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# System prepended metadata

title: IceCube-210629A - Spectroscopic observation of AT2021osi

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# IceCube-210629A - Spectroscopic observation of AT2021osi

Simeon Reusch, Jannis Necker, Robert Stein (DESY), Anna Franckowiak (DESY/Ruhr-University Bochum), Sven Weimann (Ruhr-University Bochum), Sjoert van Velzen (Leiden University), Marek Kowalski (DESY), Mansi Kasliwal and Matthew Graham (Caltech) report:

We observed ZTF candidate AT2021osi (Necker et al, GCN 30349), a possible counterpart to high-energy neutrino IceCube-210629A (Santander et. al, GCN 30342), with the Gemini GMOS-N spectrograph on 2 July 2021. Using the R400 grating (1 arcsec slit), we obtained 2 x 750s observations under our ToO program GN-2021A-Q-116 (PI: Kasliwal). These were reduced and flux-calibrated with PypeIt (Prochaska et al. 2020).

The spectrum of AT2021osi shows AGN-like features, namely prominent and broad Balmer lines (alpha, beta and gamma). Based on these lines, we also infer a redshift z=0.194.

We thank the GMOS-N observing staff for quickly scheduling and executing our observations, in particular Atsuko Nitta.