{
  "bibcode": "2021GCN.30731....1K",
  "body": "D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, \nDARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all \nHETH/IAA-CSIC), A. Fernandez, and I. Hermelo (all CAHA) report:\n\nWe observed GRB 210820A (Swift detection: Beardmore et al., GCN #30664) \nwith CAFOS mounted on the 2.2m CAHA telescope at Calar Alto, Alemria, \nSpain, under inclement conditions (bright moonlight, passing clouds, low \ntransparency). We obtained 10 x 90 s each in filters B, V, Rc. Stacks \nreveal no detection of the afterglow in B (very shallow because of \nmoonlight) and Rc (shallow because of incoming clouds which also \nprevented further observations). However, the afterglow (Beardmore et \nal., GCN #30664; Butler et al., GCN #30672; LaPorte & Beardmore, GCN \n#30686; Nicuesa Guelbenzu et al., GCN #30695) is clearly detected in V, \nsomewhat north of a source also seen in Pan-STARRS and in SDSS.\n\nWe find the afterglow to be V = 22.43 +/- 0.15 mag (AB mag, derived from \ntwo SDSS field stars transformed to V via the equations of Lupton 2005) \nat 0.43868 days after the GRB.",
  "circularId": 30731,
  "createdOn": 1630087416000,
  "email": "kann@iaa.es",
  "subject": "GRB 210820A: CAHA 2.2m Optical Detection",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 210820A"
}