R. P. Mignani
Being fast rotating objects, isolated neutron stars (INSs) are obvious targets for high-time resolution observations. With the number of optical/UV/IR INS detections now increased to 24, timing observations become more and more important in INS astrophysics.
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The Neutron Star Interior Composition Explorer (NICER) presents an exciting new capability for exploring the modulation properties of X-ray emitting neutron stars, including large area, low background, extremely precise absolute event time stamps, superb low-energy response and flexible scheduling. The Pulsation Searches and Multiwavelength Coordination working group has designed a 2.5 Ms observing program to search for emission and characterize the modulation properties of about 30 known or suspected neutron star sources across a number of source categories. A key early goal will be to search…
We present the results of our extensive binary orbital motion corrected pulsation search for 13 low mass X-ray binaries (LMXBs). These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1122 Hz, and have a binary orbital period varying from 2.1 to 18.9 hours. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer (RXTE) data of these sources. Then, we applied Doppler corrections to these pulsation episodes to discard the smearing effect of the binary orbital mo…
Accreting millisecond X-ray pulsars are an important subset of low-mass X-ray binaries in which coherent X-ray pulsations can be observed during occasional, bright outbursts (X-ray luminosity $L_X\sim 10^{36}$ erg s$^{-1}$). These pulsations show that matter is being channeled onto the neutron star's magnetic poles. However, such sources spend most of their time in a low-luminosity, quiescent state ($L_X\lesssim 10^{34}$ erg s$^{-1}$), where the nature of the accretion flow onto the neutron star (if any) is not well understood. Here we report that the millisecond pulsar/low-mass X-ray binary t…
Highly magnetized neutron stars are promising candidates to explain some of the most peculiar astronomical phenomena, for instance, fast radio bursts, gamma-ray bursts, and superluminous supernovae. Pulsations of these highly magnetized neutron stars are also speculated to produce detectable gravitational waves. In addition, pulsations are important probes of the structure and equation of state of the neutron stars. The major challenge in studying the pulsations of highly magnetized neutron stars is the demanding numerical cost of consistently solving the nonlinear Einstein and Maxwell equatio…
On the lack of X-ray pulsation in most neutron star low-mass X-ray binaries
本研究提出内盘延伸至中子星表面猝灭脉冲发射的模型，解释了大多数LMXBs缺乏X射线脉冲及AMXPs稀少且为暂现源的现象。
Measuring the spin of Accreting Neutron Stars is important because it can provide constraints on the Equation of State of ultra-dense matter. Particularly crucial to our physical understanding is the discovery of sub-millisecond pulsars, because this will immediately rule out many proposed models for the ground state of dense matter. So far, it has been impossible to accomplish this because, for still unknown reasons, only a small amount of Accreting Neutron Stars exhibit coherent pulsations. An intriguing explanation for the lack of pulsations is that they form only on neutron stars accreting…
LS I +61$^{\circ}$ 303 is one of the rare gamma-ray binaries, emitting most of their luminosity in photons with energies beyond 100 MeV. The $\sim$26.5 d orbital period is clearly detected at many wavelengths. Additional aspects of its multi-frequency behavior make it the most interesting example of the class. The morphology of high-resolution radio images changes with orbital phase displaying a cometary tail pointing away from the high-mass star. LS I +61$^{\circ}$ 303 also shows superorbital variability. A couple of energetic ($\sim 10^{37}$ erg s$^{-1}$), short, magnetar-like bursts have be…
Fitting the thermal X-ray spectra of neutron stars (NSs) in quiescent X-ray binaries can constrain the masses and radii of NSs. The effect of undetected hot spots on the spectrum, and thus on the inferred NS mass and radius, has not yet been explored for appropriate atmospheres and spectra. A hot spot would harden the observed spectrum, so that spectral modeling tends to infer radii that are too small. However, a hot spot may also produce detectable pulsations. We simulated the effects of a hot spot on the pulsed fraction and spectrum of the quiescent NSs X5 and X7 in the globular cluster 47 T…
