While observations of many high-precision radio pulsars of order $\lesssim1~μ$s across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronomía) has begun observations of the brightest-known millisecond pulsar, J0437$-$4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR's capability to monitor this pulsar daily coupled with the pulsar's brightness allows for high-precision pulse arrival-time measurements. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437$-$4715 will provide a significant sensitivity increase in NANOGrav's "blind spot" in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array's sensitivity will improve by a factor of $\approx$2-4 over 10 years for 20% of the sky with the inclusion of this pulsar as compared to a static version of the PTA used in NANOGrav's most recent limits. More modest instrumentation result in factors of $\approx$1.4-3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data given the potential achievable sensitivity.
The Argentine Institute of Radio astronomy (IAR) is equipped with two single-dish 30-m radio antennas capable of performing daily observations of pulsars and radio transients in the southern hemisphere at 1.4 GHz. We aim to contribute to pulsar timing studies related to short time-scale interstellar scintillation and searches for sources of continuous gravitational waves. We performed high-cadence (almost daily) and long-duration observations of the bright millisecond pulsar J0437$-$4715 for over a year, gathering more than 700 hours of good-quality data with timing precision better than 1~$μ$…
We present a deep Chandra X-ray Observatory study of the peculiar binary radio millisecond pulsar PSR J1740--5340 and candidate millisecond pulsars (MSPs) in the globular cluster NGC 6397. The X-rays from PSR J1740--5340 appear to be non-thermal and exhibit variability at the binary period. These properties suggest the presence of a relativistic intrabinary shock formed due to interaction of a relativistic rotation-powered pulsar wind and outflow from the unusual "red-straggler/sub-subgiant" companion. We find the X-ray source U18 to show similar X-ray and optical properties to those of PSR J1…
The Argentine Institute of Radio astronomy (IAR) is equipped with two single-dish 30mts radio antennas capable of performing daily observations of pulsars and radio transients in the southern hemisphere at 1.4 GHz. We aim to introduce to the international community the upgrades performed and to show that IAR observatory has become suitable for investigations in numerous areas of pulsar radio astronomy, such as pulsar timing arrays, targeted searches of continuous gravitational waves sources, monitoring of magnetars and glitching pulsars, and studies of short time scale interstellar scintillati…
Despite the fact that pulsars have been observed for almost half a century, many questions have remained unanswered. We use the analysis of X-ray observations in order to study the polar cap region of radio pulsars. The size of the hot spots implies that the magnetic field configuration just above the stellar surface differs significantly from a purely dipole one. We can estimate the surface magnetic field as of the order of $10^{14}\,{\rm G}$. On the other hand, the temperature of the hot spots is about a few million Kelvins. Based on these two facts the Partially Screened Gap (PSG) model was…
We report the first detection of a glitch in the radio pulsar PSR J0908$-$4913 (PSR B0906$-$49) during regular timing observations by the Molonglo Observatory Synthesis Telescope (MOST) as part of the UTMOST project.
