2,641 research outputs found
Coherently Dedispersed Polarimetry of Millisecond Pulsars
We present a large sample of high-precision, coherently-dedispersed
polarization profiles of millisecond pulsars (MSPs) at frequencies between 410
and 1414 MHz. These data include the first polarimetric observations of several
of the pulsars, and the first low-frequency polarization profiles for others.
Our observations support previous suggestions that the pulse shapes and
polarimetry of MSPs are more complex than those of their slower relatives. An
immediate conclusion is that polarimetry-based classification schemes proposed
for young pulsars are of only limited use when applied to millisecond pulsars.Comment: 28 pages, 10 figures. Text matches version that appeared in ApJS.
Full paper with high-resolution figures available at
ftp://ftp.jb.man.ac.uk/pub/psr/papers/msppolpton.ps.g
The radio luminosity distribution of pulsars in 47 Tucanae
We have used the Australia Telescope Compact Array to seek the integrated
radio flux from all the pulsars in the core of the globular cluster 47 Tucanae.
We have detected an extended region of radio emission and have calibrated its
flux against the flux distribution of the known pulsars in the cluster. We find
the total 20-cm radio flux from the cluster's pulsars to be S = 2.0 +/- 0.3
mJy. This implies the lower limit to the radio luminosity distribution to be
L_1400 = 0.4 mJy kpc^2 and the size of the observable pulsar population to be N
< 30.Comment: 7 pages, 4 figures, MNRAS in pres
Constraining Radio Emission from Magnetars
We report on radio observations of five magnetars and two magnetar candidates
carried out at 1950 MHz with the Green Bank Telescope in 2006-2007. The data
from these observations were searched for periodic emission and bright single
pulses. Also, monitoring observations of magnetar 4U0142+61 following its 2006
X-ray bursts were obtained. No radio emission was detected was detected for any
of our targets. The non-detections allow us to place luminosity upper limits
(at 1950 MHz) of approximately L < 1.60 mJy kpc^2 for periodic emission and L <
7.6 Jy kpc^2 for single pulse emission. These are the most stringent limits yet
for the magnetars observed. The resulting luminosity upper limits together with
previous results are discussed, as is the importance of further radio
observations of radio-loud and radio-quiet magnetars.Comment: 11 pages, 4 figure
A Strong Upper Limit on the Pulsed Radio Luminosity of the Compact Object 1RXS J141256.0+792204
The ROSAT X-ray source 1RXS J141256.0+792204 has recently been identified as
a likely compact object whose properties suggest it could be a very nearby
radio millisecond pulsar at d = 80 - 260pc. We investigated this hypothesis by
searching for radio pulsations using the Westerbork Synthesis Radio Telescope.
We observed 1RXS J141256.0+792204 at 385 and 1380MHz, recording at high time
and frequency resolution in order to maintain sensitivity to millisecond
pulsations. These data were searched both for dispersed single pulses and using
Fourier techniques sensitive to constant and orbitally modulated periodicities.
No radio pulsations were detected in these observations, resulting in pulsed
radio luminosity limits of L_400 ~ 0.3 (d/250pc)^2 mJy kpc^2 and L_1400 ~ 0.03
(d/250pc)^2 mJy kpc^2 at 400 and 1400MHz respectively. The lack of detectable
radio pulsations from 1RXS J141256.0+792204 brings into question its
identification as a nearby radio pulsar, though, because the pulsar could be
beamed away from us, this hypothesis cannot be strictly ruled out.Comment: To appear in A&A. 3 page
Discovery of 10 pulsars in an Arecibo drift-scan survey
We present the results of a 430-MHz survey for pulsars conducted during the
upgrade to the 305-m Arecibo radio telescope. Our survey covered a total of
1147 square degrees of sky using a drift-scan technique. We detected 33
pulsars, 10 of which were not known prior to the survey observations. The
highlight of the new discoveries is PSR J0407+1607, which has a spin period of
25.7 ms, a characteristic age of 1.5 Gyr and is in a 1.8-yr orbit about a
low-mass (>0.2 Msun) companion. The long orbital period and small eccentricity
(e = 0.0009) make the binary system an important new addition to the ensemble
of binary pulsars suitable to test for violations of the strong equivalence
principle. We also report on our initially unsuccessful attempts to detect
optically the companion to J0407+1607 which imply that its absolute visual
magnitude is > 12.1. If, as expected on evolutionary grounds, the companion is
an He white dwarf, our non-detection imples a cooling age of least 1 Gyr.Comment: 8 pages, 3 figures, accepted for publication in MNRA
A Binary Millisecond Pulsar in Globular Cluster NGC6544
We report the detection of a new 3.06 ms binary pulsar in the globular
cluster NGC6544 using a Fourier-domain ``acceleration'' search. With an implied
companion mass of ~0.01 solar masses and an orbital period of only P_b~1.7
hours, it displays very similar orbital properties to many pulsars which are
eclipsed by their companion winds. The orbital period is the second shortest of
known binary pulsars after 47 Tuc R. The measured flux density of 1.3 +/- 0.4
