Observations of microglitches in HartRAO radio pulsars

A detailed observation of microglitch phenomenon in relatively slow radio pulsars is presented. Our analyses for these small amplitude jumps in pulse rotation frequency ($\nu$) and/or spin down rate ($\dot{\nu}$) combine the traditional manual detection method (which hinges on careful visual inspections of the residuals of pulse phase residuals) and a new, and perhaps more objective, automated search technique (which exploits the power of the computer, rather than the eyes, for resolving discrete events in pulsar spin parameters). The results of the analyses of a sample of 26 radio pulsars reveal that: (i) only 20 pulsars exhibit significant fluctuations in their arrival times to be considered suitable for meaningful microglitch analyses; (ii) a phenomenal 299 microglitch events were identified in $\nu$ and/or $\dot{\nu}$: 266 of these events were found to be simultaneously significant in $\nu$ and $\dot{\nu}$, while 19 and 14 were noticeable only in $\nu$ and $\dot{\nu}$, respectively; (iii) irrespective of sign, the microglitches have fractional sizes which cover about 3 orders of magnitude in $\nu$ and $\dot{\nu}$ ($10^{-11} < |\Delta{\nu}/\nu| < 2.0\times10^{-8}$ and $5.0\times10^{-5} < |\Delta{\dot{\nu}}/\dot{\nu}| < 2.0\times10^{-2}$) with median values as $0.78\times10^{-9}$ and $0.36\times10^{-3}$, respectively.Comment: 12 pages, 3 figures, 2 Tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Particle Emission-dependent Timing Noise of Pulsars?

Though pulsars spin regularly, the differences between the observed and predicted ToA (time of arrival), known as "timing noise", can still reach a few milliseconds or more. We try to understand the noise in this paper. As proposed by Xu & Qiao in 2001, both dipole radiation and particle emission would result in pulsar braking. Accordingly, possible fluctuation of particle current flow is suggested here to contribute significant ToA variation of pulsars. We find that the particle emission fluctuation could lead to timing noise which can't be eliminated in timing process, and that a longer period fluctuation would arouse a stronger noise. The simulated timing noise profile and amplitude are in accord with the observed timing behaviors on the timescale of years.Comment: 6 pages, 2 figures. (Accepted by Chin. Phys. Lett.

Timing noise analysis of 27 HartRAO radio pulsars A. E. Chukwude

&nbsp; COMMUNICATION IN PHYSICAL SCIENCES 1(1): 7-20 Author: A.E. Chukwude Timing observations on 27 radio pulsars obtained at Hartebeesthoek Radio Astronomy Observatory' (HanRAO) between 1984 and 1999 were analyzed in order to provide an in-depth empirical description of continuous, random rotational fluctuations in radio pulsars. The results of the detailed tinte-domain analyses, which are based on the strength parameter and structure function techniques, show that (i) the observed rotational fluctuations in five pulsars are apparently too weak to allow for any nteaningful timing noise analysis; (ii) the timing activity of most (&gt; 60%) of the remainder of 22 pulsars cannot be explained in terms ofsimple idealized randont walk processes only and (iii) the observed timing activity of three, three, and two objects are characterised by rotational fluctuations whose statistics appear consistent with random walks in pulse phase, pulse frequency and slowing down rate, respectively. We discuss the results in the framework of the current understanding of radio pulsar timing noise phenomenology

On the statistical implication of timing noise for pulsar braking index

Timing data on 27 radio pulsars spanning more than 13 years were analysed in order to investigate the correlations of radio pulsar timing noise (random fluctuations in the observed pulse phase – RPTN), with the observed electromagnetic torque braking index ($n_{\mathrm{obs}}$). The results reveal significant correlations ($r \geq 90$%) between the statistics used to parameterize RPTN and the absolute magnitude of the observed second time derivative of the pulse (rotation) frequency ($\ddot{\nu}_{\mathrm{obs}}$). These correlations, most plausibly, suggest that the observed braking indices of most pulsars, obtained through the traditional phase-connected method, are strongly dominated by intrinsic variability in their spin rates. The implication of this result for a significant measurement of pulsar systematic frequency second derivative is discussed

