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Register a new userCorrelated emission and spin-down variability in radio pulsars
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The recent revelation that there are correlated period derivative and pulse shape changes in pulsars has dramatically changed our understanding of timing noise as well as the relationship between the radio emission and the properties of the magnetosphere as a whole. Using Gaussian processes we are able to model timing and emission variability using a regression technique that imposes no functional form on the data. We revisit the pulsars first studied by Lyne et al. (2010). We not only confirm the emission and rotational transitions revealed therein, but reveal further transitions and periodicities in 8 years of extended monitoring. We also show that in many of these objects the pulse profile transitions between two well-defined shapes, coincident with changes to the period derivative. With a view to the SKA and other telescopes capable of higher cadence we also study the detection limitations of period derivative changes.
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The analysis of distributions of some parameters of radio pulsars emitting X-ray radiation was carried out. The majority of such pulsars has short spin periods with the average value $< P >$ = 133 msec. The distribution of period derivatives reveals a bimodality, dividing millisecond ($< log dfrac{dP}{dt}>$ = -19.69) and normal ($< log dfrac{dP}{dt}> $ = -13.29) pulsars. Magnetic fields at the surface of the neutron star are characterized by the bimodal distribution as well. The mean values of $<log B_s>$ are $8.48$ and $12.41$ for millisecond pulsars and normal ones, respectively. The distribution of magnetic fields near the light cylinder, it does not show the noticeable bimodality. The median value of $log B_{lc}$ = 4.43 is almost three orders higher comparing with this quantity ($<log B_{lc}>$ = 1.75) for radio pulsars without registered X-ray emission. Losses of rotational energy ($<log dfrac{dE}{dt}>$ = 35.24) are also three orders higher than corresponding values for normal pulsars. There is the strong correlation between X-ray luminosities and losses of rotational energies. The dependence of the X-ray luminosity on the magnetic field at the light cylinder has been detected. It shows that the generation of the non-thermal X-ray emission takes place at the periphery of the magnetosphere and is caused by the synchrotron mechanism. We detected the positive correlations between luminosities in radio, X-ray and gamma -ray ranges. Such correlations give the possibility to carry out a purposeful search for pulsars in one of these ranges if they radiate in other one.
Through high-precision radio timing observations, we show that five recycled pulsars in the direction of the Galactic Centre (GC) have anomalous spin period time derivative ($dot P$) measurements -- PSRs J1748$-$3009, J1753$-$2819, J1757$-$2745, and J1804$-$2858 show negative values of $dot P$ and PSR J1801$-$3210 is found to have an exceptionally small value of $dot P$. We attribute these observed $dot P$ measurements to acceleration of these pulsars along their lines-of-sight (LOSs) due to the Galactic gravitational field. Using models of the Galactic mass distribution and pulsar velocities, we constrain the distances to these pulsars, placing them on the far-side of the Galaxy, providing the first accurate distance measurements to pulsars located in this region and allowing us to consider the electron density along these LOSs. We find the new electron density model YMW16 to be more consistent with these observations than the previous model NE2001. The LOS dynamics further constrain the model-dependent intrinsic $dot P$ values for these pulsars and they are consistent with measurements for other known pulsars. In the future, the independent distance measurements to these and other pulsars near the GC would allow us to constrain the Galactic gravitational potential more accurately.
We report the time variability of the late-time radio emission in a Type-I superluminous supernova (SLSN), PTF10hgi, at z = 0.0987. The Karl G. Jansky Very Large Array 3 GHz observations at 8.6 and 10 years after the explosion both detected radio emission with a ~40% decrease in flux density in the second epoch. This is the first report of a significant variability of the late-time radio light curve in a SLSN. Through combination with previous measurements in two other epochs, we constrained both the rise and decay phases of the radio light curve over three years, peaking at approximately 8-9 years after the explosion with a peak luminosity of L(3GHz) = 2 x 10^21 W/Hz. Possible scenarios for the origin of the variability are an active galactic nucleus (AGN) in the host galaxy, an afterglow caused by the interaction between an off-axis jet and circumstellar medium, and a wind nebula powered by a newly-born magnetar. Comparisons with models show that the radio light curve can be reproduced by both the afterglow model and magnetar wind nebula model. Considering the flat radio spectrum at 1-15 GHz and an upper limit at 0.6 GHz obtained in previous studies, plausible scenarios are a low-luminosity flat-spectrum AGN or a magnetar wind nebula with a shallow injection spectral index.
The influence of disc radiation capture upon black hole rotational evolution is negligible for radiatively inefficient discs. For the standard thin disc model it is a slight but potentially important effect leading to the equilibrium spin parameter value of about 0.998. For optically thin discs, the fraction of disc radiation captured by the black hole is however about two times larger. In some disc radiation models, inner parts of the accretion flow are optically thin, advection-dominated flows, and the thin disc ends at some transition radius R_{tr}. The thermal energy of the disc stored in trapped radiation is released at this radius. Angular distribution of the radiation released at this radial photosphere facilitates its capture by the black hole. For accretion rates close to critical and disc truncation radius of (2..4) GM/c^2, radiation capture is most efficient in spinning the black hole down that may lead to a_{eq} ~ 0.996..0.997 or less depending on the mass accretion rate. For an accretion flow radiating some constant fraction epsilon of dissipated energy, the equilibrium Kerr parameter is shown to obey the relation 1-a_{eq} propto epsilon^{3/2} as long as 1-a_{eq} << 1. Deviations from Keplerian law near the last stable orbit dominate over the radiation capture effect if they exceed 1..2%.
Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.
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