{
  "bibcode": "2012GCN.13921....1E",
  "body": "P. A. Evans, K.L. Page and J.P. Osborne (U Leicester) report on behalf\nof the Swift-XRT team:\n\nWe have analysed 12 ks of XRT data for GRB 121027A (Evans  et al. GCN\nCirc. 13906), from 57 s to 76.2 ks after the  BAT trigger. The data\ncomprise 2.0 ks in Windowed Timing (WT) mode (the first 9 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. The enhanced XRT position for this burst was given by Beardmore\net al. (GCN. Circ 13916).\n\nThis burst is unusual in showing multiple strong rebrightenings at high\nflux in X-rays, a rebrightening has also reported in the IR (Levan et\nal GCN 13920). This behaviour is reminiscent of the tidal disruption\nevent Swift J1644.\n\nThe light curve initially follows a power-law decay with an index of\nalpha~1.8. This is interrupted by a flare beginning at T+220 s and\nlasting ~300 s, after which the decay appears much steeper: alpha~6.6.\nHowever at T+800 s the count rate jumps sharply, increasing by more\nthan 2 orders of magnitude in under 300 s; by T+1.1 ks the count rate\nis ~30 ct/sec, corresponding to an observed flux of ~1e-9 erg/cm^2/s.\nAt this point the GRB left Swift's observing window, however during the\nnext observation (T+5.3 ks to T+6ks) the count rate remained high,\nincreasing from ~20 ct/s at the start of the observation to ~60 ct/s at\nthe end. The MAXI observation (GCN 13908) occurred between these\nobservations, and the flux reported by MAXI is consistent with the\nSwift flux of ~1-2 e-9 erg cm^2/s. Over the next 4 exposures (T+11 ks\nto T+30 ks), the count-rate declines with an index of ~3.8 to a level\nof ~0.08 ct/s, it then remains at that level until T+76 ks, where our\ncurrent observations end. The hardness ratio follows the count-rate\nduring the rebrightenings (i.e. the emission is harder when brighter),\nwhich is typical of flaring activity.\n\nA spectrum formed from the first observation in WT mode data can be\nfitted with an absorbed power-law with a photon spectral index\tof 2.55\n(+/-0.06). The best-fitting absorption column is  2.80 (+0.16, -0.15) x\n10^21 cm^-2, in excess of the Galactic value of 1.5 x 10^20 cm^-2\n(Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.94\n(+0.29, -0.27) and a best-fitting absorption column of 1.1 (+0.7, -0.6)\nx 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 3.8 x 10^-11 (4.8 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.1 (+0.7, -0.6) x 10^21 cm^-2\nGalactic foreground: 1.5 x 10^20 cm^-2\nExcess significance: 2.5 sigma\nPhoton index:\t     1.94 (+0.29, -0.27)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00536831.\n\nMulti-wavelength follow-up is strongly recommended.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 13921,
  "createdOn": 1351502961000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 121027A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 121027A"
}