The Geometry of PSR B0031-07

PSR B0031-07 is well known to exhibit three different modes of drifting sub-pulses (mode A, B and C). It has recently been shown that in a multifrequency observation, consisting of 2700 pulses, all driftmodes were visible at low frequencies, while at 4.85 GHz only mode-A drift or non-drifting emission was detected. This suggests that modes A and B are emitted in sub-beams, rotating at a fixed distance from the magnetic axis, with the mode-B sub-beams being closer to the magnetic axis than the mode-A sub-beams. Diffuse emission between the sub-beams can account for the non-drifting emission. Using the results of an analysis of simultaneous multifrequency observations of PSR B0031-07, we set out to construct a geometrical model that includes emission from both sub-beams and diffuse emission and describes the regions of the radio emission of PSR B0031-07 at each emission frequency for driftmodes A and B. Based on the vertical spacing between driftbands, we have determined the driftmode of each sequence of drift. To restrict the model, we calculated average polarisation and intensity characteristics for each driftmode and at each frequency. The model reproduces the observed polarisation and intensity characteristics, suggesting that diffuse emission plays an important role in the emission properties of PSR B0031-07. The model further suggests that the emission heights of this pulsar range from a few kilometers to a little over 10 kilometers above the pulsar surface. We also find that the relationships between height and frequency of emission that follow from curvature radiation and from plasma-frequency emission could not be used to reproduce the observed frequency dependence of the width of the average intensity profiles.Comment: 15 pages, 9 figures, 8 tables, accepted for publication in A&

Women empowerment through green mussel (Perna viridis) farming : Focus on Kerala

Mussel farming is one of the best ideas for the utilisation of natural resources as well as human resources in a sustainable manner. It is an activity with potential to empower women by giving them a chance to earn additional income for their family, thereby making them self-reliant. Thus, looking at the larger picture mussel farming could bring about an improvement in the socio-economic condition of families in the coastal States of India. Additionally, it also ensures production of healthy and protein rich food for the consumers

Book of Abstracts & Lead Articles The Second International Symposium Remote Sensing for Ecosystem Analysis and Fisheries

SAFARI (Societal Applications in Fisheries and Aquaculture using Remotely-Sensed Imagery) is an initiative which provides a forum for coordination, at the international level, of activities in global fisheries research and management. The forum is open to all interested parties, including policy makers, research scientists, government managers, and those involved in the fishing industries. SAFARI organizes international workshops and symposia as a platform to discuss the latest research in Earth observation and fisheries management, information sessions aimed at the fisheries industry, government officials and resource managers, representation at policy meetings, and producing publications relevant to the activities. SAFARI gains worldwide attention through collaboration with other international networks, such as ChloroGIN (Chlorophyll Global Integrated Network), IOCCG (International Ocean-Colour Coordinating Group), POGO (Partnership for Observation of the Global Oceans) and the oceans and society: Blue Planet Initiative of the intergovernmental organization, the Group on Earth Observations (GEO)

Local Pulsars; A note on the Birth-Velocity Distribution

We explore a simple model for the representation of the observed distributions of the motions, and the characteristic ages of the local population of pulsars. The principal difference from earlier models is the introduction of a unique value, S, for the kick velocity with which pulsars are born. We consider separately the proper motion components in galactic longitude and latitude, and find that the distributions of the velocity components parallel and perpendicular to the galactic plane are represented satisfactorily by S=200 km/sec, and leave no room for a significant fraction of much higher velocities. The successful proposition of a unique value for the kick velocity may provide an interesting tool in attempts to understand the physical process leading to the expulsion of the neutron star.Comment: To be published in JAA, 14 pages, 7 figure

