Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...482..874d&link_type=abstract
Astrophysical Journal v.482, p.874
Astronomy and Astrophysics
Astronomy
30
Acceleration Of Particles, Gamma Rays: Theory, Ism: Individual Alphanumeric: W44, Radiation Mechanisms: Nonthermal, Ism: Supernova Remnants, Stars: Pulsars: Individual Alphanumeric: Psr B1853+01
Scientific paper
We show that relativistic bremsstrahlung and inverse Compton scattering of radio-emitting electrons can easily account for the observed gamma -ray spectrum of 2EG J1857+0118 if the field strength in the shell is below ~30 mu G. This source is located at the eastern border of the composite SNR W44, where the expanding radio shell is interacting with a dense molecular cloud. The nondetection of this remnant above 250 GeV implies a cutoff or steepening in the electron spectrum above ~100 GeV. The E-1.66 spectrum of this radio/ gamma -ray--emitting electron component is too flat to have its origin in standard first-order Fermi acceleration, but electron injection into the shell by the pulsar PSR B1853+01 over the 2 x 104 yr lifetime may explain why the Crab-like radio spectrum (S nu ~ nu -0.33) is about the hardest of all shell-type remnants. The injected energy would be sufficient to account for the required energy of 6 x 1049 ergs if the initial spin-down power of PSR B1853+01 was about 10 times larger than the present spin-down power of the Crab pulsar. A steeper Fermi electron component may be present, but the observational data are not constraining enough to provide a meaningful limit on the presence of an additional ~E-2 shell-type electron component. The predicted gamma -ray contribution from high-energy proton-gas interactions is about 20% of the observed EGRET flux above 100 MeV, which confirms our conclusion that the gamma -ray emission from W44 is dominated by a leptonic component.
de Jager Ocker C.
Mastichiadis Apostolos
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