We investigate the birthrate problem for low-mass X-ray binaries(LMXBs) and millisecond radio pulsars(MRPs) in this paper.We consider intermediate-mass and low-mass X-ray binaries(I/LMXBs) to be the progenitors of MRP...We investigate the birthrate problem for low-mass X-ray binaries(LMXBs) and millisecond radio pulsars(MRPs) in this paper.We consider intermediate-mass and low-mass X-ray binaries(I/LMXBs) to be the progenitors of MRPs,and calculate their evolutionary response to the cosmic star formation rate(SFR) both semi-analytically and numerically.With a typical value(1 Gyr) of the LMXB lifetime,one may expect comparable birthrates of LMXBs and MRPs,but the calculated number of LMXBs is an order of magnitude higher than that observed in the Galaxy.Instead,we suggest that the birthrate problem could be solved if most MRPs have evolved from faint to rather than bright LMXBs.The former may have a population of-104 in the Galaxy.展开更多
Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected pr...Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected previously in NGC 7078 and NGC 6440 are identified. Pulsars in NGC 6121, NGC 6440 and NGC 7078 cannot be detected because of the insufficient survey sensitivity and resolution. There may be a pulsar in the core of Terzan 1. The nature of the extended radio source near the core of NGC 6440 remains unclear. In the core of a globular cluster, there may be many neutron stars or an intermediate mass black hole, but this cannot be clarified with the current radio observations.展开更多
The Crab Pulsar was observed at 1540MHz with the 25m radio telescope at Urumqi with a filterbank de-dispersion backend. A total of 2436 giant pulses with pulse energies larger than 4300 Jy μs were detected in two obs...The Crab Pulsar was observed at 1540MHz with the 25m radio telescope at Urumqi with a filterbank de-dispersion backend. A total of 2436 giant pulses with pulse energies larger than 4300 Jy μs were detected in two observing sets. All of these giant pulses are located in the main pulse （MP） and inter pulse （IP） windows of the average profile of the Crab Pulsar. The ratio of the numbers of giant pulses detected in the IP and MP windows is about 0.05. Our results show that, at 1540MHz, the emission in the IP is contributed by giant and normal pulses, while that in the MP is almost dominated by giant pulses. The distribution of energy of the 2436 giant pulses at 1540 MHz can be described by a power-law with index α = 3.13 ± 0.09. The intrinsic threshold of giant pulse energy in the MP window is about 1400Jy μs at 1540MHz.展开更多
Resonant cyclotron scattering （RCS） in pulsar magnetospheres is considered. The photon diffusion equation （Kompaneets equation） for RCS is derived. The photon system is modeled three dimensionally. Numerical calcu...Resonant cyclotron scattering （RCS） in pulsar magnetospheres is considered. The photon diffusion equation （Kompaneets equation） for RCS is derived. The photon system is modeled three dimensionally. Numerical calculations show that there exist not only up scattering but also down scattering of RCS, depending on the parameter space. RCS＇s possible applications to spectral energy distributions of magnetar candidates and radio quiet isolated neutron stars （INSs） are pointed out. The optical/UV excess of INSs may be caused by the down scattering of RCS. The calculations for RX J1856.5-3754 and RX J0720.4-3125 are presented and compared with their observational data. In our model, the INSs are proposed to be normal neutron stars, although the quark star hypothesis is still possible. The low pulsation amplitude of INSs is a natural consequence in the RCS model.展开更多
We have used the unique low frequency sensitivity of the Large Phased Array （LPA） radio telescope of Pushchino Radio Astronomy Observatory to collect a dataset consisting of single pulse observations of second perio...We have used the unique low frequency sensitivity of the Large Phased Array （LPA） radio telescope of Pushchino Radio Astronomy Observatory to collect a dataset consisting of single pulse observations of second period pulsars in the Northern Hemisphere. During observation sessions in 2011- 2017, we collected data on 71 pulsars at a frequency of 111 MHz using a digital pulsar receiver. We have discovered Giant Radio Pulses （GRPs） from pulsars B0301＋09 and B 1237＋25, and confirmed earlier reported generation of anomalously strong （probable giant） pulses from B 1133＋16 in a