Rocking the Lighthouse: Circumpulsar Asteroids and Radio Intermittency

We propose that neutral, circumpulsar debris entering the light cylinder can account for many time-dependent pulsar phenomena that are otherwise difficult to explain. Neutral material avoids propeller ejection and injects sufficient charges -- after heating, evaporation, and ionization -- to alter current flows and pair-production and thus trigger, detune, or extinguish coherent emission. Relevant phenomena, with time scales from seconds to months, include nulls, rotating radio transients (RRATs), rapid changes in pulse profile (``mode changes''), variable subpulse drift rates, quasi-periodic bursts from B1931+24, and torque variations. Over the 10 Myr lifetime of a canonical pulsar with trillion-gauss surface magnetic field, less than a millionth of an Earth mass of material is needed to modulate the Goldreich-Julian current by 100%. Circumpulsar material originates from metal-rich, supernova fallback gas that aggregates into asteroids. Debris disks can inject sufficient material on time scales of interest, yet be too tenuous to form large planets detectable in pulse timing data. Asteroid migration results from collisions and the radiation-driven Yarkovsky and Poynting-Robertson effects. For B1931+24, an asteroid in a $\sim 40$~day elliptical orbit pollutes the magnetosphere stochastically through collisions with other debris. Injection is less likely for hot, young and highly magnetized pulsars or millisecond pulsars that pre-ionize any debris material well outside their small magnetospheres. Injection effects will therefore be most prominent in long-period, cooler pulsars, consistent with the distribution of relevant objects in perid and period derivative. A pulsar's spin history and its radiation-beam orientation may influence whether it displays nulling, RRATs and other effects.Comment: 20 pages, 6 figures, submitted to Ap

An Idealized Pulsar Magnetosphere: the Relativistic Force-Free Approximation

The non-dissipative relativistic force-free condition should be a good approximation to describe the electromagnetic field in much of the pulsar magnetosphere, but we may plausibly expect it to break down in singular domains. Self-consistent magnetospheric solutions are found with field lines closing both at and within the light-cylinder. In general, the detailed properties of the solutions may be affected critically by the physics determining the appropriate choice of equatorial boundary condition beyond the light-cylinder.Comment: 31 pages, 3 figure

Inferring Initial Spin Periods for Neutron Stars in Composite Remnant

We propose a method to infer the initial spin period of pulsars residing in composite supernova remnants. Such a remnant consists of both a plerionic and a shell type component, corresponding respectively to the pulsar wind nebula driven by the spindown luminosity of the central pulsar, and the blastwave bounding the supernova remnant. Theoretical investigations including hydrodynamical simulations have shown that at late times (~ 1,000 - 10,000 years), a simple scaling law connects the radius of the supernova shell to the radius of the plerion. The energy content of the plerion and the total mechanical energy of the supernova remnant enter into this scaling law. One can use this scaling law to estimate the initial spin period of pulsars residing in composite remnants. We discuss potential pitfalls of this method, including the effect of a small remnant age and of strong radiative losses in the plerion.Comment: 4 pages, 2 figures, accepted by ApJ

Birth and Evolution of Isolated Radio Pulsars

We investigate the birth and evolution of Galactic isolated radio pulsars. We begin by estimating their birth space velocity distribution from proper motion measurements of Brisken et al. (2002, 2003). We find no evidence for multimodality of the distribution and favor one in which the absolute one-dimensional velocity components are exponentially distributed and with a three-dimensional mean velocity of 380^{+40}_{-60} km s^-1. We then proceed with a Monte Carlo-based population synthesis, modelling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam surveys. We present a population model that appears generally consistent with the observations. Our results suggest that pulsars are born in the spiral arms, with a Galactocentric radial distribution that is well described by the functional form proposed by Yusifov & Kucuk (2004), in which the pulsar surface density peaks at radius ~3 kpc. The birth spin period distribution extends to several hundred milliseconds, with no evidence of multimodality. Models which assume the radio luminosities of pulsars to be independent of the spin periods and period derivatives are inadequate, as they lead to the detection of too many old simulated pulsars in our simulations. Dithered radio luminosities proportional to the square root of the spin-down luminosity accommodate the observations well and provide a natural mechanism for the pulsars to dim uniformly as they approach the death line, avoiding an observed pile-up on the latter. There is no evidence for significant torque decay (due to magnetic field decay or otherwise) over the lifetime of the pulsars as radio sources (~100 Myr). Finally, we estimate the pulsar birthrate and total number of pulsars in the Galaxy.Comment: 27 pages, including 15 figures, accepted by Ap