AstroNote 2025-303

At MJD 60969.1, we obtained a spectrum of SN2025aarn (flagged in AstroNote 2025-302 as a blue, fast-rising transient) with the Alhambra Faint Object Spectrograph and Camera (ALFOSC), mounted on the 2.56m Nordic Optical Telescope (NOT) on the Roque de los Muchachos Observatory in La Palma, Spain, using Grism 4 that has resolution of R=360 with the 1” slit.

The spectrum exhibits a blue continuum, with noticeable, albeit shallow Balmer P-Cygni lines at the redshift of the host galaxy 0.0157 from DESI DR1. The spectrum strongly resembles spectra of some young Type II SNe (SN2024ggi; e.g. Shrestha et al. 2024), and we classify it as such. 

We also report a polarimetric observation of the SN taken together with the spectrum. The ALFOSC V-band imaging polarimetry shows P= 0.1+/-0.15%, being perfectly consistent with three bright Milky Way stars in the field of view. This implies the SN photosphere is consistent with high spherical symmetry at the epoch, as is typical of Type II SNe early in their evolution.

Further follow-up observations are encouraged.

We thank NOT staff for taking these observations.

Based on observations made with the Nordic Optical Telescope, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. The NOT data were obtained under program ID P72-014.