Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity di...Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions （δv）： it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70 - 178km s^-1, which are near the statistical result of 90 - 270km s^-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t 〉 10^8 yr only if av 〈 25km s^-1.展开更多
The intensity distribution of emission beam and the new radio luminosity formula of pulsars are presented on the basis of the geometrical relations of polar-cap model. There are 102 pulsars with the new radio luminosi...The intensity distribution of emission beam and the new radio luminosity formula of pulsars are presented on the basis of the geometrical relations of polar-cap model. There are 102 pulsars with the new radio luminosity values. It is shown that the radio luminosity can be described only by one relation L∞(B/p^2)^(1.1) or L∞Q'^(-1.4) over the whole range of period and period derivatives, which is contrary to other recently suggested luminosity laws.展开更多
Through the analysis of representative samples of field galaxies,both local(z~0.027)and distant(z~0.7),we explore the barred galaxy fraction and its dependence on stellar mass,color,and morphology,aiming to understand...Through the analysis of representative samples of field galaxies,both local(z~0.027)and distant(z~0.7),we explore the barred galaxy fraction and its dependence on stellar mass,color,and morphology,aiming to understand the evolution of these structural components through cosmic time.To this end,two complementary bar detection techniques were employed:elliptical isophote fitting and two-dimensional Fourier analysis,both applied to deep optical images.The observational samples were drawn from previously established and calibrated catalogs to ensure a homogeneous selection in stellar mass,enabling a robust comparison between local galaxies(z~0.027)and those in the distant Universe(z~0.7).This study systematically applies both isophotal fitting and Fourier decomposition across a wide redshift range,offering a comprehensive view of the evolution of bar incidence as a function of stellar mass and morphology.The results indicate that the fraction of barred galaxies is significantly higher in the local Universe than at earlier epochs,particularly among spiral galaxies.Furthermore,a clear correlation is observed between the presence of bars and stellar mass,especially in the high-mass regime(log(M_*/M☉)>10.5).In distant galaxies,this fraction is lower across all mass ranges,which may be related to more active dynamical processes.Overall,the findings reinforce the idea that stellar bars emerge as a consequence of dynamical cooling and the progressive stabilization of galactic disks,playing a key role in gas transport and the internal structural evolution of galaxies from z~1 to the present day.展开更多
We have investigated the relation between the orbital period P<SUB>orb</SUB> and the spin period P<SUB>s</SUB> of neutron stars in OB/X-ray binaries. By simulating the time-development of the m...We have investigated the relation between the orbital period P<SUB>orb</SUB> and the spin period P<SUB>s</SUB> of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M<SUB>☉</SUB> donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B<SUB>0</SUB> stronger than about 3×10<SUP>12</SUP> G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B<SUB>0</SUB> < 3×10<SUP>12</SUP> G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the P<SUB>s</SUB>-P<SUB>orb</SUB> diagram.展开更多
Detection of γ-ray emissions from a class of active galactic nuclei （viz blazars）, has been one of the important findings from the Compton Gamma-Ray Observatory （CGRO）. However, their γ-ray luminosity function h...Detection of γ-ray emissions from a class of active galactic nuclei （viz blazars）, has been one of the important findings from the Compton Gamma-Ray Observatory （CGRO）. However, their γ-ray luminosity function has not been well determined. Few attempts have been made in earlier works, where BL Lacs and Flat Spectrum Radio Quasars （FSRQs） have been considered as a single source class. In this paper, we investigated the evolution and γ-ray luminosity function of FSRQs and BL Lacs separately. Our investigation indicates no evolution for BL Lacs, however FSRQs show significant evolution. Pure luminosity evolution is assumed for FSRQs and exponential and power law evolution models are examined. Due to the small number of sources, the low luminosity end index of the luminosity function for FSRQs is constrained with an upper limit. BL Lac luminosity function shows no signature of break. As a consistency check, the model source distributions derived from these luminosity functions show no significant departure from the observed source distributions.展开更多
A new physical parameter Q=log(We/P2/3) is defined as a criterion for judging whether a radio pulsar is a normal pulsar or a recycled pulsar originating from accreting binary systems.Based on the definition,the observ...A new physical parameter Q=log(We/P2/3) is defined as a criterion for judging whether a radio pulsar is a normal pulsar or a recycled pulsar originating from accreting binary systems.Based on the definition,the observational characteristics and the evolution of the two groups of pulsars are discussed.展开更多
