Millisecond Pulsar PSR J1023 Research Articles

XMM-Newton spectral and timing observations of the millisecond pulsar PSR J0218+4232

We present XMM-Newton MOS imaging and PN timing data of the millisecond pulsar PSR J0218+4232. We confirm the previously detected pulsations of PSR J0218+4232 and we show that the folded lightcurve is dependent on energy. We present the broad band (0.2−10.0 keV) spectrum of this millisecond pulsar, as well as the spectra of: the pulsed emission, the individual pulses, the interpulse and the non-pulsed region and we compare our results with previous data from Rosat, BeppoSAX and Chandra. We discuss the results of the spectral fitting in the context of recent pulsar models.

Chandra and RXTE studies of the X-ray/γ-ray millisecond pulsar PSR J0218+4232

We report on high-resolution spatial and timing observations of the millisecond pulsar PSR J0218+4232 performed with the Chandra X-ray Observatory (CXO) and the Rossi X-ray Timing Explorer (RXTE). With these observations we were able to study: (a) the possible spatial extent at X-ray energies of the DC source coincident with PSR J0218+4232 in detail (CXO); (b) the relative phasing between the X-ray, radio and γ-ray profiles (CXO and RXTE); and (c) the spectral properties at energies beyond 10 keV (RXTE). We found no indications for extended emission at X-ray energies down to ∼1″ scales and confirmed the presence of a point-like DC-component. The two non-thermal pulses in the X-ray profile are found to be aligned with two of the three pulses visible at radio-frequencies and more importantly with the two γ-ray pulses seen in the EGRET 100–1000 MeV pulse profile. The latter reduces now the random occurrence probability for the detected γ-ray signal to ∼10 −6, which corresponds to a 4.9 σ detection significance. This strengthens the credibility of our earlier claimed detection of pulsed high-energy γ-ray emission from this millisecond pulsar. The pulsed RXTE spectrum appears to extend to ∼20 keV and can be described by a power-law with a photon index of 1.14, slightly softer than measured by BeppoSAX and XMM for energies below 10 keV. We compare the high-energy characteristics of PSR J0218+4232 with those of two other X-ray emitting millisecond pulsars PSR B1821-24 and PSR B1937+21.

Temperature and cooling age of the white dwarf companion of PSR J0218+4232

We report on Keck optical BVRI images and spectroscopy of the companion of the binary millisecond pulsar PSR J0218+4232. A faint bluish (V=24.2, B-V=0.25) counterpart is observed at the pulsar location. Spectra of this counterpart reveal Balmer lines which confirm that the companion is a Helium-core white dwarf. We find that the white dwarf has a temperature of Teff=8060+-150 K. Unfortunately, the spectra are of insufficient quality to put a strong constraint on the surface gravity, although the best fit is for low log g and hence low mass (~0.2 Msun), as expected. We compare predicted white dwarf cooling ages with the characteristic age of the pulsar and find similar values for white dwarf masses of 0.19 to 0.3 Msun. These masses would imply a distance of 2.5 to 4 kpc to the system. The spectroscopic observations also enable us to estimate the mass ratio between the white dwarf and the pulsar. We find q=7.5+-2.4, which is consistent with the current knowledge of white dwarf companions to millisecond pulsars.

DeepBVRimaging of the field of the millisecond pulsar PSR J0030+0451 with the VLT

We report on deep BVR-imaging of the field of the nearby millisecond pulsar PSR J0030+0451 obtained with the ESO/VLT/FORS2. We do not detect any optical counterpart down to B > 27.3, V > 27. 0a ndR > 27.0 in the immediate vicinity of the radio pulsar position. The closest detected sources are offset by >3 �� , and they are excluded as counterpart candidates by our astrometry. Using our upper limits in the optical, and including recent XMM-Newton X-ray data we show that any nonthermal power-law spectral component of neutron star magnetospheric origin, as suggested by the interpretation of X-ray data, must be suppressed by at least a factor of ∼500 in the optical range. This either rules out the nonthermal interpretation or suggests a dramatic spectral break in the 0.003−0.1 keV range of the power-law spectrum. Such a situation has never been observed in the optical/X-ray spectral region of ordinary pulsars, and the origin of such a break is unclear. An alternative interpretation with a purely thermal X-ray spectrum is consistent with our optical upper limits. In this case the X-ray emission is dominated by hot polar caps of the pulsar.

High‐Resolution Spatial and Timing Observations of Millisecond Pulsar PSR J0218+4232 withChandra

We report on high-resolution spatial and timing results for binary millisecond pulsar PSR J0218+4232 obtained with the Chandra HRC-I and HRC-S in imaging mode. We found no indications for extended emission at 1 arcsec scales. With the HRC-S observation we obtained a 0.08-10 keV pulse profile with high statistics which could be compared in absolute time with the pulse profiles at radio-frequencies and at high-energy gamma-rays. The two X-ray pulses at aligned with 2 of the 3 radio-pulses, and with the 2 gamma-ray pulses.

