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    \quad\quad ACTA ASTRONOMICA SINICA \hfill
    \hspace{2mm} Vol.44\vspace{2mm}}}} %%%%%%%
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    {\small\rm  suppl.\hfill R. N. Manchester: Pulsars: Recent Results from Parkes  %%（作者：题目名称）
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    Vol.44~ Suppl.
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    \small ACTA ASTRONOMICA SINICA
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      Feb.,~2003 \\[-1.5 true mm] %%January
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\vs\vs\vs \bc {\Large\bf
Pulsars: Recent Results from Parkes    %%（文题）
%\\[1ex]
%$\!\!^*$
}

\vs\vs{\normalsize R. N. Manchester}  %%（本文作者）

\vs (\footnotesize {\it Australia Telescope National Facility,
CSIRO, Epping NSW 1710, Australia}) \\%%（本文作者单位）
\vs\vs \ec

\normalsize
\begin{quotation}

 \no{\bf A{\scriptsize\bf BSTRACT }}~~~\small
In the past few years, groups working at the 64-m Parkes radio
telescope have made major contributions to the subject of pulsar
astronomy. Large-scale surveys for pulsars using the Parkes
multibeam receiver have discovered about 700 previously unknown
pulsars, nearly doubling the number known. More directed searches
toward both supernova remnants and globular clusters have
discovered a significant number of pulsars, many of which are
intrinsically interesting. Finally, timing and scintillation
observations of some well-known pulsars have revealed a number of
interesting effects.

 %\vn
 %\no{\bf Key words}~~  pulsar-mode  change-spectrum
\end{quotation}

%%%% 正文
 \para{\large\bf{1}~~ Introduction}

\vs\vs  The 64-m Parkes radio telescope, operated by the Australia
Telescope National Facility, CSIRO, and located near the town of
Parkes in central New South Wales, has a long history of
involvement in pulsar research. Just a few weeks after the
announcement of the discovery of pulsars (Hewish et al. 1968), the
first multi-frequency spectra of individual pulses were obtained
(Robinson et al. 1968).  A year or so later, the polarization of
the Vela pulsar was measured, leading to the magnetic-pole model
for pulsar emission (Radhakrishnan \& Cooke 1969) and the first
pulsar glitch was observed (Radhakrishnan \& Manchester 1969). The
first pulsars to be discovered at Parkes were announced by
Komesaroff et al. (1973) in one of the first pulsar searches to
exploit digital signal processing techniques.

Several very successful large-scale searches for pulsars followed.
The Second Molonglo Pulsar survey, in which candidates from the
Molonglo telescope near Canberra were confirmed at Parkes,
discovered 155 pulsars and more than doubled the number of pulsars
known at the time (Manchester et al. 1978). The first known
extra-galactic pulsar was discovered in the Large Magellanic Cloud
by McCulloch et al. (1983). The first confirmed pulsar in the
globular cluster 47 Tucanae, a millisecond pulsar (MSP), was
discovered by Manchester et al. (1990) and was quickly followed by
the discovery of an additional ten MSPs in the same cluster
(Manchester et al. 1991, Robinson et al. 1995).  The first major
survey of the southern Galactic plane at 1400\,MHz by Johnston et
al. (1992) discovered 46 pulsars, including the interesting
long-period high-mass binary system PSR B1259$-$63. The Parkes
70\,cm survey (Lyne et al. 1998) was the first extensive survey of
the southern hemisphere with a system sensitive to MSPs and
discovered 101 pulsars, of which 17 had millisecond periods,
including the nearest and strongest MSP known, PSR J0437$-$4715.

By 1997, pulsar surveys at Parkes had discovered nearly one third
of the 750 or so pulsars known. In this year, a major advance in
the capability of the Parkes telescope for large-scale surveys at
frequencies around 1400\,MHz was made with the construction of the
multibeam receiver (Staveley-Smith et al. 1996). This receiver
gives 13 simultaneous beams on the sky, multiplying the efficiency
of large-scale surveys by roughly a factor of 13. Since then,
observations using this receiver have again (nearly) doubled the
number of known radio pulsars to about 1500. This means that the
Parkes radio telescope has {\it discovered twice as many pulsars
as the rest of the world's telescopes put together!} Most of the
new discoveries have been made by the Parkes multibeam pulsar
survey, a survey of a 10\dg -wide strip along the southern
Galactic plane, but significant numbers have been found in
higher-latitude wide-area surveys as well.

