TITLE:   GCN CIRCULAR
NUMBER:  39949
SUBJECT: GRB 250330A: BOOTES-7 early optical upper limit
DATE:    25/03/30 18:13:56 GMT
FROM:    I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>

I. Perez-Garcia, A. J. Castro-Tirado, E. Fernandez-Garcia, S.-Y. Wu, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy (IAA-CSIC), C. Perez del Pulgar (Univ. de Malaga), G. Garcia-Segura (Inst. de Astronomia, UNAM), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), Y.-D. Hu (GuangXi Univ.), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report:

Following the detection of GRB 250330A by Swift/BAT (Cenko et al., GCNC [39938](https://gcn.nasa.gov/circulars/39938)) and Fermi (Fermi GRB Team, GCNC [39944](https://gcn.nasa.gov/circulars/39944)), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) responded to the alert on Nov. 9, 06:08:48 UT (i.e. 57s after trigger, and 70s after the event). Within the reported Swift/XRT error circle (Page et al., GCNC [39940](https://gcn.nasa.gov/circulars/39940)) , no optical transient is detected down to 17.6 mag (clear filter). On a coadd (620s) of images at 06:31:17 UT (mid exposure time; i.e. 23.8 min post burst), nothing is detected down to 19.3 mag, in agreement with the deeper VLT/FORS2 observations taken later on (Becerra et al., GCNC [39941](https://gcn.nasa.gov/circulars/39941)).

We thank the staff at San Pedro de Atacama Celestial Observations for their excellent support.