{
  "bibcode": "2006GCN..5901....1L",
  "body": "V. Lipunov, V.Kornilov, D.Kuvshinov, N.Tyurina, A.Belinski, E.Gorbovskoy,\nA.Krylov, G.Borisov, A.Sankovich, V.Vladimirov, P.Gritsyk\n\nSternberg Astronomical Institute, Moscow Union 'Optic'\n\nMASTER  robotic system (http://observ.pereplet.ru)\nresponded to GRB060926 (Holland  et al., GCN Circ 5612) under the good \nconditions (V. Lipunov et al., GCN Circ 5632).\n\nThe first image was started at 2006-09-26 16:49:57 UT, 76 s  after the GRB\ntime (355 mm telescope, 6 square degrees FOV, 2.1'' per pix, CCD Alta U16).\nThe unfiltered image is calibrated relative to USNO A2.0 (0.8 R + 0.2 B).\nWe find (Lipunov et al., GCN5632) faint OT on the first and on  the \ncoadded images at position:\n\naplha = 17 35 43.66\ndec   = 13 02 18.3\nerr = +- 0.7''\n\nwich coincided with the Holland  et al.(GCN Circ 5612) OT position.\n\n  We have refind analysis of the images. We discovery optical\nflare around 500-700 s after the GRB time (see picture):\n\nStart    Mean   Exposure        Magnitude            Flux, \ntime     time     time                          erg/(sm2*sec*eV)\n\n  76 s     91 s     30 s         17.3+-0.3        (1,4+-0,3)E-13 \n150 s    165 s     30 s     \t18.5+-0.3        (4,6+-1,1)E-14 \n165 s\t 343 s    5x30 s        19.3+-0.3        (2,2+-0,5)E-14 \n255 s    432 s    5x30 s        18.9+-0.3\t (3,2+-0,8)E-14 \n343 s\t 519 s    5x30 s        18.5+-0.3    \t (4,6+-1,1)E-14 \n432 s\t 608 s    5x30 s        18.3+-0.3    \t (5,8+-1,3)E-14\n519 s\t 707 s    5x30 s        18.4+-0.3        (5,1+-1,2)E-14 \n608 s\t 804 s\t  5x30 s        18.7+-0.3\t (3,9+-0,9)E-14 \n707 s\t1001 s    5x30 s        20.0+-0.3    \t (1,2+-0,3)E-14 \n804 s\t1200 s    5x30 s        20.1+-0.3    \t (1,1+-0,3)E-14 \n901 s\t1298 s    5x30 s      > 20.1+-0.3    \t<(1,1+-0,3)E-14\n\nThe light curve is available at \nhttp://observ.pereplet.ru/images/GRB060926/light_curve_new.jpg .\n\nBetween 91s and 255s a power-law decline with a temporal index \nof -1.40+/-0.24 is estimated. Between 707s and 1200s a power-law decline \nwith a temporal index of -3.30+/-0.70 is estimated. After 1000 s  a \npower-law decline with a temporal index 0.73 +-0.1 was observed\n(A. Stefanescu et al., GCN 5623).\n\nWe remember that X-ray flare in GRB 060926  was descovered\nby XRT team (M. Perri et al., GCN 5622).\n\nThe X-ray spectrum covering the time period from T+67s to T+878s is well\nfit by an absorbed power-law with a photon index of 2.1(+/-0.3) and column\ndensity of (2.2+/-0.9)e21 cm**-2 (M. Perri et al., GCN 5622). They note \nthe Galactic column density in the direction of the source is 7.3e20 \ncm**-2 .\nThis means that absorbtion  is about 1 magnitude in our band.\nThe optical-xray data is well fit by power-low with a photon index of \n1.7+-0.2 during all our time observation.\n\n\nWe thanks to Dr.K.A.Postnov for usefull discussion and comments.\n\nThis work is supported by RFFI  04-02-16411 grant.\nThis message can be cited.\nMailto: lipunov@sai.msu.ru",
  "circularId": 5901,
  "createdOn": 1165512995000,
  "email": "gcncirc@observ.inetcomm.ru",
  "subject": "GRB 060926: MASTER: discovery of the optical flare",
  "submitter": "Vladimir Lipunov at Moscow State U/Krylov Obs  <gcncirc@observ.inetcomm.ru>",
  "eventId": "GRB 060926"
}