AstroNote 2024-204

Munoz-Arancibia, on behalf of the ALeRCE broker, reported recently (AstroNote 2024-197) on two ongoing transients separated by ~12 arcsec towards the Seyfert 2 galaxy 2MASX J15122674+3232460. Both transients were discovered using the ZTF public alerts. AT 2024nqr (ZTF24aauekqv, ATLAS24kmi, GOTO24dil, PS24grn) was first reported to TNS by Sollerman et al.
(TNS Astronomical Transient Report No. 216737) and AT 2024pgd (ZTF24aauywft) was reported to TNS by Pérez-Fournon et al. (TNS Astronomical Transient Report No. 218533). The two transients could be supernova siblings in the same host galaxy or different images of a transient at a higher redshift gravitationally lensed by 2MASX J15122674+3232460.

On the night of July 27 2024 we obtained long-slit spectra with GTC OSIRIS+ that confirm that both transients are type Ia supernovae at the redshift of z = 0.089149 +/- 0.000030 of 2MASX J15122674+3232460 (SDSS J151226.70+323247.0, LEDA 2001870) observed at about two weeks after maximum light. The current ZTF and ATLAS forced photometry light curves are consistent with a small delay of the times of peak magnitude of the two supernovae, of about 3-5 days, one of the shortest observed in supernova siblings (see, e.g. Dhawan et al. 2024).

The ZTF light curves of these SNe are available at the ZTF/LSST brokers, e.g.:

SN 2024nqr (ZTF24aauekqv) Lasair

SN 2024nqr (ZTF24aauekqv) ALeRCE

SN 2024pgd (ZTF24aauywft) Lasair

SN 2024pgd  (ZTF24aauywft) ALeRCE

Positions of SN 2024nqr (East) and SN 2024pgd (West) on the Legacy Surveys imaging

Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma (program GTCMULTIPLE4E-24A).

We are very grateful to GTC staff for the observations.