Search for Ultra-High-Energy Radiation from $\bf \gamma$-ray Bursts

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Session 74 -- Gamma-Ray Bursts
Oral presentation, Thursday, 2:30-4:00, Zellerbach Auditorium Room

[74.05] Search for Ultra-High-Energy Radiation from $\bf \gamma$-ray Bursts

D.A.~Williams, M.~Cavalli-Sforza, D.~Coyne, D.~Dorfan, L.~Kelley, S. Klein, R.~Schnee, T.~Yang, (U.C.Santa Cruz), S.~Biller, P.~Chumney, M.~Harmon, A.~Shoup, G.B.~Yodh (U.C.Irvine), D.E.~Alexandreas (U.C.Irvine, INFN-Padova), G.E.~Allen, C.Y.~Chang, M.L.~Chen, C.~Dion, J.A.~Goodman, T.J.~Haines, M.J.~Stark (U.Maryland), G.M.~Dion (U.Maryland, ICRR-Tokyo), D.~Berley (U.Maryland, NSF), R.L.~Burman, C.M.~Hoffman, D.E.~Nagle, D.M. Schmidt, C. Sinnis, D.D.~Weeks (LANL), W.P.~Zhang (LANL, NASA-GSFC), R.W.~Ellsworth (George Mason U.), J.-P.~Wu (U.C.Riverside)

Using data from the CYGNUS extensive air shower array, we have searched for evidence of emission of ultra-high-energy radiation coincident with $\gamma$-ray bursts observed by the BATSE instrument on the Compton Gamma-Ray Observatory. No statistically significant excess was found for any point in the sky within 4$\sigma$ of BATSE's best location coordinates for any of the 56 bursts examined. Furthermore, no events were seen in the 1.5$^{\circ}$ radius circular bin surrounding $\gamma$-ray burst GRB 920720, whose location was determined accurately by the Compton/Ulysses/PVO Interplanetary Network of satellites. Flux upper limits depend greatly on the actual zenith angle of the burst. Typical fluence upper limits above 100 TeV are $\sim$10$^{-6}$ erg cm$^{-2}$. The fluence upper limit for GRB 920720 is 2 $\times$ 10$^{-6}$ erg cm$^{-2}$.

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