Most young neutron stars belonging to the class of Central Compact Objects in supernova remnants (CCOs) do not have known periodicities. We investigated seven such CCOs to understand the common reasons for the absence of detected pulsations. Making use of XMM-Newton, Chandra, and NICER observations, we perform a systematic timing and spectral analysis to derive updated sensitivity limits for both periodic signals and multi-temperature spectral components that could be associated with radiation from hotspots on the neutron star surface. Based on these limits, we then investigated for each targe…
A fraction of massive stars are expected to collapse into compact objects (accreting black holes or rapidly rotating neutron stars) that successfully produce gamma-ray bursts (GRBs). We examine the possibility of directly observing these gamma-ray burst compact objects (GCOs) using post-explosion observations of past and future GRB sites. In particular, we present a search for early pulsations from the nearby (z=0.0335) gamma-ray burst GRB 060218, which exhibited features possibly consistent with a rapidly spinning neutron star as its underlying GCO. We also consider alternative techniques tha…
We report the detection of weak pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a period of $\sim$ 1.5 s and a pulsed fraction of $\sim$ 5%. We use Monte Carlo simulations to demonstrate that the individual detections are unlikely to originate in false Poisson noise detections given their very close frequencies; their strong similarity to other pulsations detected from ULXs also argues they are real. The presence of a large bubble nebula surr…
NGC 2403 XMM4: evidence for a super-Eddington neutron star with a possible transient pulsation
基于20年多波段观测数据，发现X射线源NGC 2403 XMM4光度低于ULX阈值但表现出超爱丁ington吸积特征，并探测到约3.32 Hz暂现脉冲，推断其吸积天体为中子星。
In these lectures presented at Baikal summer school on physics of elementary particles and astrophysics 2011, I present a wide view of neutron star astrophysics with special attention paid to young isolated compact objects and studies of the properties of neutron star interiors using astronomical methods.
Isolated Neutron Stars are known to be endowed with extreme magnetic fields, whose maximum intensity ranges from 10^12 to 10^15 G, which permeates their magnetospheres. Their surrounding environment is also strongly magnetised, especially in the compact nebulae powered by the relativistic wind from young neutron stars. The radiation from isolated neutron stars and their surrounding nebulae is, thus, supposed to bring a strong polarisation signature. Measuring the neutron star polarisation brings important information on the properties of their magnetosphere and of their highly magnetised envir…
Can accreting isolated neutron stars be detected?
该研究通过银河系中孤立中子星的群体合成建模，发现目前中子星在喷流阶段的自转减速速率是影响吸积孤立中子星数量的主要不确定因素，未来Gaia发现的宽低质量双星观测可能澄清这些问题。
Neutron stars in low mass X-ray binaries are hypothesised to emit continuous gravitational waves that may be detectable by ground-based observatories. The torque balance model predicts that a higher accretion rate produces larger-amplitude gravitational waves, hence low mass X-ray binaries with high X-ray flux are promising targets for gravitational wave searches. The detection of X-ray pulsations would identify the spin frequency of these neutron stars, and thereby improve the sensitivity of continuous gravitational-wave searches by reducing the volume of the search parameter space. We perfor…
Isolated Neutron Stars
本文以观测为导向综述了孤立中子星的分类，涵盖从旋转供能脉冲星到磁星等各类性质，并指出跨类源指向大统一。
We present a comprehensive X-ray study of the neutron star low-mass X-ray binary IGR J17062-6143, which has been accreting at low luminosities since its discovery in $2006$. Analysing NuSTAR, XMM-Newton and Swift observations, we investigate the very faint nature of this source through three approaches: modelling the relativistic reflection spectrum to constrain the accretion geometry, performing high-resolution X-ray spectroscopy to search for an outflow, and searching for the recently reported millisecond X-ray pulsations. We find a strongly truncated accretion disk at $77^{+22}_{-18}$ gravi…
A four-year sky survey with the use of the eROSITA telescope on board the Spektr-RG observatory will provide the best coverage in the soft (0.5-2 keV) and standard (2-10 keV) X-ray ranges, both in terms of sensitivity and angular resolution. We have analysed the possibility of detecting various types of isolated neutron stars with eROSITA. Among already known objects, eROSITA will be able to detect more than 160 pulsars, 21 magnetars, 7 central compact objects, all seven sources of the Magnificent Seven, and two other X-ray isolated neutron stars during the four-year survey mission.
