris during the explosion. These findings contribute to the ongoing efforts to classify and understand the diverse behaviors of Type Ia supernovae, which play a crucial role in cosmology due to their use as standard candles for measuring cosmic distances. As more such events are studied, scientists hope to refine models of stellar evolution and better interpret the signals received from distant parts of the universe. The investigation of SN 2023vjh continues to provide valuable data that may help unravel the mysteries behind these powerful stellar explosions.