[vsnet-grb-info 28108] GRB 210610A: CAHA 2.2m observations and light-curve behavior

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30211
SUBJECT: GRB 210610A: CAHA 2.2m observations and light-curve behavior
DATE:    21/06/11 20:58:31 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann at iaa.es>

D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), J. F. Agui Fernandez, C. C. Thoene, M. Blazek (all 
HETH/IAA-CSIC), A. Fernandez, I. Hermelo, and S. Pedraz (all CAHA) 
report:

We observed the afterglow (Page et al., GCN #30160; Hosokawa et al., 
GCNs #30161, #30169; Xu et a., GCN #30162; Kumar et al., GCN #30163; 
Lipunov et al., GCN #30166; de Wet et al., GCN #30168; Sun et al., GCN 
#30185; Watson et al., GCN #30191; Zheng et al., GCN #30203) of GRB 
210610A, discovered by Swift (Page et al., GCN #30160) and also detected 
by Konus-Wind (Frederiks et al., GCN #30197) at redshift z=3.54 (Zhu et 
al., GCN #30164; Dutta et al., GCN #30200). with CAFOS mounted on the 
2.2m telescope at Calar Alto, Almeria, Spain. We obtained 5 x 180 s in 
Sloan i' before switching to observations of GRB 210610B. After these, 
we obtained 3 x 300 s each in Sloan r' and g'.

The afterglow is detected in individual frames. Stacking the images, we 
measure, against nearby comparison stars from the SDSS catalog (AB mags, 
not corrected for Galactic extinction):

i' = 20.18 +/- 0.04 mag at 0.23677 d;
r' = 20.87 +/- 0.05 mag at 0.36333 d;
g' = 21.92 +/- 0.08 mag at 0.37687 d.

Using our data as well as data given in the GCN Circulars cited above, 
we find that after 0.03 d, the light curve can be described with a 
broken power-law fit, with alpha_1 = 0.84, alpha_2 = 1.24, and t_break = 
0.16 d. Earlier data is brighter than the back-extrapolation of the fit, 
indicating a steeper decay must have taken place.