Search for very high energy gamma radiation from the radio bright region DR4 of the SNR G78.2+2.1

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Cortina, J.
Fernández, J.
Fonseca González, Mª Victoria
González, J. G.
Martínez, S.
Mirzoyan, R.
Moralejo, A.
Padilla, L.
Sánchez, J. A.
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Data from the HEGRA air shower array are used to set an upper limit on the emission of gamma-radiation above 25 (18) TeV from the direction of the radio bright region DR4 within the SNR G78.2 + 2.1 of 2.5 (7.1). 10^-13 cm^-2 sec^-1. The shock front of SNR G78.2 + 2.1 probably recently overtook the molecular cloud Gong 8 which then acts as a target for the cosmic rays produced within the SNR, thus leading to the expectation of enhanced gamma-radiation. Using a model of Drury, Aharonian and Völk which assumes that SNRs are the sources of galactic cosmic rays via first order Fermi acceleration, we calculated a theoretical prediction for the gamma-ray flux from the DR4 region and compared it with our experimental flux limit. Our 'best estimate' value for the predicted flux lies a factor of about 18 above the upper limit for gamma-ray energies above 25 TeV. Possible reasons for this discrepancy are discussed.
© EDP Sciencies. The support by the Deutsche Forschungsgemeinschaft DFG, the German Ministry for Research and Technology BMFT and the Spanish Research Council CICYT is gratefully acknowledged. We further thank the Instituto de Astrofisica de Canarias IAC and its president F. Sanchez for supplying excellent working conditions at La Palma.
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