statistically significant dataset. Data for these pulsars and from B0950＋08 and B 1112＋50, earlier reported as pulsars generating GRPs, were analyzed to evaluate their behavior over long time intervals. It was found that the statistical criterion （power-law spectrum of GRP distribution of energy and peak flux density） seems not to be strict for pulsars with a low magnetic field at their light cylinder. Moreover, spectra of some of these pulsars demonstrate unstable behavior with time and have a complex multicomponent shape. In the dataset for B0950＋08, we have detected the strongest GRP from a pulsar with a low magnetic field at its light cylinder ever reported, having a peak flux density as strong as 16.8 kJy.展开更多
Since 2013, round-the-clock monitoring of the sky has been carried out simultaneously in 96 beams using a high-sensitivity radio telescope called the Large Phased Array （LPA） at the frequency 110.25 MHz. These obser...Since 2013, round-the-clock monitoring of the sky has been carried out simultaneously in 96 beams using a high-sensitivity radio telescope called the Large Phased Array （LPA） at the frequency 110.25 MHz. These observations are made under the program of interplanetary plasma investigation. The same data are used to search for pulsars by means of power spectra. To increase the sensitivity of the pulsar search, 500-600 power spectra corresponding to different days of observations are summed. In the integrated spectra of known pulsars, besides expected improvement in signal-to-noise （S/N） ratio for the frequency harmonics, some features are explored in this paper. We present the 27 strongest pulsars which are in a field with declination 21° - 42°. The observable details in the integrated power spectra are connected with the presence of pulsar periods of the second （P2） and third （P3） class, which have been identified. Empirical relations for calculating these periods are obtained. The value P2 is estimated for 26 pulsars, and for 15 sources it is made for the first time. The value P3 is estimated for 13 pulsars, among them these values are given for five sources for the first time.展开更多
The single pulse observation of PSR J1752+2359 at 1250 MHz made using the Five-hundredmeter Aperture Spherical radio Telescope(FAST)is presented.We show that the pulsar exhibits two distinct emission states:a normal s...The single pulse observation of PSR J1752+2359 at 1250 MHz made using the Five-hundredmeter Aperture Spherical radio Telescope(FAST)is presented.We show that the pulsar exhibits two distinct emission states:a normal state with continuous normal pulse emission and a rotating radio transient(RRAT)-like state with sporadic emission.This makes PSR J1752+2359 the third pulsar that exhibits switching between RRAT-like and pulsar-like states.Our data show that,during the observation,20 per cent of the time for this pulsar was in the normal state and 80 per cent in the RRAT-like state.A quasiperiodic switching,with a periodicity of around 568 spin periods,between the two states was observed.The pulse energies for the two states both follow log-normal distributions.We demonstrate that the polarization profiles and the linear polarization position angle(PA)swings differ significantly between the two states.There is a phase offset of about 0°.35 between the pulse profile peaks of the two states.We argue that the emission geometry in the magnetosphere may be different for the two states.展开更多
We suggest a two-dimensional time dependent analytic model to describe the accretion of matter onto a neutron star moving at a high speed across the ejecta left in the aftermath of a supernova explosion. The formation...We suggest a two-dimensional time dependent analytic model to describe the accretion of matter onto a neutron star moving at a high speed across the ejecta left in the aftermath of a supernova explosion. The formation of a strange star resulting from the accretion is also addressed. The newborn neutron star is assumed to move outward at a kick velocity of Vns- 10^3 kin s^-1, and the accretion flow is treated as a dust flow. When the neutron star travels across the ejecta with high speed, it sweeps up material, and when the accreted mass has reached a critical value, the neutron star will undergo a phase transition, for instance, to become a strange star. Our results show that the accretion rate decreases in a complicated way in time, not just a power law dependence： it drops much faster than the power law derived by Colpi et al. We also found that the total accreted mass and the phase transition of the neutron star depend sensitively on the velocity of supernova ejecta.展开更多