We present an analysis of 745.6 ks of archival Chandra X-ray Observatory Advanced CCD Imaging Spectrometer data accumulated between 2000 and 2016 of the millisecond pulsar (MSP) population in the rich Galactic globular cluster Terzan 5. Eight of the 37 MSPs with precise positions are found to have plausible X-ray source matches. Despite the deep exposure, the remaining MSPs are either marginally detected or have no obvious X-ray counterparts, which can be attributed to the typically soft thermal spectra of rotation-powered MSPs, which are strongly attenuated by the high intervening absorbing c…
An analysis of arrival directions of extensive air showers (EAS) registered with the EAS MSU and EAS-1000 prototype arrays has revealed a region of excessive flux of PeV cosmic rays in the direction toward pulsars PSR J1840+5640 and LAT PSR J1836+5925 at significance level up to 4.5sigma. The first of the pulsars was discovered almost 30 years ago and is a well-studied old radio pulsar located at the distance of 1.7pc from the Solar system. The second pulsar belongs to a new type of pulsars, discovered by the space gamma-ray observatory Fermi, pulsations of which are not observed in optical an…
Using the 1.3m and 2.4m telescopes of the MDM Observatory, we identified the close companions of two eclipsing millisecond radio pulsars discovered by the Green Bank Telescope in searches of Fermi Gamma-ray Space Telescope sources, and measured their light curves. PSR J1301+0833 is a black widow pulsar in a 6.5 hr orbit whose companion star is strongly heated on the side facing the pulsar. It varies from R = 21.8 to R > 24 around the orbit. PSR J1628-3205 is a "redback," a nearly Roche-lobe filling system in a 5.0 hr orbit whose optical modulation in the range 19.0 < R < 19.4 is dominated by s…
We report the discovery of pulsed γ-ray emission and X-ray emission from the black widow millisecond pulsar PSR J2051-0827 by using the data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope and the Advanced CCD Imaging Spectrometer array (ACIS-S) on the Chandra X-ray Observatory. Using 3 years of LAT data, PSR J2051-0827 is clearly detected in γ-ray with a signicance of \sim 8σ in the 0.2 - 20 GeV band. The 200 MeV - 20 GeV γ-ray spectrum of PSR J2051-0827 can be modeled by a simple power- law with a photon index of 2.46 \pm 0.15. Significant (\sim 5σ) γ-ray pul…
We present the analysis of the Chandra X-ray Observatory observations of the eccentric gamma-ray binary PSR B1259-63/LS 2883. The analysis shows that the extended X-ray feature seen in previous observations is still moving away from the binary with an average projected velocity of about 0.07c and shows a hint of acceleration. The spectrum of the feature appears to be hard (photon index of 0.8) with no sign of softening compared to previously measured values. We interpret it as a clump of plasma ejected from the binary through the interaction of the pulsar with the decretion disk of the O-star …
Two energetic hard X-ray bursts have recently triggered the Fermi and Swift space observatories from the rotation powered pulsar, PSR J1119-6127. We have performed in depth spectral and temporal analyses of these two events. Our extensive searches in both observatory data for lower luminosity bursts uncovered 10 additional events from the source. We report here on the timing and energetics of the 12 bursts from PSR J1119-6127 during its burst active phase of 2016 July 26 and 28. We also found a spectral softer X-ray flux enhancement in a post burst episode, which shows evidence of cooling. We …
Using observations made with the XMM-Newton Observatory, we report the first X-ray detection of the high magnetic field radio pulsar PSR B1916+14. We show that the X-ray spectrum of the pulsar can be well fitted with an absorbed blackbody with temperature in the range of 0.08-0.23 keV, or a neutron star hydrogen atmosphere model with best-fit effective temperature of $\sim$0.10 keV, higher than expected from fast cooling models. The origin of the likely thermal emission is not well constrained by our short observation and is consistent with initial cooling or return-current heating. We found n…
