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تسجيل مستخدم جديدLong 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 syste
m, 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.
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um 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.
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