{
  "bibcode": "2012GCN.13069....1D",
  "body": "P. D'Avanzo, A. Melandri (INAF-OAB), E. Palazzi (INAF-IASF Bo), S. Campana\n(INAF-OAB), M. Della Valle (INAF-OAC), E. Pian (INAF-OATs), R. Salvaterra\n(INAF-IASF Mi), G. Tagliaferri (INAF-OAB) report on behalf of the CIBO\ncollaboration:\n\nWe observed the optical counterpart of GRB 111228A (Ukwatta et al., GCN\n12737) with the Italian 3.6m TNG telescope on 2012 Feb 1.16 UT (34.5 days\npost burst) and March 13.91 UT (76.2 days post burst). Observations were\ncarried out in the R and I bands. The counterpart is well detected in the\ntwo epochs in both filters, with a magnitude R = 24.3 in the March\nobservation (calibrated using Landolt standard stars). The late value is\nlikely dominated by the host galaxy.\n\nDifferential photometry reveals that the source faded between the two\nepochs by 0.4 +/- 0.2 and 0.9 +/- 0.1 mag in the R and I band,\nrespectively. The observed fading indicates that a transient component was\npresent during our February observation. This could be due to residual\nafterglow emission, or to the presence of an emerging supernova (SN).\n\nAfter subtracting the host galaxy flux, the color of the transient on\nFebruary 1 is very red, with\nR-I ~ 2. This color is not typical of GRB afterglows, and is much redder\nthan measured at early times for this object (e.g.,  r'-i' = 0.17 AB at t\n= 0.57 days: Nicuesa Guelbenzu et al., GCN 12757). Such a red spectrum, on\nthe contrary, is consistent with that of a type-Ic SN at z=0.72 (e.g.,\nDittman et al., GCN 12759), since the observed R band corresponds to the\nrest-frame U, where severe line blanketing suppresses the SN flux.  Also,\nthe I-band magnitude of the transient is comparable to that of SN 1998bw\nclose to the peak of luminosity, placed at z=0.72.\n\nAlthough a more accurate analysis of the afterglow behaviour is necessary,\nbased on the above arguments, we believe to have detected the emission\nfrom the SN associated with GRB 111228A.\n\n\nWe acknowledge the TNG staff for their support, in particular Luca Di\nFabrizio and Daniele Carosati.",
  "circularId": 13069,
  "createdOn": 1331902988000,
  "email": "paolo.davanzo@brera.inaf.it",
  "subject": "GRB 111228A: possible detection of the SN with the TNG",
  "submitter": "Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>",
  "eventId": "GRB 111228A"
}