In usual statistical analyses,because of diversities of proper parameters of pulsars,some interesting features might be smeared.In order to remove these diversities,we use the mean values for all quantities of pulsars...In usual statistical analyses,because of diversities of proper parameters of pulsars,some interesting features might be smeared.In order to remove these diversities,we use the mean values for all quantities of pulsars,instead of values of individual one to do statistical analyses.Logp/p3-logτand LogL-logτhave been plotted.The most interesting feature is that the radio luminosity of pulsar evidently appears to regrow up after its initial dropping.This feature is difficult to understand in usual models.Two tentatlive interpretations have been given.展开更多
Purpose In order to carry out in-orbit calibration,the hard X-ray modulation telescope satellite(HXMT)has made a number of observations of Crab pulsar.We study the long-term evolution of the X-ray flux of the Crab pul...Purpose In order to carry out in-orbit calibration,the hard X-ray modulation telescope satellite(HXMT)has made a number of observations of Crab pulsar.We study the long-term evolution of the X-ray flux of the Crab pulsar with these observational data.Methods We use nearly four years Crab pulsar’s data obtained by HXMT and the neutron star interior composition of explorer to test whether L_(x)∝L_(sd)^(α) holds for an individual pulsar,where L_(x) is the pulsed X-ray luminosity and Lsd is its spin-down luminosity.We also combine the earlier results obtained with PCA and HEXTE data(Yan et al.in ApJ 865:21,2018)to get the long-term evolution characteristics of the Crab pulsar.Results We find the X-ray flux evolution can be fitted by a linear correlation:L_(x)∝L_(sd)^(1.42±0.18).In soft X-ray energy band(1–10 keV)and hard X-ray energy band(27–250 keV),αdoes not change significantly with either energy or phase.However,this will need to be confirmed in future.For example,the interpulse component of hard X-ray may follow L_(x)∝L_(sd)^(0.96±0.34),which may be different from the correlation of soft X-rays and main pulse component.On the other hand,the hard X-ray flux evolution shows that the performance of high energy X-ray telescope(HE)onboard HXMT,such as effective area,is stable.Conclusion We conclude that the X-ray luminosity of the Crab pulsar closely correlates with its spin-down luminosity.However,the emission mechanism responsible for these phenomena remains not fully understood.展开更多
We review recent progress in theoretical understanding of X-ray binaries,which has largely been driven by new observations.We select several topics including formation of compact low-mass X-ray binaries,the evolutiona...We review recent progress in theoretical understanding of X-ray binaries,which has largely been driven by new observations.We select several topics including formation of compact low-mass X-ray binaries,the evolutionary connection between low-mass X-ray binaries and binary and millisecond radio pulsars,and ultraluminous X-ray sources,to illustrate the interplay between theories and observations.展开更多
The role and implication of binding energy through the accretion-induced collapse(AIC)of accreting white dwarfs(WDs)for the production of millisecond pulsars(MSPs)are investigated.The binding energy model is examined ...The role and implication of binding energy through the accretion-induced collapse(AIC)of accreting white dwarfs(WDs)for the production of millisecond pulsars(MSPs)are investigated.The binding energy model is examined due to the dynamic process in closed binary systems,and the possible mass of the companion sufficient to induce their orbital parameters is investigated.The deterministic nature of this interaction has a strong sensitivity to the equation of state of the binary systems(where the compactness of a neutron star is proportional to the amount of binding energy)associated with their initial conditions.This behavior mimics the commonly assumed mass and amount of accreted matter under the instantaneous mass loss(ΔM~0.18M_(⊙)).As a result,this indicates an increase in the MSP’s gravitational mass due to angular momentum losses.The outcome of such a system is then a circular binary MSP in which the companion is a low-mass WD,thus distinguishing the binary formation scenarios.In addition,the results of this work could provide constraints on the expected mass and binding energy of a neutron star based on the accretion rate.展开更多
