{
  "bibcode": "2001GCN..1002....1H",
  "body": "An Early Break in the Optical Light Curve of GRB 010222\n\nStephen Holland (Notre Dame)\nJohan Fynbo (ESO)\nJavier Gorosabel (DSRI)\nArne Henden (USNO)\nJens Hjorth (Copenhagen)\nBrian Jensen (Copenhagen)\nHolger Pedersen (Copenhagen)\n\n     We have obtained deep Cousins R-band images of the optical\nafterglow associated with GRB 010222 using the 2.5m Nordic Optical\nTelescope (NOT) at La Palma and the USNO 1.0m telescope at Flagstaff\nStation.  Preliminary magnitudes, using Rc = 17.175 for Stanek's\n(2001a, GCN 970) Star \"A\", as calibrated by Henden (2001, GCN 987),\nare:\n\n    UT(middle)          Rc     err    Telescope\n -----------------------------------------------\n  2001:02:23.0102     19.733  0.014      NOT\n  2001:02:23.0171     19.707  0.013      NOT\n  2001:02:23.0216     19.739  0.012      NOT\n  2001:02:23.0844     19.829  0.011      NOT\n  2001:02:23.0889     19.852  0.010      NOT\n  2001:02:23.1463     19.933  0.009      NOT\n  2001:02:23.1661     19.960  0.014      NOT\n  2001:02:23.2116     20.031  0.009      NOT\n  2001:02:23.2858     20.126  0.018      NOT\n  2001:02:24.0701     20.950  0.024      NOT\n  2001:02:24.1313     20.975  0.024      NOT\n  2001:02:24.1358     21.012  0.025      NOT\n  2001:02:24.1410     21.052  0.025      NOT\n  2001:02:24.1579     21.006  0.023      NOT\n  2001:02:24.1750     21.043  0.025      NOT\n  2001:02:24.1863     21.000  0.023      NOT\n  2001:02:24.2469     21.035  0.022      NOT\n  2001:02:25.0534     21.536  0.057      NOT\n  2001:02:25.0579     21.426  0.058      NOT\n  2001:02:25.2535     21.638  0.044      NOT\n  2001:02:25.2583     21.667  0.041      NOT\n  2001:02:22.4874     18.39   0.05       USNO\n  2001:02:22.5241     18.51   0.05       USNO\n  2001:02:22.5236     18.67   0.06       USNO\n  2001:02:22.5385     18.66   0.06       USNO\n  2001:02:24.4632     21.23   0.06       USNO\n -----------------------------------------------\n\n     In order to maintain as much uniformity as possible in the\nphotometry we first restrict ourselves to data taken with the NOT.\nThis data extends from 0.70 to 2.95 days after the burst and is\nconsistent with a single power law with a slope of -1.24 +/- 0.02 (Q <\n99.954%).\n\n     We supplemented this data with R-band photometry of GRB 010222\nfrom Stanek et al. (2001a, GCN 970), Price et al. (2001, GCN 973),\nOrosz (2001, GCN 976), Stanek et al. (2001b, GCN 983), Masetti et\nal. (2001, GCN 985), Oksanen et al. (2001, GCN 990), Stanek & Falco\n(2001, GCN 991), Velentini et al. (2001, GCN 992), Watanabe et\nal. (2001, GCN 993), and Veillet (2001, GCN 1000).  All the photometry\nwas adjusted to the photometric zero points of Henden (2001a, GCN\n987), except for that of Veillet (2001, GCN 1000), which was used \"as\nis\".  The photometry was corrected for Galactic extinction assuming a\nreddening of E(B-V) = 0.023 and an R-band extinction of A_R = 0.061.\n\n     The complete data set is not consistent with a single power law\n(Q < 0.001%).  Photometry earlier than 0.33 days after the burst is\nweakly consistent with a single power law with a slope of -0.71 +/-\n0.13 (Q = 77.969%), and the photometry later than 0.57 days after the\nburst is consistent with a single power law with a slope of -1.24 +/-\n0.02 (Q = 99.990%).  Fitting a broken power law (see Holland et al.,\n2000, A&A, 364, 467 for the method) to the light curve yields a break\nat 0.48 +/- 0.11 days (11.5 +/- 2.6 hours) after the burst, and slopes\nof -0.72 +/- 0.13 before the break and -1.24 +/- 0.02 after the break\n(Q = 99.991%).  The smooth function of Beuermann et al. (1999, A&A,\n352, L26) with slopes of -0.67 +/- 0.34 before the break, -1.29 +/-\n0.06 after the break, and an exponent of 1.8 +/- 4.4 provides a\nslightly better fit (Q = 99.998%) to the data than the broken power\nlaw does.  Our fits suggest that the break occurred rapidly between\n0.33 and 0.57 days (8 and 14 hours) after the burst.  A plot of the\nlight curve and the two fits, along with a deep composite image of the\nfield containing the GRB, is available at\n\"http://www.nd.edu/~sholland/grb/grb010222/index.html\".\n\nThis message may be cited.",
  "circularId": 1002,
  "createdOn": 983567946000,
  "email": "sholland@nd.edu",
  "subject": "GRB 010222, Optical Observations",
  "submitter": "Stephen Holland at U. of Notre Dame  <sholland@nd.edu>",
  "eventId": "GRB 010222"
}