LFBOT ATeL#17646: MISTRAL photometric and spectroscopic observations
ATel #17649; B. Schneider (LAM), C. Adami (LAM/Pytheas/AMU), S. Basa (UAR Pytheas), N. Globus (UNAM), A. M. Watson (UNAM), E. Le Floc'h (CEA-Saclay), W. H. Lee (UNAM)
on 6 Feb 2026; 22:45 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Noemie Globus (globus@astro.unam.mx)
We observed the field of the candidate LFBOT reported by Tsuboi et al. (ATeL #17646) and observed by Gill et al. (ATeL #17647) and Pereyra et al. (ATeL #17648) with the MISTRAL spectro imager at the T193 telescope of the Observatoire de Haute-Provence, France (https://ohp.osupytheas.fr/mistral-spectro-imager/) on the night of 2026-02-06 UT.
MISTRAL imaged the position in g, r and i bands. The data were analysed in STDWeb/STDPipe (Karpov 2025). We still detect the transient with the following magnitudes:
r = 16.97 +/- 0.01 at 19:27 UT with a 180s exposure
g = 16.83 +/- 0.01 at 19:37 UT with a 160s exposure
i = 17.08 +/- 0.01 at 19:42 UT with a 270s exposure
We also used MISTRAL in spectroscopic mode to obtain two spectra, of 25 and 20 minutes each. By summing these spectra, we obtained a nearly featureless blue spectrum, very similar to the public spectrum of AT2018cow. Using this as a template, the best-fit redshift for the current object is approximately 0.01, strongly suggesting that we are observing an LFBOT. The absence of emission lines also argues against a stellar origin, but we encourage continued follow-up to confirm its nature.
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean-Pierre Troncin and the SOPHIE observer Mathilde Timmermans.