We analyze new XMM-Newton and archival Chandra observations of the middle-aged $γ$-ray radio-quiet pulsar J1957+5033. We detect, for the first time, X-ray pulsations with the pulsar spin period of the point-like source coinciding by position with the pulsar. This confirms the pulsar nature of the source. In the 0.15--0.5 keV band, there is a single pulse per period and the pulsed fraction is $\approx18\pm6$ per cent. In this band, the pulsar spectrum is dominated by a thermal emission component that likely comes from the entire surface of the neutron star, while at higher energies ($\gtrsim0.7…
Weakly magnetic, millisecond spinning neutron stars attain their very fast rotation through a 1E8-1E9 yr long phase during which they undergo disk-accretion of matter from a low mass companion star. They can be detected as accretion-powered millisecond X-ray pulsars if towards the end of this phase their magnetic field is still strong enough to channel the accreting matter towards the magnetic poles. When mass transfer is much reduced or ceases altogether, pulsed emission generated by particle acceleration in the magnetosphere and powered by the rotation of the neutron star is observed, prefer…
The cooling theory of neutron stars is corroborated by its comparison with observations of thermally emitting isolated neutron stars and accreting neutron stars in binary systems. An important ingredient for such an analysis is the age of the object, which, typically, is obtained from the spin-down history. This age is highly uncertain if the object's magnetic field varies appreciably over time. Other age estimators, such as supernova remnant ages and kinematic ages, only apply to few handful of neutron stars. We conduct a population synthesis study of the nearby isolated thermal emitters and …
The zoo of isolated neutron stars
本文综述了孤立中子星（包括旋转供能脉冲星、磁星、X射线暗孤立中子星和中央致密天体）的观测特性与理论模型，突出其多样性及最新发现。
4U 2206+54 is a high mass X-ray binary which has been suspected to contain a neutron star accreting from the wind of its companion BD +53 2790. Reig et al. have recently detected 5560 s period pulsations in both RXTE and INTEGRAL observations which they conclude are due to the spin of the neutron star. We present observations made with Suzaku which are contemporaneous with their RXTE observation of this source. We find strong pulsations at a period of 5554 +/- 9 s in agreement with their results. We also present a reanalysis of BeppoSAX observations of 4U 2206+54 made in 1998, in which we find…
The zoo of isolated neutron stars
本文综述射电脉冲星、磁星、邻近冷却中子星和快速射电暴源等孤立中子星类型，结合长周期脉冲星发现，探讨磁旋转演化、磁场衰减及与回落物质相互作用模型。
There exists a special class of X-ray pulsars that exhibit very slow pulsation of $P_{\rm spin}>1000$ s in the high mass X-ray binaries (HMXBs). We have studied the temporal and spectral properties of these superslow pulsation neutron star binaries in hard X-ray bands with INTEGRAL observations. Long-term monitoring observations find spin period evolution of two sources: spin-down trend for 4U 2206+54 ($P_{\rm spin}\sim 5560$ s with $\dot{P}_{\rm spin}\sim 4.9\times 10^{-7}$ s s$^{-1}$) and long-term spin-up trend for 2S 0114+65 ($P_{\rm spin}\sim 9600$ s with $\dot{P}_{\rm spin}\sim -1\times …
PSR J1023+0038 is a rapidly-spinning neutron star with a low-mass-binary companion that switches between a radio pulsar and low-luminosity disk state. In 2013, it transitioned to its current disk state accompanied by brightening at all observed wavelengths. In this state, PSR J1023+0038 now shows optical and X-ray pulsations and abrupt X-ray luminosity switches between discrete 'low' and 'high' modes. Continuum radio emission, denoting an outflow, is also present and brightens during the X-ray low modes. Here, we present a simultaneous optical, ultraviolet (UV) and X-ray campaign comprising Ke…
We study evolution of isolated neutron stars on long time scale and calculate distribution of these sources in the main evolutionary stages: Ejector, Propeller, Accretor, and Georotator. We compare different initial magnetic field distributions taking into account a possibility of magnetic field decay, and include in our calculations the stage of subsonic Propeller. It is shown that though the subsonic propeller stage can be relatively long, initially highly magnetized neutron stars ($B_0\ga 10^{13}$ G) reach the accretion regime within the Galactic lifetime if their kick velocities are not to…
We study the effects of finite stellar temperatures on the oscillations of superfluid neutron stars. The importance of these effects is illustrated with a simple example of a radially pulsating general relativistic star. Two main effects are taken into account: (i) temperature dependence of the entrainment matrix and (ii) the variation of the size of superfluid region with temperature. Four models are considered, which include either one or both of these two effects. Pulsation spectra are calculated for these models, and asymptotes for eigenfrequencies at temperatures close to critical tempera…
Almost 30 Isolated Neutron Stars (INSs) of different flavours have been identified at optical, ultraviolet, or infrared (UVOIR) wavelengths. Here, I present a short review of the historical background and describe the scientific impact of INS observations in the UVOIR. Then, I focus on UVOIR observations of rotation-powered pulsars, so far the most numerous class of INSs identified at these wavelengths, and their observational properties. Finally, I present the results of new UVOIR observations and an update of the follow-ups of gamma-ray pulsars detected by Fermi.