Using observations made with the XMM-Newton Observatory, we report the probable X-ray detection of the high-magnetic-field radio pulsar PSR J1734-3333. This pulsar has an inferred surface dipole magnetic field of B = 5.2e13 G, just below that of one anomalous X-ray pulsar (AXP). We find that the pulsar has an absorbed 0.5-2.0 keV flux of (5-15)e-15 erg/s/cm^2 and that its X-ray luminosity L_X is well below its spin down luminosity E_dot, with L_X < 0.1E_dot. No pulsations were detected in these data although our derived upper limit is unconstraining. Like most of the other high-B pulsars, PSR …
Optical observations of pulsars are crucial to study the neutron star properties, from the structure and composition of the interior, to the properties and geometry of the magnetosphere. Historically, X and gamma-ray observations have paved the way to the pulsar optical identifications. The launch of Fermi opened new perspectives in the optical-to-gamma-ray studies of neutron stars, with the detection of more than 80 pulsars. Here, we aim to search for optical emission from two Fermi pulsars which are interesting targets on the basis of their spin-down age, energetics, and distance: PSR J1357-…
We present timing solutions of PSR B0950+08, using 14 years of observations at Nanshan 26-m Radio Telescope of Xinjiang Astronomical Observatory. The braking index of PSR B0950+08 varies from --367 392 to 168 883, which shows an oscillation with large amplitude ($\sim 10^5$) and uncertainty. Considering the variation of braking indices and the most probable kinematic age of PSR B0950+08, a model withe long-term magnetic field decay modulated by short-term oscillations is proposed to explain the timing data. With this magnetic field decay model, we discuss the spin and thermal evolution of PSR …
Reliable timing calibration is essential for the accurate comparison of XMM-Newton light curves with those from other observatories, to ultimately use them to derive precise physical quantities. The XMM-Newton timing calibration is based on pulsar analysis. However, as pulsars show both timing noise and glitches, it is essential to monitor these calibration sources regularly. To this end, the XMM-Newton observatory performs observations twice a year of the Crab pulsar to monitor the absolute timing accuracy of the EPIC-pn camera in the fast Timing and Burst modes. We present the results of thi…
(Abridged) In 1999, Chandra revealed a 150"-radius X-ray halo surrounding the 40"-radius PWN G21.5-0.9. A 2005 imaging study showed that the halo is limb-brightened, and suggested this feature is a candidate for the long-sought SNR shell. We present a spectral analysis of G21.5-0.9, using the longest effective observation to date (578.6 ks with ACIS, 278.4 ks with HRC) to study unresolved questions about the spectral nature of remnant features, such as the limb-brightening of the X-ray halo and the bright knot in the northern part of the halo. The Chandra analysis favours the non-thermal inter…
In this paper, we report a detailed investigation of the multiwavelength properties of a newly detected gamma-ray pulsar, PSR J2021+4026, in both observational and theoretical aspects. We firstly identify an X-ray source in the XMM-Newton serendipitous source catalogue, 2XMM J202131.0+402645, located within the 95% confidence circle of PSR J2021+4026. With an archival Chandra observation, this identification provides an X-ray position with arcsecond accuracy which is helpful in facilitating further investigations. Searching for the pulsed radio emission at the position of 2XMM J202131.0+402645…
We present multi-wavelength observations of the radio magnetar PSR J1622-4950 and its environment. Observations of PSR J1622-4950 with Chandra (in 2007 and 2009) and XMM (in 2011) show that the X-ray flux of PSR J1622-4950 has decreased by a factor of ~50 over 3.7 years, decaying exponentially with a characteristic time of 360 +/- 11 days. This behavior identifies PSR J1622-4950 as a possible addition to the small class of transient magnetars. The X-ray decay likely indicates that PSR J1622-4950 is recovering from an X-ray outburst that occurred earlier in 2007, before the 2007 Chandra observa…
Seven years of pulse time-of-arrival measurements have been collected from observations of the young pulsar PSR B2334+61 using the Nanshan radio telescope of Urumqi Observatory. A phase-connected solution has been obtained over the whole data span, 2002 August to 2009 August. This includes a very large glitch that occurred between 2005 August 26 and September 8 (MJDs 53608 and 53621). The relative increase in rotational frequency for this glitch, $Δν_{g}/ν~\sim~20.5\times10^{-6}$, is the largest ever seen. Although accounting for less than 1\% of the glitch, there were two well-defined exponen…
