[vsnet-grb-info 16219] GRB 150222A: I-band observations from OSN

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17500
SUBJECT: GRB 150222A: I-band observations from OSN
DATE:    15/02/23 13:41:59 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte at iaa.es>

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) 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) and Nicuesa Guelbenzu et al.
(GCN 17495) or any other object within the enhanced XRT error circle (Beardmore
et al. GCN 17494). 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; Klotz et al. GCN 17488; Malesani et al. GCN 17493; Kuin et al. GCN 17499)