{
  "bibcode": "2005GCN..3532....1G",
  "body": "P. Garnavich (Notre Dame), M. Pahre (CfA), A. Noriega-Crespo (CalTech),\nK.Z. Stanek (CfA, OSU), S.T. Holland (GSFC), D. Bersier (STScI),\nT. Matheson (NOAO), R. Perna (U. Colorado), K. Krisciunas (Notre Dame)\n\nAfter confirmation of a bright optical afterglow associated with\nGRB 050525 (Band et al. GCN 3466; Rykoff et al. GCN 3465;3468) we\ntriggered a \"target-of-opportunity\" (ToO) program on the Spitzer Space\nTelescope. Observations began on May 27.26 (UT), or 2.26 days\nafter the burst, with IRAC imaging followed by IRS spectroscopy,\nMIPS mapping and finally another epoch of IRAC images ending on\nMay 27.56 (UT).\n\nSoon after triggering the ToO, the brightness of the afterglow\nswitched to a steeper decline rate (Mirabal et al. GCN 3488;\nKaplan et al. GCN 3507) making a rapid response essential.\n\nThe first epoch of imaging shows point source at the position of the\nafterglow (Rykoff et al. GCN 3468; Yanagisawa et al. GCN 3489)\nin the 3.6,4.5 and 8.0 micron IRAC channels and in the 24 micron\nMIPS band.\n\nA second epoch of IRAC imaging and MIPS mapping was performed\non May 29. The source is seen to fade in IRAC between the two\nepochs of the first visit and is beyond the detection limit\nduring the second visit. The MIPS 24 micron source is also\nseen to fade between visits.\n\nThis is the first confirmed detection of a GRB afterglow at\nmid-infrared wavelengths. Preliminary estimate of the flux in\nthe IRAC channels combined with K-band observations of Kaplan et al.\n(GCN 3507) suggests a spectral energy distribution consistent\nwith a power-law. The index of the power-law  between 2 and 8 microns\nis 1.3+/-0.2. This is surprisingly steep and further analysis\nis continuing.\n\nThe IRAC 3.6 micron images taken at two epochs can be viewed at:\nhttp://www.nd.edu/~pgarnavi/grb050525/irac.jpg\n\nWe thank Nancy Silbermann and the Spitzer Science Center for\nrapidly responding to a complex target-of-opportunity observation.\n\nThis message may be cited.",
  "circularId": 3532,
  "createdOn": 1118184824000,
  "email": "pgarnavi@nd.edu",
  "subject": "GRB 050525a, Mid-Infrared Observations",
  "submitter": "Peter Garnavich at U of Notre Dame  <pgarnavi@nd.edu>",
  "eventId": "GRB 050525A"
}