Relic gravitational waves （RGWs）, a background originating during inflation, would leave imprints on pulsar timing residuals. This makes RGWs an important source for detection of RGWs using the method of pulsar timi...Relic gravitational waves （RGWs）, a background originating during inflation, would leave imprints on pulsar timing residuals. This makes RGWs an important source for detection of RGWs using the method of pulsar timing. In this paper, we discuss the effects of RGWs on single pulsar timing, and quantitatively analyze the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noises in pulsar timing residuals are understood, even though simultaneously observing multiple millisecond pulsars is a more powerful technique for extracting gravitational wave signals. We correct the normalization of RGWs using observations of the cosmic microwave background （CMB）, which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We obtained new constraints on RGWs using recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio r = 0.2 due to the tensor-type polarization observations of CMB by BICEP2 as a reference value, even though its reliability has been brought into question. Moreover, the constraints on RGWs from CMB and Big Bang nucleosynthesis will also be discussed for comparison.展开更多
The pulsar timing residuals induced by gravitational waves from non- evolving single binary sources are affected by many parameters related to the relative positions of the pulsar and the gravitational wave sources. W...The pulsar timing residuals induced by gravitational waves from non- evolving single binary sources are affected by many parameters related to the relative positions of the pulsar and the gravitational wave sources. We will analyze the various effects due to different parameters. The standard deviations of the timing residuals will be calculated with a variable parameter fixing a set of other parameters. The or- bits of the binary sources will be generally assumed to be elliptical. The influences of different eccentricities on the pulsar timing residuals will also be studied in detail. We find that the effects of the related parameters are quite different, and some of them display certain regularities.展开更多
We investigate a unique accreting millisecond pulsar with X-ray eclipses, SWIFT J1749.4-2807 （hereafter J1749）, and try to set limits on the binary system by various methods including use of the Roche lobe, the mass...We investigate a unique accreting millisecond pulsar with X-ray eclipses, SWIFT J1749.4-2807 （hereafter J1749）, and try to set limits on the binary system by various methods including use of the Roche lobe, the mass-radius relations of both main sequence （MS） and white dwarf （WD） companion stars, as well as the measured mass function of the pulsar. The calculations are based on the assumption that the radius of the companion star has reached its Roche radius （or is at 90%）, but the pulsar＇s mass has not been assumed to be a certain value. Our results are as follows. The companion star should be an MS one. For the case that the radius equals its Roche one, we have a companion star with mass M ≈ 0.51 Me and radius Rc ≈ 0.52 R⊙, and the inclination angle is i ≈ 76.5°; for the case that the radius reaches 90% of its Roche one, we have M ≈ 0.43M⊙, Rc ≈ 0.44R⊙ and i ≈ 75.7°. We also obtain the mass of J1749, Mp ≈ 1 M⊙, and conclude that the pulsar could be a quark star if the ratio of the critical frequency of rotation-mode instability to the Keplerian one is higher than - 0.3. The relatively low pulsar mass （about - M⊙） may also challenge the conventional recycling scenario for the origin and evolution of millisecond pulsars. The results presented in this paper are expected to be tested by future observations.展开更多
