Synchrotron intensity gradients as tracers of magnetic field
  On the basis of the modern understanding of MHD turbulence, we propose a new
way of using synchrotron radiation, namely using synchrotron intensity
gradients for tracing astrophysical magnetic fields. We successfully test the
new technique using synthetic data obtained with the 3D MHD simulations and
provide the demonstration of the practical utility of the technique by
comparing the directions of magnetic field that are obtained with PLANCK
synchrotron intensity dats to the directions obtained with PLANCK synchrotron
polarization data. We demonstrate that the synchrotron intensity gradients
(SIGs) can reliably trace magnetic field in the presence of noise and can
provide detailed maps of magnetic-field directions. We also show that the SIGs
are relatively robust for tracing magnetic fields while the low spacial
frequencies of the synchrotron image are removed. This makes the SIGs
applicable to tracing of magnetic fields using interferometric data with single
dish measurement absent. We discuss the synergy of using the SIGs together with
synchrotron polarization in order to find the actual direction of the magnetic
field and quantify the effects of Faraday rotation as well as with other ways
of studying astrophysical magnetic fields. We test our method in the presence
of noise and the resolution effects. We stress the complementary nature of the
studies using the SIG technique and those employing the recently-introduced
velocity gradient techniques that traces the magnetic fields using
spectroscopic data.
