{
  "bibcode": "2018GCN.22542....1K",
  "body": "Klotz A., Noysena K., Atteia J.L. (CNRS-OMP-IRAP),\nBoer M., Eymar L. (CNRS-ARTEMIS),\nGendre B. (UVI - Etelman Obs.) report:\n\nWe imaged the field of GRB 180325A detected by SWIFT\n(trigger 817564) with the TAROT robotic telescope (D=25cm)\nlocated at the Calern observatory, France.\n\nThe observations started 26s after the GRB trigger\n(14s after the notice). The elevation of the field decreased\nfrom 37 degrees above horizon and weather conditions\nwere excellents.\n\nWe detect clearly the optical transcient (OT) reported by\nTroja et al. (GCN 22532), Guidorzi et al. (GCN 22534),\nHeintz et al. GCN 22535), D'Avanzo et al. (GCNC 22536),\nWatson  et al. (GCNC 22537), Garnavich  et al. (GCNC 22538),\nStrobl et al. (GCNC 22541).\n\nThe first image is trailed with a duration of 60.0s\n(see the description in Klotz et al., 2006, A&A 451, L39).\nWe detect the OT at a magnitude of:\nt0+26s to t0+86s : r(AB) = 17.2 +/- 0.3\n\nIt is important to notice that a bright gamma flash in\nSwift-BAT data occured between 70 and 92 seconds. We\ndo not detect any significant optical flux increase\nduring the range 70 to 86 seconds of the first TAROT\nexposure.\n\nAfter an overhead time of 13 seconds the second image\nof 30s exposure in tracking mode started 99 seconds\nafter the trigger. In this image the OT has brightened\nby about 1 magnitude. The third image shows a rapid\ndecrease of 1 magnitude compatible with a decay index\nof about 3 followed by a mean decay of 0.45 until\n1.7 hour after the trigger confirming the small decay\nvalue published by Littlefield and Garnavich (GCNC 22538).\n\nThe photometric analysis of the TAROT images are given:\n\nt1(h)  t2(h)  r(AB) 1sig\n0.0277 0.0361 16.24 0.09\n0.0391 0.0474 17.22 0.20\n0.0504 0.0815 17.68 0.19\n0.0843 0.1093 18.02 0.30\n0.2062 0.2872 18.56 0.30\n0.2951 0.4364 18.78 0.39\n0.4392 1.1843 18.94 0.22\n1.2400 1.6746 19.26 0.36\n\nMagnitudes were estimated with the nearby star\nNOMAD-1 1144-0181799 R=14.440 (V-R)=0.65, converted into\nr(AB) system and are not corrected for galactic dust extinction.\n\nNote that the TAROT light curve is compatible with an\noptical flash occuring with a lag of 20 +/- 10 seconds\nafter the bright gamma emission peak as mentioned\nby Strobl et al. (GCNC 22541).",
  "circularId": 22542,
  "createdOn": 1521988591000,
  "email": "Alain.Klotz@free.fr",
  "subject": "GRB 180325A: TAROT Calern observatory optical observations",
  "submitter": "Alain Klotz at IRAP-CNRS-OMP  <Alain.Klotz@free.fr>",
  "eventId": "GRB 180325A"
}