Radio profile instability in the millisecond pulsar PSR J0437−4715 resulting from spiky emission

The instability in one of the components of the radio integrated profile (IP) of the millisecond pulsar PSR J0437−4715 is correlated with the occurrence of the spiky emission in that component. It is speculated that the instability in other components is also as a result of the spiky emission. This might have important implications for interpreting the individual components of the IP as independent beams or regions of emission.

A test of general relativity from the three-dimensional orbital geometry of a binary pulsar.

Binary pulsars provide an excellent system for testing general relativity because of their intrinsic rotational stability and the precision with which radio observations can be used to determine their orbital dynamics. Measurements of the rate of orbital decay of two pulsars have been shown to be consistent with the emission of gravitational waves as predicted by general relativity, but independent verification was not possible. Such verification can in principle be obtained by determining the orbital inclination in a binary pulsar system using only classical geometrical constraints. This would permit a measurement of the expected retardation of the pulse signal arising from the general relativistic curvature of space-time in the vicinity of the companion object (the 'Shapiro delay'). Here we report high-precision radio observations of the binary millisecond pulsar PSR J0437-4715, which establish the three-dimensional structure of its orbit. We see the Shapiro delay predicted by general relativity, and we determine the mass of the neutron star and its white dwarf companion. The determination of such masses is necessary in order to understand the origin and evolution of neutron stars.

No evidence for coherent diffractive radiation patterns in the millisecond pulsar PSR J0437-4715

An independent analysis of the 326.5-MHz data obtained by the Ooty Radio Telescope reveals no evidence for coherent diffractive radiation patterns in the millisecond pulsar PSR J0437–4715.

Likely detection of pulsed high-energy γ-rays from millisecond pulsar PSR J0218+4232

AbstractWe report on the likely detection of pulsed high-energyγ-rays from the binary millisecond pulsar PSR J0218+4232 in 100–1000 MeV data from CGRO EGRET. Imaging analysis demonstrates that the highly significantγ-ray source 2EG J0220+4228 (∼ 10σ) is for energies > 100 MeV positionally consistent with both PSR J0218+4232 and the BL Lac 3C66A. However, above 1 GeV 3C66A is the evident counterpart, whereas between 100 and 300 MeV PSR J0218+4232 is the most likely one. Timing analysis using one ephemeris valid for all EGRET observations yields in the 100-1000 MeV range a double-pulse profile at a ∼ 3.5σsignificance level. The phase separation is similar to the component separation of ∼ 0.47 observed at X-rays. A comparison of theγ-ray profile with the 610 MHz radio profile in absolute phase shows that the twoγ- ray pulses coincide with two of the three emission features in the complex radio profile.

Radio Emission of PSR J0437−4715 at 327 MHz

More than 412,000 single pulses from the brightest millisecond radio pulsar PSR J0437-4715 were obtained at 327 MHz using the Ooty Radio Telescope. This pulsar displays neither the nulling nor the systematic drifting phenomenon found in several normal (long period) pulsars. A rigorous upper limit to the percentage of nulling in PSR J0437-4715 is 0.0016%. However, its integrated profile varies on timescales ranging from ≈ 500 periods to days; the variation is slow and unlike the mode-changing phenomenon of normal pulsars. About 3% of the intensity of PSR J0437-4715 varies quasi-periodically, particularly at early pulse phases within the integrated profile. Its fluctuation spectrum has a weak feature at the mean value of 0.253 ± 0.002 cycles per period, with an average rms width of 0.067 ± 0.005 cycles per period, but both parameters vary from phase to phase within the integrated profile, which has not been noticed so far in pulsars. Our results are important to resolve the issue whether the radio emission of millisecond pulsars is similar to that of normal pulsars.

Radio Pulse Properties of the Millisecond Pulsar PSR J0437−4715. I. Observations at 20 Centimeters

