Over the past week, NuSTAR observed supernova SN 2026sqf, a rare type of supernova, which was discovered on July 8th by an amateur astronomer in Utah. Supernovae, or exploding stars, are empirically classified based on how their brightness and spectroscopic properties evolve over time. Some supernovae, such as Type II supernovae, occur at the end of a massive star’s life. Others, known as Type Ia supernovae, are the result of a binary star system where a white dwarf accretes from its companion and crosses over a critical mass limit that causes it to detonate completely.  One very rare subclass of the latter, representing <<1% of Type Ia supernovae, have spectra that show narrow emission lines due to interactions with dense gas and dust surrounding the star.  This matter is called circumstellar material (CSM) and these rare cosmic explosions are called Type Ia-CSM supernovae.  Studying such events provide one of the few direct probes of mass loss from the supernova progenitor system in its late evolutionary stages.  However, the high-energy view of such systems remains almost entirely unexplored.  Until recently, SN 2012ca, detected by NASA's Chandra X-ray Observatory months to years after the explosion, was the only SN Ia-CSM detected in X-rays.  High-energy X-rays above ~10 keV, as probed by NuSTAR, are critical to constrain the temperature of the emitting plasma and break degeneracies that are inherent to modeling X-ray spectra when only low-energy data is available. NuSTAR observations of SN 2026sqf in the nearby galaxy NGC 3310 represents, to our knowledge, the first high-energy X-ray observation of a Type Ia-CSM supernova. These data will enable unique constraints on the temperature and properties of the material surrounding this system, which, in turn, will provide clues to the properties of its progenitor.

Author: Nayana AJ, Postdoctoral Scholar (UC Berkeley)