{
  "bibcode": "2021GCN.29318....1K",
  "body": "D. A. Kann (HETH/IAA-CSIC), A. Rossi (INAF-OAS), A. de Ugarte Postigo \n(HETH/IAA-CSIC, DARK/NBI), C. C. Thoene (HETH), M. Blazek, J. F. Agui \nFernandez (both HETH/IAA-CSIC), and J. I. Vico Linares (CAHA) report:\n\nWe observed the afterglow position (Troja et al., GCN #29233) of the \nbright Swift/Fermi GRB 210104A (Swift detection: Troja et al., GCN \n#29233; GBM detection: Fermi GBM Team, GCN #29232; Biltzinger et al., \nGCN #29234; Konus-Wind detection: Frederiks et al., GCN #29258; CALET \ndetection: Cherry et al., GCN #29268; AstroSat CZTI detection: Nadella \net al., GCN #29299) with CAFOS at the 2.2m telescope at Calar Alto, \nAlmeria, Spain, in the Rc band. We obtained 6 x 600 s exposures, \ncentered at 11.4624 days after the GRB, under good conditions but \nmediocre seeing.\n\nAfter removing the halo of a nearby star, the afterglow (Xin et al., GCN \n#29235; Hu et al., GCN #29236; Hosokawa et al., GCN #29237; Kim et al., \nGCNs #29238,29265,29283; Horiuchi et al., GCN #29241; Breeveld et al., \nGCN #29247; Lipunov et al., GCN #29248; Zhu et al., GCN #29252; Paek et \nal., GCN #29254; Kumar et al., GCN #29257; Smartt et al., GCN #29262; \nAnandagoda et al., GCN #29273; Gokuldass et al., GCN #29274; Mao et al., \nGCN #29275; Moskvitin et al., GCN #29277; Belkin et al., GCN #29286; \nNakamura et al., GCN #292291) is faintly but clearly detected.\n\nAgainst three SDSS comparison stars (transformed to Rc band using the \nLupton 2005 equations, then transformed back to AB magnitude), we \nmeasure Rc = 23.67 +/- 0.14 mag. This value is in agreement with the \nextrapolation of the light curve decay reported by Belkin et al., GCN \n#29286 (A. Pozanenko, priv. comm.). This implies there is no significant \nevidence for a supernova rise, and therefore the redshift of GRB 210104A \nis conservatively estimated to be z > 0.4 (e.g., SN 2012eb associated \nwith GRB 120714B at z ~ 0.4 peaks at r' ~ 22.2 mag 12 days after \ntrigger, Klose et al. 2019, A&A, 622, A138).\n\nWe thank Alexei Pozanenko for discussions.",
  "circularId": 29318,
  "createdOn": 1610985086000,
  "email": "kann@iaa.es",
  "subject": "GRB 210104A: Late-time CAHA 2.2m detection",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 210104A"
}