Forty years passed since the optical identification of the first isolated neutron star (INS), the Crab pulsar. 25 INSs have been now identified in the optical (O), near-ultraviolet (nUV), or near-infrared (nIR), hereafter UVOIR, including rotation-powered pulsars (RPPs), magnetars, and X-ray-dim INSs (XDINSs), while deep investigations have been carried out for compact central objects (CCOs), Rotating RAdio transients (RRATs), and high-magnetic field radio pulsars (HBRPs). In this review I describe the status of UVOIR observations of INSs, their emission properties, and I present the results f…
IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to determine the nature of the compact object in this system. This source exhibits high levels of aperiodic variability, but no periodic pulsations are detected with a 90% confidence upper limit of 2% fractional rms between 0.00003-88 Hz, a frequency range that includes the typical pulse periods of neutron stars (NSs) in HMXBs (0.1-10$^3$ s). Altho…
Forty years elapsed since the optical identification of the first isolated neutron star (INS), the Crab pulsar. 25 INSs have been now identified in the optical (O), near-ultraviolet (nUV), or near-infrared (nIR), hereafter UVOIR, including rotation-powered pulsars (RPPs), magnetars, and X-ray-dim INSs (XDINSs), while deep investigations have been carried out for compact central objects (CCOs), Rotating RAdio transients (RRATs), and high-magnetic field radio pulsars (HBRPs). In this review I describe the status of UVOIR observations of INSs, their emission properties, and I present recent resul…
Most isolated neutron stars have been discovered thanks to the detection of their pulsed non-thermal emission, at wavelengths spanning from radio to gamma-rays. However, if the beamed non-thermal radiation does not intercept our line of sight or it is too faint or absent, isolated neutron stars can also be detected through their thermal emission, which peaks in the soft X-ray band and is emitted nearly isotropically. In the past thirty years, several thermally-emitting isolated neutron stars have been discovered thanks to X-ray all-sky surveys, observations targeted at the center of supernova …
The observed polarization properties of thermal radiation from isolated, cooling neutron stars depend on both the emission processes at the surface and the effects of the magnetized vacuum which surrounds the star. Here we investigate the polarized thermal emission from X-ray Dim Isolated Neutron Stars, taking RX J1856.5-3754 as a representative case. The physical conditions of the star outermost layers in these sources is still debated, and so we consider emission from a magnetized atmosphere and a condensed surface, accounting for the effects of vacuum polarization as the radiation propagate…
We study the thermal evolution of axisymmetric rotating neutron stars in full general relativity. To this aim we develop "NSCool 2D Rot", a major upgrade of the 1D neutron stars thermal evolution code "NSCool" by D. Page. As a first application of our new code we address the standard cooling of isolated neutron stars with rotation frequencies up to the mass shedding limit. We investigate the effects of the equation of state (EOS) by considering different combinations of core and crust EOSs. The results indicate complex time-dependent evolution of temperature distribution throughout the whole v…
We report the initial results of deep eROSITA monitoring of the "magnificent seven" isolated neutron stars (INSs). Thanks to a combination of high count statistics and good energy resolution, the eROSITA datasets unveil the increasingly complex energy distribution of these presumably simple thermal emitters. For three targets, we report the detection of multiple (in some cases, phase-dependent) spectral absorption features and deviations from the dominant thermal continuum. Unexpected long-term changes of spectral state and timing behaviour have additionally been observed for two INSs. The res…
Studying the variability of fluorescence emission and the presence of clumpy wind in HMXB GX 301$-$2 using XMM-Newton
本文分析 GX 301−2 的 XMM-Newton 观测，发现铁荧光线变化及 671.8 秒次级脉动，并将其解释为距中子星约 5 光秒的逆行恒星风团块产生的拍频信号。
For some neutron stars (NSs) in the binary systems, the masses have been accurately measured. While for the isolated neutron stars (INSs), no mass measurement has been reported yet. The situation will change soon thanks to the successful performance of the Neutron Star Interior Composition Explorer (NICER), with which the radius and mass of the isolated PSR J0030+0451 can be simultaneously measured. For most INSs, no mass measurements are possible for NICER because of observational limitations. Benefiting from recent significant progress made on constraining the equation of state of NSs, in th…
