4,641 research outputs found
Profile morphology and polarization of young pulsars
We present polarization profiles at 1.4 and 3.1 GHz for 14 young pulsars with
characteristic ages less than 75 kyr. Careful calibration ensures that the
absolute position angle of the linearly polarized radiation at the pulsar is
obtained. In combination with previously published data we draw three main
conclusions about the pulse profiles of young pulsars. (1) Pulse profiles are
simple and consist of either one or two prominent components. (2) The linearly
polarized fraction is nearly always in excess of 70 per cent. (3) In profiles
with two components the trailing component nearly always dominates, only the
trailing component shows circular polarization and the position angle swing is
generally flat across the leading component and steep across the trailing
component.
Based on these results we can make the following generalisations about the
emission beams of young pulsars. (1) There is a single, relatively wide cone of
emission from near the last open field lines. (2) Core emission is absent or
rather weak. (3) The height of the emission is between 1 and 10 per cent of the
light cylinder radius.Comment: Accepted for publication in MNRAS. 16 page
A Temporal Map in Geostationary Orbit: The Cover Etching on the EchoStar XVI Artifact
Geostationary satellites are unique among orbital spacecraft in that they
experience no appreciable atmospheric drag. After concluding their respective
missions, geostationary spacecraft remain in orbit virtually in perpetuity. As
such, they represent some of human civilization's longest lasting artifacts.
With this in mind, the EchoStar XVI satellite, to be launched in fall 2012,
will play host to a time capsule intended as a message for the deep future.
Inspired in part by the Pioneer Plaque and Voyager Golden Records, the EchoStar
XVI Artifact is a pair of gold-plated aluminum jackets housing a small silicon
disc containing one hundred photographs. The Cover Etching, the subject of this
paper, is etched onto one of the two jackets. It is a temporal map consisting
of a star chart, pulsar timings, and other information describing the epoch
from which EchoStar XVI came. The pulsar sample consists of 13 rapidly rotating
objects, 5 of which are especially stable, having spin periods < 10 ms and
extremely small spindown rates.
In this paper, we discuss our approach to the time map etched onto the cover
and the scientific data shown on it; and we speculate on the uses that future
scientists may have for its data. The other portions of the EchoStar XVI
Artifact will be discussed elsewhere.Comment: Accepted for publication in Astronomical Journa
A strong correlation in radio pulsars with implications for torque variations
We present an analysis of the spin-down parameters for 131 radio pulsars for
which has been well determined. These pulsars have characteristic
ages ranging from yr and spin periods in the range 0.4--30 s;
nearly equal numbers of pulsars have as . We find a
strong correlation of with , {\em independent of the sign
of} . 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
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