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Register a new userOn The Evolution of The Radio Pulsar PSR J1734-3333
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Authors
S. Caliskan
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Recent measurements showed that the period derivative of the high-B radio pulsar PSR J1734-3333 is increasing with time. For neutron stars evolving with fallback disks, this rotational behavior is expected in certain phases of the long-term evolution. Using the same model as employed earlier to explain the evolution of anomalous X-ray pulsars and soft gamma-ray repeaters, we show that the period, the first and second period derivatives and the X-ray luminosity of this source can simultaneously acquire the observed values for a neutron star evolving with a fallback disk. We find that the required strength of the dipole field that can produce the source properties is in the range of 10^{12} - 10^{13} G on the pole of the neutron star. When the model source reaches the current state properties of PSR J1734-3333, accretion onto the star has not started yet, allowing the source to operate as a regular radio pulsar. Our results imply that PSR J1734-3333 is at an age of ~ 3 x 10^4 - 2 x 10^5 years. Such sources will have properties like the X-ray dim isolated neutron stars or transient AXPs at a later epoch of weak accretion from the diminished fallback disk.
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The low braking-index pulsar PSR J1734$-$3333 could be born with superhigh internal magnetic fields $B_{rm in}sim10^{15}-10^{16}$ G, and undergo a supercritical accretion soon after its formation in a supernova explosion. The buried multipole magnetic fields will merger into a dipole magnetic field. Since the magnetic flow transfers from the core to the crust of the pulsar, its surface dipole field grows quickly at a power-law form assumed until it saturates at the level of internal dipole field. The increase in surface dipole magnetic field results in the observed low braking index of $n=0.9(2)$. Keeping an average field growth index $varepsilon=1.34(6)$, this pulsar will become a magnetar with surface dipole magnetic field at the equator $B_{rm d}sim 2.6(1)times 10^{14}$,G and $sim 5.3(2)times 10^{14}$,G after next 50,kyrs and 100,kys, respectively.
The very small braking index of PSR J1734-3333, $n=0.9pm0.2$, challenges the current theories of braking mechanisms in pulsars. We present a possible interpretation that this pulsar is surrounded by a fall-back disk and braked by it. A modified braking torque is proposed based on the competition between the magnetic energy density of a pulsar and the kinetic energy density of a fall-back disk. With this torque, a self-similar disk can fit all the observed parameters of PSR J1734-3333 with natural initial parameters. In this regime, the star will evolve to the region having anomalous X-ray pulsars and soft gamma repeaters in the $P-dot{P}$ diagram in about 20000 years and stay there for a very long time. The mass of the disk around PSR J1734-3333 in our model is about $10M_{oplus}$, similar to the observed mass of the disk around AXP 4U 0142+61.
We apply theoretical spin-down models of magnetospheric evolution and magnetic field decay to simulate the possible evolution of PSR J0250+5854, which is the slowest-spinning radio pulsar detected to date. Considering the alignment of inclination angle in a 3-D magnetosphere, it is possible that PSR J0250+5854 has a high magnetic field comparable with magnetars or/and high magnetic field pulsars, if a small inclination angle is considered. Our calculations show that similar long-period pulsars tend to have a relatively low period derivative in this case. In another case of magnetic field decay, calculations also show a possible connection between PSR J0250+5854 and high dipole-magnetic field magnetars. The evolutionary path indicates a relatively high spin-down rate for similar long-period pulsars.
We present radio observations of the most slowly rotating known radio pulsar PSR J0250+5854. With a 23.5 s period, it is close, or even beyond, the $P$-$dot{P}$ diagram region thought to be occupied by active pulsars. The simultaneous observations with FAST, the Chilbolton and Effelsberg LOFAR international stations, and NenuFAR represent a five-fold increase in the spectral coverage of this object, with the detections at 1250 MHz (FAST) and 57 MHz (NenuFAR) being the highest- and lowest-frequency published respectively to date. We measure a flux density of $4pm2$ $mu$Jy at 1250 MHz and an exceptionally steep spectral index of $-3.5^{+0.2}_{-1.5}$, with a turnover below $sim$95 MHz. In conjunction with observations of this pulsar with the GBT and the LOFAR Core, we show that the intrinsic profile width increases drastically towards higher frequencies, contrary to the predictions of conventional radius-to-frequency mapping. We examine polarimetric data from FAST and the LOFAR Core and conclude that its polar cap radio emission is produced at an absolute height of several hundreds of kilometres around 1.5 GHz, similar to other rotation-powered pulsars across the population. Its beam is significantly underfilled at lower frequencies, or it narrows because of the disappearance of conal outriders. Finally, the results for PSR J0250+5854 and other slowly spinning rotation-powered pulsars are contrasted with the radio-detected magnetars. We conclude that magnetars have intrinsically wider radio beams than the slow rotation-powered pulsars, and that consequently the latters lower beaming fraction is what makes objects such as PSR J0250+5854 so scarce.
The recently constructed theory of radio wave propagation in the pulsar magnetosphere outlines the general aspects of the radio light curve and polarization formation. It allows us to describe general properties of mean profiles, such as the position angle ($PA$) of the linear polarization, and the circular polarization for the realistic structure of the pair creation region in the pulsar magnetosphere. In this work, we present an application of the radio wave propagation theory to the radio observations of pulsar PSR J1906+0746. This pulsar is particularly interesting because observations of relativistic spin-precession in a binary system allows us to put strong constraints on its geometry. Because it is an almost orthogonal rotator, the pulsar allows us to observe both magnetic poles; as we show, this is crucial for testing the theory of radio wave propagation and obtaining constraints on the parameters of magnetospheric plasma. Our results show that plasma parameters are qualitatively consistent with theories of pair plasma production in polar cap discharges. Specifically, for PSR J1906+0746, we constrain the plasma multiplicity $lambda sim 10^3$ and the Lorentz-factor of secondary plasma $gamma sim $ a few hundred.
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