Particle astrophysics at the galactic center
The presence of turbulence in astrophysical magnetic fields can have a significant effect on the diffusion of particles and, therefore, should be taken into account when performing simulations involving particle propagation. After reviewing the construction of the turbulent magnetic field component, we incorporate this feature in two separate projects. In the first, we consider the possible source(s) of hadronic cosmic rays thought to be responsible for the diffuse TeV γ-ray emission in the vicinity of the Galactic center. Assuming a completely turbulent magnetic field with an average strength of 10–100µG, we find that relativistic protons do not travel far enough to produce γ-rays spatially correlated with the giant molecular clouds, as seen by HESS, when injected into the interstellar medium by a single point source, such as the supermassive black hole Sagittarius A*. Increasing the number of point sources to five does improve the longitudinal extent of the emission but either shows only weak correlation with the molecular gas or highlights the source positions—both pictures are inconsistent with HESS observations. We conclude that protons must be accelerated throughout the Galactic center region via e.g. a second-order Fermi process in order to reproduce the HESS γ-ray map if the magnetic field there is completely turbulent.
Secondly, we examine the possible link between the asymmetric 511keV electron-positron annihilation emission from the inner Galactic disk and hard low mass X-ray binaries (LMXBs). Three different magnetic field configurations were considered: a completely turbulent field, a field in which the turbulent component has equal energy density as the mean component, and a strongly ordered field with little turbulence. Assuming the environment around each LMXB system is the same, we find that the LMXBs alone cannot account for all the positrons necessary to sufficiently fill the region regardless of the particular magnetic field structure chosen. Another transport mechanism (e.g. a galactic wind) in addition to the diffusive motion caused by the magnetic field fluctuations and/or allowing the LMXBs to be embedded in different phases of the interstellar medium is needed for the LMXB picture to remain a viable possibility.