A strong ν¨−ν˙\ddot{\nu} - \dot{\nu} correlation in radio pulsars with implications for torque variations

We present an analysis of the spin-down parameters for 131 radio pulsars for which $\ddot\nu$ has been well determined. These pulsars have characteristic ages ranging from $10^{3} - 10^{8}$ yr and spin periods in the range 0.4--30 s; nearly equal numbers of pulsars have $\ddot\nu>0$ as $\ddot\nu<0$. We find a strong correlation of $\ddot\nu$ with $\dot{\nu}$, {\em independent of the sign of} $\ddot\nu$. We suggest that this trend can be accounted for by small, stochastic deviations in the spin-down torque that are directly proportional (in magnitude) to the spin-down torque.Comment: MNRAS, 4 pages, 2 figures. Minor editorial changes and typos correcte

Timing Measurements of the Relativistic Binary Pulsar PSR B1913+16

We present results of more than three decades of timing measurements of the first known binary pulsar, PSR B1913+16. Like most other pulsars, its rotational behavior over such long time scales is significantly affected by small-scale irregularities not explicitly accounted for in a deterministic model. Nevertheless, the physically important astrometric, spin, and orbital parameters are well determined and well decoupled from the timing noise. We have determined a significant result for proper motion, $\mu_{\alpha} = -1.43\pm0.13$, $\mu_{\delta}=-0.70\pm0.13$ mas yr$^{-1}$. The pulsar exhibited a small timing glitch in May 2003, with ${\Delta f}/f=3.7\times10^{-11}$, and a smaller timing peculiarity in mid-1992. A relativistic solution for orbital parameters yields improved mass estimates for the pulsar and its companion, m_1=1.4398\pm0.0002 \ M_{\sun} and m_2=1.3886\pm0.0002 \ M_{\sun}. The system's orbital period has been decreasing at a rate $0.997\pm0.002$ times that predicted as a result of gravitational radiation damping in general relativity. As we have shown before, this result provides conclusive evidence for the existence of gravitational radiation as predicted by Einstein's theory.Comment: Published in APJ, 722, 1030 (2010

Arecibo HI Absorption Measurements of Pulsars and the Electron Density at Intermediate Longitudes in the First Galactic Quadrant

We have used the Arecibo telescope to measure the HI absorption spectra of eight pulsars. We show how kinematic distance measurements depend upon the values of the galactic constants R_o and Theta_o, and we select our preferred current values from the literature. We then derive kinematic distances for the low-latitude pulsars in our sample and electron densities along their lines of sight. We combine these measurements with all others in the inner galactic plane visible from Arecibo to study the electron density in this region. The electron density in the interarm range 48 degrees < l < 70 degrees is [0.017 (-0.007,+0.012) (68% c.l.)] cm^(-3). This is 0.75 (-0.22,+0.49) (68% c.l.) of the value calculated by the Cordes & Lazio (2002) galactic electron density model. The model agrees more closely with electron density measurements toward Arecibo pulsars lying closer to the galactic center, at 30 degrees<l<48 degrees. Our analysis leads to the best current estimate of the distance of the relativistic binary pulsar B1913+16: d=(9.0 +/- 3) kpc. We use the high-latitude pulsars to search for small-scale structure in the interstellar hydrogen observed in absorption over multiple epochs. PSR B0301+19 exhibited significant changes in its absorption spectrum over 22 yr, indicating HI structure on a ~500 AU scale.Comment: Accepted by Astrophysical Journal September 200

Nonlocalized faulting in a thick lithosphere : application to lunar contraction

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001.Includes bibliographical references (p. 67-74).We reexamine the longstanding hypothesis that lunar contraction is constrained by the lack of a visible global system of compressive faults. We model the lunar lithosphere as a layered elastic medium that fails according to a Mohr-Coulomb criterion. We use elastic constants inferred from lunar seismic profiles, and use a finite element code to model the response of this lithosphere to contraction. We find that fault localization and propagation are strongly affected by the thickness of the lithosphere. A thin lithosphere promotes fault localization by extending through the entire lithosphere and thus enabling large stress relief and large displacements. For a thick elastic lithosphere the mode of faulting is less localized and many faults form in the upper part of the lithosphere, each with small displacements. Furthermore, localization in a thin lithosphere enables fault propagation through a compliant layer, such as a 1-3 km megaregolith layer, while for a thick lithosphere faults cannot penetrate this layer. Thus, the lack of an observed global system of compressive faults, similar to the locate scarps observed on the surface of Mercury, may not be due to the absence of an episode of global contraction on the moon, but rather due to the thickness of the lithosphere at that time.by Ori Weisberg.S.M