The spin evolution of isolated neutron stars (NSs) is dominatd by their magnetic fields. The measured braking indices of young NSs show that the spin-down mechanism due to magnetic dipole radiation with constant magnetic fields is inadequate. Assuming that the NS magnetic field is buried by supernova fallback matter and re-emerges after accretion stops, we carry out Monte-Carlo simulation of the evolution of young NSs, and show that most of the pulsars have the braking indices ranging from -1 to 3. The results are compatible with the observational data of NSs associated with supernova remnants…
X-ray emission is a common feature of all varieties of isolated neutron stars (INS) and, thanks to the advent of sensitive instruments with good spectroscopic, timing, and imaging capabilities, X-ray observations have become an essential tool in the study of these objects. Non-thermal X-rays from young, energetic radio pulsars have been detected since the beginning of X-ray astronomy, and the long-sought thermal emission from cooling neutron star's surfaces can now be studied in detail in many pulsars spanning different ages, magnetic fields, and, possibly, surface compositions. In addition, o…
The recent discovery of periodic pulsations from several members of the ultraluminous X-ray source (ULX) family in nearby galaxies as well as in our own galaxy unveiled the nature of the accreting compact object. Neutron stars rather than black holes are currently believed to power a substantial number of ULXs whether or not pulsations are observed. The detection of cyclotron absorption lines in the X-ray spectrum of a ULX provides an alternative way to identify the compact object as a neutron star. Among the non-pulsating ULXs, the presence of a cyclotron resonance scattering feature (CRSF) i…
X-ray observations of Isolated Neutron Stars
本文综述孤立中子星的X射线观测，梳理其分类与多样性表现，并指出不同类别间联系比以往认为的更紧密，且复杂磁场拓扑并非磁星独有，为统一演化图景提供新视角。
The dim isolated neutron stars (XDINs) have periods in the same range as the anomalous X-ray pulsars (AXPs) and the soft gamma-ray repeaters (SGRs). We apply the fallback disk model, which explains the period clustering and other properties of AXP/SGRs, to the six XDINs with measured periods and period derivatives. Present properties of XDINs are obtained in evolutionary scenarios with surface dipole magnetic fields $B_0 \sim 10^{12}$ G. The XDINs have gone through an accretion epoch with rapid spin-down earlier, and have emerged in their current state, with the X-ray luminosity provided by ne…
The precise origin of short gamma ray bursts (SGRBs) remains an important open question in relativistic astrophysics. Increasingly, observational evidence suggests the merger of a binary compact object system as the source for most SGRBs, but it is currently unclear how to distinguish observationally between a binary neutron star progenitor and a black hole-neutron star progenitor. We suggest the quasi-periodic signal of jet precession as an observational signature of SGRBs originating in mixed binary systems, and quantify both the fraction of mixed binaries capable of producing SGRBs, and the…
Indication of rapid magnetic field decay in X-ray Dim Isolated Neutron Star RX J0720.4-3125
本文利用孤立中子星RX J0720.4-3125的X射线光度、自转周期二阶导数和磁场独立测量，证明其自转周期导数演化与偶极场磁能耗散速率一致，揭示磁场衰减时标约为一万年。
Isolated Neutron Stars are some of the most exciting stellar objects known to astronomers: they have the most extreme magnetic fields, with values up to $10^{15}$ G, and, with the exception of stellar-mass black holes, they are the most dense stars, with densities of $\approx 10^{14}$ g cm$^{-3}$. As such, they are perfect laboratories to test theories of electromagnetism and nuclear physics under conditions of magnetic field and density unattainable on Earth. In particular, the interaction of radiation with strong magnetic fields is the cause of the {\em vacuum birefringence}, an effect predi…
We perform population synthesis studies of different types of neutron stars (thermally emitting isolated neutron stars, normal radio pulsars, magnetars) taking into account the magnetic field decay and using results from the most recent advances in neutron star cooling theory. For the first time, we confront our results with observations using {\it simultaneously} the Log N -- Log S distribution for nearby isolated neutron stars, the Log N -- Log L distribution for magnetars, and the distribution of radio pulsars in the $P$ -- $\dot P$ diagram. For this purpose, we fix a baseline neutron star …
Peculiar groups of X-ray emitting isolated neutron stars, which include magnetars, the "Magnificent Seven", and central compact objects in supernova remnants, escape detection in standard pulsar surveys. Yet, they constitute a key element in understanding the neutron star evolution and phenomenology. Their use in population studies in the galactic scale has been hindered by the scarcity of their detection. The all-sky survey of eROSITA on-board the forthcoming Spectrum-RG mission has the unique potential to unveil the X-ray faint part of the population and constrain evolutionary models. To cre…