The relation between the spin period and the orbital period in high-mass X-ray binaries is investigated.Be/X-ray binaries and SG/X-ray binaries occupy different areas in Corbet's diagram.The two SG/X-ray binaries,...The relation between the spin period and the orbital period in high-mass X-ray binaries is investigated.Be/X-ray binaries and SG/X-ray binaries occupy different areas in Corbet's diagram.The two SG/X-ray binaries,IGR J18483-0311 and OAO 1657-415,however,appear to occupy a transition region between Be/X-ray binaries and wind-fed SG/X-ray binaries.This can be understood by noting that the neutron stars in the two SG/X-ray binaries have not reached their equilibrium spin periods when the donors evolved off the main sequence.Here,we provide an alternative scenario to explain their location in Corbet's diagram:the SG/X-ray binaries are the descendants of Be/X-ray binaries,i.e.the supergiants in these systems were formed from O-type emission line stars instead of normal main-sequence stars.Furthermore,we suggest that there are two types of SG/X-ray binaries:one is directly evolved from a normal OB-type main sequence and neutron star system without an X-ray history,and the other evolved from a Be/X-ray binary with an X-ray history.展开更多
The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L....The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L. In this paper, we use a sample of 43 Swift bursts, which was taken from Ukwatta et al., to investigate whether this relation depends on redshift. Both the z-correction and the k-correction are taken into account. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: for each bin, where ?lag0 is the time-lag in the burst’s source frame, and is the corresponding mean value for the entire sample. The goal is to see whether the two fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that both the normalization, A, and the slope, B, seem to vary in a systematic way with redshift. We note that although good best-fits were obtained, with reasonable values for both the linear regression coefficient, r, and the reduced chi-squared, the data showed large scatter. Also, the number of GRBs in the sample studied is not large, and thus our conclusions are only tentative at this point. A flat universe with M = 0.27, ?? = 0.73, and a Hubble constant, H0 = 70 km.s-1.Mpc-1 is assumed.展开更多
The very small braking index of PSR J1734-3333, n = 0.9 ± 0.2, chal- lenges the current theories of braking mechanisms in pulsars. We present a possible interpretation that this pulsar is surrounded by a fall-hac...The very small braking index of PSR J1734-3333, n = 0.9 ± 0.2, chal- lenges the current theories of braking mechanisms in pulsars. We present a possible interpretation that this pulsar is surrounded by a fall-hack disk and braked by it. A modified braking torque is proposed based on the competition between the magnetic energy density of the pulsar and the kinetic energy density of the fall-back disk. With this torque, a self-similar disk can fit all the observed parameters of PSR J1734-3333 with natural initial values of parameters. In this regime, the star will evolve to the re- gion having anomalous X-ray pulsars and soft gamma repeaters in the P -/5 diagram in about 20 000 years and stay there for a very long time. The mass of the disk around PSR J1734-3333 in our model is about 10M similar to the observed mass of the disk around AXP 4U 0142＋61.展开更多
We used the Sloan Digital Sky Survey(SDSS)Data Release 5(DR5)to study the morphological properties of 1137 nearby infrared(IR)galaxies,most of which are brighter than 15.9 mag in r-band.This sample was drawn from a cr...We used the Sloan Digital Sky Survey(SDSS)Data Release 5(DR5)to study the morphological properties of 1137 nearby infrared(IR)galaxies,most of which are brighter than 15.9 mag in r-band.This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite(IRAS)point source catalog redshift survey with DR5 at z≤0.08.Based on this IR galaxy sample,we constructed five volume-limited sub-samples with IR luminosity ranging from 10^9.5 L⊙to 10^12L⊙.By deriving the IR luminosity functions(LF)for different morphological types,we found that normal spiral galaxies are the dominant population below LIR~8~10^10 L⊙;while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR≈5×10^10L⊙.As the IR luminosity decreases,the IR galaxies become more compact and have lower stellar masses.The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe,while,in contrast,the contribution from peculiar galaxies is only 39%.展开更多
We employ the supernova fallback disk model to simulate the spin evolution of isolated young neutron stars(NSs). We consider the submergence of the NS magnetic fields during the supercritical accretion stage and its s...We employ the supernova fallback disk model to simulate the spin evolution of isolated young neutron stars(NSs). We consider the submergence of the NS magnetic fields during the supercritical accretion stage and its succeeding reemergence. It is shown that the evolution of the spin periods and the magnetic fields in this model is able to account for the relatively weak magnetic fields of central compact objects and the measured braking indices of young pulsars. For a range of initial parameters, evolutionary links can be established among various kinds of NS sub-populations including magnetars, central compact objects and young pulsars. Thus, the diversity of young NSs could be unified in the framework of the supernova fallback accretion model.展开更多
基金Supported by the National Natural Science Foundation of China.
