TITLE:   GCN CIRCULAR
NUMBER:  27821
SUBJECT: GRB 200524A: CrAO optical observations
DATE:    20/05/25 16:02:51 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI), A. Pozanenko (IKI),  V. Rumyantsev (CrAO),  A. Volnova 
(IKI), E. Mazaeva (IKI) report on behalf of larger GRB follow-up 
collaboration:

We observed Fermi-LAT  GRB 200524A (Dirirsa et al., GCN 27797; see also 
Pookalil et al., GCN 27809; Capalbi  et al., GCN 27811; Gupta et al., 
GCN 27818) with ZTSH 2.6m telescope of CrAO observatory starting on 
2020-05-24 (UT) 19:35:16 (Rumyantsev et al., GCN 27802). Optical 
afterglow discovered by ZTF (Ho et al., GCN 27799) and confirmed by 
several observations (Kumar et al., GCN 27800; Rumyantsev et al., GCN 
27802; Sanwal et al., GCN 27803; Perley et al., GCN 27805; Kumar et al., 
GCN 27806; de Ugarte Postigo et al., GCN 27807; Blazek et al., GCN 
27810; Ogawa et al., GCN 27813; Izzo, GCN 27817). Preliminary photometry 
of the afterglow is following

Date,      UT start, t-T0,   Exp., Filter,  OT,   Err., UL
                     (mid, days)
2020-05-24 19:35:16  0.60644 240   R        20.43 0.05 22.6
2020-05-24 19:39:28  0.60935 240   R        20.48 0.05 22.7
2020-05-24 19:43:39  0.61226 240   R        20.52 0.05 22.7
2020-05-24 19:47:52  0.61519 240   R        20.55 0.05 22.6
2020-05-24 19:52:03  0.61809 240   R        20.60 0.08 22.5
2020-05-24 19:56:15  0.62101 240   R        20.59 0.09 22.5
2020-05-24 20:00:27  0.62392 240   R        20.60 0.09 22.3

The photometry is based on nearby USNO-B1.0 stars
USNO-B1.0_id R2
1508-0206198 15.78
1509-0204466 16.48
1509-0204434 16.53