TITLE:   GCN CIRCULAR
NUMBER:  27604
SUBJECT: GRB 200412B: continued AbAO, Mondy, TSHAO, Terskol optical observations
DATE:    20/04/18 16:55:29 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI), A. Pozanenko (IKI), A.V. Shein (INASAN), I.A. Izvekova 
(ICAMER NASU),  E. Klunko (ISTP),  M. Eselevich (ISTP), R. Ya. 
Inasaridze (AbAO), V.R. Ayvazian (AbAO),  G. V.  Kapanadze (AbAO), I. 
Reva (FAPHI),  E. Mazaeva (IKI), A. Volnova  (IKI),  I. Molotov (KIAM) 
report on behalf of  GRB IKI FuN:

We observed the field of GRB 200412B (Fermi GBM team, GCN 27547; Mailyan
et al., GCN 27558; see also Burgess et al., GCN 27548; Longo et al., GCN
27557; Page et al., GCN 27561; Gupta et al., GCN 27563; Zheng et al., 
GCN 27565)  with Zeiss-2000 of Mt.Terskol observatory, Zeiss-1000 1-m 
telescope of Tien Shan Astronomical Observatory,  AZT-33IK 1.5-m 
telescope of Sayan observatory (Mondy) and AS-32 (0.7m) telescope of 
Abastumani Observatory.  We  still detected  the afterglow of GRB 
200412B  (Lipunov et al., GCNs 27555, 27556; see also e.g. Kumar et al., 
GCN 27564; Belkin et al., GCN 27566, Stecklum et al., GCN 27567,
Moskvitin GCN 27570; Xin  et al., GCN 27571).  Preliminary photometry of 
the afterglow is following.

Date       UT start  t-T0       Filter  OT Err. UL   Observatory
                     (mid, days)
2020-04-13 23:10:27 1.59707 18*120 R 20.57 0.03 22.8 Terskol Z-2000
2020-04-15 14:55:11 3.25105 15*120 V 21.95 0.14 22.8 Mondy AZT-33IK
2020-04-16 17:04:23 4.33800 11*120 R n/d   n/d  20.5 Mondy AZT-33IK
2020-04-16 22:30:40 4.57812 61*60  R n/d   n/d  22.2 AbAO AS-32
2020-04-17 14:51:32 5.25754 28*120 R 23.22 0.28 23.4 Mondy AZT-33IK
2020-04-17 19:53:06 5.47912 91*60  R n/d   n/d  22.3 TSHAO Z-1000
2020-04-17 20:12:07 5.48573 36*120 R 23.29 0.29 23.4 Terskol Z-2000

The photometry is based on nearby USNO-B1.0 stars.
The light curve based on on above photometry  and photometry published 
earlier (Belkin  et al., GCN 27574;  Belkin  et al., GCN 27566;  Belkin 
et al., GCN 27583) can be found at 
http://grb.rssi.ru/GRB200412B/GRB200412B_LC.png
(For reference, we also posted the photometric results of the Tautenburg 
Observatory (Klose et al., GCN 27593; Stecklum et al., GCN 27582; Klose 
et al., GCN 27575; Stecklum et al., GCN 27567).

The index of power law decay taken from our R-filter observations up to 
2.3 days is -1.58+/-0.07 (see also  Xin  et al. GCN 27571; Klose et al., 
GCN 27575). Later we may assume  a jet break previously suggested by 
Klose et al. (GCN 27575) and Stecklum et al. (GCN 27567).