1994•Monthly Notices of the Royal Astronomical SocietyRequires access
Upper limits on the high-energy gamma-ray fluxes from Formula and Formula
K. T. S. Brazier, David L. Bertsch, Carl E. Fichtel, J. M. Fierro, Robert C. Hartman, S. D. Hunter, G. Kanbach, D. A. Kniffen, Y. C. Lin, John R. Mattox II, H. A. Mayer‐Hasselwander, P. F. Michelson, C. von Montigny, H. I. Nel, P. L. Nolan, Edward J. Schneid, Parameswaran Sreekumar, D. J. Thompson
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Abstract
The high-energy gamma-ray telescope EGRET observed the positions of two young pulsars, |${\rm PSR} \ 1951 + 32$| and |$1509 - 58$|, during its all-sky survey. Despite their youth and relative proximity to the Earth, neither pulsar is detected as a point source or in periodicity analysis. Flux limits of a few |$\times 10^{-7}\ {\rm photon\enspace cm}^{-2} {\rm s}^{-1}$| are obtained for emission above 100 MeV, and |$\sim 10^{-6}\ {\rm photon\enspace cm}^{-2} {\rm s}^{-1}$| for 30–100 MeV. For the conventional assumption of beaming into 1 sr, the flux limits suggest that less than 3.2 per cent of the radiation from |${\rm PSR} \ 1509-58$|, and less than 1.8 per cent from |${\rm PSR} \ 1951 + 32$|, is in the form of beamed high-energy gamma-rays. The |${\rm PSR} \ 1509 - 58$| limits lie approximately one order of magnitude below the extrapolated hard X-ray spectrum and suggest that the spectrum steepens in the MeV region.