The multibeam receiver has proved valuable in wide-area
surveys. The low system noise and wide bandwidth of the system
allowed very sensitive searches directed at specific objects using
just the central beam of the receiver. Such searches have nearly
doubled the number of known pulsars associated with globular clusters
(and significantly increased the number of clusters with known
pulsars) and discovered a number of young and interesting pulsars
associated with supernova remnants. The sensitivity of the system,
combined with improved data recording and analysis techniques, has
also produced some interesting results from timing and scintillation
studies of previously known pulsars.

\para{\large\bf{2}~~Pulsar Surveys with the Parkes Multibeam System}

\vs\vs The Parkes multibeam receiver has 13 beams arranged in two
hexagons surrounding a central beam, each with dual polarization
and system temperature of about 22\,K. Pulsar searches use a
filterbank receiver/digitiser system with $96\times 3$\,MHz
channels, centered at 1374\,MHz, on each polarization of each
beam. Data are one-bit digitized and recorded on digital linear
tape for subsequent analysis. Two major surveys have been made
with this system: the Parkes multibeam pulsar survey and the
Swinburne intermediate-latitude survey.
\begin{figure}[th]
\center {\includegraphics
[angle=270,scale=0.6]{manchester_fig1.ps}}

   \parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize

      Fig.\,1~~ Distribution of known Galactic disk pulsars projected on the
Galactic plane. The underlying greyscale is the Taylor \& Cordes
(1993) Galactic electron density model which was used to derive
pulsar distances from the dispersion measure.}
    \end{figure}

The Parkes multibeam survey is a collaboration between groups from
the United Kingdom, United States, Italy, Canada and Australia and
covers a 10\dg-wide strip along the southern Galactic plane
between Galactic longitudes of 260\dg and 50\dg.  It has been
outstandingly successful, discovering more than 620 pulsars.
Descriptions of the receiver and data recording and analysis
systems, details of the first 100 pulsars discovered and
references to earlier papers reporting especially interesting
objects are given by Manchester et al. (2001). Morris et al.
(2002) and Kramer et al. (2003) report the discovery of a further
120 and 200 pulsars, respectively, and discuss some of the
implications of the results. The survey has a limiting flux
density of approximately 0.2\,mJy, several times more sensitive
than any previous large-scale survey, and uses a sampling interval
of 250\,$\mu$s. It achieves this high sensitivity with a
combination of low system noise, wide bandwidth (288\,MHz) and
long integration time (35 min).  Following determination of
accurate periods and positions, newly discovered pulsars are
listed on a website
(http://www.atnf.csiro.au/research/pulsar/pmsurv/).  This site
currently lists parameters for 519 pulsars.

Because of the high sensitivity of the survey, most of the newly
discovered pulsars are relatively distant and have high dispersion
measures -- the median value is about 350\,cm$^{-3}$\,pc compared
to 90\,cm$^{-3}$\,pc for previously known pulsars. As Fig. 1
shows, many of the pulsars at distances comparable to the Galactic
Center and even beyond. They therefore form an excellent sample
for studies of the interstellar medium, including improvement of
the electron density model and investigations of the Galactic
magnetic field (e.g., Han et al. 2002).
\begin{figure}[h]
\center {\includegraphics [scale=0.6]{manchester_fig2.ps}}
   \parbox[tb]{12cm}
   %{\hspace{3.5cm}
   {%\center
   \footnotesize
      Fig.\,2~~ Distribution of known Galactic disk pulsars in the $P$ ---
$\dot P$ plane. Binary pulsars are indicated by circle around the
point and pulsars detected only at high energies are marked with
an open star. This latter group includes the anomalous X-ray
pulsars (AXPs) and soft gamma-ray repeaters (SGRs) which have very
long periods and high implied magnetic fields.}
    \end{figure}

A complimentary survey, optimised for detection of millisecond
pulsars, is being undertaken by a group from Swinburne University
of Technology and Caltech using the multibeam receiver at Parkes.
This survey is covering several strips parallel to that of the
Parkes multibeam survey but at higher latitudes. It uses a smaller
sampling interval, 125\,$\mu$s, and just 4 min per pointing. While
this survey has a lower sensitivity overall, these parameters,
combined with the higher Galactic latitude of the search area,
give it a relatively higher sensitivity to millisecond pulsars.
The first phase of the survey (Edwards et al. 2001) covers strips
with 5\dg < |b| < 15\dg and has been very successful, discovering
69 pulsars including eight millisecond pulsars.

