{
  "bibcode": "2010GCN.10680....1M",
  "body": "D. Malesani (DARK/NBI), A. J. Levan (Univ. Warwick), N. R. Tanvir (Univ. \nLeicester), J. P. U. Fynbo (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and \nSAp/CEA), report on behalf of a larger collaboration:\n\nWe are observing the field of GRB 100425A (Grupe et al., GCN 10673) with \nthe ESO VLT equipped with the X-shooter spectrograph.\n\nIn the R-band acquisition image, taken starting around 06:51 UT \n(approximately 4 hr after the GRB), we detect two sources within the \nrefined XRT error circle (http://www.swift.ac.uk/sper/), at coordinates:\n\nA: RA(J2000) = 19:56:47.30, Dec(J2000) = -26:25:49.3\nB: RA(J2000) = 19:56:47.13, Dec(J2000) = -26:25:50.1\n\nSource A is visible in the DSS, and has a similar magnitude to its \narchival value. Source B is not readily visible in the DSS and has a \nmagnitude R = 20.55 +- 0.2, which is at the limit of the DSS \nsensitivity. The large error comes mostly from calibration scatter in \ncomparison with USNO-B1 stars.\n\nIn a second image taken starting at 7:44 UT (4.9 hr after the GRB), \nsource B has faded by 0.17 +- 0.08 mag.\n\nGiven the consistency of its position with the XRT error circle and the \nmoderate evidence for variability, we propose source B as the optical \nafterglow of GRB 100425A.\n\nA finding chart from the X-shooter image can be seen at the following URL:\n\nhttp://www.astro.ku.dk/~malesani/GRB/100425A/GRB100425A_finder.png\n\nFurther observations and analysis are ongoing. We acknowledge a \nparticularly helpful and attentive support from the ESO staff in \nParanal, especially Jonathan Smoker, Lorena Faundez, Manuel Olivares \nand Steffen Mieske.",
  "circularId": 10680,
  "createdOn": 1272185076000,
  "email": "malesani@dark-cosmology.dk",
  "subject": "GRB 100425A: candidate optical afterglow from the VLT",
  "submitter": "Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>",
  "eventId": "GRB 100425A"
}