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Title:
Modeling the Galactic Center Magnetic Field Using Synchrotron Flux Density Maps
Authors:
Cowin, Benjamin J.; Morris, M.
Affiliation:
AA(University of Washington), AB(UC, Los Angeles)
Publication:
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #172.02; Bulletin of the American Astronomical Society, Vol. 38, p.1147
Publication Date:
12/2006
Origin:
AAS
Bibliographic Code:
2006AAS...20917202C

Abstract

Within the central few hundred parsecs of our Galaxy, a large-scale, diffuse non-thermal radio source (DNS) has been observed at several radio wavelengths. We have used the brightness distribution of this synchrotron source to model the strength and geometry of the large-scale magnetic field in the Galactic center region. A previous investigation of 330 and 74 MHz imaging data (LaRosa et al. 2005, ApJ 626, L23) concluded that the large-scale magnetic field in the region is relatively weak, only about 10 microgauss. However, their assumption that the magnetic field and cosmic rays are in a minimum-energy state across this region is unlikely to be valid because the ordered magnetic field implied by the vertical orientation of most of the nonthermal radio filaments observed there is inconsistent with the minimum-energy requirement that there be a substantial energy exchange between the cosmic rays and the magnetic field on time scales short compared to the energy loss time of the relativistic particles. Our new analysis of the existing DNS data abandons the minimum energy assumption, and instead assumes a cosmic ray propagation model that places the origin of the cosmic ray electrons in the Galactic disk, and invokes Liouville's theorem to yield a constant electron energy distribution function across the Galaxy, assuming that the cosmic ray electrons diffuse along the initially vertical magnetic field lines that connect the Galactic center to the disk. By tailoring the magnetic field geometry to reproduce the observed shape and intensity of the 330 MHz synchrotron emission, we find that the average field predicted by this model is at least 100 microgauss on a scale of several hundred parsecs, and the field peaks at approximately 500 microgauss at the center of the DNS.

This work was supported by an NSF/REU grant to UCLA.

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