AstroNote 2026-152

AT 2026nik was first detected by the Zwicky Transient Facility on MJD 61182.2 with magnitudes of g = 18.35 ± 0.08 and r = 18.78 ± 0.10, implying a MW extinction corrected colour of g-r ~ -0.5. An earlier ATLAS detection on MJD 61180.0 was reported soon after at c = 19.60, implying a >1 mag rise in 2 days. Liverpool Telescope IO:O follow-up on MJD 91182.9 confirmed its exceptionally blue colour, from which we find g = 18.27 ± 0.05 and r = 18.71 ± 0.06. An additional LT epoch was taken on MJD 61185.0; we measure g = 18.53 ± 0.15, implying that the transient may have started fading (low SNR due to being <10 degrees from the moon).

We obtained a spectrum with the Next Generation Palomar Spectrograph (NGPS; AstroNote 2024-340) on the Palomar 200-inch Hale Telescope, covering an observed wavelength range of 3065.8A - 10236A. This spectrum showed a featureless, blue continuum, similar to the Gemini South GMOS spectrum reported in AstroNote 2026-151. The spectrum shows two potential narrow absorption lines in the blue (at wavelengths of 3305 and 3313.5 Angstroms) consistent with the Mg II doublet at z = 0.182.

If correct, this implies peak rest-frame absolute magnitudes from LT of M_g = -21.38 and M_r = -20.94 after MW extinction correction and a simple 2.5log10(1+z) K-correction. We note that this, and its so far featureless spectra, are consistent with the optical properties of previously classified Luminous Fast Blue Optical Transients (LFBOTs) such as AT2018cow and AT2026dbl. We thus encourage multi-wavelength follow-up.

Based on observations obtained with the Samuel Oschin Telescope 48-inch at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan, and OKC, University of Stockholm, Sweden. Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA.

Based on observations made with the Liverpool Telescope operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council.

NGPS is a new medium-resolution, single-object, long-slit optical spectrograph on the Palomar 200-in Hale Telescope at Palomar Observatory. NGPS replaces the Double Beam Spectrograph (DBSP; Oke & Gunn 1982), the workhorse Palomar 200-in optical spectrograph for four decades. NGPS is designed to be over a factor of three higher throughput than DBSP.  NGPS is a partnership between Caltech, Peking University, the National Astronomical Observatories of the Chinese Academy of Sciences, and Jet Propulsion Laboratory. The NGPS team acknowledges generous support from Caltech, the National Science Foundation (2018866), the Heising Simons Foundation (2020-1865), Strategic Priority Research Program of the Chinese Academy of Sciences (XDB0550100), and the National Natural Science Foundation of China (11927804).