{
  "bibcode": "2008GCN..7327....1V",
  "body": "Paul Vreeswijk, Johan Fynbo, Bo Milvang-Jensen, Daniele Malesani,\nJens Hjorth (DARK/NBI), Pall Jakobsson (U. Hertfordshire),\nAndreas Jaunsen (U. Oslo), Nial Tanvir (U. Leicester) report\non behalf of a larger collaboration:\n\nThe Swift localization of GRB 080218B (Schady et al., GCN 7314) was\nobserved with FORS2 mounted at the VLT Antu telescope on Cerro Paranal\nin Rapid-Response Mode, and with SOFI at the NTT on La Silla. Starting\nat Feb 19, 1:03 UT (roughly 1 hour after the burst) VLT/FORS2\nperformed the imaging sequence R-I-z-V-B-R (30-150s per filter)\nthrough thin cirrus, at an airmass of 2.5, and with an effective\nseeing of 1.5\". NTT/SOFI imaged the afterglow location at an airmass\nof 1.3-1.5 and in 1.4\" seeing conditions in Ks-J-H-Ks (10 min. per\nfilter), starting at Feb 19, 2:52 UT.\n\nNo object is detected within the enhanced XRT error circle (Osborne et\nal., GCN 7320) down to the following limiting magnitudes (2 sigma):\nB>22.1, V>22.7, R>22.9, I>22.6, J>20.6, H>20.1 and Ks>19.4.  The\ncorresponding upper limit on the optical to X-ray spectral slope,\nbeta_OX, is 0.24, rendering the burst dark according to the definition\nproposed by Jakobsson et al. (2004, ApJ, 617, L21). A spectrum of an\nobject just outside the XRT error circle at R.A. 11:51:49.25,\ndecl. -53:05:50.1 (J2000), shows it to be a Galactic star of type M6V.\n\nWe acknowledge the excellent support of ESO's night astronomers at La\nSilla Paranal Observatory, and in particular that of Linda\nSchmidtobreick, Colin Snodgrass, Stephane Brillant and Lorenzo Monaco.",
  "circularId": 7327,
  "createdOn": 1203699089000,
  "email": "pmv@dark-cosmology.dk",
  "subject": "ESO optical and NIR observations of GRB 080218B",
  "submitter": "Paul Vreeswijk at Dark Cosmology Centre,U.of Copenhagen  <pmv@dark-cosmology.dk>",
  "eventId": "GRB 080218B"
}