GCN Circular 17500

Antonio de Ugarte Postigo (IAA-CSIC, DARK/NBI), Christina Thoene (IAA-CSIC), 
and Victor Casanova (IAA-CSIC) report on behalf of a larger collaboration:

We observed the field of GRB 150222A (Bernardini et al., GCN 17486
Not found
 
 
) with the 
1.5 m telescope at Sierra Nevada Observatory (Granada, Spain). 
Observations consisted of 34x300s in I-band and ranged from 2:46 to 5:44 UT 
(mid epoch at 4:15 UT, or 11.31 hr after the burst trigger). Observing conditions 
were poor, with a seeing of 2.9". We do not detect the optical counterpart 
candidate reported by Mazaeva et al. (GCN 17489
Not found
 
 
) and Nicuesa Guelbenzu et al.
(GCN 17495
Not found
 
 
) or any other object within the enhanced XRT error circle (Beardmore
et al. GCN 17494
Not found
 
 
). The 3-sigma limit of the combined image is I(Vega) = 22.5 mag,
as compared with USNOB-1.0 stars.
 
Considering an optical decay slope of alpha ~ 1.1 (where F_nu ~ t^(-alpha)) 
between the epochs of Mazaeva et al. and Nicuesa Guelbenzu et al., and a typical 
GRB colour, our observation is consistent with the expected brightness and is also 
consistent with the non-detections reported by other groups (Ivanov et al. GCN 
17487
Not found
 
 
; Klotz et al. GCN 17488
Not found
 
 
; Malesani et al. GCN 17493
Not found
 
 
; Kuin et al. GCN 17499
Not found
 
 
)