Early ZTF and UVOT Observations of ZTF20aaelulu, a Supernova Candidate in M100

ATel #13391; A. Y. Q. Ho (Caltech), S. Schulze (Weizmann), D. Perley (LJMU), J. Sollerman (OKC), Y. Yang (Weizmann), O. Yaron (Weizmann), M. M. Kasliwal (Caltech) on behalf of the Zwicky Transient Facility collaboration
on 9 Jan 2020; 04:01 UT
Credential Certification: Mansi Manoj Kasliwal (mansi@astro.caltech.edu)

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We report early photometry of ZTF20aaelulu (AT2020oi) from the Zwicky Transient Facility (ZTF; ATel #11266) and Swift/UVOT. ZTF20aaelulu is a rapidly rising transient coincident with M100 (z=0.0052) that was announced to TNS by the ALeRCE event broker (TNS report 51926, Forster et al.) based on a single r-band detection in the public ZTF alert stream. The first ZTF detection of ZTF20aaelulu was on UT 2020 Jan 07.46 (JD 2458855.9588) at g=16.97 mag, and the next detection showed a rise of nearly 1 mag (to g=16.09) in the next 1 day (JD 2458857.0417). The color in the first epoch is blue (g-r=-0.31). The Neil Gehrels Swift Observatory began observing ZTF20aaelulu on 8 January 2020 at 10:48 UT (PI: Foley and Schulze). A sequence of images in all UVOT filters was obtained. We measured the brightness of the galaxy at the explosion site using archival Swift data and the same source and background regions like for the new UVOT observations. Afterwards, we numerically subtracted the host flux from the recent observations to obtain the brightness of the transient. We report the following magnitudes:
JD FILTER MAG_AB ERROR
2458856.95600 UVW2 17.97 0.33
2458856.96320 UVM2 18.16 0.34
2458856.95120 UVW1 17.54 0.25
2458856.95260 U 16.54 0.14
2458856.95360 B 16.22 0.15
2458856.95840 V 15.94 0.20
using a circular aperture with a radius of 3’’ and centred at RA, DEC (J2000) = 12:22:54.910,+15:49:24.97. Further Swift observations are scheduled and additional follow-up is encouraged. ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. Alert distribution service provided by DIRAC@UW. Alert filtering is being undertaken by the GROWTH marshal system, supported by NSF PIRE grant 1545949.