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Evidence for a Weak Galactic Center Magnetic Field from Diffuse Low Frequency Nonthermal Radio Emission | | T. N. LaRosa
; C. L. Brogan
; S. N. Shore
; T. J. Lazio
; N. E. Kassim
; M. E. Nord
; | | Date: |
12 May 2005 | | Journal: | Astrophys.J. 626 (2005) L23-L28 | | Subject: | astro-ph | | Affiliation: | Kennesaw State Univ.), C. L. Brogan (Inst. for Astron., Univ. of Hawaii), S. N. Shore (Dip. di Fisica, Univ. di Pisa), T. J. Lazio, N. E. Kassim (Remote Sensing, NRL), and M. E. Nord (NRL; Univ. of New Mexico | | Abstract: | New low-frequency 74 and 330 MHz observations of the Galactic center (GC) region reveal the presence of a large-scale ($6arcdeg imes 2arcdeg$) diffuse source of nonthermal synchrotron emission. A minimum energy analysis of this emission yields a total energy of $sim (phi^{4/7}f^{3/7}) imes 10^{52}$ ergs and a magnetic field strength of $sim 6(phi/f)^{2/7}$ muG (where $phi$ is the proton to electron energy ratio and $f$ is the filling factor of the synchrotron emitting gas). The equipartition particle energy density is $1.2(phi/f)^{2/7}$ evcm, a value consistent with cosmic-ray data. However, the derived magnetic field is several orders of magnitude below the 1 mG field commonly invoked for the GC. With this field the source can be maintained with the SN rate inferred from the GC star formation. Furthermore, a strong magnetic field implies an abnormally low GC cosmic-ray energy density. We conclude that the mean magnetic field in the GC region must be weak, of order 10 muG (at least on size scales $ga 125arcsec$). | | Source: | arXiv, astro-ph/0505244 | | Services: | Forum | Review | PDF | Favorites | |
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