{
"subject": "V,R,I band observations of GRB000926",
"bibcode": "2000GCN...850....1R",
"createdOn": 971547107000,
"circularId": 850,
"submitter": "Evert Rol at U.Amsterdam ",
"email": "evert@astro.uva.nl",
"body": "E. Rol, P. M. Vreeswijk (U. of Amsterdam) and N. Tanvir (U. of\nHertfordshire), on behalf of a larger collaboration, report:\n\nWe have obtained Sloan i and Harris R & V band images of the field of\nGRB 000926 (GCN #801), using the Wide Field Camera on the 2.5m Isaac\nNewton Telescope at La Palma. Using aperture photometry (with a radius\ntwice the FWHM), we find the magnitude of the OT, relative\nto the reference star of Halpern et al. (GCN #824), to be as follows:\n\n\n\n date (UT) filter rel-mag error exp-time\n (Sept 2000) (secs)\n - ------------------------------------------------\n 27.919 i 2.406 0.007 300\t \n 27.924 i 2.439 0.007 300\n 27.929 i 2.454 0.008 300\n 30.850 i 5.403 0.009 600\n\t\t\t\t\t \t \n 27.892 R 2.369 0.007 300\t \n 27.896 R 2.386 0.007 300\n 27.901 R 2.396 0.008 300\n\t\t\t\t\t \t \n 27.906 V 2.271 0.009 300\n 27.910 V 2.298 0.009 300\n 27.915 V 2.301 0.010 300\n 30.839 V 5.352 0.096 600\n\n\n(errors are statistical only)\n\n\nWe have fitted the R band data, together with all published data (GCNs\n#809, #814, #816, #819, #820, #824, #825, GCN #829, #831, #840), with a\nsmoothly broken power-law, and a constant flux (presumably from the\nunderlying host galaxy). The fitted function is\n\n F(t) = { F_1^(-n) + F_2^(-n) }^(-1/n) + F_host,\n\n with F_i = k_i t ^(-a_i), n > 0; i = 1, 2.\n\na_1 and a_2 correspond to the early and late time power-law indices,\nrespectively. The break time t_0 corresponds to the time when F_1 = F_2.\n\n(see e.g. Beuermann, K., et al 1999, A&A, 352, L26-L30)\n\n\nWe obtain the following parameters for the R band data, with n fixed at 1:\n\n a_1 = 1.1 +- 0.2\n a_2 = 3.2 +- 0.4\n t_0 = 2.0 +- 0.4\n host: R = 24.2 +- 0.3\n\nErrors are 1 sigma; chi^2/DOF = 69/31. Excluding the host,\nwe find a chi^2/DOF = 83/32.\n\nThe fit shows a rather large increase in the decay-rate of the OT flux\naround two days after the burst (from a power-law index of 1.1 to\n3.2). Fitting for n as well (which can be used to define the\nsharpness of the break) gives the same results as above, with n = 1.1\n+- 0.8.\n\n\nGraphs of these fits can be found at\n\n\thttp://www.astro.uva.nl/~evert/grb000926/\n\n\n\nWe acknowledge the help of the observers Chris Blake and Steve Rawlings\n(U. of Oxford), and the ING staff."
}