We present a total of 48 minutes of observations of the nearby, bright millisecond pulsar PSR J0437-4715 taken at the Parkes Observatory in Australia. The data were obtained at a central radio frequency of 1380 MHz using a high-speed tape recorder that permitted coherent Nyquist sampling of 50 MHz of bandwidth in each of two polarizations. Using the high time resolution available from this voltage recording technique, we have studied a variety of single-pulse properties, many for the first time in a millisecond pulsar. We show that individual are broad band, have pulse widths ranging from ~10 (~06 in pulse longitude) to ~300 μs (~20°) with a mean pulse width of ~65 μs (~4°), exhibit a wide variety of morphologies, and can be highly linearly polarized. Single pulse peaks can be as high as 205 Jy (over ~40 times the average pulse peak), and have a probability distribution similar to those of slow-rotating pulsars. We observed no single pulse energy exceeding ~4.4 times the average pulse energy, ruling out giant pulses as have been seen for the Crab and PSR B1937+21 pulsars. PSR J0437-4715 does not exhibit classical microstructure or show any signs of a preferred timescale that could be associated with primary emitters; single pulse modulation has been observed to be consistent with amplitude-modulated noise down to timescales of 80 ns. We observe a significant inverse correlation between pulse peak and width. Thus, the average pulse profile produced by selecting for large pulse peaks is narrower than the standard average profile. We find no evidence for diffractive quantization effects in the individual pulse arrival times or amplitudes as have been reported for this pulsar at lower radio frequency using coarser time resolution. Overall, we find that the single-pulse properties of PSR J0437-4715 are similar to those of the common slow-rotating pulsars, even though this pulsar's magnetosphere and surface magnetic field are several orders of magnitude smaller than those of the general population. The pulsar radio emission mechanism must therefore be insensitive to these fundamental neutron star properties.

Millisecond Pulsar Alignment: PSR J0437−4715

The abundances of both orthogonal and nearly aligned neutron stars among the disk population millisecond pulsars appear to be excessively large, relative to those of canonical pulsars. Both of these excesses are expected in strongly spun-up neutron stars. Their surface magnetic field evolution mirrors the changes in the core magnetic field configuration caused by the strong interaction between a core's spinning-up superfluid neutrons and its magnetized superconducting protons. We discuss special observable properties of such a nearly aligned millisecond pulsar and propose an explanation of the apparent paradox for interpreting observations of the very close millisecond pulsar PSR J0437-4715: a strongly modulated X-ray light curve and an extraordinarily broad radio-pulse structure that covers more than three-fourths of the spin period. The former is usually associated with emission polar caps that are being eclipsed by the star's own rotation, while the latter strongly supports alignment and a viewing angle that allows uninterrupted observation of the polar cap.

Coherent Radiation Patterns Suggested by Single-Pulse Observations of a Millisecond Pulsar

We have observed intense radiation spikes from the millisecond pulsar PSR J0437-4715 and find their distribution in pulsar spin phase to be quite unlike the integrated pulse profile. The spikes are observed almost exclusively in a 10° phase window centered on the main pulse. Within that window the phase distribution has a periodic variation, producing a pattern reminiscent of the diffraction fringes associated with coherent emission from a finite aperture. We propose a source model in which the spikes are emitted coherently from a region with spatial scale ≈ 100 m.

Model Atmospheres for Low-Field Neutron Stars

We compute model atmospheres and emergent spectra for low-field (B ≲ 10<SUP>10</SUP> G) neutron stars, using new opacity and equation of state data from the OPAL project. These computations, incorporating improved treatments of flux transport and convective stability, provide spectra for hydrogen, solar abundance, and iron atmospheres. We compare our results to high field magnetic atmospheres, available only for hydrogen. An application to apparently thermal flux from the low-field millisecond pulsar PSR J0437-4715 shows that H atmospheres fit substantially better than Fe models. We comment on extension to high fields and the implication of these results for neutron star luminosities and radii.

Extreme Ultraviolet Emission from Neutron Stars

We summarize the detections of extreme ultraviolet (EUV) emission from neutron stars. Three firm detections have been made of spin-powered pulsars: the aged millisecond pulsar PSR J0437−4715, the middle-aged X-ray pulsar Geminga, and the radio pulsar PSR B0656+14. These observations allow us to evaluate both power-law and thermal-law emission models as the source of the EUV flux. For the case of PSR B0656+14 the lack of flux modulation with pulse period argues that the EUV radiation originates from the cooling neutron star surface rather than from a hot polar cap. If the emission is from a thermalized neutron star surface, then limits can be placed on the surface temperature. For the case of Geminga we can explain the observed EUV flux using thermal models that are consistent with standard neutron cooling scenarios. We also have a weak indication that the EUV emission from Geminga is pulsed in a manner consistent with the lowest energy channel observed with Rosat. For the case of the millisecond pulsar PSR J0437−4715 standard neutron star cooling models require surface re-heating. We compare different heating models to the data on this object. We rule out re-heating by crust-core friction, and find that models for the accretion from the interstellar medium, accretion from the white dwarf companion and a particle-wind nebula do not account for the EUV luminosity. Models of pulsar re-heating by magnetic monopole catalysis of nucleon decay are used to establish new limits to the flux of monopoles in the Galaxy. A single power-law source with properties derived from X-ray data cannot explain the EUV flux from PSR J0437−4715. The strongest model for explaining the EUV emission consists of a large ~ 3 km2 polar cap heated from particle production in the pulsar magnetic field. We consider the prospects for detecting other neutron stars in the extreme ultraviolet.