文摘Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions （δv）： it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70 - 178km s^-1, which are near the statistical result of 90 - 270km s^-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t 〉 10^8 yr only if av 〈 25km s^-1.
基金Project supported by the National Natural Science Foundation of China.
文摘The intensity distribution of emission beam and the new radio luminosity formula of pulsars are presented on the basis of the geometrical relations of polar-cap model. There are 102 pulsars with the new radio luminosity values. It is shown that the radio luminosity can be described only by one relation L∞(B/p^2)^(1.1) or L∞Q'^(-1.4) over the whole range of period and period derivatives, which is contrary to other recently suggested luminosity laws.
基金financial support from the Secretaría Nacional de Ciencia,Tecnologia e Innovacion(SENACYT),through the Departamento de Fortalecimiento a los Posgrados Nacionalesthe coordination of the program"MOVILIDAD DE INVESTIGACION."+3 种基金the financial support provided by PAPIIT projects IN108323 and IN111825 from DGAPA-UNAMsupport from the Agencia Nacional de Investigación y Desarrollo(ANID)through Basal project FB210003FONDECYT Regular projects 1241426 and 123044Millennium Science Initiative Program NCN2024_112。
文摘Through the analysis of representative samples of field galaxies,both local(z~0.027)and distant(z~0.7),we explore the barred galaxy fraction and its dependence on stellar mass,color,and morphology,aiming to understand the evolution of these structural components through cosmic time.To this end,two complementary bar detection techniques were employed:elliptical isophote fitting and two-dimensional Fourier analysis,both applied to deep optical images.The observational samples were drawn from previously established and calibrated catalogs to ensure a homogeneous selection in stellar mass,enabling a robust comparison between local galaxies(z~0.027)and those in the distant Universe(z~0.7).This study systematically applies both isophotal fitting and Fourier decomposition across a wide redshift range,offering a comprehensive view of the evolution of bar incidence as a function of stellar mass and morphology.The results indicate that the fraction of barred galaxies is significantly higher in the local Universe than at earlier epochs,particularly among spiral galaxies.Furthermore,a clear correlation is observed between the presence of bars and stellar mass,especially in the high-mass regime(log(M_*/M☉)>10.5).In distant galaxies,this fraction is lower across all mass ranges,which may be related to more active dynamical processes.Overall,the findings reinforce the idea that stellar bars emerge as a consequence of dynamical cooling and the progressive stabilization of galactic disks,playing a key role in gas transport and the internal structural evolution of galaxies from z~1 to the present day.
基金Supported by the National Natural Science Foundation of China.
文摘We have investigated the relation between the orbital period P<SUB>orb</SUB> and the spin period P<SUB>s</SUB> of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M<SUB>☉</SUB> donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B<SUB>0</SUB> stronger than about 3×10<SUP>12</SUP> G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B<SUB>0</SUB> < 3×10<SUP>12</SUP> G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the P<SUB>s</SUB>-P<SUB>orb</SUB> diagram.
文摘Detection of γ-ray emissions from a class of active galactic nuclei （viz blazars）, has been one of the important findings from the Compton Gamma-Ray Observatory （CGRO）. However, their γ-ray luminosity function has not been well determined. Few attempts have been made in earlier works, where BL Lacs and Flat Spectrum Radio Quasars （FSRQs） have been considered as a single source class. In this paper, we investigated the evolution and γ-ray luminosity function of FSRQs and BL Lacs separately. Our investigation indicates no evolution for BL Lacs, however FSRQs show significant evolution. Pure luminosity evolution is assumed for FSRQs and exponential and power law evolution models are examined. Due to the small number of sources, the low luminosity end index of the luminosity function for FSRQs is constrained with an upper limit. BL Lac luminosity function shows no signature of break. As a consistency check, the model source distributions derived from these luminosity functions show no significant departure from the observed source distributions.
