{
  "bibcode": "2021GCN.29716....1K",
  "body": "D. A. Kann (HETH/IAA-CSIC), M. Jelinek (ASU CAS Ondrejov), A. de Ugarte \nPostigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene, M. Blazek, J. F. Agui \nFernandez (all HETH/IAA-CSIC), A. Sota, and R. M. Eloy (both IAA-CSIC) \nreport:\n\nWe observed the optical afterglow of GRB 210312B (INTEGRAL detection: \nMereghetti et al., GCN #29650) with both the 1.5m T150 and the 0.9m T90 \ntelescopes of the Observatorio de Sierra Nevada (OSN),\nGranada, Spain. We obtained 5 x 90 s exposures in B, V, Rc, and 6 x 90 s \nin Ic, followed by 21 x 180 s exposures in Rc with the T150 telescope, \nand 18 x 180 s in Rc with the T90 telescope in parallel, starting at \n2021-03-12 22:51:28.19 UT. The afterglow is detected in multiple \ncombined images from T150, and in the complete combined T90 image. We \nfurthermore obtained 10 x 500 s Rc images in the second night with the \nT150. The afterglow is detected in the combined image.\n\n From three stacked images observed from 0.09577 to 0.14106 days after \nthe GRB, we detect a potential plateau phase, measuring Rc ~ 21.69 mag \n(AB mag, vs. a nearby Pan-STARRS star converted to Rc following the \nLupton transformations, then transformed back to AB mag; errors range \nfrom 0.04 to 0.11 mag). Then at 1.0850 days, we find the afterglow has \nsignificantly decayed to Rc = 23.04 +/- 0.07 mag (AB).\n\nUsing photometry from our GTC observations (Kann et al., GCNs #29653, \n#29655) as well as earlier photometry from the Ondrejov D50, we find a \nbroken power-law decay with a late slope of alpha ~ 2.2. The second-day \nOSN detection is in excess of the extrapolated decay, indicating that \nthe host galaxy may contribute already, or that another rebrightening \nhas taken place.\n\n[GCN OPS NOTE(01apr21):  The typo in the SUBJECT line \"230312B\" was\nchanged to 210312B.]",
  "circularId": 29716,
  "createdOn": 1616615139000,
  "email": "kann@iaa.es",
  "subject": "GRB 210312B: OSN Afterglow Observations",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 210312B"
}