Texas Tech University（德州理工大学）；Green Bank Observatory（格林班克天文台）；University of Puerto Rico at Mayagüez（波多黎各大学马亚圭斯分校）；University of North Carolina, Chapel Hill（北卡罗来纳大学教堂山分校）；West Virginia University（西弗吉尼亚大学）
PSR B1259-63/LS 2883 is a binary system in which a 48-ms pulsar orbits around a Be star in a high eccentric orbit with a long orbital period of about 3.4 yr. It is special for having asymmetric two-peak profiles in both the X-ray and the TeV light curves. Recently, an unexpected GeV flare was detected by $Fermi$ gamma-ray observatory several weeks after the last periastron passage. In this paper, we show that this observed GeV flare could be produced by the Doppler-boosted synchrotron emission in the bow shock tail. An anisotropic pulsar wind model, which mainly affects the energy flux injecti…
We have performed a series of Chandra X-ray Observatory observations of the gamma-ray binary LS 2883, which is comprised of a young pulsar (PSR B1259-63) orbiting a massive Be star with a period of 1236.7 days. The system was observed in 5 epochs, spanning a range from 352 to 1175 days after the periastron passage on 2014 May 4. The observations confirmed the recurrent nature of the high-speed ejecta that appear as an extended X-ray structure (clump) moving away from the binary. Compared to the results of the previous monitoring campaign (between the 2010 and 2014 periastron passages), this ti…
Mitigating the Timing Impact of Anomalous Pulse Profile Shape Variability in PSR J1713+0747 with Gaussian Component Modeling
NANOGrav Physics Frontiers Center（NANOGrav物理前沿中心）；SETI Institute（SETI研究所）；Center for Gravitation, Cosmology and Astrophysics, Department of Physics and Astronomy, University of Wisconsin-Milwaukee（威斯康星大学密尔沃基分校物理与天文学系引力、宇宙学与天体物理中心）；Department of Physics, Oregon State University（俄勒冈州立大学物理系）；Department of Physics and Astronomy, Vanderbilt University（范德堡大学物理与天文学系）；Department of Physics and Astronomy, University of British Columbia（不列颠哥伦比亚大学物理与天文学系）；Department of Physics and Astronomy, George Mason University（乔治梅森大学物理与天文学系）；National Radio Astronomy Observatory（美国国家射电天文台）；Institute of Astrophysics, FORTH（希腊基础与研究基金会天体物理研究所）
Middle-aged, cooling neutron stars are observed both as relatively rapidly spinning radio pulsars and as more slowly spinning, strongly magnetized isolated neutron stars (INSs), which stand out by their thermal X-ray spectra. The difference between the two classes may be that the INSs initially had much stronger magnetic fields, which decayed. To test this, we used the Chandra X-ray Observatory to observe 1RXS J072559.8-261229, a possible X-ray counterpart to PSR J0726-2612, which, with its 3.44s period and 3e13G inferred magnetic field strength, is the nearest and least extincted among the po…
We report the probable identification of the X-ray counterpart to the gamma-ray pulsar PSR J2021+4026 using imaging with the Chandra X-ray Observatory ACIS and timing analysis with the Fermi satellite. Given the statistical and systematic errors, the positions determined by both satellites are coincident. The X-ray source position is R.A. 20h21m30.733s, Decl. +40 deg 26 min 46.04sec (J2000) with an estimated uncertainty of 1.3 arsec combined statistical and systematic error. Moreover, both the X-ray to gamma-ray and the X-ray to optical flux ratios are sensible assuming a neutron star origin f…
PSR J1809-1917 is a young ($τ=51$ kyr) energetic ($\dot{E}=1.8\times10^{36}$ erg s$^{-1}$) radio pulsar powering a pulsar wind nebula (PWN). We report on the results of three Chandra X-ray Observatory observations which show that the PWN consists of a small ($\sim 20''$) bright compact nebula (CN) and faint extended emission seen up to $2'$ from the pulsar. The CN is elongated in the northeast-southwest direction and exhibits morphological and flux variability on a timescale of a few months. We also find evidence of small arcsecond-scale jets extending from the pulsar along the same direction,…
With a parallactic distance of 170 pc, PSR J2144-3933 is the closest isolated radio pulsar currently known. It is also the slowest (P = 8.51 s) and least energetic (Edot = 2.6E28 erg/s) radio pulsar; its radio emission is difficult to account for with standard pulsar models, since the position of PSR J2144-3933 in the period-period derivative diagram is far beyond the typical radio `death lines'. Here we present the first deep X-ray and optical observations of PSR J2144-3933, performed in 2009 with XMM-Newton and European Southern Observatory (ESO)/Very Large Telescope (VLT), from which we der…
