Implications on spatial models of interstellar gamma-ray inverse-Compton emission from synchrotron emission studies in radio and microwaves

Abstract

Cosmic rays interacting with gas and photon fields in the Galaxy produce interstellar gamma-ray emission (IGE), which accounts for almost 50% of the photons detected at gamma-ray energies. Models of this IGE have to be very accurate for interpreting the high-quality observations by present gamma-ray telescopes, such as Fermi Large Area Telescope (LAT). Standard models of IGE, used as reference models for analyses of the Fermi LAT data, show spatial discrepancies with respect to the data, underlining the necessity of more realistic models. The same CR electrons that produce the inverse-Compton component of the IGE produce also interstellar synchrotron emission observed in radio and microwave. However, present standard models do not take advantage of results coming from studies of this interstellar synchrotron emission. Accounting for such results, in this work we show how they affect the calculated spatial maps of the large-scale inverse-Compton component of the IGE, which are usually used in studies of Fermi LAT data. It is found that these results significantly affect these spatial model maps even at a 60% level. In particular, propagation models based on synchrotron studies produce a more peaked inverse-Compton emission in the inner Galaxy region with respect to the standard models used to analyze Fermi LAT data. The conclusion is that radio and microwave observations can be included in a multifrequency self-consistent approach for a more accurate modeling of the IGE finalized to a physical comprehensive interpretation of gamma-ray data and its present unexplained features. Model parameters are provided, which supply a more realistic basis for high-energy gamma-ray studies.