So far quite a few ultraluminous X-ray(ULX) pulsars have been discovered.In this work,we construct a super-Eddington,magnetic accretion disk model to estimate the dipole magnetic field of eight ULX pulsars based on th...So far quite a few ultraluminous X-ray(ULX) pulsars have been discovered.In this work,we construct a super-Eddington,magnetic accretion disk model to estimate the dipole magnetic field of eight ULX pulsars based on their observed spin-up variations and luminosities.We obtain two branches of dipole magnetic field solutions.They are distributed in the range of B-(0.156-64.5) × 10^(10) G and-(0.275-79.0) × 10^(13) G corresponding to the low-and high-B solutions respectively.The low magnetic field solutions correspond to the state that the neutron stars are far away from the spin equilibrium,and the high magnetic field solutions are close to the spin equilibrium.The ultra-strong magnetic fields derived in Be-type ULX pulsars imply that the accretion mode in Be-type ULX pulsars could be more complicated than in the persistent ULX pulsars and may not be accounted for by the magnetized accretion disk model.We suggest that the transition between the accretor and the propeller regimes may be used to distinguish between the low-and high-B magnetic field solutions in addition to the detection of the cyclotron resonance scattering features.展开更多
The recent discoveries of pulsed X-ray emission from three ultraluminous X-ray(ULX)sources have finally enabled us to recognize a subclass within the ULX class:the great pretenders,neutron stars(NSs) that appear to em...The recent discoveries of pulsed X-ray emission from three ultraluminous X-ray(ULX)sources have finally enabled us to recognize a subclass within the ULX class:the great pretenders,neutron stars(NSs) that appear to emit X-ray radiation at isotropic luminosities L^(39)X= 7 × 10 erg s^(-1)-1 × 10^(41) erg s^(-1) only because their emissions are strongly beamed toward our direction and our sight lines are offset by only a few degrees from their magnetic-dipole axes.The three known pretenders appear to be stronger emitters than the presumed black holes of the ULX class,such as Holmberg II& IX X-1,IC10 X-1 and NGC 300 X-1.For these three NSs,we have adopted a single reasonable assumption,that their brightest observed outbursts unfold at the Eddington rate,and we have calculated both their propeller states and their surface magnetic-field magnitudes.We find that the results are not at all different from those recently obtained for the Magellanic Be/X-ray pulsars:the three NSs reveal modest magnetic fields of about 0.3–0.4 TG and beamed propeller-line X-ray luminosities of ~10^(36)-10^(37) erg s^(-1),substantially below the Eddington limit.展开更多
基金supported by the National Key Research and Development Program of China (2016YFA0400803)the National Natural Science Foundation of China under grant Nos.11773015 and 10241301Project U1838201 supported by NSFC and CAS。
文摘So far quite a few ultraluminous X-ray(ULX) pulsars have been discovered.In this work,we construct a super-Eddington,magnetic accretion disk model to estimate the dipole magnetic field of eight ULX pulsars based on their observed spin-up variations and luminosities.We obtain two branches of dipole magnetic field solutions.They are distributed in the range of B-(0.156-64.5) × 10^(10) G and-(0.275-79.0) × 10^(13) G corresponding to the low-and high-B solutions respectively.The low magnetic field solutions correspond to the state that the neutron stars are far away from the spin equilibrium,and the high magnetic field solutions are close to the spin equilibrium.The ultra-strong magnetic fields derived in Be-type ULX pulsars imply that the accretion mode in Be-type ULX pulsars could be more complicated than in the persistent ULX pulsars and may not be accounted for by the magnetized accretion disk model.We suggest that the transition between the accretor and the propeller regimes may be used to distinguish between the low-and high-B magnetic field solutions in addition to the detection of the cyclotron resonance scattering features.
基金DMC,SGTL and RC were supported by NASA grant NNX14-AF77GDK was supported by a NASA ADAP grant
文摘The recent discoveries of pulsed X-ray emission from three ultraluminous X-ray(ULX)sources have finally enabled us to recognize a subclass within the ULX class:the great pretenders,neutron stars(NSs) that appear to emit X-ray radiation at isotropic luminosities L^(39)X= 7 × 10 erg s^(-1)-1 × 10^(41) erg s^(-1) only because their emissions are strongly beamed toward our direction and our sight lines are offset by only a few degrees from their magnetic-dipole axes.The three known pretenders appear to be stronger emitters than the presumed black holes of the ULX class,such as Holmberg II& IX X-1,IC10 X-1 and NGC 300 X-1.For these three NSs,we have adopted a single reasonable assumption,that their brightest observed outbursts unfold at the Eddington rate,and we have calculated both their propeller states and their surface magnetic-field magnitudes.We find that the results are not at all different from those recently obtained for the Magellanic Be/X-ray pulsars:the three NSs reveal modest magnetic fields of about 0.3–0.4 TG and beamed propeller-line X-ray luminosities of ~10^(36)-10^(37) erg s^(-1),substantially below the Eddington limit.
