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Session 55 - Supernova Remnants.
Oral session, Tuesday, January 14
Harbour A,

[55.05] Are Low-Latitude Unidentified Gamma-Ray Sources Old Supernova Remnants?

C. D. Dermer (NRL), S. J. Sturner (NRL,NASA/GSFC), J. R. Mattox (Boston U.)

There are 96 unidentified sources of > 100 MeV radiation detected with the EGRET instrument on the Compton Gamma Ray Observatory, of which 40 are at low latitudes (|b|< 10^\circ). We have developed a statistical test that shows a strong association between the low-latitude \gamma-ray sources and young pulsars with spin-down ages <10^6 yrs. The pulsars are not, however, positionally coincident with the \gamma-ray sources. We explain this result if some \gamma-ray sources are SNRs that are undetected at other wavelengths with a pulsar witness, leaving the scene at hundreds of km s^-1, marking the location of the \gamma-ray bright SNRs. Numerical simulations of particle acceleration and radiation from SNRs are presented which show that > 100 MeV \gamma rays from secondary pion production can dominate the emission if the ratio of SN energy going into nonthermal electrons and protons varies considerably from source to source. If protons diffuse through the interstellar medium with mean free paths much shorter than the mean free paths of electrons, we also expect to find SNRs which are bright at \gamma-ray energies.

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