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Astron. Astrophys. 329, 639-658 (1998)

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Constraints on cosmic-ray origin from TeV gamma-ray observations of supernova remnants

J.H. Buckley 1, C.W. Akerlof 2, D.A. Carter-Lewis 3, M. Catanese 3, M.F. Cawley 4, V. Connaughton 5, D.J. Fegan 6, J.P. Finley 7, J.A. Gaidos 7, A.M. Hillas 8, F. Krennrich 3, R.C. Lamb 9, 3, R.W. Lessard 7, J.E. McEnery 6, G. Mohanty 3, J. Quinn 10, 6, A.J. Rodgers 8, H.J. Rose 8, A.C. Rovero 11, M.S. Schubnell 2, G. Sembroski 7, R. Srinivasan 7, T.C. Weekes 10 and J. Zweerink 3

1 Department of Physics, Washington University, St. Louis, MD 63130, USA
2 Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109-1120, USA
3 Department of Physics and Astronomy, Iowa State University, Ames, IA 50011-3160, USA
4 Physics Department, St.Patrick's College, Maynooth, Ireland
5 NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
6 Physics Department, University College, Dublin 4, Ireland
7 Department of Physics, Purdue University, West Lafayette, IN 47907, USA
8 Physics Department, University of Leeds, Leeds, LS2 9JT, Yorkshire, UK
9 Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
10 Whipple Observatory, Harvard-Smithsonian CfA, P.O. Box 97, Amado AZ 85645-0097, USA
11 Insituto de Astronoma y Fsca del Espacio, CC 67, Suc. 28, (1428) Buenos Aires, Argentina

Received 5 June 1997 / Accepted 21 July 1997


If supernova remnants (SNRs) are the site of cosmic-ray acceleration, the associated nuclear interactions should result in an observable flux of [FORMULA] -rays for the nearest SNRs. Measurements of the TeV [FORMULA] -ray flux from six nearby, radio-bright SNRs have been made with the Whipple Observatory imaging air erenkov telescope over the period September 1993 to June 1996. No significant emission has been detected and upper limits on the [FORMULA] 300 GeV flux are reported. Three of these SNRs (IC443, [FORMULA] -Cygni and W44) are spatially coincident with low-latitude otherwise unidentified sources detected with the Energetic Gamma-Ray Experiment Telescope (EGRET). If the EGRET [FORMULA] -ray fluxes result from cosmic-ray interactions then the EGRET and Whipple data are found to be collectively inconsistent with a cosmic-ray source spectrum flatter than [FORMULA]. The Whipple upper limits for IC443 and [FORMULA] -Cygni are also inconsistent with a priori predictions if these remnants are indeed expanding into regions where the average density of the interstellar medium is enhanced by the presence of molecular clouds. These data weaken the case for the simplest models of shock acceleration and energy dependent propagation of cosmic rays.

Key words: gamma-rays: observations – SNRs – cosmic rays – ISM: IC 443; fl Cyg SNR; W 44

Send offprint requests to: J.H. Buckley

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997