Early Accretion Onset in Long-Period Isolated Pulsars
该研究模拟长初始自转周期孤立中子星的磁旋转演化，发现低速天体可在几十亿年内进入星际介质吸积阶段，并可能显著增加银河系孤立吸积体的预测数量。
Since the discovery of the first radio pulsar fifty years ago, the population of neutron stars in our Galaxy has grown to over 2,600. A handful of these sources, exclusively seen in X-rays, show properties that are not observed in normal pulsars. Despite their scarcity, they are key to understanding aspects of the neutron star phenomenology and evolution. The forthcoming all-sky survey of eROSITA will unveil the X-ray faint end of the neutron star population at unprecedented sensitivity; therefore, it has the unique potential to constrain evolutionary models and advance our understanding of th…
Photon-axion mixing can create observable signatures in thermal spectra of isolated, cooling neutron stars. Their shape depends on the polarization properties of the radiation, which, in turn, are determined by the structure of stellar outermost layers. Here we investigate the effect of mixing on the spectrum and polarimetric observables, polarization fraction and polarization angle, using realistic models of surface emission. We focus on RX J1856.5-3754, the only source among the X-ray dim isolated neutron stars for which polarimetric measurements in the optical band were performed. Our resul…
Transient discs around isolated accreting neutron stars
本文通过种群合成研究发现，仅约0.02%的孤立吸积中子星能形成吸积盘，这类盘吸积中子星在亮X射线源中较多，或可作为长周期射电暂现源。
G315.4-2.3 is a young Galactic supernova remnant (SNR), whose identification as the remains of a Type-II supernova (SN) explosion has been debated for a long time. In particular, recent multi-wavelength observations suggest that it is the result of a Type Ia SN, based on spectroscopy of the SNR shell and the lack of a compact stellar remnant.However, two X-ray sources, one detected by Einstein and ROSAT (Source V) and the other by Chandra (Source N) have been proposed as possible isolated neutron star candidates. In both cases, no clear optical identification was available and, therefore, we p…
The new results of our observing campaign targeting the isolated neutron star 2XMM J104608.7-594306 in the Carina Nebula are used to understand how peculiar groups of isolated neutron stars relate to each other, as well as to the bulk of the normal radio pulsar population.
Non pulsating neutron stars in low mass X-ray binaries largely outnumber those that show pulsations. The lack of detectable pulses represents a big open problem for two important reasons. The first is that the structure of the accretion flow in the region closest to the neutron star is not well understood and it is therefore unclear what is the mechanism that prevents the pulse formation. The second is that the detection of pulsations would immediately reveal the spin of the neutron star. Aql X-1 is a special source among low mass X-ray binaries because it has showed the unique property of pul…
Search for Radio Pulsations from Neutron Star Candidates in Detached Binaries
通过射电观测未发现分离双星系统中中子星候选体的射电脉冲，表明其可能为古老无线电安静的脉冲星或几何束流效应。
We report results of XMM-Newton observations of a $γ$-ray pulsar J0633+0632 and its wind nebula. We reveal, for the first time, pulsations of the pulsar X-ray emission with a single sinusoidal pulse-profile and a pulsed fraction of $23 \, \pm \, 6$ per cent in the 0.3--2 keV band. We confirm previous Chandra findings that the pulsar X-ray spectrum consists of thermal and non-thermal components. However, we do not find the absorption feature that was previously detected at about 0.8 keV. Thanks to the greater sensitivity of XMM-Newton, we get stronger constraints on spectral model parameters co…
We consider a simulated population of isolated Galactic neutron stars. The rotational frequency of each neutron star evolves through a combination of electromagnetic and gravitational wave emission. The magnetic field strength dictates the dipolar emission, and the ellipticity (a measure of a neutron star's deformation) dictates the gravitational wave emission. Through both analytic and numerical means, we assess the detectability of the Galactic neutron star population and bound the magnetic field strength and ellipticity parameter space of Galactic neutron stars with or without a direct grav…
The nearby isolated neutron stars are a group of seven relatively slowly rotating neutron stars that show thermal X-ray spectra, most with broad absorption features. They are interesting both because they may allow one to determine fundamental neutron-star properties by modeling their spectra, and because they appear to be a large fraction of the overall neutron-star population. Here, we describe a series of XMM-Newton observations of the nearby isolated neutron star RX J0806.4-4123, taken as part of larger program of timing studies. From these, we limit the spin-down rate to dnu/dt=(-4.3+/-2.…
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