{
  "bibcode": "2002GCN..1443....1S",
  "body": "Isabel Salamanca, Evert Rol (University of Amsterdam), Nial Tanvir\n(University of Hertfordshire), Lex Kaper (UoA), on behalf of a larger\ncollaboration, report:\n\nWe have performed differential photometry of the sources detected by\nChandra  (GCN #1399) in the field of view of GRB 020531\n(GCN #1399, #1402). The observations were done with the WFC on the\nINT at La Palma. For more details see GCN 1433.\n\nOf the 13 sources detected by Chandra, we detect 5 in both epochs:\ncx00, cx15, cx48, cx55, cx56. Four more sources are detected only in\nthe second epoch: cx05,cx47,cx58 and cx52.  We remark that the source\ncx00 is also visible in the DSS.\n\nWe have perfomed differential photometry of the first 4 sources by\ncomparing them with 12 stars in the field. The relative accuracy\nattained is 0.01 mag. The absolute photometry was done via the\nphotometry performed by Henden etal. (GCN #1422). The estimated error\nin the zero point is higher, 0.4 mag, due to the fact that the\nobservations were performed under non-photometric conditions.\n\n\nBelow is a summary of the magnitudes of each object:\n\nId\t\tV mag\n\t31 May\t   \t2 June\n=====================================\n 5\t>24.7\t\t24.5\n15 \t21.73\t\t21.80\n--- ---------------------------------\n28\t>24.7\t\t>25.2\n36\t>24.7\t\t>25.2\n41\t>24.7\t\t>25.2\n47\t>24.7\t\t23.8\n48\t23.27\t\t23.20\n51\t>24.7\t\t>25.2\n52\t>24.7\t\t24.0\n55\t23.15\t\t23.19\n56\t21.71\t\t21.60\n58\t>24.7\t\t~25.2\n\nThe proposed afterglow candidate, cx48 (GCN #1426, #1427 and #1428) is\n0.07 +/- 0.01 mag brighter in the second epoch than in the first.\n\n\nThis message may be cited.\n\n\n\n\n\n-- \nDr. Isabel E. de Salamanca\nAnton Pannekoek Institute, UvA\nAmsterdam - The Netherlands.",
  "circularId": 1443,
  "createdOn": 1025168860000,
  "email": "isabel@science.uva.nl",
  "subject": "GRB 020531: optical photometry of Chandra sources",
  "submitter": "Isabel Salamanca at U. of Amsterdam  <isabel@science.uva.nl>",
  "eventId": "GRB 020531"
}