GCN Circular 4265
Pablo Saz Parkinson (UC Santa Cruz) on behalf of the Milagro collaboration reports: We have searched Milagro data for emission at GeV/TeV energies from GRB 051109A (GCN Circ 4213, G. Tagliaferri et al.), during the burst duration (36 s) reported by the Swift team (GCN Circ 4217, E. Fenimore et al.). No evidence for prompt GeV/TeV emission was found. A preliminary analysis, assuming a differential photon spectral index of -2.4, gives an upper limit on E^2dN/dE at 99% confidence of: E^2dN/dE at 2.5 TeV < 8.4 * 10^(-8) erg cm^(-2) (No EBL absorption assumed) The spectrum of the host galaxy of the proposed afterglow of GRB 051109A implies a redshift of 2.346 (GCN Circ 4221, R. Quimby et al.). TeV photons are attenuated by pair production with infrared photons in intergalactic space so we also calculate upper limits assuming different extragalactic infrared background light (EBL) absorption models, one by Kneiske et al. 2004 (A&A 413, 807) and one by Primack et al. 2005 (AIP Conf. Proc. 745, p. 23). We find 99% confidence level upper limits on E^2dN/dE of: E^2dN/dE at 55 GeV < 1.7 * 10^(-3) erg cm^(-2) (Primack et al. EBL model) E^2dN/dE at 60 GeV < 2.3 * 10^(-4) erg cm^(-2) (Kneiske et al. EBL model) The energies quoted represent the approximate median energy of the events that would be detected assuming a power law spectrum with differential index -2.4 convolved with each of the absorption models. These upper limits are preliminary and will be refined with further analysis.