One of the basic pulsar parameters is the slow-down rate, normally
expressed as a dimensionless period time-derivative $\dot P$.
Measurement of this parameter allows determination of the
characteristic age of the pulsar, $\tau = P/(2\dot P)$, and the
surface-dipole magnetic field in gauss, $B_s = 3.2 \times 10^{-19}
P\dot P$. The $P$ --- $\dot P$ diagram, shown in Fig.\,2 for all
known pulsars, is a basic tool of pulsar astronomy. Young pulsars
have high surface-dipole fields and spin down rapidly, whereas
millisecond pulsars have very small period derivatives, implying
low magnetic fields and ages of $10^9$ years or more. A large
proportion of millisecond pulsars are binary. Also shown in
Fig.\,2 are the so-called `anomalous X-ray pulsars' (AXPs) and
`soft gamma-ray repeaters' (SGRs) which have long pulsation
periods and extremely strong implied magnetic field strengths.
AXPs and SGRs are detected only at X-ray and higher energies. Some
young pulsars, including the youngest known, PSR J1846$-$0258
which is associated with the supernova remnant Kes 75 (Gotthelf et
al. 2000) are also detectable only at X-ray energies.

One of the more significant results to come from the Parkes
multibeam survey is the detection of a large number of relatively
young pulsars with very large implied magnetic-field strengths.
Indeed, as Fig. 2 shows, the ten radio pulsars with the largest
derived magnetic field strengths were all detected in this survey.
Some of these pulsars have relatively long periods and are located
close to the region of $P - \dot P$ space occupied by the AXPs and
SGRs (Camilo et al. 2000a). Despite this, these are radio pulsars,
so far undetectable at X-ray wavelengths (Pivovaroff et al. 2000).
AXPs and SGRs, on the other hand, have no detectable pulsed radio
emission.

\para{\large\bf{3}~~Pulsar -- Supernova Remnant Associations}

\vs\vs The youngest pulsar so far discovered in the Parkes
multibeam survey, PSR J1119$-$6127, has a characteristic age of
only 1700 years. An associated supernova remnant might be expected
for such a young pulsar, but there was no catalogued remnant at
the pulsar position. A deep image at 1.4\,GHz made using the
Australia Telescope Compact Array (Fig.\,3) clearly revealed
emission centered on the pulsar which is almost certainly an
associated supernova remnant (Crawford et al. 2001).

\begin{figure}[tbhp]
\begin{minipage}[t]{0.48\textwidth}
\includegraphics[scale=0.37]{manchester_fig3.ps}
\par\vspace{0pt}
\parbox[tb]{6.7cm}{\footnotesize  Fig.\,3 (left) Image of the supernova remnant
G292.2$-$0.5 at 1.4 GHz obtained with the ATCA. The position of
the young pulsar PSR J1119$-$6127 is marked with a cross.
(Crawford et al. 2001)}
\end{minipage}
\hfill
\begin{minipage}[t]{0.48\textwidth}
\includegraphics[scale=0.51]{manchester_fig4.ps}
\par\vspace{0pt}
\parbox[tb]{6.7cm}{\footnotesize  Fig.\,4 (right) Image of the
supernova remnant G352.2$-$0.1 from the 843\,MHz Molonglo Galactic
Plane Survey (Green et al. 1999). The cross marks the position of
the young pulsar PSR 1726$-$3530.}
\end{minipage}
\end{figure}


Examination of the Molonglo Galactic Plane Survey (Green et al.
1999) at the positions of several other young pulsars from the
Parkes multibeam survey shows radio nebulae which may be
associated supernova remnants.  One of the better examples is PSR
J1726$-$3530 which has a characteristic age of 14\,kyr and a
surprisingly long period of 1110\,ms. As Fig. 4 shows, this pulsar
is centrally located within a faint bilateral nebula. Such
bilateral structures are relatively common among known supernova
remnants and so it is probable that this faint nebula is a
supernova remnant associated with PSR J1726$-$3530.