If the binding energy of the pulsar＇s surface is not so high （the case of a neutron star）, both negative and positive charges will flow out freely from the surface of the star. An annular free flow model for 7-ray ...If the binding energy of the pulsar＇s surface is not so high （the case of a neutron star）, both negative and positive charges will flow out freely from the surface of the star. An annular free flow model for 7-ray emission of pulsars is suggested. It is emphasized that： （1） Two kinds of acceleration regions （annular and core） need to be taken into account. The annular acceleration region is defined by the magnetic field lines that cross the null charge surface within the light cylinder. （2） If the potential drop in the annular region of a pulsar is high enough （normally the case for young pulsars）, charges in both the annular and the core regions could be accelerated and produce primary gamma-rays. Secondary pairs are generated in both regions and stream outwards to power the broadband radiations. （3） The potential drop grows more rapidly in the annular region than in the core region. The annular acceleration process is a key process for producing the observed wide emission beams. （4） The advantages of both the polar cap and outer gap models are retained in this model. The geometric properties of the 7-ray emission from the annular flow are analogous to that pre-sented in a previous work by Qiao et al., which match the observations well. （5） Since charges with different signs leave the pulsar through the annular and the core regions respectively, the current closure problem can be partially solved.展开更多
We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approxima...We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10-6-10-5 M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.展开更多
PSR B0540-69 has a braking index measurement in its persistent state： n = 2.129± 0.012. Recently, it has been reported to have changes in its spin-down state： a sudden 36% increase in the spin- down rate. Combi...PSR B0540-69 has a braking index measurement in its persistent state： n = 2.129± 0.012. Recently, it has been reported to have changes in its spin-down state： a sudden 36% increase in the spin- down rate. Combining the persistent state braking index measurement with different spin-down states, PSR B0540-69 is more powerful than intermittent pulsars in constraining pulsar spin-down models. The pulsar wind model is applied to explain the variable timing behavior of PSR B0540-69. The braking index of PSR B0540-69 in its persistent state results from the combined effect of magnetic dipole radiation and particle wind. The particle density reflects the magnetospheric activity in real-time and may be responsible for the changing spin-down behavior. Corresponding to the 36% increase in the spin-down rate of PSR B0540-69, the relative increase in the particle density is 88% in the vacuum gap model. The braking index calculated with the model in the new state is n = 1.79. Future observations that measure the braking index of PSR B0540-69 in the new spin-down state will be very powerful in distinguishing between different pulsar spin-down models and different particle acceleration models in the wind braking scenario. The variable timing behavior of PSR J 1846-0258 is also understandable in the pulsar wind model.展开更多
Motivated by the Fermi observations of some γ-ray pulsars in which the phases of radio and γ-ray peaks are almost the same, we investigate the outer gap model in a retarded dipole with a current-induced magnetic fie...Motivated by the Fermi observations of some γ-ray pulsars in which the phases of radio and γ-ray peaks are almost the same, we investigate the outer gap model in a retarded dipole with a current-induced magnetic field and apply it to explain pulsed γ-ray properties of the Crab pulsar. Our results show that the observed γ-ray energy-dependent light curves, which almost align with the radio light curve and phase averaged spectrum for the Crab pulsar, are reproduced well.展开更多
Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies.The Large Area Telescope（LAT） aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamm...Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies.The Large Area Telescope（LAT） aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamma-selected pulsars with almost no distance information.We study the relation between gammaray emission efficiency（η=Lγ/E˙） and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT.We have introduced three generation-order parameters to describe the gamma-ray emission properties of pulsars,and find a strong correlation of η-ζ3,a generation-order parameter which reflectsγ-ray photon generation in the pair cascade processes induced by magnetic field absorption in a pulsar＇s magnetosphere. A good correlation of η-BLC,the magnetic field at the light cylinder radius,is also found.These correlations are the distance indicators in gamma-ray pulsars used to evaluate distances for gamma-selected pulsars.Distances of 25 gamma-selected pulsars are estimated,which could be tested by other distance measurement methods.The physical origin of the correlations may also be interesting for pulsar studies.展开更多