mJy at 1332 MHz indicates that the pulsar is almost certainly the known
steep-spectrum point source near the core of NGC6544.Comment: Accepted by ApJ Letters on 11 October 2000, 5 page
A radio supernova remnant associated with the young pulsar J1119-6127
We report on Australia Telescope Compact Array observations in the direction
of the young high magnetic-field pulsar J1119-6127. In the resulting images we
identify a non-thermal radio shell of diameter 15', which we classify as a
previously uncatalogued young supernova remnant, G292.2-0.5. This supernova
remnant is positionally coincident with PSR J1119-6127, and we conclude that
the two objects are physically associated. No radio emission is detected from
any pulsar wind nebula (PWN) associated with the pulsar; our observed upper
limits are consistent with the expectation that high magnetic-field pulsars
produce radio nebulae which fade rapidly. This system suggests a possible
explanation for the lack of an associated radio pulsar and/or PWN in many
supernova remnants.Comment: 13 pages, 6 embedded eps figures. Accepted to Ap
Rewriting Logic Semantics of a Plan Execution Language
The Plan Execution Interchange Language (PLEXIL) is a synchronous language
developed by NASA to support autonomous spacecraft operations. In this paper,
we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance
logical engine. The rewriting logic semantics is by itself a formal interpreter
of the language and can be used as a semantic benchmark for the implementation
of PLEXIL executives. The implementation in Maude has the additional benefit of
making available to PLEXIL designers and developers all the formal analysis and
verification tools provided by Maude. The formalization of the PLEXIL semantics
in rewriting logic poses an interesting challenge due to the synchronous nature
of the language and the prioritized rules defining its semantics. To overcome
this difficulty, we propose a general procedure for simulating synchronous set
relations in rewriting logic that is sound and, for deterministic relations,
complete. We also report on two issues at the design level of the original
PLEXIL semantics that were identified with the help of the executable
specification in Maude
Simulating the WFIRST coronagraph Integral Field Spectrograph
A primary goal of direct imaging techniques is to spectrally characterize the
atmospheres of planets around other stars at extremely high contrast levels. To
achieve this goal, coronagraphic instruments have favored integral field
spectrographs (IFS) as the science cameras to disperse the entire search area
at once and obtain spectra at each location, since the planet position is not
known a priori. These spectrographs are useful against confusion from speckles
and background objects, and can also help in the speckle subtraction and
wavefront control stages of the coronagraphic observation. We present a
software package, the Coronagraph and Rapid Imaging Spectrograph in Python
(crispy) to simulate the IFS of the WFIRST Coronagraph Instrument (CGI). The
software propagates input science cubes using spatially and spectrally resolved
coronagraphic focal plane cubes, transforms them into IFS detector maps and
ultimately reconstructs the spatio-spectral input scene as a 3D datacube.
Simulated IFS cubes can be used to test data extraction techniques, refine
sensitivity analyses and carry out design trade studies of the flight CGI-IFS
instrument. crispy is a publicly available Python package and can be adapted to
other IFS designs.Comment: 15 page
Measurement of Relativistic Orbital Decay in the PSR B1534+12 Binary System
We have made timing observations of binary pulsar PSR B1534+12 with radio
telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new
observations with data collected up to seven years earlier, we obtain a
significantly improved solution for the astrometric, spin, and orbital
parameters of the system. For the first time in any binary pulsar system, no
fewer than five relativistic or "post-Keplerian" orbital parameters are
measurable with useful accuracies in a theory-independent way. We find the
orbital period of the system to be decreasing at a rate close to that expected
from gravitational radiation damping, according to general relativity, although
the precision of this test is limited to about 15% by the otherwise poorly
known distance to the pulsar. The remaining post-Keplerian parameters are all
consistent with one another and all but one of them have fractional accuracies
better than 1%. By assuming that general relativity is the correct theory of
gravity, at least to the accuracy demanded by this experiment, we find the
masses of the pulsar and companion star each to be 1.339+-0.003 Msun and the
system's distance to be d = 1.1+-0.2 kpc, marginally larger than the d ~ 0.7
kpc estimated from the dispersion measure. The increased distance reduces
estimates of the projected rate of coalescence of double neutron-star systems
in the universe, a quantity of considerable interest for experiments with
terrestrial gravitational wave detectors such as LIGO.Comment: 17 pages, 4 figures, submitted to the Ap
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