TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5061 SUBJECT: GRB 060427B Milagro GeV/TeV Observations DATE: 06/05/03 00:01:46 GMT FROM: Pablo Saz Parkinson at UCSC/Milagro 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 060427B (GCN Circ 5030, K. Hurley et al.), during the burst duration (0.2 s) reported by the IPN team. 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 TeV < 4.8 * 10^(-8) erg cm^(-2) (No EBL absorption) TeV photons are attenuated by pair production with infrared photons in intergalactic space. We calculate an upper limit assuming a redshift of 0.5 (a value representative of short/hard bursts) using the extragalactic infrared background light (EBL) absorption model of 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 150 GeV < 5.1 * 10^(-6) erg cm^(-2) (Primack 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 the absorption model. These upper limits are preliminary and will be refined with further analysis.