{
  "bibcode": "2007GCN..6448....1S",
  "body": "Pablo Saz Parkinson (UC Santa Cruz) on behalf of the Milagro\ncollaboration reports:\n\nWe have searched Milagro data for emission at GeV/TeV energies from GRB\n070521 detected by Swift (GCN Circ 6431, C. Guidorzi et al.), during the\nmain period of emission lasting 60s (GCN Circ 6440, D. Palmer et al.).\n\nNo evidence for prompt GeV/TeV emission was found. TeV photons are\nattenuated by pair production with infrared photons in intergalactic\nspace. We calculate an upper limit assuming two possible values for the\nredshift: z=0.03 (GCN Circ 6433, E. O. Ofek et al.), and z=0.55 (GCN Circ\n6444, T. Hattori et al.) using the extragalactic infrared background light\n(EBL) absorption model of Primack et al. 2005 (AIP Conf. Proc. 745, p.\n23).\n\nA preliminary analysis, assuming a differential photon spectral\nindex of -2.4, gives upper limits on E^2dN/dE at 99% confidence of:\n\nE^2 dN/dE at 250 GeV < 3.5 * 10^(-7) erg cm^(-2) (Assuming z=0.03)\n\nand\n\nE^2 dN/dE at 200 GeV < 5.5 * 10^(-6) erg cm^(-2) (Assuming z=0.55)\n\nThe energies quoted represent the approximate median energy of the\nevents that would be detected assuming a power law spectrum with\ndifferential index -2.4 convolved with the absorption model.\nThese upper limits are preliminary and will be refined with further\nanalysis.",
  "circularId": 6448,
  "createdOn": 1179798569000,
  "email": "pablo@scipp.ucsc.edu",
  "subject": "GRB 070521 Milagro GeV/TeV Observations",
  "submitter": "Pablo Saz Parkinson at UCSC/Milagro  <pablo@scipp.ucsc.edu>",
  "eventId": "GRB 070521"
}