{
  "bibcode": "2021GCN.29257....1K",
  "body": "Amit Kumar (ARIES), Rahul Gupta (ARIES), Dimple (ARIES), Ankur Ghosh\n(ARIES), Nikita Rawat (ARIES), Brajesh Kumar (ARIES), Vibhore Negi (ARIES),\nAmar Aryan (ARIES), Shashi B. Pandey (ARIES), and Kuntal Misra (ARIES)\nreport:\n\nWe observed the optical afterglow of the Fermi (Fermi GBM team GCNC 29232,\nBiltzinger et al. GCNC 29234) and Swift detected GRB 210104A (Troja et al.\nGCNC 29233) with the 1.3m Devsthal Fast Optical Telescope (DFOT) at\nAryabhatta Research Institute of Observational Sciences (ARIES), Nainital\n(India), from 2021-01-04 17:50:11 to 2021-01-04 18:35:28 UTC (from ~6.386\nto 7.141 hours after the burst). We observed 10 frames each of 240 seconds\nin the Bessell R filter. We clearly detected the optical afterglow of GRB\n210104A in all individual frames within the Swift XRT enhanced error circle\n(Beardmore et al. 29245) as reported by Xin et al. GCN 29235 and later by\nHu et al. GCN 29236, Hosokawa et al. GCN 29237, Kim et al. GCN 29238,\nTakashi et al. GCN 29241, Lipunov et al. GCN 29248, Zhu et al. GCN 29252\nand Gregory et al. GCN 29254.\n\nThe estimated preliminary magnitude for the first R-band image is as\nfollows:\n\nT_start-T0 (hours) Start Date (UTC) Filter Magnitude (mag)\n\n-----------------------------------------------------------\n-----------------------------------------------------------\n6.386 2021-01-04T17:50:11 R 18.95 +- 0.07\n\n\nPhotometry is done based on the USNO-B1.0 catalog. The quoted magnitude is\nnot corrected for the Galactic extinction in the direction of GRB 210104A.\n\nThis message may be cited.",
  "circularId": 29257,
  "createdOn": 1609846739000,
  "email": "amitkundu515@gmail.com",
  "subject": "GRB 210104A: 1.3m DFOT Optical Afterglow Detection",
  "submitter": "Amit Kumar at ARIES, India  <amitkundu515@gmail.com>",
  "eventId": "GRB 210104A"
}