文摘A new physical parameter Q=log(We/P2/3) is defined as a criterion for judging whether a radio pulsar is a normal pulsar or a recycled pulsar originating from accreting binary systems.Based on the definition,the observational characteristics and the evolution of the two groups of pulsars are discussed.
文摘In usual statistical analyses,because of diversities of proper parameters of pulsars,some interesting features might be smeared.In order to remove these diversities,we use the mean values for all quantities of pulsars,instead of values of individual one to do statistical analyses.Logp/p3-logτand LogL-logτhave been plotted.The most interesting feature is that the radio luminosity of pulsar evidently appears to regrow up after its initial dropping.This feature is difficult to understand in usual models.Two tentatlive interpretations have been given.
基金support from the National Program on Key Research and Development Project(Grant No.2021YFA0718500)from the Minister of Science and Technology of China(MOST)supports from the National Natural Science Foundation of China under Grants U1938102,12273043,U1838201,U1838202,U1938109 and U1938108supported by International Partnership Program of Chinese Academy of Sciences(Grant No.113111KYSB20190020).
文摘Purpose In order to carry out in-orbit calibration,the hard X-ray modulation telescope satellite(HXMT)has made a number of observations of Crab pulsar.We study the long-term evolution of the X-ray flux of the Crab pulsar with these observational data.Methods We use nearly four years Crab pulsar’s data obtained by HXMT and the neutron star interior composition of explorer to test whether L_(x)∝L_(sd)^(α) holds for an individual pulsar,where L_(x) is the pulsed X-ray luminosity and Lsd is its spin-down luminosity.We also combine the earlier results obtained with PCA and HEXTE data(Yan et al.in ApJ 865:21,2018)to get the long-term evolution characteristics of the Crab pulsar.Results We find the X-ray flux evolution can be fitted by a linear correlation:L_(x)∝L_(sd)^(1.42±0.18).In soft X-ray energy band(1–10 keV)and hard X-ray energy band(27–250 keV),αdoes not change significantly with either energy or phase.However,this will need to be confirmed in future.For example,the interpulse component of hard X-ray may follow L_(x)∝L_(sd)^(0.96±0.34),which may be different from the correlation of soft X-rays and main pulse component.On the other hand,the hard X-ray flux evolution shows that the performance of high energy X-ray telescope(HE)onboard HXMT,such as effective area,is stable.Conclusion We conclude that the X-ray luminosity of the Crab pulsar closely correlates with its spin-down luminosity.However,the emission mechanism responsible for these phenomena remains not fully understood.
基金supported by the National Basic Research Program of China(Grant No.2009CB-824800)the National Natural Science Foundation of China(Grant No.10873008)
文摘We review recent progress in theoretical understanding of X-ray binaries,which has largely been driven by new observations.We select several topics including formation of compact low-mass X-ray binaries,the evolutionary connection between low-mass X-ray binaries and binary and millisecond radio pulsars,and ultraluminous X-ray sources,to illustrate the interplay between theories and observations.
文摘The role and implication of binding energy through the accretion-induced collapse(AIC)of accreting white dwarfs(WDs)for the production of millisecond pulsars(MSPs)are investigated.The binding energy model is examined due to the dynamic process in closed binary systems,and the possible mass of the companion sufficient to induce their orbital parameters is investigated.The deterministic nature of this interaction has a strong sensitivity to the equation of state of the binary systems(where the compactness of a neutron star is proportional to the amount of binding energy)associated with their initial conditions.This behavior mimics the commonly assumed mass and amount of accreted matter under the instantaneous mass loss(ΔM~0.18M_(⊙)).As a result,this indicates an increase in the MSP’s gravitational mass due to angular momentum losses.The outcome of such a system is then a circular binary MSP in which the companion is a low-mass WD,thus distinguishing the binary formation scenarios.In addition,the results of this work could provide constraints on the expected mass and binding energy of a neutron star based on the accretion rate.
