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...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.展开更多
We show that the explosive transition of the neutron star （NS） to a quark star （QS） （a Quark Nova） in Cassiopeia A （Cas A） a few days following the supernova （SN） proper can account for several of the puzzli...We show that the explosive transition of the neutron star （NS） to a quark star （QS） （a Quark Nova） in Cassiopeia A （Cas A） a few days following the supernova （SN） proper can account for several of the puzzling kinematic and nucleosynthetic features that are observed. The observed decoupling between Fe and 44Ti and the lack of Fe emission within 44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by relativistic QN neutrons. Our model predicts the 44Ti to be more prominent to the NW of the central compact object （CCO） than in the SE and little of it along the NE-SW jets, in agreement with NuStar observations. Other intriguing features of Cas A are addressed, such as the lack of a pulsar wind nebula and the reported few percent drop in the CCO temperature over a period of 10 yr.展开更多
We present high spatial resolution X-ray spectroscopy of the supernova remnant Cassiopeia A with the Chandra observations. The X-ray emitting region of this remnant was divided into 38 × 34 pixels of 10″× 1...We present high spatial resolution X-ray spectroscopy of the supernova remnant Cassiopeia A with the Chandra observations. The X-ray emitting region of this remnant was divided into 38 × 34 pixels of 10″× 10″ each. Spectra of 960 pixels were created and fitted with an absorbed two component non-equilibrium ionization model. From the results of the spectral analysis we obtained maps of absorbing column density, temperatures, ionization ages, and the abundances of Ne, Mg, Si, S, Ca and Fe. The Si, S and possibly Ca abundance maps show obvious jet structures, while Fe does not follow the jet but seems to be distributed perpendicular to it. The abundances of Si, S and Ca show tight correlations between one another over a range of about two dex. This suggests that they are ejecta from explosive O- burning and incomplete Si-burning. Meanwhile, the Ne abundance is well correlated with that of Mg, indicating them to be the ashes of explosive C/Ne burning. The Fe abundance is positively correlated with that of Si when the latter is lower than 3 times the solar value, and is negatively correlated when higher. We suggest that such a two phase correlation is due to the different ways in which Fe was synthesized.展开更多
We utilize the PAdova and TRieste Stellar Evolution Code(PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters.Multicolor-photometric ob...We utilize the PAdova and TRieste Stellar Evolution Code(PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters.Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the WilsonDevinney(W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary(f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference?T = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe(DCRL method) and depending on calculation of the W-D code(DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M1 = 1.19±0.23 M⊙ with M2 = 0.76±0.18 M⊙ by the DCRL method and M1 = 1.22±0.26 M⊙ with M2 = 0.78±0.20 M ⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period(Porb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the(O-C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body(M3 sin i′= 0.279 M⊙) is derived from our two methods.展开更多
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)+1 种基金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))。
文摘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 operating grants from the National Science and Engineering Research Council of Canada (NSERC)
文摘We show that the explosive transition of the neutron star （NS） to a quark star （QS） （a Quark Nova） in Cassiopeia A （Cas A） a few days following the supernova （SN） proper can account for several of the puzzling kinematic and nucleosynthetic features that are observed. The observed decoupling between Fe and 44Ti and the lack of Fe emission within 44Ti regions is expected in the QN model owing to the spallation of the inner SN ejecta by relativistic QN neutrons. Our model predicts the 44Ti to be more prominent to the NW of the central compact object （CCO） than in the SE and little of it along the NE-SW jets, in agreement with NuStar observations. Other intriguing features of Cas A are addressed, such as the lack of a pulsar wind nebula and the reported few percent drop in the CCO temperature over a period of 10 yr.
基金the National Natural Science Foundation of China through Grants 10533020 and 10573017
文摘We present high spatial resolution X-ray spectroscopy of the supernova remnant Cassiopeia A with the Chandra observations. The X-ray emitting region of this remnant was divided into 38 × 34 pixels of 10″× 10″ each. Spectra of 960 pixels were created and fitted with an absorbed two component non-equilibrium ionization model. From the results of the spectral analysis we obtained maps of absorbing column density, temperatures, ionization ages, and the abundances of Ne, Mg, Si, S, Ca and Fe. The Si, S and possibly Ca abundance maps show obvious jet structures, while Fe does not follow the jet but seems to be distributed perpendicular to it. The abundances of Si, S and Ca show tight correlations between one another over a range of about two dex. This suggests that they are ejecta from explosive O- burning and incomplete Si-burning. Meanwhile, the Ne abundance is well correlated with that of Mg, indicating them to be the ashes of explosive C/Ne burning. The Fe abundance is positively correlated with that of Si when the latter is lower than 3 times the solar value, and is negatively correlated when higher. We suggest that such a two phase correlation is due to the different ways in which Fe was synthesized.
基金supported by the program of the Light in China’s Western Region (LCWR,Grant No. 2015-XBQN-A-02)the National Natural Science Foundation of China (Grant Nos. 11273051, 11661161016, 11473024 and 11863005)+1 种基金the 13th Fiveyear Information Plan of Chinese Academy of Sciences (Grant No. XXH13503-03-107)the Youth Innovation Promotion Association CAS (Grant No. 2018080)
文摘We utilize the PAdova and TRieste Stellar Evolution Code(PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters.Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the WilsonDevinney(W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary(f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference?T = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe(DCRL method) and depending on calculation of the W-D code(DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M1 = 1.19±0.23 M⊙ with M2 = 0.76±0.18 M⊙ by the DCRL method and M1 = 1.22±0.26 M⊙ with M2 = 0.78±0.20 M ⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period(Porb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the(O-C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body(M3 sin i′= 0.279 M⊙) is derived from our two methods.
