AstroNote 2026-220

In our search for recent LSST supernova candidates using the LSST brokers, we noticed two recent transients likely located in SDSS J234757.66+001135.0, a spiral galaxy with SDSS and DESI DR1 spectroscopy (z (SDSS) = 0.1845583 +/- 0.0000239, SDSS DR19).

AT 2026rcf (LSST-AP-DO-170595943092060203, with coordinates RA, Dec (J2000) = 23:47:57.495, +00:11:36.78, was discovered by ALeRCE (Forster et al. TNS Astronomical Transient Report No. 311452), with a first LSST detection on 2026-06-28 at 09:54:07 UT at a magnitude of i-LSST = 20.6361 +/- 0.0241. A detection by WFST (WFST260703bhzyi) was reported to TNS by Xu et al. at g-WFST = 20.56 +/- 0.09 on 2026-07-03 at 19:46:33 UT.

AT 2026tzm (WFST260708atocd, with coordinates RA, Dec (J2000) = 23:47:57.850, +00:11:36.76 was discovered by WFXT (Xu et al. TNS Astronomical Transient Report No. 314578) with a first WFST detection on 2026-07-08 at 19:48:00 UT at g-WFST = 21.30 +/- 0.08. It was detected by LSST (LSST-AP-DO-170657505023098990) on 2026-07-12 at 08:24:18 UT at r-LSST = 20.8263 +/- 0.0149 (reported to TNS by Forster et al., ALeRCE). AT 2026rcf and AT 2026tzm are located 1.7" N, 2.5" W (9.4 kpc) and 1.7" N, 2.8" E (9.9 kpc), respectively, from the galaxy centre. 

The two transients are also detected in our follow up observations using Las Cumbres Observatory 1-m telescopes and Sinistro cameras.

The time difference between the first detections of the two transients is of only 10.41 days and the angular separation is of 5.3 arcsec. If the transients are located in SDSS J234757.66+001135.0 their absolute magnitudes at the current observed maximum light are consistent with those of SNe Ia (or other types of supernovae of similar peak luminosity). However, the current information on the evolution of the two light curves is very limited. 

We encourage spectral classification and photometric follow up of the two transients to confirm their redshifts, types, and phases and to check if they are at the redshift of the apparent host galaxy or if they are two images of a background lensed supernova. 

The LSST light curves and image cutouts are available at the LSST brokers:

AT 2026rcf (LSST-AP-DO-170595943092060203)

Lasair 
ALeRCE 
ANTARES 
Fink 
Babamul 

AT 2026tzm (LSST-AP-DO-170657505023098990)

Lasair
ALeRCE 
ANTARES 
Fink 
Babamul 
 

This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, SGLF and Superluminous Supernovae surveys).

Information on the LSST alerts and brokers.