11 research outputs found
New Pulsars from an Arecibo Drift Scan Search
We report the discovery of pulsars J0030+0451, J0711+0931, and J1313+0931
that were found in a search of 470 square degrees at 430 MHz using the 305m
Arecibo telescope. The search has an estimated sensitivity for long period, low
dispersion measure, low zenith angle, and high Galactic latitude pulsars of ~1
mJy, comparable to previous Arecibo searches. Spin and astrometric parameters
for the three pulsars are presented along with polarimetry at 430 MHz. PSR
J0030+0451, a nearby pulsar with a period of 4.8 ms, belongs to the less common
category of isolated millisecond pulsars. We have measured significant
polarization in PSR J0030+0451 over more than 50% of the period, and use these
data for a detailed discussion of its magnetospheric geometry. Scintillation
observations of PSR J0030+0451 provide an estimate of the plasma turbulence
level along the line of sight through the local interstellar medium.Comment: 21 pages, 4 figures, Accepted for Publication in Ap
Profile instabilities of the millisecond pulsar PSR J1022+1001
We present evidence that the integrated profiles of some millisecond pulsars
exhibit severe changes that are inconsistent with the moding phenomenon as
known from slowly rotating pulsars. We study these profile instabilities in
particular for PSR J1022+1001 and show that they occur smoothly, exhibiting
longer time constants than those associated with moding. In addition, the
profile changes of this pulsar seem to be associated with a relatively
narrow-band variation of the pulse shape. Only parts of the integrated profile
participate in this process which suggests that the origin of this phenomenon
is intrinsic to the pulsar magnetosphere and unrelated to the interstellar
medium. A polarization study rules out profile changes due to geometrical
effects produced by any sort of precession. However, changes are observed in
the circularly polarized radiation component. In total we identify four
recycled pulsars which also exhibit instabilities in the total power or
polarization profiles due to an unknown phenomenon (PSRs J1022+1001,
J1730-2304, B1821-24, J2145-0750).
The consequences for high precision pulsar timing are discussed in view of
the standard assumption that the integrated profiles of millisecond pulsars are
stable. As a result we present a new method to determine pulse times-of-arrival
that involves an adjustment of relative component amplitudes of the template
profile. Applying this method to PSR J1022+1001, we obtain an improved timing
solution with a proper motion measurement of -17 \pm 2 mas/yr in ecliptic
longitude. Assuming a distance to the pulsar as inferred from the dispersion
measure this corresponds to an one-dimensional space velocity of 50 km/s.Comment: 29 pages, 12 figures, accepted for publication in Ap
Arecibo timing observations of 17 pulsars along the Galactic plane
We present phase-coherent timing solutions obtained for the first time for 17
pulsars discovered at Arecibo by Hulse & Taylor (1975ab) in a 430-MHz survey of
the Galactic plane. This survey remains the most sensitive of the Galactic
plane at 430 MHz and has comparable equivalent sensitivity to the 1400-MHz
Parkes multibeam survey. Comparing both surveys we find that, as expected, the
one at 430 MHz is limited in depth by interstellar dispersion and scattering
effects; and that the detection rate of pulsars with high spin-down luminosity
( erg s) at the low frequency is a factor of 5 smaller
than at high frequency. We also present scatter-broadening measurements for two
pulsars and pulse nulling and mode-changing properties for two others.Comment: 10 pages, 3 figures, accepted for publication in A
The characteristics of millisecond pulsar emission: I. Spectra, pulse shapes and the beaming fraction
We have monitored a large sample of millisecond pulsars using the 100-m
Effelsberg radio telescope in order to compare their radio emission properties
to the slowly rotating population. With some notable exceptions, our findings
suggest that the two groups of objects share many common properties. A
comparison of the spectral indices between samples of normal and millisecond
pulsars demonstrates that millisecond pulsar spectra are not significantly
different from those of normal pulsars. There is evidence, however, that
millisecond pulsars are slightly less luminous and less efficient radio
emitters compared to normal pulsars. We confirm recent suggestions that a
diversity exists among the luminosities of millisecond pulsars with the
isolated millisecond pulsars being less luminous than the binary millisecond
pulsars. There are indications that old millisecond pulsars exhibit somewhat
flatter spectra than the presumably younger ones. We present evidence that
millisecond pulsar profiles are only marginally more complex than those found
among the normal pulsar population. Moreover, the development of the profiles
with frequency is rather slow, suggesting very compact magnetospheres. The
profile development seems to anti-correlate with the companion mass and the
spin period, again suggesting that the amount of mass transfer in a binary
system might directly influence the emission properties. The angular radius of
radio beams of millisecond pulsars does not follow the scaling predicted from a
canonical pulsar model which is applicable for normal pulsars. Instead they are
systematically smaller. The smaller inferred luminosity and narrower emission
beams will need to be considered in future calculations of the birth-rate of
the Galactic population.Comment: 40 pages, 14 figures, accepted for publication in Ap
The characteristics of millisecond pulsar emission: II. Polarimetry
We have made polarimetric monitoring observations of millisecond pulsars
visible from the northern hemisphere at 1410 MHz. Their emission properties are
compared with those of normal pulsars. Although we demonstrated in paper I that
millisecond pulsars exhibit the same flux density spectra and similar profile
complexity, our results presented here suggest that millisecond pulsar profiles
do not comply with the predictions of classification schemes based on
``normal'' pulsars. The frequency development of a large number of millisecond
pulsar profiles is abnormal when compared with the development seen for normal
pulsars. Moreover, the polarization characteristics suggest that
millisecond-pulsar magnetospheres might not simply represent scaled versions of
the magnetospheres of normal pulsars, supporting results of paper I. However,
phenomena such as mode-changing activity in both intensity and polarization are
recognized here for the first time (e.g., J1730--2304). This suggests that
while the basic emission mechanism remains insensitive to rotational period,
the conditions that, according to the canonical pulsar model, regulate the
radio emission, might be satisfied at different regions in millisecond pulsar
magnetospheres.
At least three types of model have been proposed to describe the millisecond
pulsar magnetospheres. A comparison of the predictions of these models with the
observations suggests that individual cases are better explained by different
processes. However, we show that millisecond pulsars can be grouped according
to common emission properties, a grouping that awaits verification from future
multifrequency observations.Comment: 38 pages, 8 figures, accepted for publication in ApJ, (see
astro-ph/9801177 for paper I