[vsnet-grb-info 28308] GRB 210704A: CAHA 2.2m telescope optical limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30411
SUBJECT: GRB 210704A: CAHA 2.2m telescope optical limit
DATE:    21/07/07 22:53:14 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072 at hotmail.com>

T.-R. Sun, Y.-D. Hu, E. Fernandez-Garcia, A. J. Castro-Tirado  M. D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), P. Martin-Fernandez (CAHA) on behalf of a larger collaboration, report:

Following the detection of GRB210704A by Fermi (Kunzweiler et al. GCNC 30369), AGILE (Ursi et al. GCNC 30372), AstroSat (Prasad et al. GCNC 30378) and Konus-Wind (Ridnaia et al. GCNC 30388), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). A series of r-band images were gathered starting on July 6, 20:40 UT (i.e. 2.05 day post trigger). On the co-added image (9 x 300s), no optical object is detected down to 22.7 mag at the afterglow position reported by Swift/XRT (Evans et al. GCNC 30374), Assy (Kim et al. GCNC 30384) and TNG (D'Avanzo et al. GCNC 30385). Combined with the additional detections (de Ugarte Postigo et al. GCNC 30392, Kann et al. GCNC 30391, Kann et al. GCNC 30401), the optical afterglow decaying lightcurve is confirmed.

We thank the staff at Calar Alto observatory for their excellent support.