AstroNote 2025-345

SN 2025ahqr (ZTF25acepvuo) was discovered in Zwicky Transient Facility (ZTF; Bellm+19) data and sent to TNS on 2025-12-20 (MJD=61029.38). It was first detected in ZTF data at MJD=61002.55 with m=20.03 +/- 0.151 mag (AB) in g-band. Subsequent g-band detections show a slow rise to m=19.47 +/- 0.132 mag at MJD=61010.49: a ~0.5 mag rise over about eight days. The first r-band detection occurred much later at MJD=61028.52 with m=18.55 +/- 0.062 mag. The ZTF alert and alert forced photometry light curves show erroneous non-detections making it challenging to precisely estimate a g-r color, although we roughly approximate it to have g-r >~ 1.5 mag suggesting that SN 2025ahqr is strongly extincted by dust. 

SN 2025ahqr is located in Messier 108 (M108), which the ELVES survey (Carlsten+22) measures to have z=0.002328. The Cosmicflows-3 survey (Tully+16) measures a redshift-independent distance to M108 of 9.04 +/- 0.45 Mpc (distance modulus=29.78 mag) using the Tully-Fisher relation. The distance measurement implies an absolute magnitude of M = -11.23 mag from the recent ZTF r-band detection before Milky Way line-of-sight and host galaxy reddening correction. We note that this absolute magnitude will brighten significantly once the photometry is corrected for reddening from the host galaxy.

We obtained P60/SEDM spectroscopy at MJD=61029.34 and Gemini-N/GMOS rapid ToO spectroscopy (PI Rehemtulla) at MJD=61029.57. The GMOS spectrum was obtained with the R400 and B480 gratings and was reduced using the DRAGONS pipeline. The spectrum revealed features and expansion velocities often seen in Type Iax SNe (Foley+13), especially those in the low luminosity subclass. The most prominent feature is the Ca II near infrared triplet which is detected at v ~ 4,000 km/s. We also detect features at <~4,000 km/s which align with species observed in other Type Iax: O I, Na I, Si II. We match our GMOS spectra to those from other low luminosity Iax and find clear similarities (see attached figure). Our spectrum of SN 2025ahqr best matches to others at a phase of about three weeks after peak.

Originally prototyped by SN 2008ha (Foley+09), only very few other low luminosity Type Iax SNe are known: SN 2010ae (Stritzinger+14), iPTF 16fnm (Miller+17), SN 2019gsc (Srivastav+20), SN 2019ttf (De+20), SN 2020kyg (Srivastav+22), SN 2021fcg (Karambelkar+21), SN 2024vjm (Kwok+25), and SN 2025xjd (Rehemtulla+25). SN 2025ahqr’s redshift of 0.002328 places it as the most nearby low luminosity SN Iax of those listed here. We encourage photometric and spectroscopic follow-up observations to track the evolution of this rare transient.

We sincerely thank the Gemini observers for quickly obtaining these observations.

Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA.

SED Machine is based upon work supported by the National Science Foundation under Grant No. 1106171.

Zwicky Transient Facility access for N.R., C.L. and A.A.M. was supported by Northwestern University and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). N.R. is supported by a Northwestern University Presidential Fellowship.