Relativistic beaming and orientation effects in core-dominated quasars

In this paper, we investigate the relativistic beaming effects in a well-defined sample of core-dominated quasars using the correlation between the relative prominence of the core with respect to the extended emission (defined as the ratio of the core- to the lobe- flux density measured in the rest frame of the source) and the projected linear size as an indicator of relativistic beaming and source orientation. Based on the orientation-dependent relativistic beaming and unification paradigm for high luminosity sources in which the Fanaroff-Riley class-II radio galaxies form the unbeamed parent population of both the lobe- and coredominated quasars which are expected to lie at successively smaller angles to the line of sight, we find that the flows in the cores of these coredominated quasars are highly relativistic, with optimum bulk Lorentz factor, $\gamma_{opt}\sim6-16$, and also highly anisotropic, with an average viewing angle, $\sim9^0-16^0$. Furthermore, the largest boosting occurs within a critical cone angle of $\approx4^0 - 10^0$. The results suggest that relativistic bulk flow appears to extend to kiloparsec scales in these sources

Periodicities in rotation and DM of PSR B1557–50

We have analysed the pulse arrival time data of the pulsar B1557-50 collected over a period of nearly 13 years, from 1986 July to 1999 May, in order to investigate the long-term spin behaviour. The results reveal sustained cyclic variations in both the timing residuals and dispersion measure (DM) of this object. Both the timing and DM sequences are well described by two harmonically-related periodicities of ~1600 and 800 days. The variations in spin-down rate and DM are significantly anticorrelated in the sense that maximum $\dot{\nu}$ corresponds to minimum DM. Interpretation of the data in terms of free precession of an isolated radio pulsar suggests a wobble angle $\theta \approx 0.01^{\circ}$. The data are consistent with at least 6.5% of the stellar moment of inertia being coupled to the crust

Measurements of radio pulsar braking indices

A quantitative analysis of radio pulsar timing noise is presented. Our analysis employs the recently reported strong correlation (with correlation coefficient r = 0.95) between the observed second time derivative of the pulse rotation frequency ($\ddot{\nu}_{\mathrm{obs}}$), obtained from fully phase-coherent timing analyses, and a timing noise statistic ($\sigma_{\mathrm{R23}}$), used to quantify the amount of pulsar rotational fluctuations absorbed by the coefficient of the cubic term, to isolate the presumed deterministic braking index from the effects attributable to pulsar timing activity. Application of this method to a sample of 27 radio pulsars, whose timing data span ~9–13 years, reveals that (i) for 22 pulsars, a sensible braking index measurement was impossible: with numerical values of the braking index either appreciably less than the corresponding uncertainty or anomalously large; (ii) save for the relatively large uncertainties, the braking index appears to be significantly measured in five pulsars. Current results are discussed in the context of the prevailing standard model for radio pulsar spin-down

Spectral Properties of Fermi Blazars and their Unification Schemes

We use the distributions of spectral indices (αv ) of a large homogenous sample of Fermi-detected blazars to re-investigate the relationship between flat spectrum radio quasars (FSRQs) and subclasses of BL Lac objects (BL Lacs). We compute the broadband synchrotron and Compton spectral indices from radio-to-X-ray and X-ray to y-ray bands, respectively. Analyses of our data show continuity in the distributions of the spectral indices from FSRQs to HSP through LSP and ISP subclasses of BL Lacs. We find from y-ray luminosity distribution that the jetted radio galaxies form the low-luminosity tail of the distribution, which is suggestive that the sequence can be extended to the young jetted galaxy populations. We observe a significant difference in the shape of Compton and synchrotron spectra: significant anti-correlation (r ∼−0.80) exists between the broadband Compton and synchrotron spectral indices. Furthermore, the broadband spectral indices vary significantly with redshift (z) at low redshift (z < 0.3) and remain fairly constant at high (z ≥ 0.3) redshift. The trend of the variations suggests a form of evolutionary connection between subclasses of blazars. Thus, while selection effect may be significant at low redshift, evolutionary sequence can also be important. Our results are not only consistent with a unified scheme for blazars and their young jetted galaxy counterparts but also suggest that the broadband spectral sequence of blazars is not a secondary effect of redshift dependence