Fast radio bursts （FRBs） are a type of newly-discovered transient astronomical phenomenon. They have short durations, high dispersion measures and a high event rate. However, due to unknown dis- tances and undetecte...Fast radio bursts （FRBs） are a type of newly-discovered transient astronomical phenomenon. They have short durations, high dispersion measures and a high event rate. However, due to unknown dis- tances and undetected electromagnetic counterparts at other wavebands, it is difficult to further investigate FRBs. Here we propose a method to study their environmental magnetic field using an indirect method. Starting withdispersion measures and rotation measures （RMs）, we try to obtain the parallel magnetic field component ^-B ││ which is the average value along the line of sight in the host galaxy. Because both RMs and redshifls are now unavailable, we demonstrate the dependence of ^-B ││ on these two separate quantities. This result, if the RM and redshift of an FRB are measured, would be expected to provide a clue towards understanding an environmental magnetic field of an FRB.展开更多
基金supported by the National Basic Research Program of China (Grant No. 2009CB824800)
文摘We investigate the birthrate problem for low-mass X-ray binaries(LMXBs) and millisecond radio pulsars(MRPs) in this paper.We consider intermediate-mass and low-mass X-ray binaries(I/LMXBs) to be the progenitors of MRPs,and calculate their evolutionary response to the cosmic star formation rate(SFR) both semi-analytically and numerically.With a typical value(1 Gyr) of the LMXB lifetime,one may expect comparable birthrates of LMXBs and MRPs,but the calculated number of LMXBs is an order of magnitude higher than that observed in the Galaxy.Instead,we suggest that the birthrate problem could be solved if most MRPs have evolved from faint to rather than bright LMXBs.The former may have a population of-104 in the Galaxy.
文摘Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected previously in NGC 7078 and NGC 6440 are identified. Pulsars in NGC 6121, NGC 6440 and NGC 7078 cannot be detected because of the insufficient survey sensitivity and resolution. There may be a pulsar in the core of Terzan 1. The nature of the extended radio source near the core of NGC 6440 remains unclear. In the core of a globular cluster, there may be many neutron stars or an intermediate mass black hole, but this cannot be clarified with the current radio observations.
文摘The Crab Pulsar was observed at 1540MHz with the 25m radio telescope at Urumqi with a filterbank de-dispersion backend. A total of 2436 giant pulses with pulse energies larger than 4300 Jy μs were detected in two observing sets. All of these giant pulses are located in the main pulse （MP） and inter pulse （IP） windows of the average profile of the Crab Pulsar. The ratio of the numbers of giant pulses detected in the IP and MP windows is about 0.05. Our results show that, at 1540MHz, the emission in the IP is contributed by giant and normal pulses, while that in the MP is almost dominated by giant pulses. The distribution of energy of the 2436 giant pulses at 1540 MHz can be described by a power-law with index α = 3.13 ± 0.09. The intrinsic threshold of giant pulse energy in the MP window is about 1400Jy μs at 1540MHz.
基金Supported by the National Natural Science Foundation of China
文摘Resonant cyclotron scattering （RCS） in pulsar magnetospheres is considered. The photon diffusion equation （Kompaneets equation） for RCS is derived. The photon system is modeled three dimensionally. Numerical calculations show that there exist not only up scattering but also down scattering of RCS, depending on the parameter space. RCS＇s possible applications to spectral energy distributions of magnetar candidates and radio quiet isolated neutron stars （INSs） are pointed out. The optical/UV excess of INSs may be caused by the down scattering of RCS. The calculations for RX J1856.5-3754 and RX J0720.4-3125 are presented and compared with their observational data. In our model, the INSs are proposed to be normal neutron stars, although the quark star hypothesis is still possible. The low pulsation amplitude of INSs is a natural consequence in the RCS model.
基金supported in part by the Program of the Presidium of Russian Academy of Sciences“Nonstationary processes in the Universe”
文摘We have used the unique low frequency sensitivity of the Large Phased Array （LPA） radio telescope of Pushchino Radio Astronomy Observatory to collect a dataset consisting of single pulse observations of second period pulsars in the Northern Hemisphere. During observation sessions in 2011- 2017, we collected data on 71 pulsars at a frequency of 111 MHz using a digital pulsar receiver. We have discovered Giant Radio Pulses （GRPs） from pulsars B0301＋09 and B 1237＋25, and confirmed earlier reported generation of anomalously strong （probable giant） pulses from B 1133＋16 in a statistically significant dataset. Data for these pulsars and from B0950＋08 and B 1112＋50, earlier reported as pulsars generating GRPs, were analyzed to evaluate their behavior over long time intervals. It was found that the statistical criterion （power-law spectrum of GRP distribution of energy and peak flux density） seems not to be strict for pulsars with a low magnetic field at their light cylinder. Moreover, spectra of some of these pulsars demonstrate unstable behavior with time and have a complex multicomponent shape. In the dataset for B0950＋08, we have detected the strongest GRP from a pulsar with a low magnetic field at its light cylinder ever reported, having a peak flux density as strong as 16.8 kJy.
基金support of a grant from the Russian Foundation for Basic Research(16–02–00954)
文摘Since 2013, round-the-clock monitoring of the sky has been carried out simultaneously in 96 beams using a high-sensitivity radio telescope called the Large Phased Array （LPA） at the frequency 110.25 MHz. These observations are made under the program of interplanetary plasma investigation. The same data are used to search for pulsars by means of power spectra. To increase the sensitivity of the pulsar search, 500-600 power spectra corresponding to different days of observations are summed. In the integrated spectra of known pulsars, besides expected improvement in signal-to-noise （S/N） ratio for the frequency harmonics, some features are explored in this paper. We present the 27 strongest pulsars which are in a field with declination 21° - 42°. The observable details in the integrated power spectra are connected with the presence of pulsar periods of the second （P2） and third （P3） class, which have been identified. Empirical relations for calculating these periods are obtained. The value P2 is estimated for 26 pulsars, and for 15 sources it is made for the first time. The value P3 is estimated for 13 pulsars, among them these values are given for five sources for the first time.
基金supported by the open program of the Key Laboratory of Xinjiang Uygur Autonomous Region(No.2020D04049)the Joint Research Fund in Astronomy under cooperative agreement between the National Natural Science Foundation of China(NSFC)and the Chinese Academy of Sciences(CAS)(Nos.U1831102 and U1731238)+3 种基金the NSFC project(Nos.12041303 and 12041304)the National Key Research and Development Program of China(No.2016YFA0400804)the National SKA Program of China(No.2020SKA0120200)supported by the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the CAS。
文摘The single pulse observation of PSR J1752+2359 at 1250 MHz made using the Five-hundredmeter Aperture Spherical radio Telescope(FAST)is presented.We show that the pulsar exhibits two distinct emission states:a normal state with continuous normal pulse emission and a rotating radio transient(RRAT)-like state with sporadic emission.This makes PSR J1752+2359 the third pulsar that exhibits switching between RRAT-like and pulsar-like states.Our data show that,during the observation,20 per cent of the time for this pulsar was in the normal state and 80 per cent in the RRAT-like state.A quasiperiodic switching,with a periodicity of around 568 spin periods,between the two states was observed.The pulse energies for the two states both follow log-normal distributions.We demonstrate that the polarization profiles and the linear polarization position angle(PA)swings differ significantly between the two states.There is a phase offset of about 0°.35 between the pulse profile peaks of the two states.We argue that the emission geometry in the magnetosphere may be different for the two states.
基金Supported by the National Natural Science Foundation of China.
文摘We suggest a two-dimensional time dependent analytic model to describe the accretion of matter onto a neutron star moving at a high speed across the ejecta left in the aftermath of a supernova explosion. The formation of a strange star resulting from the accretion is also addressed. The newborn neutron star is assumed to move outward at a kick velocity of Vns- 10^3 kin s^-1, and the accretion flow is treated as a dust flow. When the neutron star travels across the ejecta with high speed, it sweeps up material, and when the accreted mass has reached a critical value, the neutron star will undergo a phase transition, for instance, to become a strange star. Our results show that the accretion rate decreases in a complicated way in time, not just a power law dependence： it drops much faster than the power law derived by Colpi et al. We also found that the total accreted mass and the phase transition of the neutron star depend sensitively on the velocity of supernova ejecta.
