AstroNote 2023-274

SN2023rgo is a transient coincident with the galaxy UGC 03416 (z=0.0133), located 6.5" S and 1.5" E of the galaxy core. Its ZTF light curve has remained approximately flat at r~19.3 mag, with a few undulations and a color g-r = 0.4 mag, for nearly 50 days.

An LRIS spectrum obtained on 2023-10-17 shows narrow galaxy emission lines at z=0.226, revealing SN2023rgo to be a background source unrelated to UGC 03416. At this redshift, the transient's peak absolute magnitude is M_r = -20.8 mag (including cosmological K-correction of 2.5*log(1+z)). Furthermore, the spectrum is well matched with SN Ic templates at the same redshift. Combining the light curve and spectroscopic information, we conclude SN2023rgo is in fact a Type I superluminous supernova, and the association with UGC 03416 is entirely coincidental.

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 Grants No. AST-2034437 and a collaboration including current partners Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley , the University of Wisconsin at Milwaukee, University of Warwick, Ruhr University, Cornell University, Northwestern University and Drexel University. Operations are conducted by COO, IPAC, and UW.