{
  "bibcode": "2020GCN.29169....1X",
  "body": "D. Xu (NAOC), D. B. Malesani (DTU Space), P. Galindo (NOT), Z.P. Zhu \n(NAOC, HUST), D. A. Kann (HETH/IAA-CSIC), report on behalf of a larger \ncollaboration:\n\nWe observed the field of GRB 201223A (Gropp et al., GCN 29158) using the \n2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. \nWe obtained 2x120s Sloan r-band frames starting at 02:21:52 UT on \n2020-12-24, i.e., 8.4 hr after the BAT trigger.\n\nThe previously reported optical afterglow (Lipunov et al. GCN 29157; \nGropp et al., GCN 29158; Zhu et al. GCN 29159; Hu et al. GCN 29160; \nHosokawa et al. GCN 29164; Romanov et al. GCN 29165; Xin et al. GCN \n29166; Belkin et al., GCN 29167; Kumar et al., GCN 29168) is not \ndetected in the stacked image, down to a limiting magnitude of r > 22.0 mag.\n\nFurther analysis of our previous NEXT observations (Zhu et al. GCN \n29159) shows that the afterglow is decaying as F_rband ~ t^(-\\alpha), \nwhere \\alpha = 1.1 since the very beginning. The afterglow would be \nslightly fainter than 22.0 mag if this powerlaw decay is extrapolated \nuntil the NOT observational time, being consistent with the observed NOT \nupper limit. So the afterglow could be decaying in a single powerlaw \nuntil the NOT observation or have broken to a steeper decay before the \nNOT observation.",
  "circularId": 29169,
  "createdOn": 1608820147000,
  "email": "dxu@nao.cas.cn",
  "subject": "GRB 201223A: NOT optical upper limit and NEXT powerlaw decay",
  "submitter": "Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>",
  "eventId": "GRB 201223A"
}