AstroNote 2021-91

The Zwicky Transient Facility (ZTF; Bellm et al. 2019; Graham et al. 2019) Infant Supernova Science Program (Gal-Yam 2019) reports the early discovery and rapid follow-up of AT 2021gno (ZTF21aaqhhfu) and AT 2021gmj (ZTF21aaqgmjt), following the methodology outlined by Gal-Yam et al. (2011).

AT 2021gno was first detected on ZTF r-band images obtained on March 20, 2020 at 05:38 UT (Bruch et al., 2021, TNS Report 103274). AT 2021gmj was discovered by Valenti et al. (2021, TNS Report 103223) on March 20, 2020 at 07:40 UT and independently discovered with ZTF on March 20, 2020 at 05:48 UT by Forster et al. (2021, TNS Report, 103276). Both objects were detected about 2 days after the last non-detection. Both objects were picked up by a custom filter for infant SNe on the AMPEL broker system (Nordin et al. 2019). The objects were saved by duty astronomers and rapid follow-up was triggered.

Assuming the redshifts of the apparent hosts (AT 2021gno in NGC 4165, z=0.0062 and AT 2021gmj in NGC 3310 with z=0.0033, both from NED) the SNe were discovered around absolute magnitude Mr=-14 and -14.5 respectively. Rapid Swift observations have been triggered and additional observations are ongoing.

We will continue to distribute alerts on such early SN detections via AstroNotes; additional follow-up observations of both transients are encouraged.

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 Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.