We describe the first X-ray observations of five short orbital period ($P_B < 1$ day), $γ$-ray emitting, binary millisecond pulsars. Four of these, PSRs J0023+0923, J1124$-$3653, J1810+1744, and J2256$-$1024 are `black-widow' pulsars, with degenerate companions of mass $\ll0.1 M_{\odot}$, three of which exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing `redback' with a near Roche-lobe filling $\sim$0.2 solar mass non-degenerate companion. Data were taken using the \textit{Chandra X-Ray Observatory} and covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215…
We present the Neil Gehrels Swift Observatory (Swift), Fermi Large Area Telescope (Fermi-LAT), and Karl G. Jansky Very Large Array (VLA) observations of the gamma-ray binary PSR J2032+4127/MT91 213, of which the periastron passage has just occurred in November 2017. In the Swift X-ray light curve, the flux was steadily increasing before mid-October 2017, however, a sharp X-ray dip on a weekly time-scale is seen during the periastron passage, followed by a post-periastron X-ray flare lasting for ~20 days. We suggest that the X-ray dip is caused by (i) an increase of the magnetization parameter …
Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 193 countries, to search for new neutron stars using data from electromagnetic and gravitational-wave detectors. This paper presents a detailed description of the search for new radio pulsars using Pulsar ALFA survey data from the Arecibo Observatory. The enormous computing power allows this search to cover a new region of parameter space; it can detect pulsars in binary systems with orbital periods as short as 11 minutes. We also describe the first Einstein@Home discovery, the 40.8 Hz isolated pulsar PSR J…
We present observations of fields containing eight recently discovered binary millisecond pulsars using the telescopes at MDM Observatory. Optical counterparts to four of these systems are detected, one of which, PSR J2214+3000, is a novel detection. Additionally, we present the fully phase-resolved B, V, and R light curves of the optical counterparts to two objects, PSR J1810+1744 and PSR J2215+5135 for which we employ model fitting using the ELC model of Orosz & Hauschildt (2000) to measure the unknown system parameters. For PSR J1810+1744 we find that the system parameters cannot be fit eve…
We describe the first X-ray observations of binary millisecond pulsars PSRs J0023+0923, J1810+1744, J2215+5135, and J2256-1024. All four are Fermi gamma-ray sources and three are 'black-widow' pulsars, with companions of mass < 0.1 solar masses. Data were taken using the Chandra X-Ray Observatory and covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and J2256-1024, show significant orbital variability and X-ray flux minima at the times of eclipses observed at radio wavelengths. This phenomenon is consistent with intrabinary shock emission characteristic of black-widow p…
We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks total exposure, performed over an 8 month period). We investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (CN), and extended tail. We find that the CN morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line-of-sight, as inferred from the radio data. On larger scales, emission from the 7' (2 pc) tail is clearly seen. We also found hints …
We report the discovery of a synchrotron nebula, G283.1-0.59, associated with PSR J1015-5719. Radio observations using the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array at 36, 16, 6, and 3 cm reveal a complex morphology. The pulsar is embedded in the "head" of the nebula with fan-shaped diffuse emission. This is connected to a circular bubble of 20" radius and a collimated tail extending over 1'. Polarization measurements show a highly ordered magnetic field in the nebula. It wraps around the edge of the head and shows an azimuthal configuration near the pu…
