Understanding the Multiwavelength Observation of Geminga’s Tev Halo: The Role of Anisotropic Diffusion of Particles

In this Letter, we propose that the x-ray and the TeV observations in the vicinity of Geminga can be understood in the framework of anisotropic diffusion of injected electrons or positrons. This interpretation only requires the turbulence in the vicinity of Geminga to be sub-Alfvénic with the local mean magnetic field direction approximately aligned with our line of sight towards Geminga, without invoking extreme conditions for the environment, such as an extremely small diffusion coefficient and a weak magnetic field of submicrogauss as suggested in previous literature.

Figure 1

Sketch figure for the geometry. See text for more details.

Figure 2

Predicted 8–40 TeV SBP with different Alfvénic Mach number $M_A=0.1$, 0.2, 0.3 and different viewing angle $\varphi =0°$, 5°.

Figure 3

Results with $\varphi =0°$ and $\varphi =5°$ for $M_A=0.2$. Upper: the predicted multiwavelength flux from a region within 10° from Geminga (black curves) and from a region within ${600}^{\prime \prime }$ from Geminga (blue curves). Solid curves represent the result of $\varphi =0°$ while dashed curves represent the result of $\varphi =5°$. The magenta bow tie and the cyan arrow represent the flux measured by HAWC and the upper limit from $XMM$-Newton respectively. Lower: the predicted 1D ($\zeta$ averaged) SBP in 8–40 TeV in comparison with the measured one by HAWC, which is shown as blue circles.