{
  "bibcode": "1999GCN...233....1M",
  "body": "GRB 990123 BVRI Photometry\n\nN. Masetti, E. Palazzi, E. Pian, F. Frontera (ITESRE-CNR, Bologna), C.\nBartolini, A. Guarnieri, A. Piccioni (Astronomy Dept., Univ. Bologna), \nG. Valentini (Teramo Astr. Obs.) and E. Costa (IAS-CNR) report:\n\n\"We have imaged the field of GRB990123 with the Bologna Astronomical\nObservatory 1.5m telescope equipped with BFOSC, using Johnson B and V, and\nCousins R and I filters in January 24-26. \n\nCalibrations were done referring to GCN 206 for the B image, to GCN 204\nfor the R image, and using the standard star BD+252534 (Taylor et al.\n1989, AJ 97, 1798) for the V and I images. \n\nIn the appended table the preliminary magnitudes of the optical transient\n(GCN 201) are reported along with the observation dates.\n\nPower-law fits to the R and V band data yield temporal decay indices of\nalpha = 1.20 +- 0.08 and alpha = 1.25 +- 0.16, respectively (errors are 1\nsigma), with satisfactory chi square values.  No indication is found of a\nflattening of the light curve due to an underlying galaxy. \n\nSuggestion of a slight flux increase is seen on January 25 in both R and V\nbands, as opposed to the overall fading trend.  This is however not\nsignificant. \n\nThe BVRI spectral continuum of the optical transient in the first night\n(average time of Jan 24.16), dereddened with E(B-V) = 0.016 (GCN 207), has\na power-law shape (f_nu = k*nu^{-beta}) with best-fit slope \nbeta = 1.1 +- 0.2 (1 sigma). \n\nThe BVRI light curves and the radio-to-X-ray spectral energy distribution\nof the transient are also shown at the Web site\n\nhttp://tonno.tesre.bo.cnr.it/~masetti/grb990123.html\n\nMultiwavelength observations, particularly in the near-infrared and\nmillimetric bands, are needed and urged.\n\n\n\n      Date (UT)    mag    error  band\n  -----------------------------------\n  1998 Jan 24.122  19.36  0.20    I\n           24.142  19.79  0.10    R\n           24.164  19.97  0.16    V\n           24.194  20.64  0.07    B\n           24.216  19.92  0.10    R\n           25.138  20.91  0.10    R\n           25.159  20.77  0.10    R\n           25.181  21.01  0.20    V   \n           25.203  20.93  0.20    V\n           26.154  21.77  0.16    V\n           26.154  21.56  0.10    R\n\n\nThis message can be cited.\"",
  "circularId": 233,
  "createdOn": 917465065000,
  "email": "pian@tesre.bo.cnr.it",
  "subject": "GRB990123, Optical BVRI Observations",
  "submitter": "Elena Pian at ITESRE-CNR,Bologna  <pian@tesre.bo.cnr.it>",
  "eventId": "GRB 990123"
}