We report the detection of a counterpart to AT2021yja, a nearby supernova candidate in NGC 1325 (22 Mpc), in imaging obtained 22 hours before the ATLAS discovery (Smith et al., AstroNote 2021-235). The source is clearly detected in a single epoch of gri imaging obtained with the multi-channel MuSCAT3 imager on the Faulkes-North telescope at Haleakala, Hawaii at UTC 2021-09-07 15:02:28 (through program FTPEPO2017AB-002). At that time, the source had the following brightnesses:
MJD Filter Mag Err
59464.6267 gp 20.4 0.2
59464.6267 ip 20.7 0.2
59464.6267 rp 20.7 0.2
We also note a HST/WFPC2 F606W image obtained on UTC 1997-03-26 13:01:55.200 with a possible counterpart at the location of this source. Aperture photometry of the HST counterpart suggests it was 21 mag at the time. The agreement between this magnitude and the counterpart observed ~22 hours before the ATLAS discovery suggests they may be the same source. In either case, the relatively faint magnitude of the MuSCAT3 source observed 22 hours before the ATLAS discovery of a source with m_c = 15.3 mag suggests an extremely rapid rise, and combined with the absolute magnitude of -16.4 mag, a likely young supernova.
| Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| TNS | 2021yja | 03:24:21.174 | -21:33:56.23 | 03:24:21.180 | -21:33:56.20 | SN IIP | 0.0053 |
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