AstroNote 2026-276

AT2026ziu (ZTF26abpyrfi) was initially reported as a new astronomical transient on 2026-08-19 at 21:10:22 by GOTO (O’Neill et al., Transient Report # 320913) at a magnitude of 19.68. 

ZTF initially detected this event on 2026-08-19 at 04:09:16, with an r-band magnitude of 20.54 ± 0.15. This transient brightened rapidly, reaching r = 18.95 ± 0.12 within 3 days (a rise of ~0.53 mag/day); as a result, it was flagged as part of a pipeline to identify fast transients in the ZTF alert stream (Ho et al. 2023, ApJ 949, 120). The rapid rise to peak and blue color (g - r = –0.37 ± 0.15) motivated us to obtain follow-up observations with both the Next Generation Palomar Spectrograph (NGPS) on the P200 telescope and the GMOS spectrograph on Gemini-South. 

The NGPS spectrum was obtained on 25 August (6 d since first detection), and showed a mostly featureless blue continuum with narrow, weak H-alpha in emission at a redshift of 0.086, which we assume to be the redshift of the transient. We then triggered our fast transients program on Gemini-South (PI: Hinds), and obtained a spectrum on 3 September (15 d since first detection). This spectrum showed several narrow host galaxy lines, which we masked out prior to fitting with SNID-SAGE (Stoppa et al., 2026). The best-fit supernova was a Type Ic supernova several days after the peak, which agrees with the epoch of this spectrum relative to the photometric peak (around 24 August). 

However, there still exists some ambiguity in the template match between a normal Type Ic and a Ic-BL supernova. This event’s rapid rise, blue early color, and luminous peak (g ~ -19.7) appear to be somewhat inconsistent with the properties of the broader class of Type Ic SNe. We encourage further analysis of this interesting event by the community.