AstroNote 2023-66

AT 2023dbc (ZTF23aadaxfn) is a very red, rising optical transient discovered in M108 using Zwicky Transient Facility survey data (Ho et al., AstroNote 2023-57).  The first detection was on 2023 March 13.  A tentative classification of SN II has been claimed based on a YFOSC spectrum (Li et al., TNSCR 559)

We have obtained follow-up spectroscopy of this source using a number of facilities, including the Palomar 60-inch Telescope, the Liverpool Telescope, the Nordic Optical Telescope, and Keck I.  The initial spectra (between March 14-17 UT) show only a red continuum with no clear features except for a broad dip (full width ~1000 Angstroms) at around 7500 Angstroms and narrow features (in emission and absorption) originating from the host galaxy.  There is no evidence for hydrogen in these spectra beyond narrow emission associated with the underlying HII region.

Our most recent observation was acquired with the Low-Resolution Imaging Spectrometer (LRIS) on Keck I on March 20 UT.  This spectrum shows several clear absorption features centered at approximately 5950 Angstroms, 7950 Angstroms, and 10100 Angstroms, each with a velocity width of about 15000 km/s.   Using SNID, the spectrum is well-matched to template spectra of the Type Ic supernova PTF12gzk (Ben-Ami et al. 2012, ApJ, 760, 33) with a large amount of reddening (A_V ~ 3 mag).  The large extinction is consistent with strong Na I D narrow absorption seen in these spectra.

Based on the LRIS spectrum, we suggest the most likely classification of this event is Type Ic.  This would be among the nearest Type Ic SNe discovered to date, and we encourage follow-up at a variety of wavelengths despite the significant host extinction.

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.