摘要
Cassiopeia A,the brightest radio supernova remnant(SNR)in the sky,has several unique characteristics in comparison to its peers.Besides its radio brightness and prominent soft-concave radio spectrum,itsγ-ray spectrum appears to have a low-energy cutoff near 2 GeV,and it is the only SNR with prominent hard X-ray emission.While the unusual radio properties may be attributed to strong emission from reverse shocks,the hard X-ray emission has been associated with high-speed inward shocks induced by high density gases.Then,the low-energyγ-ray spectral cutoff could be attributed to slow penetration of lower energy particles accelerated near the inward shocks into high-density emission zone.In this paper,we carry out magneto-hydrodynamic(MHD)simulations of shocks in Cassiopeia A and demonstrate that its inward shock structure can indeed be reproduced via shock interactions with clumps of gases with a density of 20 cm-3.
基金
supported by the National Key Research&Development Program of China(2018YFA0404203)
the National Natural Science Foundation of China(Grant Nos.U1931204,U1738122,11761131007,11673060and 11433004)
the International Partnership Program of Chinese Academy of Sciences(114332KYSB20170008)
Top Talents Program of Yunnan Province,and the Natural Science Foundation of Yunnan Province(2016FB003 and 2018FY001(-003))。
