http://arxiv.org/abs/1903.06421
Geminga pulsar is surrounded by a multi-TeV $\gamma$-ray halo radiated by high energy electrons and positrons accelereted by the central pulsar wind nebula (PWN). The angular profile of the $\gamma$-ray emission reported by HAWC indicates an anomalously slow diffusion for cosmic-ray electrons and positrons in the halo region around Geminga. In the paper we study the possible mechanism for the origin of slow diffusion. At first, we consider the self-generated Alfv\’en waves due to streaming instability of the electrons and positrons released by Geminga. However, even considering a very optimistic scenario for the wave growth, we find this mechanism DOES NOT work to account for the extremely slow diffusion at the present day if taking the proper motion of the pulsar into account. The reason is straightforward as the PWN is too weak to generate enough high energy electrons and positrons to stimulate strong turbulence at the late time. We then propose an assumption that the strong turbulence is generated by the shock wave of the parent supernova remnant of Geminga. Geminga may still be in the downstream region of the shock wave and embedded in a slow-diffusion circumstance. The TeV halos around PSR B0656+14 and Vela X may also be explained under this assumption.
F. Kun, B. Xiao-Jun and Y. Peng-Fei
Mon, 18 Mar 19
64/102
Comments: 7 pages, 5 figures, submitted to MNRAS. Comments are welcome
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