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TITLE:   GCN CIRCULAR
NUMBER:  28453
SUBJECT: IceCube-200916A: AbAO observations of optical candidates ZTF20acaapwk/AT2020tno, ZTF20acaapwo/AT2020tnp
DATE:    20/09/18 18:18:13 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), V. R. 
Ayvazian (AbAO),  G. V.  Kapanadze (AbAO),   A. Volnova (IKI), I. 
Molotov (KIAM)  report on behalf of IKI-GRB-FuN:

We observed the two candidate counterparts from ZTF (Reusch et al., GCN 
28441) of the neutrino event IceCube-200916A (Blaufuss et. al, GCN 
28433) with  AS-32 telescope of Abastumani observatory in R-filter.
In stacked images we cannot resolve point like sources of the 
candidates. Photometry of candidates include their (presumably) 
underlying host galaxies and presented below.


IAU Name, Date,      UT start, MJD,   Exp.,  Filter, OT, Err., UL, Ref.
                     (mid, days)

AT2020tno 2020-09-18 01:00:49 59110.04918 20*60 R  16.88 0.02 20.3 (1)
AT2020tnp 2020-09-18 01:39:12 59110.07306 12*60 R  19.62 0.22 20.0 (2)

The photometry is based on nearby USNO-B1.0 stars
Ref.(1)
USNO-B1.0_id R2
1049-0143702 14.84
1048-0142480 14.23
Ref.(2)
USNO-B1.0_id R2
1044-0132913 15.48
1044-0132991 15.73

In the case of AT2020tno the brightness is not distinguished from 
magnitude of underlying object in catalogues.
The brightens of AT2020tnp  is might be somewhat brighter than reported 
by ZTF (r=20.41 +/- 0.14; Reusch et al., GCN 28441) and apparently 
brighter than reported in catalogues.

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TITLE:   GCN CIRCULAR
NUMBER:  28465
SUBJECT: IceCube-200916A - ZTF20acaapwk/SN2020tno classified as SN Ia
DATE:    20/09/21 14:30:23 GMT
FROM:    Simeon Reusch at DESY  <simeon.reusch@desy.de>

Simeon Reusch, Robert Stein, Anna Franckowiak (DESY), Steve Schulze (WIS) and Jesper Sollerman (Stockholm University) report:

We observed ZTF candidate ZTF20acaapwk/SN2020tno (Reusch et al., GCN 28441; see also Belkin et al., GCN 28453), a possible counterpart to high-energy neutrino IceCube-200916A (Blaufuss, GCN 28433), using the NOT+ALFOSC spectrograph on 21 September 2020.

We classify SN2020tno as a type Ia supernova, thereby excluding any connection to IC200916A.

ZTF20acaapwo/AT2020tnp remains a candidate.

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The data presented here were obtained with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA.