Using archival Fermi-LAT data with a time span of~12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We...Using archival Fermi-LAT data with a time span of~12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We show that theγ-ray luminosity(L_(γ))and emissivity(i.e.,ε_(γ)=L_(γ)/M,with M the cluster mass)are good indicators of the population and abundance of MSPs in GlCs,and they are highly dependent on the dynamical evolution history of the host clusters.Specifically speaking,the dynamically older GlCs with more compact structures are more likely to have larger L_(γ)andε_(γ),and these trends can be summarized as strong correlations with cluster stellar encounter rateΓand the specific encounter rate(Λ=Γ/M),with L_(γ)∝Γ^(0.7±0.11)andε_(γ)∝Λ^(0.73±0.13)for dynamically normal GlCs.However,as GlCs evolve into deep core collapse,these trends are found to be reversed,implying that strong encounters may have lead to the disruption of Low-Mass X-ray Binaries and ejection of MSPs from core-collapsed systems.Besides,the GlCs are found to exhibit largerε_(γ)with increasing stellar mass function slope(ε_(γ)∝10^((0.52±0.1)α)),decreasing tidal radius(ε_(γ)∝R_(t)^(-10±0.22))and distances from the Galactic Center(GC,ε_(γ)∝R_(gc)^(-1.13±0.21)).These correlations indicate that,as GlCs losing kinetic energy and spiral in toward the GC,tidal stripping and mass segregation have a preference in leading to the loss of normal stars from GlCs,while MSPs are more likely to concentrate to cluster center and be deposited into the GC.Moreover,we gaugeε_(γ)of GlCs is~10-1000 times larger than the Galactic bulge,the latter is thought to reside thousands of unresolved MSPs and may be responsible for the GC 7-ray excess,which supports that GlCs are generous contributors to the population of MSPs in the GC.展开更多
We investigate the population and several properties of radio pulsars whose emission does not null(non-nulling)through simulation of a large pulsar sample.Emission from a pulsar is identified as non-nulling if(i)the e...We investigate the population and several properties of radio pulsars whose emission does not null(non-nulling)through simulation of a large pulsar sample.Emission from a pulsar is identified as non-nulling if(i)the emission does not cease across the whole pulse profile,and(ii)the emission is detectable.For(i),we adopt a model for switching in the plasma charge density,and emission persists if the charge density is non-zero.For(ii),we assume that detectable emission originates from source points where it is emitted tangentially to the magnetic field-line and parallel to the line-of-sight.We find that pulsars exhibiting non-nulling emission possess obliquity angles with an average of 42°.5,and almost half the samples maintain a duty cycle between 0.05 and 0.2.Furthermore,the pulsar population is not fixed but dependent on the obliquity angle,with the population peaking at 20°.In addition,three evolutionary phases are identified in the pulsar population as the obliquity angle evolves,with the majority of samples having an obliquity angle between 20°and 65°.Our results also suggest that emission from a pulsar may evolve between nulling and non-nulling during its lifetime.展开更多
We report the results of a search for radio pulsars in five supernova remnants(SNRs)with the FAST telescope.The observations were made using the 19-beam receiver in“snapshot”mode.The integration time for each pointi...We report the results of a search for radio pulsars in five supernova remnants(SNRs)with the FAST telescope.The observations were made using the 19-beam receiver in“snapshot”mode.The integration time for each pointing was 10 min.We discovered a new pulsar,PSR J1845–0306,which has a spin period of 983.6 ms and a dispersion measure of 444.6±2.0 cm^(−3)·pc,in observations of SNR G29.6+0.1.To judge the association between the pulsar and the SNR,further verification is needed.We also re-detected some known pulsars in the data from SNRs G29.6+0.1 and G29.7–0.3.No pulsars were detected in the observations of the other three SNRs.展开更多
We investigate the single-pulse emission variations of two pulsars,PSRs J0211+4235 and J0553+4111,observed with the Five-hundred-meter Aperture Spherical radio Telescope at the 1.25 GHz central frequency.The observati...We investigate the single-pulse emission variations of two pulsars,PSRs J0211+4235 and J0553+4111,observed with the Five-hundred-meter Aperture Spherical radio Telescope at the 1.25 GHz central frequency.The observation sessions span from 2020 December to 2021 July,with 21 and 22 observations for them respectively.The integrated pulse profile of PSR J0211+4235 shows that there is a weak pulse component following the main component,and PSR J0553+4111 displays a bimodal profile with a bridge component in the middle.PSR J0211+4235 presents significant nulling phenomenon with nulling duration lasting from 2 to 115 pulses and burst duration lasting from 2 to 113 pulses.The NF of each observation is determined to be 45%-55%.No emission greater than threeσis found in the mean integrated profile of all nulling pulses.In most cases,the pulse energy changes abruptly during the transition from null to burst,while in the transition from burst to null there are two trends:abrupt and gradual.We find that the nulling phenomenon of PSR J0211+4235 is periodic by the Fourier transform of the null and burst state.In addition,the single-pulse modulation characteristics of these two pulsars are investigated,and the distributions of modulation index,LRFS and 2DFS are analyzed with PSRSALSA.The left peak of PSR J0553+4111 has intensity modulation.Finally,the polarization properties of these two pulsars are obtained through polarization calibration,and their characteristics are analyzed.The possible physical mechanisms of these phenomena are discussed.展开更多
Pulsar polarization profiles form a very basic database for understanding the emission processes in a pulsar magnetosphere.After careful polarization calibration of the 19-beam L-band receiver and verification of beam...Pulsar polarization profiles form a very basic database for understanding the emission processes in a pulsar magnetosphere.After careful polarization calibration of the 19-beam L-band receiver and verification of beamoffset observation results,we obtain polarization profiles of 682 pulsars from observations by the Five-hundredmeter Aperture Spherical radio Telescope(FAST)duringthe Galactic Plane Pulsar Snapshot survey and other normal FAST projects.Among them,polarization profiles of about 460 pulsars are observed for the first time.The profiles exhibit diverse features.Some pulsars have a polarization position angle curve with a good S-shaped swing,some with orthogonal modes;some have components with highly linearly polarized components or strong circularly polarized components;some have a very wide profile,coming from an aligned rotator,and some have an interpulse from a perpendicular rotator;some wide profiles are caused by interstellar scattering.We derive geometric parameters for 190 pulsars from the S-shaped position angle curves or with orthogonal modes.We find that the linear and circular polarization or the widths of pulse profiles have various frequency dependencies.Pulsars with a large fraction of linear polarization are more likely to have a large Edot.展开更多
The braking indices of pulsars may contain important information about the internal physics of neutron stars(NSs),such as neutron superfluidity and internal magnetic fields.As a subsequent paper of Cheng et al.,we per...The braking indices of pulsars may contain important information about the internal physics of neutron stars(NSs),such as neutron superfluidity and internal magnetic fields.As a subsequent paper of Cheng et al.,we perform the same analysis as that done in the previous paper to other young pulsars with a steady braking index,n.Combining the timing data of these pulsars with the theory of magnetic field decay,and using their measured magnetic tilt angles,we can set constraints on the number of precession cycles,ξ,which represents the interactions between superfluid neutrons and other particles in the NS interior.For the pulsars considered in this paper,the results show thatξis within the range of a few×10~3 to a few×10~6.Interestingly,for the Crab and Vela pulsars,the constraints onξobtained with our method are generally consistent with that derived from modeling of the glitch rise behaviors of the two pulsars.Furthermore,we find that the internal magnetic fields of pulsar with n<3 may be dominated by the toroidal components.Our results may not only help to understand the interactions between the superfluid neutrons and other particles in the interior of NSs but also be important for the study of continuous gravitational waves from pulsars.展开更多
Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation bet...Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation between average dispersion measure(■)and dispersion measure difference(ΔDM)of known pulsars in GCs is lgΔDM∝1.52lg■.The sensitivity could be the key to finding more pulsars.As a result,several years after the construction of a large radio telescope facility,the number of known GC pulsars will likely be increased accordingly.We suggest that currently GCs in the southern hemisphere could have higher possibilities for finding new pulsars.展开更多
We present a method by using the phase characteristics of radio observation data for pulsar search and candidate identification.The phase characteristics are relations between the pulsar signal and the phase correctio...We present a method by using the phase characteristics of radio observation data for pulsar search and candidate identification.The phase characteristics are relations between the pulsar signal and the phase correction in the frequency-domain,and we regard it as a new search diagnostic characteristic.Based on the phase characteristics,a search method is presented:calculating dispersion measure(DM)—frequency data to select candidate frequencies,and then confirming of candidates by using the broadband characteristics of pulsar signals.Based on this method,we performed a search test on short observation data of M15 and M71,which were observed by Five-hundredmeter Aperture Spherical radio Telescope,and some of the Galactic Plane Pulsar Snapshot survey data.Results show that it can get similar search results to PRESTO(Pulsa R Exploration and Search TOolkit)while having a faster processing speed.展开更多
Black widows(BWs)are millisecond pulsars ablating their companion stars.The out-flowing material from the companion can block the radio emission of the pulsar,resulting in eclipses.In this paper,we construct a model f...Black widows(BWs)are millisecond pulsars ablating their companion stars.The out-flowing material from the companion can block the radio emission of the pulsar,resulting in eclipses.In this paper,we construct a model for the radio eclipse by calculating the geometry of the bow shock between the winds of the pulsar and companion,where the shock shapes the eclipsing medium but had not been described in detail in previous works.The model is further used to explain the variations of the flux density and dispersion measure of three BW pulsars(i.e.,PSR B1957+20,J2055+3829,and J2051-0827)detected by the Five-hundred-meter Aperture Spherical radio Telescope.Consequently,we constrained the parameters of the three BW systems such as the inclination angles and true anomalies of the observer as well as the mass-loss rates and wind velocity of the companion stars.With the help of these constraints,it is expected that magnetic fields of companion stars and even masses of pulsars could further be determined as some extra observation can be achieved in the future.展开更多
Based on the theory and observations of glitching pulsars, we show that the ultra-cold supranuclear dense matter inside the cores of massive pulsars should condensate in vacua, as predicated by non-perturbative QCD. T...Based on the theory and observations of glitching pulsars, we show that the ultra-cold supranuclear dense matter inside the cores of massive pulsars should condensate in vacua, as predicated by non-perturbative QCD. The trapped matter here forms false vacuums embedded in flat spacetimes and completely disconnected from the outside world. Although the vacuum expectation value here vanishes, the masses and sizes of these incompressible superfluid cores are set to grow with cosmic times, in accord with the Onsager-Feynman superfluidity analysis. We apply our scenario to several well-studied pulsars, namely the Crab, Vela, PSR J0740+6620 and find that the trapped mass-contents in their cores read {0.15,0.55,0.64}, implying that their true masses are {1.55,2.35,2.72} , respectively. Based thereon, we conclude that: 1) The true masses of massive pulsars and neutron stars are much higher than detected by direct observations and, therefore, are unbounded from above, 2) The remnant of the merger event in GW170817 should be a massive NS harbouring a core with 1.66 .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
In this paper,we have investigated accreting millisecond X-ray pulsars,which are rapidly rotating neutron stars in low-mass X-ray binaries.These systems exhibit coherent X-ray pulsations that arise when the accretion ...In this paper,we have investigated accreting millisecond X-ray pulsars,which are rapidly rotating neutron stars in low-mass X-ray binaries.These systems exhibit coherent X-ray pulsations that arise when the accretion flow is magnetically channeled to the stellar surface.Here,we have developed the fundamental equations for an accretion disk around accreting millisecond X-ray pulsars in the presence of a dynamo generated magnetic field in the inner part of the disk.We have also formulated the numerical method for the structure equations in the inner region of the disk and the highest accretion rate is enough to form the inner region of the disk,which is overpowered by radiation pressure and electron scattering.Finally,we have examined our results with the effects of dynamo magnetic fields on accreting millisecond X-ray pulsars.展开更多
We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These pulsars are discovered in a pilot program of the C...We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These pulsars are discovered in a pilot program of the Commensal Radio Astronomy FAST Survey(CRAFTS)with the ultra-widebandwidth commissioning receiver.Five of them are normal pulsars and two are extreme nulling slow pulsars.PSR J2111+2132’s dispersion measure(DM:78.5 pc cm^(-3))is above the upper limits of the two Galactic free electron density models,NE2001 and YMW16,and PSR J2057+2133’s position is out of the Scutum-Crux Arm,making them uniquely useful for improving the Galactic free electron density model in their directions.We present a detailed single pulse analysis for the slow nulling pulsars.We show evidence that PSR J2323+1214’s main pulse component follows a non-Poisson distribution and marginal evidence for a sub-pulse-drift or recurrent period of 32.3±0.4 rotations from PSR J0539+0013.We discuss the implication of our finding to the pulsar radiation mechanism.展开更多
The multi-messenger observations of the merger event in GW170817 did not rule out the possibility that the remnant might be a dynamically stable neutron star with <img src="Edit_01b04c31-b94c-4b32-bd17-d6383ca...The multi-messenger observations of the merger event in GW170817 did not rule out the possibility that the remnant might be a dynamically stable neutron star with <img src="Edit_01b04c31-b94c-4b32-bd17-d6383ca16545.bmp" alt="" />. Based on this and other recent events, I argue that the universal maximum density hypothesis should be revived. Accordingly, the central densities in the cores of ultra-compact objects must be upper-limited by the critical density number <em>n</em><sub><em>cr</em></sub>, beyond which supranuclear dense matter becomes purely incompressible. Based on the spacetime-matter coupling in GR, it is shown that the topology of spacetime embedding incompressible quantum fluids with <em>n</em>=<em style="white-space:normal;">n</em><sub style="white-space:normal;"><em>cr </em></sub>must be Minkowski flat, which implies that spacetime at the background of ultra-compact objects should be bimetric.展开更多
A conservative constraint on the rest mass of the photon can be estimated under the assump- tion that the frequency dependence of dispersion from astronomical sources is mainly contributed by the nonzero photon mass e...A conservative constraint on the rest mass of the photon can be estimated under the assump- tion that the frequency dependence of dispersion from astronomical sources is mainly contributed by the nonzero photon mass effect. Photon mass limits have been set earlier through the optical emissions of the Crab Nebula pulsar, but we demonstrate that these limits can be significantly improved with the dispersion measure (DM) measurements of radio pulsars in the Large and Small Magellanic Clouds. The combination of DM measurements of pulsars and distances of the Magellanic Clouds provides a strict upper limit on the photon mass as low as mγ≤2.0 ~ 10-45 g, which is at least four orders of magnitude smaller than the constraint from the Crab Nebula pulsar. Although our limit is not as tight as the current best result (~ 10-47 g) from a fast radio burst (FRB 150418) at a cosmological distance, the cosmological origin of FRB 150418 remains under debate; and our limit can reach the same high precision of FRB 150418 when it has an extragalactic origin ( ~10-45 g).展开更多
In this article we modify our previous model for the mechanisms underlying the glitch phenomena in pulsars. Accordingly, pulsars are born with embryonic cores that are made of purely incompressible superconducting glu...In this article we modify our previous model for the mechanisms underlying the glitch phenomena in pulsars. Accordingly, pulsars are born with embryonic cores that are made of purely incompressible superconducting gluon-quark superfluid (henceforth SuSu-cores). As the ambient medium cools and spins down due to emission of magnetic dipole radiation, the mass and size of SuSu-cores must grow discretely with time, in accordance with the Onsager-Feynmann analysis of superfluidity. Here we argue that the spacetime embedding glitching pulsars is dynamical and of bimetric nature: inside SuSu-cores the spacetime must be flat, whereas the surrounding region, where the matter is compressible and dissipative, the spacetime is Schwarzschild. It is argued here that the topological change of spacetime is derived by the strong nuclear force, whose operating length scales are found to increase with time to reach O (1) cm at the end of the luminous lifetimes of pulsars. The here-presented model is in line with the recent radio- and gravitational wave observations of pulsars and merger of neutron stars.展开更多
The Crab and Vela are well-studied glitching pulsars and the data obtained so far should enable us to test the reliability of models of their internal structures. Very recently it was proposed that glitching pulsars a...The Crab and Vela are well-studied glitching pulsars and the data obtained so far should enable us to test the reliability of models of their internal structures. Very recently it was proposed that glitching pulsars are embedded in bimetric spacetime: their incompressible superfluid cores (SuSu-cores) are embedded in flat spacetime, whereas the ambient compressible and dissipative media are enclosed in Schwarzschild spacetime. In this letter we apply this model to the Crab and Vela pulsars and show that a newly born pulsar initially of and an embryonic SuSu-core of could evolve into a Crab-like pulsar after 1000 years and into a Vela-like pulsar 10,000 years later to finally fade away as an invisible dark energy object after roughly 10 Myr. Based thereon we infer that the Crab and the Vela pulsars should have SuSu-cores of and , respectively. Furthermore, the under- and overshootings phenomena observed to accompany the glitch events of the Vela pulsar are rather a common phenomenon of glitching pulsars that can be well-explained within the framework of bimetric spacetime.展开更多
We investigate the statistical effects of non-discrete timing irregularities on observed radio pul- sar braking indices using correlations between the second derivative of the measured anomalous frequency (vobs) and...We investigate the statistical effects of non-discrete timing irregularities on observed radio pul- sar braking indices using correlations between the second derivative of the measured anomalous frequency (vobs) and some parameters that have been widely used to quantify pulsar timing fluctuations (the timing activity parameter (A), the amount of timing fluctuations absorbed by the cubic term (crR23) and a measure of pulsar rotational stability (δz)) in a large sample of 366 Jodrell Bank Observatory radio pulsars. The result demonstrates that anomalous braking indices are largely artifacts produced by aggregations of fluc- tuations that occur within or outside the pulsar system. For a subsample of 223 normal radio pulsars whose observed timing activity appeared consistent with instabilities in rotation of the underlying neutron stars (or timing noise) over timescales of - 10 - 40 yr,/vobs / strongly correlates (with correlation coefficient /r/ - 0.80 - 0.90) with the pulsar timing activity parameters and spin-down properties. On the other hand, no meaningful correlations (r 〈 0.3) were found between/)obs and the timing activity diagnostics and spin- down parameters in the remaining 143 objects, whose timing activity appears significantly dominated by white noise fluctuations. The current result can be better understood if the timing noise in isolated pulsars originates from intrinsic spin-down processes of the underlying neutron stars, but white noise fluctuations largely arise from processes external to the pulsar system.展开更多
Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^33 - 10^37 erg s^-1 and a photon index of 1.6-2.1 in...Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^33 - 10^37 erg s^-1 and a photon index of 1.6-2.1 in the energy range of 20-100 keV. The correlation between X-ray luminosity and spin-down power of Lx ∝ Lsd^1.31 suggests that the hard X-ray emission in rotation-powered pulsars is dominated by the pulsar wind nebula (PWN) component. Assuming spectral properties are similar in 20-100keV and 2-10 keV for both the pulsar and PWN components, the hard X-ray luminosity and flux of 39 known young X-ray pulsars and 8 millisecond pulsars are obtained, and a correlation of Lx ∝ Lsd^1.5 is derived. About 20 known young X-ray pulsars and 1 millisecond pulsars could be detected with future INTEGRAL and HXMT surveys. We also carry out Monte Carlo simulations of hard X-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics and the Lx - Lsd reltions:Lx ∝Lsd^1.31 and Lx∝Lsd^1.5 More than 40 young pulsars (mostly in the Galactic plane) could be detected after ten years of INTEGRAL surveys and the launch of HXMT. So, the young pulsars would be a significant part of the hard X-ray source population in the sky, and will contribute to unidentified hard X-ray sources in present and future hard X-ray surveys by INTEGRAL and HXMT.展开更多
Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope...Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log Blc (G) are 3.60-3.95 and 1.75 correspondingly. Moreover, their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: logE(erg s-1) = 35.37-35.53 and 32.64. The correlation between gamma- ray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand, the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.展开更多
基金supported by the Youth Program of the National Natural Science Foundation of China No.12003017。
文摘Using archival Fermi-LAT data with a time span of~12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We show that theγ-ray luminosity(L_(γ))and emissivity(i.e.,ε_(γ)=L_(γ)/M,with M the cluster mass)are good indicators of the population and abundance of MSPs in GlCs,and they are highly dependent on the dynamical evolution history of the host clusters.Specifically speaking,the dynamically older GlCs with more compact structures are more likely to have larger L_(γ)andε_(γ),and these trends can be summarized as strong correlations with cluster stellar encounter rateΓand the specific encounter rate(Λ=Γ/M),with L_(γ)∝Γ^(0.7±0.11)andε_(γ)∝Λ^(0.73±0.13)for dynamically normal GlCs.However,as GlCs evolve into deep core collapse,these trends are found to be reversed,implying that strong encounters may have lead to the disruption of Low-Mass X-ray Binaries and ejection of MSPs from core-collapsed systems.Besides,the GlCs are found to exhibit largerε_(γ)with increasing stellar mass function slope(ε_(γ)∝10^((0.52±0.1)α)),decreasing tidal radius(ε_(γ)∝R_(t)^(-10±0.22))and distances from the Galactic Center(GC,ε_(γ)∝R_(gc)^(-1.13±0.21)).These correlations indicate that,as GlCs losing kinetic energy and spiral in toward the GC,tidal stripping and mass segregation have a preference in leading to the loss of normal stars from GlCs,while MSPs are more likely to concentrate to cluster center and be deposited into the GC.Moreover,we gaugeε_(γ)of GlCs is~10-1000 times larger than the Galactic bulge,the latter is thought to reside thousands of unresolved MSPs and may be responsible for the GC 7-ray excess,which supports that GlCs are generous contributors to the population of MSPs in the GC.
基金supported by the National SKA Program of China No.2020SKA0120200the National Key Program for Science and Technology Research and Development No.2022YFC2205201+2 种基金the National Natural Science Foundation of China(NSFC,grant Nos.12288102,12041303,and 12041304)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region No.2022A03013-2the open program of the Key Laboratory of Xinjiang Uygur Autonomous Region No.2020D04049。
文摘We investigate the population and several properties of radio pulsars whose emission does not null(non-nulling)through simulation of a large pulsar sample.Emission from a pulsar is identified as non-nulling if(i)the emission does not cease across the whole pulse profile,and(ii)the emission is detectable.For(i),we adopt a model for switching in the plasma charge density,and emission persists if the charge density is non-zero.For(ii),we assume that detectable emission originates from source points where it is emitted tangentially to the magnetic field-line and parallel to the line-of-sight.We find that pulsars exhibiting non-nulling emission possess obliquity angles with an average of 42°.5,and almost half the samples maintain a duty cycle between 0.05 and 0.2.Furthermore,the pulsar population is not fixed but dependent on the obliquity angle,with the population peaking at 20°.In addition,three evolutionary phases are identified in the pulsar population as the obliquity angle evolves,with the majority of samples having an obliquity angle between 20°and 65°.Our results also suggest that emission from a pulsar may evolve between nulling and non-nulling during its lifetime.
基金supported by the National SKA Program of China (Grant No. 2020SKA0120200)the National Natural Science Foundation of China (Grant Nos. 12041303, 12273100, 12041304, and 12288102)+5 种基金the National Key R&D Program of China (Grant No. 2022YFC2205201)the West Light Foundation of the Chinese Academy of Sciences (Grant No. WLFC 2021-XBQNXZ-027)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region (Grant No. 2022A03013-4)the Natural Science Foundation of Xinjiiang Uygur Autonomous Region (Grant No. 2022D01D85)the open program of the Key Laboratory of Xinjiang Uygur Autonomous Region (Grant No. 2020D04049)partly supported by the Operation, Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments, budgeted from the Ministry of Finance of China and administrated by the CAS
文摘We report the results of a search for radio pulsars in five supernova remnants(SNRs)with the FAST telescope.The observations were made using the 19-beam receiver in“snapshot”mode.The integration time for each pointing was 10 min.We discovered a new pulsar,PSR J1845–0306,which has a spin period of 983.6 ms and a dispersion measure of 444.6±2.0 cm^(−3)·pc,in observations of SNR G29.6+0.1.To judge the association between the pulsar and the SNR,further verification is needed.We also re-detected some known pulsars in the data from SNRs G29.6+0.1 and G29.7–0.3.No pulsars were detected in the observations of the other three SNRs.
基金supported by National Key Research and Development Program of China(2022YFC2205203)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region(No.2022A03013-1)+3 种基金the National Natural Science Foundation of China(NSFC,Grant Nos.U1838109,12041304)supported by the 2021 project Xinjiang Uygur autonomous region of China for Tianshan elitesthe Youth Innovation Promotion Association of CAS under No.2023069support from the Natural Science Foundation of Shanghai(Grant No.20ZR1467600)。
文摘We investigate the single-pulse emission variations of two pulsars,PSRs J0211+4235 and J0553+4111,observed with the Five-hundred-meter Aperture Spherical radio Telescope at the 1.25 GHz central frequency.The observation sessions span from 2020 December to 2021 July,with 21 and 22 observations for them respectively.The integrated pulse profile of PSR J0211+4235 shows that there is a weak pulse component following the main component,and PSR J0553+4111 displays a bimodal profile with a bridge component in the middle.PSR J0211+4235 presents significant nulling phenomenon with nulling duration lasting from 2 to 115 pulses and burst duration lasting from 2 to 113 pulses.The NF of each observation is determined to be 45%-55%.No emission greater than threeσis found in the mean integrated profile of all nulling pulses.In most cases,the pulse energy changes abruptly during the transition from null to burst,while in the transition from burst to null there are two trends:abrupt and gradual.We find that the nulling phenomenon of PSR J0211+4235 is periodic by the Fourier transform of the null and burst state.In addition,the single-pulse modulation characteristics of these two pulsars are investigated,and the distributions of modulation index,LRFS and 2DFS are analyzed with PSRSALSA.The left peak of PSR J0553+4111 has intensity modulation.Finally,the polarization properties of these two pulsars are obtained through polarization calibration,and their characteristics are analyzed.The possible physical mechanisms of these phenomena are discussed.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.11988101 and 11833009),supported by the National Natural Science Foundation of China(NSFC,grant No.U2031115)supported by the National Key R&D Program of China(No.2021YFA1600401 and 2021YFA1600400)+1 种基金National Natural Science Foundation of China(NSFC,grant Nos.11873058 and 12133004)the National SKA program of China(No.2020SKA0120200)。
文摘Pulsar polarization profiles form a very basic database for understanding the emission processes in a pulsar magnetosphere.After careful polarization calibration of the 19-beam L-band receiver and verification of beamoffset observation results,we obtain polarization profiles of 682 pulsars from observations by the Five-hundredmeter Aperture Spherical radio Telescope(FAST)duringthe Galactic Plane Pulsar Snapshot survey and other normal FAST projects.Among them,polarization profiles of about 460 pulsars are observed for the first time.The profiles exhibit diverse features.Some pulsars have a polarization position angle curve with a good S-shaped swing,some with orthogonal modes;some have components with highly linearly polarized components or strong circularly polarized components;some have a very wide profile,coming from an aligned rotator,and some have an interpulse from a perpendicular rotator;some wide profiles are caused by interstellar scattering.We derive geometric parameters for 190 pulsars from the S-shaped position angle curves or with orthogonal modes.We find that the linear and circular polarization or the widths of pulse profiles have various frequency dependencies.Pulsars with a large fraction of linear polarization are more likely to have a large Edot.
基金supported by the National Natural Science Foundation of China(Grant Nos.12003009,and 12033001)CAS“Light of West China”Program(Grant No.2019-XBQNXZ-B-016)the National SKA program of China(Grant No.2020SKA0120300)。
文摘The braking indices of pulsars may contain important information about the internal physics of neutron stars(NSs),such as neutron superfluidity and internal magnetic fields.As a subsequent paper of Cheng et al.,we perform the same analysis as that done in the previous paper to other young pulsars with a steady braking index,n.Combining the timing data of these pulsars with the theory of magnetic field decay,and using their measured magnetic tilt angles,we can set constraints on the number of precession cycles,ξ,which represents the interactions between superfluid neutrons and other particles in the NS interior.For the pulsars considered in this paper,the results show thatξis within the range of a few×10~3 to a few×10~6.Interestingly,for the Crab and Vela pulsars,the constraints onξobtained with our method are generally consistent with that derived from modeling of the glitch rise behaviors of the two pulsars.Furthermore,we find that the internal magnetic fields of pulsar with n<3 may be dominated by the toroidal components.Our results may not only help to understand the interactions between the superfluid neutrons and other particles in the interior of NSs but also be important for the study of continuous gravitational waves from pulsars.
基金supported by the National SKA Program of China No.2020SKA0120100the National Natural Science Foundation of China(NSFC,Grant Nos.11963002,11703047,11773041,U2031119,12173052,12003047 and 12173053)+7 种基金the fostering project of Guizhou University with No.201911Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the Specialized Research Fund for State Key Laboratoriessupported by the CAS“Light of West China”Programthe Youth Innovation Promotion Association of CAS(id 2023064)supported by the Youth Innovation Promotion Association of CAS(id.2018075 and Y2022027)supported by Guizhou Provincial Basic Research Program(Natural Science)(ZK[2023]039)Key Technology R&D Program([2023]352)。
文摘Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation between average dispersion measure(■)and dispersion measure difference(ΔDM)of known pulsars in GCs is lgΔDM∝1.52lg■.The sensitivity could be the key to finding more pulsars.As a result,several years after the construction of a large radio telescope facility,the number of known GC pulsars will likely be increased accordingly.We suggest that currently GCs in the southern hemisphere could have higher possibilities for finding new pulsars.
基金supported by the National Natural Science Foundation of China(Nos.12203039 and 11873083)the National Natural Science Foundation of China(Nos.12173053 and 12041303)+4 种基金supported by the National SKA Program of China(No.2020SKA0120100)the Youth Innovation Promotion Association of CAS(id.2018075)the CAS“Light of West China”Programthe Specialized Research Fund for State Key Laboratoriesthe Science and Technology Program of Guizhou Province([2021]4001)。
文摘We present a method by using the phase characteristics of radio observation data for pulsar search and candidate identification.The phase characteristics are relations between the pulsar signal and the phase correction in the frequency-domain,and we regard it as a new search diagnostic characteristic.Based on the phase characteristics,a search method is presented:calculating dispersion measure(DM)—frequency data to select candidate frequencies,and then confirming of candidates by using the broadband characteristics of pulsar signals.Based on this method,we performed a search test on short observation data of M15 and M71,which were observed by Five-hundredmeter Aperture Spherical radio Telescope,and some of the Galactic Plane Pulsar Snapshot survey data.Results show that it can get similar search results to PRESTO(Pulsa R Exploration and Search TOolkit)while having a faster processing speed.
基金supported by the National SKA program of China(2020SKA0120300)the National Key R&D Program of China(2021YFA0718500)+2 种基金the National Natural Science Foundation of China(grant Nos.11833003,12033001)the China Postdoctoral Science Foundation(No.2023T160410)the Opening Foundation of Xinjiang Key Laboratory(No.2021D04016)。
文摘Black widows(BWs)are millisecond pulsars ablating their companion stars.The out-flowing material from the companion can block the radio emission of the pulsar,resulting in eclipses.In this paper,we construct a model for the radio eclipse by calculating the geometry of the bow shock between the winds of the pulsar and companion,where the shock shapes the eclipsing medium but had not been described in detail in previous works.The model is further used to explain the variations of the flux density and dispersion measure of three BW pulsars(i.e.,PSR B1957+20,J2055+3829,and J2051-0827)detected by the Five-hundred-meter Aperture Spherical radio Telescope.Consequently,we constrained the parameters of the three BW systems such as the inclination angles and true anomalies of the observer as well as the mass-loss rates and wind velocity of the companion stars.With the help of these constraints,it is expected that magnetic fields of companion stars and even masses of pulsars could further be determined as some extra observation can be achieved in the future.
文摘Based on the theory and observations of glitching pulsars, we show that the ultra-cold supranuclear dense matter inside the cores of massive pulsars should condensate in vacua, as predicated by non-perturbative QCD. The trapped matter here forms false vacuums embedded in flat spacetimes and completely disconnected from the outside world. Although the vacuum expectation value here vanishes, the masses and sizes of these incompressible superfluid cores are set to grow with cosmic times, in accord with the Onsager-Feynman superfluidity analysis. We apply our scenario to several well-studied pulsars, namely the Crab, Vela, PSR J0740+6620 and find that the trapped mass-contents in their cores read {0.15,0.55,0.64}, implying that their true masses are {1.55,2.35,2.72} , respectively. Based thereon, we conclude that: 1) The true masses of massive pulsars and neutron stars are much higher than detected by direct observations and, therefore, are unbounded from above, 2) The remnant of the merger event in GW170817 should be a massive NS harbouring a core with 1.66 .
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the Ethiopian Space Science and Technology InstituteEntoto Observatory and Research CenterAstronomy and Astrophysics Research and Development Department for supporting this research。
文摘In this paper,we have investigated accreting millisecond X-ray pulsars,which are rapidly rotating neutron stars in low-mass X-ray binaries.These systems exhibit coherent X-ray pulsations that arise when the accretion flow is magnetically channeled to the stellar surface.Here,we have developed the fundamental equations for an accretion disk around accreting millisecond X-ray pulsars in the presence of a dynamo generated magnetic field in the inner part of the disk.We have also formulated the numerical method for the structure equations in the inner region of the disk and the highest accretion rate is enough to form the inner region of the disk,which is overpowered by radiation pressure and electron scattering.Finally,we have examined our results with the effects of dynamo magnetic fields on accreting millisecond X-ray pulsars.
基金supported by the National Natural Science Foundation of China(Grant Nos.11988101,U2031117,11725313,12041303,11873067,U1831131 and U1631132)the China Scholarship Council(No.201704910686)+4 种基金the CASMPG LEGACY projectthe Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB23000000)the National SKA Program of China(No.2020SKA0120200)the Foundation of Guizhou Provincial Education Department(No.KY(2020)003)the Cultivation Project for FAST Scientific Payoff and the Research Achievement of CAMS-CAS。
文摘We present Arecibo 327 MHz confirmation and follow-up studies of seven new pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST).These pulsars are discovered in a pilot program of the Commensal Radio Astronomy FAST Survey(CRAFTS)with the ultra-widebandwidth commissioning receiver.Five of them are normal pulsars and two are extreme nulling slow pulsars.PSR J2111+2132’s dispersion measure(DM:78.5 pc cm^(-3))is above the upper limits of the two Galactic free electron density models,NE2001 and YMW16,and PSR J2057+2133’s position is out of the Scutum-Crux Arm,making them uniquely useful for improving the Galactic free electron density model in their directions.We present a detailed single pulse analysis for the slow nulling pulsars.We show evidence that PSR J2323+1214’s main pulse component follows a non-Poisson distribution and marginal evidence for a sub-pulse-drift or recurrent period of 32.3±0.4 rotations from PSR J0539+0013.We discuss the implication of our finding to the pulsar radiation mechanism.
文摘The multi-messenger observations of the merger event in GW170817 did not rule out the possibility that the remnant might be a dynamically stable neutron star with <img src="Edit_01b04c31-b94c-4b32-bd17-d6383ca16545.bmp" alt="" />. Based on this and other recent events, I argue that the universal maximum density hypothesis should be revived. Accordingly, the central densities in the cores of ultra-compact objects must be upper-limited by the critical density number <em>n</em><sub><em>cr</em></sub>, beyond which supranuclear dense matter becomes purely incompressible. Based on the spacetime-matter coupling in GR, it is shown that the topology of spacetime embedding incompressible quantum fluids with <em>n</em>=<em style="white-space:normal;">n</em><sub style="white-space:normal;"><em>cr </em></sub>must be Minkowski flat, which implies that spacetime at the background of ultra-compact objects should be bimetric.
基金partially supported by the National Basic Research Program of China(973 Program,Grant Nos.2014CB845800 and 2013CB834900)the National Natural Science Foundation of China(Grant Nos.11322328,11433009,11673068 and 11603076)+4 种基金the Youth Innovation Promotion Association(2011231)the Key Research Program of Frontier Sciences(QYZDBSSW-SYS005)the Strategic Priority Research Program“The Emergence of Cosmological Structures”(Grant No.XDB09000000)of the Chinese Academy of Sciencesthe Natural Science Foundation of Jiangsu Province(Grant No.BK20161096)the Guangxi Key Laboratory for Relativistic Astrophysics
文摘A conservative constraint on the rest mass of the photon can be estimated under the assump- tion that the frequency dependence of dispersion from astronomical sources is mainly contributed by the nonzero photon mass effect. Photon mass limits have been set earlier through the optical emissions of the Crab Nebula pulsar, but we demonstrate that these limits can be significantly improved with the dispersion measure (DM) measurements of radio pulsars in the Large and Small Magellanic Clouds. The combination of DM measurements of pulsars and distances of the Magellanic Clouds provides a strict upper limit on the photon mass as low as mγ≤2.0 ~ 10-45 g, which is at least four orders of magnitude smaller than the constraint from the Crab Nebula pulsar. Although our limit is not as tight as the current best result (~ 10-47 g) from a fast radio burst (FRB 150418) at a cosmological distance, the cosmological origin of FRB 150418 remains under debate; and our limit can reach the same high precision of FRB 150418 when it has an extragalactic origin ( ~10-45 g).
文摘In this article we modify our previous model for the mechanisms underlying the glitch phenomena in pulsars. Accordingly, pulsars are born with embryonic cores that are made of purely incompressible superconducting gluon-quark superfluid (henceforth SuSu-cores). As the ambient medium cools and spins down due to emission of magnetic dipole radiation, the mass and size of SuSu-cores must grow discretely with time, in accordance with the Onsager-Feynmann analysis of superfluidity. Here we argue that the spacetime embedding glitching pulsars is dynamical and of bimetric nature: inside SuSu-cores the spacetime must be flat, whereas the surrounding region, where the matter is compressible and dissipative, the spacetime is Schwarzschild. It is argued here that the topological change of spacetime is derived by the strong nuclear force, whose operating length scales are found to increase with time to reach O (1) cm at the end of the luminous lifetimes of pulsars. The here-presented model is in line with the recent radio- and gravitational wave observations of pulsars and merger of neutron stars.
文摘The Crab and Vela are well-studied glitching pulsars and the data obtained so far should enable us to test the reliability of models of their internal structures. Very recently it was proposed that glitching pulsars are embedded in bimetric spacetime: their incompressible superfluid cores (SuSu-cores) are embedded in flat spacetime, whereas the ambient compressible and dissipative media are enclosed in Schwarzschild spacetime. In this letter we apply this model to the Crab and Vela pulsars and show that a newly born pulsar initially of and an embryonic SuSu-core of could evolve into a Crab-like pulsar after 1000 years and into a Vela-like pulsar 10,000 years later to finally fade away as an invisible dark energy object after roughly 10 Myr. Based thereon we infer that the Crab and the Vela pulsars should have SuSu-cores of and , respectively. Furthermore, the under- and overshootings phenomena observed to accompany the glitch events of the Vela pulsar are rather a common phenomenon of glitching pulsars that can be well-explained within the framework of bimetric spacetime.
文摘We investigate the statistical effects of non-discrete timing irregularities on observed radio pul- sar braking indices using correlations between the second derivative of the measured anomalous frequency (vobs) and some parameters that have been widely used to quantify pulsar timing fluctuations (the timing activity parameter (A), the amount of timing fluctuations absorbed by the cubic term (crR23) and a measure of pulsar rotational stability (δz)) in a large sample of 366 Jodrell Bank Observatory radio pulsars. The result demonstrates that anomalous braking indices are largely artifacts produced by aggregations of fluc- tuations that occur within or outside the pulsar system. For a subsample of 223 normal radio pulsars whose observed timing activity appeared consistent with instabilities in rotation of the underlying neutron stars (or timing noise) over timescales of - 10 - 40 yr,/vobs / strongly correlates (with correlation coefficient /r/ - 0.80 - 0.90) with the pulsar timing activity parameters and spin-down properties. On the other hand, no meaningful correlations (r 〈 0.3) were found between/)obs and the timing activity diagnostics and spin- down parameters in the remaining 143 objects, whose timing activity appears significantly dominated by white noise fluctuations. The current result can be better understood if the timing noise in isolated pulsars originates from intrinsic spin-down processes of the underlying neutron stars, but white noise fluctuations largely arise from processes external to the pulsar system.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10803009 and 10833003)
文摘Recent INTEGRAL/IBIS hard X-ray surveys have detected about 10 young pulsars. We show hard X-ray properties of these 10 young pulsars, which have a luminosity of 10^33 - 10^37 erg s^-1 and a photon index of 1.6-2.1 in the energy range of 20-100 keV. The correlation between X-ray luminosity and spin-down power of Lx ∝ Lsd^1.31 suggests that the hard X-ray emission in rotation-powered pulsars is dominated by the pulsar wind nebula (PWN) component. Assuming spectral properties are similar in 20-100keV and 2-10 keV for both the pulsar and PWN components, the hard X-ray luminosity and flux of 39 known young X-ray pulsars and 8 millisecond pulsars are obtained, and a correlation of Lx ∝ Lsd^1.5 is derived. About 20 known young X-ray pulsars and 1 millisecond pulsars could be detected with future INTEGRAL and HXMT surveys. We also carry out Monte Carlo simulations of hard X-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics and the Lx - Lsd reltions:Lx ∝Lsd^1.31 and Lx∝Lsd^1.5 More than 40 young pulsars (mostly in the Galactic plane) could be detected after ten years of INTEGRAL surveys and the launch of HXMT. So, the young pulsars would be a significant part of the hard X-ray source population in the sky, and will contribute to unidentified hard X-ray sources in present and future hard X-ray surveys by INTEGRAL and HXMT.
基金financial support of Basic Research Program of the Presidium of the Russian Academy of Sciences"Transitional and Explosive Processes in Astrophysics(P-41)"Russian Foundation for Basic Research(grant 16–02–00954)
文摘Pulsars play a crucial astrophysical role as highly energetic compact radio, X-ray and gamma- ray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log Blc (G) are 3.60-3.95 and 1.75 correspondingly. Moreover, their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: logE(erg s-1) = 35.37-35.53 and 32.64. The correlation between gamma- ray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand, the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.