基金supported by the National Basic Research Program of China(Grant No.2009CB824800)the National High Technology Research and Development Program of China(Grant No.2008AA12Z304)the National Natural Science Foundation of China(Grant Nos.10873036 and 10673032)
文摘The relation between the spin period and the orbital period in high-mass X-ray binaries is investigated.Be/X-ray binaries and SG/X-ray binaries occupy different areas in Corbet's diagram.The two SG/X-ray binaries,IGR J18483-0311 and OAO 1657-415,however,appear to occupy a transition region between Be/X-ray binaries and wind-fed SG/X-ray binaries.This can be understood by noting that the neutron stars in the two SG/X-ray binaries have not reached their equilibrium spin periods when the donors evolved off the main sequence.Here,we provide an alternative scenario to explain their location in Corbet's diagram:the SG/X-ray binaries are the descendants of Be/X-ray binaries,i.e.the supergiants in these systems were formed from O-type emission line stars instead of normal main-sequence stars.Furthermore,we suggest that there are two types of SG/X-ray binaries:one is directly evolved from a normal OB-type main sequence and neutron star system without an X-ray history,and the other evolved from a Be/X-ray binary with an X-ray history.
文摘The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L. In this paper, we use a sample of 43 Swift bursts, which was taken from Ukwatta et al., to investigate whether this relation depends on redshift. Both the z-correction and the k-correction are taken into account. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: for each bin, where ?lag0 is the time-lag in the burst’s source frame, and is the corresponding mean value for the entire sample. The goal is to see whether the two fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that both the normalization, A, and the slope, B, seem to vary in a systematic way with redshift. We note that although good best-fits were obtained, with reasonable values for both the linear regression coefficient, r, and the reduced chi-squared, the data showed large scatter. Also, the number of GRBs in the sample studied is not large, and thus our conclusions are only tentative at this point. A flat universe with M = 0.27, ?? = 0.73, and a Hubble constant, H0 = 70 km.s-1.Mpc-1 is assumed.
基金Supported by the National Natural Science Foundation of China
文摘The very small braking index of PSR J1734-3333, n = 0.9 ± 0.2, chal- lenges the current theories of braking mechanisms in pulsars. We present a possible interpretation that this pulsar is surrounded by a fall-hack disk and braked by it. A modified braking torque is proposed based on the competition between the magnetic energy density of the pulsar and the kinetic energy density of the fall-back disk. With this torque, a self-similar disk can fit all the observed parameters of PSR J1734-3333 with natural initial values of parameters. In this regime, the star will evolve to the re- gion having anomalous X-ray pulsars and soft gamma repeaters in the P -/5 diagram in about 20 000 years and stay there for a very long time. The mass of the disk around PSR J1734-3333 in our model is about 10M similar to the observed mass of the disk around AXP 4U 0142＋61.
基金Supported by the National Natural Science Foundation of China grant Nos.10333060 and 10778622.
文摘We used the Sloan Digital Sky Survey(SDSS)Data Release 5(DR5)to study the morphological properties of 1137 nearby infrared(IR)galaxies,most of which are brighter than 15.9 mag in r-band.This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite(IRAS)point source catalog redshift survey with DR5 at z≤0.08.Based on this IR galaxy sample,we constructed five volume-limited sub-samples with IR luminosity ranging from 10^9.5 L⊙to 10^12L⊙.By deriving the IR luminosity functions(LF)for different morphological types,we found that normal spiral galaxies are the dominant population below LIR~8~10^10 L⊙;while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR≈5×10^10L⊙.As the IR luminosity decreases,the IR galaxies become more compact and have lower stellar masses.The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe,while,in contrast,the contribution from peculiar galaxies is only 39%.
基金supported by theNational Key Research and Development Program ofChina (2016YFA0400803)the National Natural Science Foundation of China (NSFC) (Grant Nos. 11333004,11773015 and 11573016)+1 种基金Project U1838201 supported by NSFC and CASthe Program for Innovative Research Team (in Science and Technology) at the University of Henan Province
文摘We employ the supernova fallback disk model to simulate the spin evolution of isolated young neutron stars(NSs). We consider the submergence of the NS magnetic fields during the supercritical accretion stage and its succeeding reemergence. It is shown that the evolution of the spin periods and the magnetic fields in this model is able to account for the relatively weak magnetic fields of central compact objects and the measured braking indices of young pulsars. For a range of initial parameters, evolutionary links can be established among various kinds of NS sub-populations including magnetars, central compact objects and young pulsars. Thus, the diversity of young NSs could be unified in the framework of the supernova fallback accretion model.
