Radio emission, cosmic ray electrons, and the production of. gamma. -rays in the galaxy

Journal Article · Sat Mar 01 04:00:00 EST 1980 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/157761· OSTI ID:5339379

Webber, W R; Simpson, G A; Cane, H V

Using a perspective based on new radio data, we have reexamined the traditional derivation of the interstellar electron spectrum using the galactic nonthermal radio spectrum. The radio spectrum derived in the polar directions is now used as a base for this derivation rather than the anticenter spectrum. The interstellar electron spectrum between 70 and 1200 MeV is found to have an exponent -2.14 +- 0.06, steeper than previously determined, and leading to electron fluxes at low energies up to a factor of 10 larger than previously predicted. The electron spectrum below approx.20 MeV measured at Earth is used along with solar modulation arguments to suggest that this interstellar electron spectrum flattens to an exponent of -1.6 +- 0.1 between 5 and 70 MeV. We then use radio maps to predict the ..gamma..-ray fluxes produced by the bremsstrahlung process to be expected from these electrons. Using the radio maps, we fiest define L/sub eff/, the effective path length for radio emission in various directions, to predict the effective path length for ..gamma..-ray emission. The spectral shapes of ..gamma..-rays predicted when the contribution from ..pi../sup 0/ decay is included, show little evidence of a pion-decay bump and agree well with those observed, indicating that large changes in the cosmic-ray electron to proton ratio from that observed locally are unlikely along a line of sight. The differences in the predicted and observed ..gamma..-ray intensities in the galactic plane are small. However, in the polar direction, the predicted ..gamma..-ray flux using the radio data is approx.6 times larger than that actually observed. This is indicative of the fact that the radio emissivity is considerably thicker than the ..gamma..-ray emissivity disk, and the cosmic-ray electron population extends beyond the gaseous disk of the Galaxy. This technique of estimating the ..gamma..-ray intensity using the radio data is compared with the usual technique which employs estimates of the column density of hydrogen.

• Research Organization: Physics Department, University of New Hampshire
• OSTI ID: 5339379
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 236:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BREMSSTRAHLUNG
COSMIC ELECTRONS
COSMIC GAMMA SOURCES
COSMIC PHOTONS
COSMIC RADIATION
COSMIC RADIO SOURCES
COSMIC RAY PROPAGATION
COSMIC RAY SOURCES
ELECTROMAGNETIC RADIATION
ELECTRON SPECTRA
ELECTRONS
ELEMENTARY PARTICLES
EMISSIVITY
ENERGY SPECTRA
FERMIONS
GAMMA RADIATION
INTERSTELLAR SPACE
IONIZING RADIATIONS
LEPTONS
MASSLESS PARTICLES
OPTICAL PROPERTIES
PHOTONS
PHYSICAL PROPERTIES
RADIATION FLUX
RADIATIONS
SPACE
SPECTRA
SURFACE PROPERTIES