EUV Observations of Pulsars

AbstractThree pulsars have been detected with the Lexan (100 Å )filter of the EUVE Deep Survey telescope: the middle-aged isolated pulsars, PSR B0656+14 and Geminga, plus the aged millisecond pulsar PSR J0437–4715. The EUV detections have been used both alone and in combination with observations in other bandpasses to limit the physical state of the objects and to test theories regarding neutron star cooling and re-heating mechanisms. For Geminga, the EUVE data suggests the presence of an optical cyclotron spectral feature superimposed on the Rayleigh-Jeans continuum tail from a hot pulsar surface. We summarize EUV pulsar observations and results.

Microstructure and patterns of coherent radiation

AbstractWe present data which indicates that micropulses from the bright millisecond pulsar PSR J0437–4715 are observed at equally-spaced preferred phases within the pulse window. We find the pattern similar to that expected if each micropulse is radiated from a source with a coherence scale of ~ 100 m.

Giant Micropulses from PSR J0437–4715

Although individual radio pulses from pulsars vary in amplitude from pulse to pulse, their height distribution in general does not extend to amplitudes more than 10 times the mean. Two notable exceptions are the Crab pulsar and PSR B1937+21 (Lundgren 1995, Cognard et al. 1996 and references therein) which occasionally emit single radio pulses that have amplitudes more than 100 times the mean. Here we report on the detection of short time-scale, extremely large amplitude radio pulses from the nearby millisecond pulsar PSR J0437–4715. The events we have observed are distinguished by having peak flux densities in excess of 10 times the average pulse amplitude, and occur only within a very narrow (80 µs) window centered on the main pulse.

EGRET High-Energy gamma -Ray Pulsar Studies. II. Individual Millisecond Pulsars

view Abstract Citations (61) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS EGRET High-Energy gamma -Ray Pulsar Studies. II. Individual Millisecond Pulsars Fierro, J. M. ; Arzoumanian, Z. ; Bailes, M. ; Bell, J. F. ; Bertsch, D. L. ; Brazier, K. T. S. ; Chiang, J. ; D'Amico, N. ; Dingus, B. L. ; Esposito, J. A. ; Fichtel, C. E. ; Hartman, R. C. ; Hunter, S. D. ; Johnston, S. ; Kanbach, G. ; Kaspi, V. M. ; Kniffen, D. A. ; Lin, Y. C. ; Lyne, A. G. ; Manchester, R. N. ; Mattox, J. R. ; Mayer-Hasselwander, H. A. ; Michelson, P. F. ; von Montigny, C. ; Nel, H. I. ; Nice, D. ; Nolan, P. L. ; Schneid, E. J. ; Shriver, S. K. ; Sreekumar, P. ; Taylor, J. H. ; Thompson, D. J. ; Willis, T. D. Abstract More than 2 yr of observations performed by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory (CGRO) are examined for evidence of high-energy γ-ray emission from individual millisecond pulsars. Upper limits are placed on steady emission. In addition, for those millisecond pulsars for which an accurate timing solution is available, upper limits to pulsed γ-ray emission are established. The results are compared with predictions of current pulsar γ-ray emission models. In particular, the absence of a detection of γ-rays from the nearby millisecond pulsar PSR J0437-4715 severely constrains theories regarding γ-ray emission from millisecond pulsars. Publication: The Astrophysical Journal Pub Date: July 1995 DOI: 10.1086/175919 Bibcode: 1995ApJ...447..807F Keywords: GAMMA RAYS: OBSERVATIONS; STARS: PULSARS: GENERAL full text sources ADS | data products SIMBAD (56) HEASARC (1) Related Materials (2) Part 1: 1994ApJ...436..229T Part 3: 1996ApJ...465..898N

The optical counterpart of the bright nearby millisecond pulsar PSR J0437-4715

view Abstract Citations (42) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Counterpart of the Bright Nearby Millisecond Pulsar PSR J0437-4715 Bailyn, Charles D. Abstract Optical imaging of the field of PSR J0437-4715 reveals a candidate optical counterpart less than 1 arcsec from the radio source location. The color and magnitude of this star are consistent with a 0.2-solar mass helium white dwarf with T(eff) about 4400 K at a distance of 150 parsecs. Such an object is expected as the binary companion of the neutron star, given the orbital characteristics determined from the radio observations. The cooling time for the white dwarf is greater than the characteristic spin-down age of the pulsar, which suggests that, in some cases, spin-down times computed from pulsar periods and period derivatives may not in fact represent an upper limit to the pulsar age. No luminosity variations over the orbital period are observed, down to a limit of a few tenths of a magnitude. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/186918 Bibcode: 1993ApJ...411L..83B Keywords: Eclipsing Binary Stars; Pulsars; Stellar Orbits; Stellar Physics; White Dwarf Stars; Image Analysis; Neutron Stars; Astrophysics full text sources ADS | data products SIMBAD (2)