The detection by the {\it Chandra} X-ray observatory of an unresolved
source and surrounding hard nebular emission in several well-known
supernova remnants strongly suggests the presence of an energetic
pulsar and surrounding pulsar wind nebula. In some of these, X-ray
pulsations have been detected (e.g. Murray et al. 2002) thereby
confirming the hypothesis, but in others no pulsations are
detectable. This has provided a stimulus for deep radio observations
in order to detect the pulsar and hence determine its properties. One
such object is the supernova remnant G292.0+1.8 in which the {\it
Chandra} image shows a region of hard emission surrounding a pointlike
source about one third of the nebular radius from the center (Hughes
et al. 2001). Camilo et al. (2002) made a 10-hour observation in the
direction of the supernova remnant using the center beam of the
multibeam receiver and analysis of these data revealed a weak 135 ms
pulsar, PSR J1124$-$5916, with a rapid spin-down rate giving a
characteristic age of 2900 years. Any doubt that this was the pulsar
associated with G292.0+1.8 was subsequently removed by the detection
of pulsations in the X-ray point source at the radio period.

As shown in Fig.\,5, despite its youth this pulsar has a radio
luminosity which is lower than that of most radio pulsars. This
figure shows that there is a very wide range of radio luminosities
for pulsars of all ages. Some of this is certainly due to beaming
effects. Polarization properties give some information on the cut
by our line of sight across the emitted beam, but these have not
yet been measured for PSR J1124$-$5916.

\begin{figure}[ht]
\center {\includegraphics [bb=0 0 450
462,scale=0.6]{manchester_fig5.ps}}
   \parbox[tb]{13cm}{
   \footnotesize

      Fig.\,5~~ Radio luminosity at 1400\,MHz plotted against characteristic
age for known radio pulsars. In the lower part of the figure mean
values over ranges of age are plotted. (Camilo et al. 2002)}

    \end{figure}

With these recent detections of supernova remnants associated with
young pulsars, the detection of weak radio pulsars in well-known
supernova remnants and other similar discoveries in the X-ray band,
the number of believable pulsar -- supernova remnant associations has
grown rapidly in the past few years to at least 27. For about one
quarter of these, the association was first established by X-ray
observations.

\para{\large\bf{4}~~Pulsars in Globular Clusters}

\vs\vs It is well known that the very dense cores of large
globular clusters are an efficient breeding ground for millisecond
pulsars. It is believed that exchange interactions in the cluster
core result in the capture of very old and slowly rotating neutron
stars into binary systems with a normal star which subsequently
evolves and spins up the neutron star to millisecond periods
through mass accretion (e.g. Kulkarni \& Anderson 1996). The
record-holder in terms of number of detected pulsars is 47
Tucanae, which now has 20 confirmed associated pulsars, all MSPs.
As mentioned in the introduction, eleven of these were discovered
in the period 1991 - 1995. The remainder has been found since 1998
using the central beam of the multibeam receiver (Camilo et al.
2000b). It is notable that, whereas seven of the 11 early
detections are isolated pulsars, all of the recent discoveries are
members of binary systems. This is largely a consequence of the
use in recent searches of algorithms with improved sensitivity to
pulsars in short-period binary systems and does not reflect any
intrinsic difference in properties.

Accurate positions as well as proper motions, period derivatives and
dispersion measures can be obtained from pulse timing measurements
extending over a few years (Freire et al. 2001a). All of the known
pulsars in 47 Tucanae lie within two arcmin of the cluster center,
reflecting the mass segregation resulting from energy equipartition in
this relaxed cluster. Measured proper motions are dominated by the
motion of the cluster as a whole, rather than by the motion of
individual pulsars within the cluster. The mean proper motion is close
to that determined from {\it Hipparcos} observations of stars in the
cluster (Odenkirchen et al. 1997) and now has a smaller uncertainty
than that measurement.

Freire et al. (2001b) noticed the interesting correlation between
period derivative and dispersion measure for pulsars in 47 Tucanae
shown in Fig. 6. Observed period derivatives are dominated by
acceleration of pulsars in the cluster gravitational field -- those on
the far side of the cluster are accelerated toward us and hence have a
negative period derivative. These pulsars also have a higher than
average dispersion measure, clearly indicating the presence of ionized
gas in the cluster. This is the first clear detection of gas
associated with a globular cluster. The total mass of gas is quite
small, only about 0.1 M$_\odot$, and much less than expected on the
basis of evolution of stars within the cluster. It is likely that the
pulsars themselves are blowing most of the stellar-wind gas from the
cluster.

\begin{figure}[tbhp]
\center {\includegraphics [scale=0.7]{manchester_fig6.eps}}
   \parbox[tb]{13cm}{
   \footnotesize

      Fig.\,6~~ Dispersion
measure versus the ratio of period derivative to period for
pulsars in the globular cluster 47 Tucanae. The strong correlation
between these quantities indicates the presence of ionized gas
within the cluster. The dotted and dashed lines indicate the
expected correlation for lines of sight passing through the
cluster core and 2 pc from it, respectively. (Freire et al.
2001b)}