The pulsar/massive star binary system PSR B1259-63 / LS 2883 is one of the best-studied gamma-ray binaries, a class of systems whose bright gamma-ray flaring can provide important insights into high-energy physics. Using the Australian Long Baseline Array we have conducted very long baseline interferometric observations of PSR B1259-63 over 4.4 years, fully sampling the 3.4-year orbital period. From our measured parallax of $0.38\pm0.05$ mas we use a Bayesian approach to infer a distance of $2.6^{+0.4}_{-0.3}$ kpc. We find that the binary orbit is viewed at an angle of $154\pm3$ degrees to the…
We present coordinated Chandra X-ray Observatory and Karl G. Jansky Very Large Array observations of the transitional millisecond pulsar PSR J1023+0038 in its low-luminosity accreting state. The unprecedented five hours of strictly simultaneous X-ray and radio continuum coverage for the first time unambiguously show a highly reproducible, anti-correlated variability pattern. The characteristic switches from the X-ray high mode into a low mode are always accompanied by a radio brightening with duration that closely matches the X-ray low mode interval. This behavior cannot be explained by a cano…
Experimental evidences indicate that formations of disks and planetary systems around pulsars are allowed. Unfortunately, direct detections through electromagnetic observations appear to be quite rare. In the case of PSR 1931+24, the hypothesis of a rigid precessing disk penetrating the pulsar light cylinder is found consistent with radio transient observations from this star. Disk self-occultation and precession may limit electromagnetic observations. Conversely, we show here that gravitational waves generated by disk precessing near the light cylinder of young and middle aged pulsars would b…
PSR J1509-5850 is a middle-aged pulsar with the period P ~ 89 ms, spin-down power Edot = 5.1 x 10^35 erg/s, at a distance of about 3.8 kpc. We report on deep Chandra X-ray Observatory observations of this pulsar and its pulsar wind nebula (PWN). In addition to the previously detected tail extending up to 7' southwest from the pulsar (the southern outflow), the deep images reveal a similarly long, faint diffuse emission stretched toward the north (the northern outflow) and the fine structure of the compact nebula (CN) in the pulsar vicinity. The CN is resolved into two lateral tails and one axi…
Time-domain analysis of an archival XMM-Newton observation unveiled a very unusual variability pattern in the soft X-ray emission of PSR J1311-3430, a black widow millisecond pulsar in a tight binary (P_B=93.8 min) with a very low-mass (M~0.01 Msun) He companion star, known to show flaring emission in the optical and in the X-rays. A series of six pulses with a regular recurrence time of ~124 min is apparent in the 0.2-10 keV light curve of the system, also featuring an initial, bright flare and a quiescent phase lasting several hours. The X-ray spectrum does not change when the pulses are see…
We report on the simultaneous Giant Metrewave Radio Telescope (GMRT) and Algonquin Radio Observatory (ARO) observations at 550-750 MHz of the scintillation of PSR B1508+55, resulting in a $\sim$10,000-km baseline. This regime of measurement lies between the shorter few 100-1000~km baselines of earlier multi-station observations and the much longer earth-space baselines. We measure a scintillation cross-correlation coefficient of $0.22$, offset from zero time lag due to a $\sim 45$~s traversal time of the scintillation pattern. The scintillation time of 135~s is $3\times$ longer, ruling out iso…
Sharpening the Mass Measurement of PSR J1048+2339 via High-Cadence Photometry
National Cheng Kung University（国立成功大学）；Chungnam National University（忠南国立大学）；National Tsing Hua University（国立清华大学）；Huazhong University of Science and Technology（华中科技大学）
We present the polarization pulse profiles for 28 pulsars observed with the Arecibo Observatory by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) timing project at 2.1 GHz, 1.4 GHz, and 430 MHz. These profiles represent some of the most sensitive polarimetric millisecond pulsar profiles to date, revealing the existence of microcomponents (that is, pulse components with peak intensities much lower than the total pulse peak intensity). Although microcomponents have been detected in some pulsars previously, we present microcomponents for PSRs B1937+21, J1713+0747, and…
We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars (MSPs) observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. We detail our observational methods and present a set of TOA measurements, based on "narro…