基金supported by the National Natural Science Foundation of China(Grant Nos.11103024,11373028 and 11403030)the Science and Technology Research Development Program of Shaanxi Province+1 种基金the CAS“Light of West China”Programthe Open Project of Key Laboratory for Research in Galaxies and Cosmology,Chinese Academy of Sciences(Grant No.14010205)
文摘Relic gravitational waves （RGWs）, a background originating during inflation, would leave imprints on pulsar timing residuals. This makes RGWs an important source for detection of RGWs using the method of pulsar timing. In this paper, we discuss the effects of RGWs on single pulsar timing, and quantitatively analyze the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noises in pulsar timing residuals are understood, even though simultaneously observing multiple millisecond pulsars is a more powerful technique for extracting gravitational wave signals. We correct the normalization of RGWs using observations of the cosmic microwave background （CMB）, which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We obtained new constraints on RGWs using recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio r = 0.2 due to the tensor-type polarization observations of CMB by BICEP2 as a reference value, even though its reliability has been brought into question. Moreover, the constraints on RGWs from CMB and Big Bang nucleosynthesis will also be discussed for comparison.
基金Supported by the National Natural Science Foundation of China
文摘The pulsar timing residuals induced by gravitational waves from non- evolving single binary sources are affected by many parameters related to the relative positions of the pulsar and the gravitational wave sources. We will analyze the various effects due to different parameters. The standard deviations of the timing residuals will be calculated with a variable parameter fixing a set of other parameters. The or- bits of the binary sources will be generally assumed to be elliptical. The influences of different eccentricities on the pulsar timing residuals will also be studied in detail. We find that the effects of the related parameters are quite different, and some of them display certain regularities.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10778611 and 10973002)the National Basic Research Program of China(Grant No. 2009CB824800)
文摘We investigate a unique accreting millisecond pulsar with X-ray eclipses, SWIFT J1749.4-2807 （hereafter J1749）, and try to set limits on the binary system by various methods including use of the Roche lobe, the mass-radius relations of both main sequence （MS） and white dwarf （WD） companion stars, as well as the measured mass function of the pulsar. The calculations are based on the assumption that the radius of the companion star has reached its Roche radius （or is at 90%）, but the pulsar＇s mass has not been assumed to be a certain value. Our results are as follows. The companion star should be an MS one. For the case that the radius equals its Roche one, we have a companion star with mass M ≈ 0.51 Me and radius Rc ≈ 0.52 R⊙, and the inclination angle is i ≈ 76.5°; for the case that the radius reaches 90% of its Roche one, we have M ≈ 0.43M⊙, Rc ≈ 0.44R⊙ and i ≈ 75.7°. We also obtain the mass of J1749, Mp ≈ 1 M⊙, and conclude that the pulsar could be a quark star if the ratio of the critical frequency of rotation-mode instability to the Keplerian one is higher than - 0.3. The relatively low pulsar mass （about - M⊙） may also challenge the conventional recycling scenario for the origin and evolution of millisecond pulsars. The results presented in this paper are expected to be tested by future observations.
基金the National Natural Science Foundation of China.
文摘If the binding energy of the pulsar＇s surface is not so high （the case of a neutron star）, both negative and positive charges will flow out freely from the surface of the star. An annular free flow model for 7-ray emission of pulsars is suggested. It is emphasized that： （1） Two kinds of acceleration regions （annular and core） need to be taken into account. The annular acceleration region is defined by the magnetic field lines that cross the null charge surface within the light cylinder. （2） If the potential drop in the annular region of a pulsar is high enough （normally the case for young pulsars）, charges in both the annular and the core regions could be accelerated and produce primary gamma-rays. Secondary pairs are generated in both regions and stream outwards to power the broadband radiations. （3） The potential drop grows more rapidly in the annular region than in the core region. The annular acceleration process is a key process for producing the observed wide emission beams. （4） The advantages of both the polar cap and outer gap models are retained in this model. The geometric properties of the 7-ray emission from the annular flow are analogous to that pre-sented in a previous work by Qiao et al., which match the observations well. （5） Since charges with different signs leave the pulsar through the annular and the core regions respectively, the current closure problem can be partially solved.
