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Register a new userLong Term Variability of a Black Widows Eclipses -- A Decade of PSR J2051$-$0827
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In this paper we report on $sim10$ years of observations of PSR J2051$-$0827, at radio frequencies in the range 110--4032 MHz. We investigate the eclipse phenomena of this black widow pulsar using model fits of increased dispersion and scattering of the pulsed radio emission as it traverses the eclipse medium. These model fits reveal variability in dispersion features on timescales as short as the orbital period, and previously unknown trends on timescales of months--years. No clear patterns are found between the low-frequency eclipse widths, orbital period variations and trends in the intra-binary material density. Using polarisation calibrated observations we present the first available limits on the strength of magnetic fields within the eclipse region of this system; the average line of sight field is constrained to be $10^{-4}$ G $lesssim B_{||} lesssim 10^2$ G, while for the case of a field directed near-perpendicular to the line of sight we find $B_{perp} lesssim 0.3$ G. Depolarisation of the linearly polarised pulses during the eclipse is detected and attributed to rapid rotation measure fluctuations of $sigma_{text{RM}} gtrsim 100$ rad m$^{-2}$ along, or across, the line of sights averaged over during a sub-integration. The results are considered in the context of eclipse mechanisms, and we find scattering and/or cyclotron absorption provide the most promising explanation, while dispersion smearing is conclusively ruled out. Finally, we estimate the mass loss rate from the companion to be $dot{M}_{text{C}} sim 10^{-12} M_odot$ yr$^{-1}$, suggesting that the companion will not be fully evaporated on any reasonable timescale.
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We have carried out high-precision timing measurements of the binary millisecond pulsar PSR J2051$-$0827 with the Effelsberg 100-m radio telescope of the Max-Planck-Institut fur Radioastronomie and with the Lovell 76-m radio telescope at Jodrell Bank. The 6.5-yrs radio timing measurements have revealed a significant secular variation of the projected semi-major axis of the pulsar at a rate of $dot xequiv d(a_{rm 1} sin i)/dt = (-0.23pm 0.03)times 10^{-12}$, which is probably caused by the Newtonian spin-orbit coupling in this binary system leading to a precession of the orbital plane. The required misalignment of the spin and orbital angular momenta of the companion are evidence for an asymmetric supernova explosion. We have also confirmed that the orbital period is currently decreasing at a rate of $dot P_{rm b}=(-15.5 pm 0.8)times 10^{-12}$s s$^{-1}$ and have measured second and third orbital period derivatives $d^2P_{rm b}/dt^2=(+2.1 pm 0.3)times 10^{-20} {rm s^{-1}}$ and $d^3P_{rm b}/dt^3 =(3.6 pm 0.6)times 10^{-28} {rm s^{-2}}$, which indicate a quasi-cyclic orbital period variation similar to those found in another eclipsing pulsar system, PSR B1957+20. The observed variation of the orbital parameters constrains the maximal value of the companion radius to $R_{rm c max} sim 0.06 R_{odot}$ and implies that the companion is underfilling its Roche lobe by 50 %. The derived variation in the quadrupole moment of the companion is probably caused by tidal dissipation similar to the mechanism proposed for PSR B1957+20. We conclude that the companion is at least partially non-degenerate, convective and magnetically active.
Timing results for the black-widow pulsar J2051-0827 are presented, using a 21-year dataset from four European Pulsar Timing Array telescopes and the Parkes radio telescope. This dataset, which is the longest published to date for a black-widow system, allows for an improved analysis that addresses previously unknown biases. While secular variations, as identified in previous analyses, are recovered, short-term variations are detected for the first time. Concurrently, a significant decrease of approx. 2.5x10-3 cm-3 pc in the dispersion measure associated with PSR J2051-0827 is measured for the first time and improvements are also made to estimates of the proper motion. Finally, PSR J2051-0827 is shown to have entered a relatively stable state suggesting the possibility of its eventual inclusion in pulsar timing arrays.
We report on an unusually bright observation of PSR J2051$-$0827 recorded during a regular monitoring campaign of black-widow pulsar systems with the Effelsberg 100-m telescope. Through fortunate coincidence, a particularly bright scintillation maximum is simultaneous with the eclipse by the companion, enabling precise measurements of variations in the flux density, dispersion measure (DM), and scattering strength throughout the eclipse. The flux density is highly variable throughout the eclipse, with a peak 1.7 times the average away from the eclipse, and yet does not significantly decrease on average. We recover the flux density variations from the measured DM variations using geometric optics, with a relative velocity as the only free parameter. We measure an effective velocity of (470 $pm$ 10) km/s, consistent with the relative orbital motion of the companion, suggesting that the outflow velocity of the lensing material is low, or is directly along the line of sight. The 2 per cent uncertainty on the effective velocity is a formal error; systematics related to our current model are likely to dominate, and we detail several extensions to the model to be considered in a full treatment of lensing. This is a demonstration of the causal link between DM and lensing; the flux density variations can be predicted directly through the derivatives of DM. Going forward, this approach can be applied to investigate the dynamics of other eclipsing systems, and to investigate the physical nature of scintillation and lensing in the ionized interstellar medium.
We have conducted radio timing observations of the eclipsing millisecond binary pulsar J2051-0827 with the European Pulsar Timing Array network of telescopes and the Parkes radio telescope, spanning over 13 years. The increased data span allows significant measurements of the orbital eccentricity, e = (6.2 {pm} 1.3) {times} 10^{-5} and composite proper motion, {mu}_t = 7.3 {pm} 0.4 mas/yr. Our timing observations have revealed secular variations of the projected semi-major axis of the pulsar orbit which are much more extreme than those previously published; and of the orbital period of the system. Investigation of the physical mechanisms producing such variations confirm that the variations of the semi-major axis are most probably caused by classical spin-orbit coupling in the binary system, while the variations in orbital period are most likely caused by tidal dissipation leading to changes in the gravitational quadrupole moment of the companion.
Decade-long monitoring of blazars at optical and infrared (OIR) wavelengths with the Small and Moderate Aperture Research Telescope System (SMARTS) in Chile and in $gamma$-rays with the Fermi Large Area Telescope (LAT) has enabled the systematic study of their multi-wavelength long-term variability. In this work we investigate, from a theoretical perspective, the long-term variability properties of blazar emission by introducing an observationally motivated time-dependence to four main parameters of the one-zone leptonic model: injection luminosity of relativistic electrons, strength of magnetic field, Doppler factor, and external photon field luminosity. For the first time, we use both the probability density function and the power spectral density of the 10 year-long Fermi-LAT light curves to create variation patterns for the model parameters. Using as test beds two bright blazars from the SMARTS sample (PKS 2155-304 and 3C 273), we compute 10 year-long OIR, X-ray, and $gamma$-ray model light curves for different varying parameters. We compare the findings of our theoretical investigation with multi-wavelength observations using various measures of variability. While no single-varying parameter simulation can explain all multi-wavelength variability properties, changes in the electron luminosity and external radiation field in PKS 2155-304 and 3C 273, respectively, can account for most of them. Our results motivate future time-dependent studies with coupling between two or more physical parameters to describe the multi-wavelength long-term blazar variability.
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