A RELATIVISTIC BREMSSTRAHLUNG INVERSE COMPTON ORIGIN FOR 2EG J1857+0118 ASSOCIATED WITH SUPERNOVA REMNANT W44/

We show that relativistic bremsstrahlung and inverse Compton scatterin g of radio-emitting electrons can easily account for the observed gamm a-ray spectrum of 2EG J1857+0118 if the held strength in the shell is below similar to 30 mu G. This source is located at the eastern border of the composite SNR W44, where the expanding radio shell is interact ing with a dense molecular cloud. The nondetection of this remnant abo ve 250 GeV implies a cutoff or steepening in the electron spectrum abo ve similar to 100 GeV. The E-1.66 spectrum of this radio/gamma-ray-emi tting electron component is too hat to have its origin in standard fir st-order Fermi acceleration, but electron injection into the shell by the pulsar PSR B1853+01 over the 2 x 10(4) yr lifetime may explain why the Crab-like radio spectrum (S-nu proportional to nu(-0.33)) is abou t the hardest of all shell-type remnants. The injected energy would be sufficient to account for the required energy of 6 x 10(49) ergs if t he initial spin-down power of PSR B1853+01 was about 10 times larger t han the present spin-down power of the Crab pulsar. A steeper Fermi el ectron component may be present, but the observational data are not co nstraining enough to provide a meaningful limit on the presence of an additional similar to E-2 shell-type electron component. The predicted gamma-ray contribution from high-energy proton-gas interactions is ab out 20% of the observed EGRET flux above 100 MeV, which confirms our c onclusion that the gamma-ray emission from W44 is dominated by a lepto nic component.