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Register a new userPSR J1024-0719: A Millisecond Pulsar in an Unusual Long-Period Orbit
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PSR J1024$-$0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to reexamination of its properties. We present updated radio timing observations along with new and archival optical data that show PSR J1024$-$0719 is most likely in a long period (2$-$20 kyr) binary system with a low-mass ($approx 0.4,M_odot$) low-metallicity ($Z approx -0.9,$ dex) main sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters.
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Binaries harbouring millisecond pulsars enable a unique path to determine neutron star masses: radio pulsations reveal the motion of the neutron star, while that of the companion can be characterised through studies in the optical range. PSR J1012+5307 is a millisecond pulsar in a 14.5-h orbit with a helium-core white dwarf companion. In this work we present the analysis of an optical spectroscopic campaign, where the companion star absorption features reveal one of the lightest known white dwarfs. We determine a white dwarf radial velocity semi-amplitude of K_2 = 218.9 +- 2.2 km/s, which combined with that of the pulsar derived from the precise radio timing, yields a mass ratio of q=10.44+- 0.11. We also attempt to infer the white dwarf mass from observational constraints using new binary evolution models for extremely low-mass white dwarfs, but find that they cannot reproduce all observed parameters simultaneously. In particular, we cannot reconcile the radius predicted from binary evolution with the measurement from the photometric analysis (R_WD=0.047+-0.003 Rsun). Our limited understanding of extremely low-mass white dwarf evolution, which results from binary interaction, therefore comes as the main factor limiting the precision with which we can measure the mass of the white dwarf in this system. Our conservative white dwarf mass estimate of M_WD = 0.165 +- 0.015 Msun, along with the mass ratio enables us to infer a pulsar mass of M_NS = 1.72 +- 0.16 Msun. This value is clearly above the canonical 1.4 Msun, therefore adding PSR J1012+5307 to the growing list of massive millisecond pulsars.
We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030$+$0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer (NICER) X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsars surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply-connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass $M$ and equatorial radius $R_mathrm{eq}$ are, respectively, $1.34_{-0.16}^{+0.15}$ M$_{odot}$ and $12.71_{-1.19}^{+1.14}$ km, whilst the compactness $GM/R_mathrm{eq}c^2 = 0.156_{-0.010}^{+0.008}$ is more tightly constrained; the credible interval bounds reported here are approximately the $16%$ and $84%$ quantiles in marginal posterior mass.
We present the discovery of a binary millisecond pulsar (MSP), PSR J2322$-$2650, found in the Southern section of the High Time Resolution Universe survey. This system contains a 3.5-ms pulsar with a $sim10^{-3}$ M$_{odot}$ companion in a 7.75-hour circular orbit. Follow-up observations at the Parkes and Lovell telescopes have led to precise measurements of the astrometric and spin parameters, including the period derivative, timing parallax, and proper motion. PSR J2322$-$2650 has a parallax of $4.4pm1.2$ mas, and is thus at an inferred distance of $230^{+90}_{-50}$ pc, making this system a candidate for optical studies. We have detected a source of $Rapprox26.4$ mag at the radio position in a single $R$-band observation with the Keck Telescope, and this is consistent with the blackbody temperature we would expect from the companion if it fills its Roche lobe. The intrinsic period derivative of PSR J2322$-$2650 is among the lowest known, $4.4(4)times10^{-22}$ s s$^{-1}$, implying a low surface magnetic field strength, $4.0(4)times10^7$ G. Its mean radio flux density of 160 $mu$Jy combined with the distance implies that its radio luminosity is the lowest ever measured, $0.008(5)$ mJy kpc$^2$. The inferred population of these systems in the Galaxy may be very significant, suggesting that this is a common MSP evolutionary path.
The predicted nature of the candidate redback pulsar 3FGL,J2039.6$-$5618 was recently confirmed by the discovery of $gamma$-ray millisecond pulsations (Clark et al. 2020, hereafter Paper,I), which identify this $gamma$-ray source as msp. We observed this object with the Parkes radio telescope in 2016 and 2019. We detect radio pulsations at 1.4,GHz and 3.1,GHz, at the 2.6ms period discovered in $gamma$-rays, and also at 0.7,GHz in one 2015 archival observation. In all bands, the radio pulse profile is characterised by a single relatively broad peak which leads the main $gamma$-ray peak. At 1.4,GHz we found clear evidence of eclipses of the radio signal for about half of the orbit, a characteristic phenomenon in redback systems, which we associate with the presence of intra-binary gas. From the dispersion measure of $24.57pm0.03$,pc,cm$^{-3}$ we derive a pulsar distance of $0.9pm 0.2$,kpc or $1.7pm0.7$,kpc, depending on the assumed Galactic electron density model. The modelling of the radio and $gamma$-ray light curves leads to an independent determination of the orbital inclination, and to a determination of the pulsar mass, qualitatively consistent to the results in Paper,I.
We present results of targeted searches for signatures of non-radial oscillation modes (such as r- and g-modes) in neutron stars using {it RXTE} data from several accreting millisecond X-ray pulsars (AMXPs). We search for potentially coherent signals in the neutron star rest frame by first removing the phase delays associated with the stars binary motion and computing FFT power spectra of continuous light curves with up to $2^{30}$ time bins. We search a range of frequencies in which both r- and g-modes are theoretically expected to reside. Using data from the discovery outburst of the 435 Hz pulsar XTE J1751$-$305 we find a single candidate, coherent oscillation with a frequency of $0.5727597 times u_{spin} = 249.332609$ Hz, and a fractional Fourier amplitude of $7.46 times 10^{-4}$. We estimate the significance of this feature at the $1.6 times 10^{-3}$ level, slightly better than a $3sigma$ detection. We argue that possible mode identifications include rotationally-modified g-modes associated with either a helium-rich surface layer or a density discontinuity due to electron captures on hydrogen in the accreted ocean. Alternatively, the frequency could be identified with that of an inertial mode or an r-mode modified by the presence of a solid crust, however, the r-mode amplitude required to account for the observed modulation amplitude would induce a large spin-down rate inconsistent with the observed pulse timing measurements. For the AMXPs XTE J1814$-$338 and NGC 6440 X-2 we do not find any candidate oscillation signals, and we place upper limits on the fractional Fourier amplitude of any coherent oscillations in our frequency search range of $7.8times 10^{-4}$ and $5.6 times 10^{-3}$, respectively. We briefly discuss the prospects and sensitivity for similar searches with future, larger X-ray collecting area missions.
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