GCN Circular 45085

C. Adami (LAM/Pytheas/AMU), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), F. Schussler (CEA Paris-Saclay) report on behalf of a larger collaboration:

We observed the WISEA J212302.62+340634.2 source (no available public spectroscopy in NED), at ~4.9arcmin from the mean coordinates of the IceCube 
event IceCube260704A (Zegarelli et al., GCN 45075
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 ), using the T193cm telescope at Observatoire de Haute-Provence (France) with the MISTRAL 
spectro-imager. 

We obtained 6 min of exposure in the r-band starting at 2026-07-05T02:04 UT (18.8h after the Zegarelli et al. trigger).
In the preliminar stacked images, we do not detect significant magnitude change as compared to the PanStarrs r-band magnitude of r=18.05.

We also observed in spectroscopic mode:

- We obtained a total of 60 min of exposures (2 x 30min) with the MISTRAL spectroscopic blue setting from 4000 to 7800 AA, starting at 2026-07-05 00:18 UT (17h after the trigger). With a preliminar data reduction, we very clearly detect Halpha (apparently with 
a single peak) at a redshift of 0.1402. We also detect very clearly an intense double-peaked [NII]@6584A emission line. No other emission 
line are visible. We detect however Magnesium@5175A, CaFe@5269A and NaD@5892A in absorption.
The log(Halpha/[NII]) is close to -0.1, likely placing this galaxy in the AGN/LINER region in a BPT diagram.
The two peaks of the [NII] emission line are separated by ~300km/s.

- We then obtained a second serie of 3 x 30min starting at 2026-07-05 23:13 UT (~40h after the trigger). With a preliminar data reduction, we still clearly detect Halpha with 
a single peak at the same redshift and with a similar intensity. The [NII]@6584A emission line may show a mild evolution: the flux is stronger and the two peaks are much less separated and proeminent.

The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the STDWeb/STDPipe tools (Karpov 2025), is in the AB system, and is not corrected for Galactic extinction.

We acknowledge the excellent support from Observatoire de Haute-Provence and in particular Jean Pierre Troncin.