AstroNote 2025-293

SN 2025xjd (ZTF25abqhqmk) was discovered in Zwicky Transient Facility (ZTF; Bellm+19) data and sent to TNS on 2025-09-13 (MJD=60931.99). The first reported detection of SN 2025xjd is from ZTF alert forced photometry and yields m=19.92 +/- 0.195 mag (AB) in r-band at MJD=60930.52. One day later (MJD=60931.51), a ZTF alert measured SN 2025xjd at m=19.55 +/- 0.196 mag in the r-band. Note the large uncertainties due to these detections originating from the ZTF twilight survey.

SN 2025xjd is located in IC 2248 (z=0.013797 / distance modulus=33.95 mag; Albareti+17), so the ZTF alert detection places SN 2025xjd at M_r = -14.4 mag. We triggered a Gemini-N/GMOS rToO (PI Rehemtulla) shortly after discovery and obtained B480+R400 spectroscopy at MJD=60932.59. This spectrum revealed features characteristic of Type Iax SNe (Foley+13): narrow, Si II doublet absorption, Fe II absorption, and (tentatively) Ca NIR triplet absorption. These features, together with their low expansion velocities (v ~ 3,000 km/s) and the faint absolute magnitude, suggest that SN 2025xjd is a low luminosity Type Iax SN. The sub-class of low luminosity Type Iax SNe, prototyped by SN 2008ha (Foley+09), includes only very few other examples: SN 2010ae (Stritzinger+14), iPTF 16fnm (Miller+17), SN 2019gsc (Srivastav+20), SN 2019ttf (De+20), SN 2020kyg (Srivastav+22), SN 2021fcg (Karambelkar+21), and SN 2024vjm (Kwok+25). The attached figure shows strong similarities between our Gemini spectrum of SN 2025xjd and other pre-peak spectra of low luminosity Type Iax SNe. A later, post-peak spectrum (MJD=60943.18) obtained with NOT/ALFOSC shows the velocity of these features decreased to v ~ 1,500 km/s.

We also requested ultraviolet imaging of SN 2025xjd with the Ultraviolet/Optical Telescope (UVOT; Roming+05) aboard the Neil Gehrels Swift Observatory (Swift; Gehrels+04). There is no clear detection at this time, however, we will obtain template imaging and attempt image subtraction once the SN has faded.

Based on our latest photometry with the SED Machine (SEDM; Blagorodnova+18), SN 2025xjd appears to have begun fading (m_g~20 mag). Large uncertainties and limited coverage make it challenging to precisely estimate SN 2025xjd’s peak magnitude, but we conservatively estimate M > -15. We encourage photometric and spectroscopic follow-up observations to track the evolution of this rare transient.

We thank the Gemini observers and staff 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., C.L., and A.A.M. are supported by DoE award #DE-SC0025599.