文摘We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10-6-10-5 M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.
基金supported by the West Light Foundation of CAS(LHXZ 201201)the 973 Program(2015CB857100)Qing Cu Hui of CAS
文摘PSR B0540-69 has a braking index measurement in its persistent state： n = 2.129± 0.012. Recently, it has been reported to have changes in its spin-down state： a sudden 36% increase in the spin- down rate. Combining the persistent state braking index measurement with different spin-down states, PSR B0540-69 is more powerful than intermittent pulsars in constraining pulsar spin-down models. The pulsar wind model is applied to explain the variable timing behavior of PSR B0540-69. The braking index of PSR B0540-69 in its persistent state results from the combined effect of magnetic dipole radiation and particle wind. The particle density reflects the magnetospheric activity in real-time and may be responsible for the changing spin-down behavior. Corresponding to the 36% increase in the spin-down rate of PSR B0540-69, the relative increase in the particle density is 88% in the vacuum gap model. The braking index calculated with the model in the new state is n = 1.79. Future observations that measure the braking index of PSR B0540-69 in the new spin-down state will be very powerful in distinguishing between different pulsar spin-down models and different particle acceleration models in the wind braking scenario. The variable timing behavior of PSR J 1846-0258 is also understandable in the pulsar wind model.
基金partially supported by the National Natural Science Foundation of China(Grant Nos.11173020 and 11433004)the Top Talents Program of Yunnan Province
文摘Motivated by the Fermi observations of some γ-ray pulsars in which the phases of radio and γ-ray peaks are almost the same, we investigate the outer gap model in a retarded dipole with a current-induced magnetic field and apply it to explain pulsed γ-ray properties of the Crab pulsar. Our results show that the observed γ-ray energy-dependent light curves, which almost align with the radio light curve and phase averaged spectrum for the Crab pulsar, are reproduced well.
基金supported by the National Natural Science Foundation of China(Grant Nos.10803009,10833003 and 11073030)
文摘Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies.The Large Area Telescope（LAT） aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamma-selected pulsars with almost no distance information.We study the relation between gammaray emission efficiency（η=Lγ/E˙） and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT.We have introduced three generation-order parameters to describe the gamma-ray emission properties of pulsars,and find a strong correlation of η-ζ3,a generation-order parameter which reflectsγ-ray photon generation in the pair cascade processes induced by magnetic field absorption in a pulsar＇s magnetosphere. A good correlation of η-BLC,the magnetic field at the light cylinder radius,is also found.These correlations are the distance indicators in gamma-ray pulsars used to evaluate distances for gamma-selected pulsars.Distances of 25 gamma-selected pulsars are estimated,which could be tested by other distance measurement methods.The physical origin of the correlations may also be interesting for pulsar studies.
基金supported by the National Basic Research Program ("973" Program) of China (Grant No. 2014CB845800)the National Natural Science Foundation of China (Grant No. 11033002)
文摘Fast radio bursts （FRBs） are a type of newly-discovered transient astronomical phenomenon. They have short durations, high dispersion measures and a high event rate. However, due to unknown dis- tances and undetected electromagnetic counterparts at other wavebands, it is difficult to further investigate FRBs. Here we propose a method to study their environmental magnetic field using an indirect method. Starting withdispersion measures and rotation measures （RMs）, we try to obtain the parallel magnetic field component ^-B ││ which is the average value along the line of sight in the host galaxy. Because both RMs and redshifls are now unavailable, we demonstrate the dependence of ^-B ││ on these two separate quantities. This result, if the RM and redshift of an FRB are measured, would be expected to provide a clue towards understanding an environmental magnetic field of an FRB.