    \end{figure}

The central beam of the Parkes multibeam receiver has also been
used to search for pulsars in other globular clusters. This search
has recently produced dividends, with a total of 11 pulsars, all
with millisecond periods and most members of binary systems, being
found in four globular clusters, none of which had known
associated pulsars prior to this search (D'Amico et al. 2001a,
2001b). For one of these clusters, NGC 6752, D'Amico et al. (2002)
find that two pulsars lying close to the cluster core have large
negative period derivatives, implying a strong gravitational
acceleration toward the core. These results suggest that the
mass-to-light ratio (in solar units) in the core region is greater
than ten, and that the central density is $>7 \times 10^5$
M$_\odot$\,pc$^{-3}$. These values are more extreme than those
estimated from optical measurements and suggest the presence of
one or more black holes at or near the centre of the cluster core.

\begin{figure}[tbhp]
\center {\includegraphics
[angle=270,scale=0.55]{manchester_fig7.ps}}
   \parbox[tb]{13cm}{
   \footnotesize
      Fig.\,7~~ Scintillation velocity for PSR J1141$-$6545 as a function of
true orbital anomaly -- slightly less than the full orbital period
is shown (Ord et al. 2002).}
    \end{figure}

\para{\large\bf{5}~~Some Recent Timing and Scintillation Results}

\vs\vs Two especially interesting recent results from Parkes
observations are described here. The first concerns timing
observations of PSR J0437$-$4715, the nearest and strongest
millisecond pulsar known. The strength of this pulsar -- its peak
flux density is often several Jy at 1400\,MHz -- allows
measurement of mean pulse profiles with very high signal-to-noise
ratio and hence highly accurate pulse timing. Observations made
over a two-year interval with a baseband recording system (van
Straten et al. 2001) have given an accurate value for the annual
parallax of the pulsar, $7.19 \pm 0.14$\,mas, implying a distance
of 140\,pc, and the first detection of an effect known as annual
orbital parallax -- the change in the projected pulsar orbit
diameter resulting from the annual orbital motion of the Earth.
This detection allowed an accurate determination of the pulsar
orbit inclination, 42\dg.75$ \pm $0\dg.09, and hence a prediction
of the size of the Shapiro delay -- the delay resulting from the
gravitational bending of the ray path as it passes near the binary
companion. The observations agree well with the prediction, with
an rms deviation from the predicted curve of only 35\,ns. These
results not only provide an independent test of general
relativity, but also are the most accurate pulsar timing
measurements ever made.



Another nice result obtained using the same baseband observing
system is the detection of an orbital variation in the timescale
of diffractive interstellar scintillation in the pulsar PSR
J1141$-$6545 by Ord et al. (2002). This pulsar, discovered in the
Parkes multibeam survey, is in an eccentric binary orbit with the
short period of 4.75 hours, allowing more than two complete orbits
to be observed in one transit of the Parkes telescope. These
showed a clear variation in the timescale for diffractive
scintillation as a function of orbital phase. Modelling of the
implied scintillation velocity (Fig. 7) gave measurements of the
pulsar space velocity (115\,km\,s$^{-1}$), the orbit inclination
(76\dg $\pm$ 2\dg.5) and the pulsar and companion masses, $1.29
\pm 0.02$\,M$_\odot$ and $1.01 \pm 0.02$\,M$_\odot$, respectively.
The derived space velocity is lower than that expected on the
basis of simulations (Tauris \& Sennels 2000), suggesting that the
birth kick was weaker than average.

\para{\large\bf{5}~~Conclusions}

\vs\vs The Parkes radio telescope has made a remarkable
contribution to pulsar astronomy, especially over the past few
years. Its huge successes in increasing the number of known
pulsars, both in the Galactic disk and in globular clusters, are
especially noteworthy. It has made significant contributions in
other areas as well, such as pulsar timing and scintillation
studies. The large database provided by the new discoveries opens
up many opportunities for further studies.

\vs\vn{\bf ACKNOWLEDGEMENTS}~~ I thank my colleagues for their
contributions to the collaborative work described here. The Parkes
radio telescope and the Compact Array are part of the Australia
Telescope which is funded by the Commonwealth of Australia for
operation as a National Facility managed by CSIRO.

\bc {\bf References} \ec

\vspace{-4mm} \no \fns

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%\end{CJK}
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