We present a new timing solution for PSR B1534+12, based on
coherently-dedispersed observations at Jodrell Bank and, recently, Arecibo. The
new data have resulted in improved measurements of the ...post-Keplerian timing
parameters, including the orbital period derivative. At present, the
poorly-known distance to the pulsar limits the precision of the measurement of
the intrinsic orbital period derivative, and hence the strength of the test of
general relativity that results from this binary system. By assuming that
general relativity is the correct theory of gravity, we may invert the test and
find an improved value of the pulsar distance.
Astrophys.J. 617 (2004) L139-L142 We report on calculations of the pulsar birthrate based on the results of the
Parkes multibeam survey. From the observed sample of more than 800 pulsars, we
compute ...the pulsar current, accounting as accurately as possible for all known
selection effects. The main goal of this work is to understand the pulsar
birthrate as a function of the surface dipole magnetic field strengths. We show
that pulsars with magnetic fields greater than 10**12.5 G account for about
half of the total birthrate.
Mon.Not.Roy.Astron.Soc. 359 (2005) 1524-1530 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.
ECONF C041213:0038,2004 This first ever double pulsar system consists of two pulsars orbiting the
common center of mass in a slightly eccentric orbit of only 2.4-hr duration.
The pair of pulsars with ...pulse periods of 22 ms and 2.8 sec, respectively,
confirms the long-proposed recycling theory for millisecond pulsars and
provides an exciting opportunity to study the works of pulsar magnetospheres by
a very fortunate geometrical alignment of the orbit relative to our
line-of-sight. In particular, this binary system represents a truly unique
laboratory for relativistic gravitational physics. This contribution serves as
an update on the currently obtained results and their consequences for the test
of general relativity in the strong-field regime. A complete and more
up-to-date report of the timing results will be presented elsewhere shortly.
Astrophys.J.624:L113-L116,2005 Analysis of 20 months of observations at the Parkes radio telescope shows
secular changes in the pulsed emission from J0737-3039B, the 2.77 s pulsar of
the ...double-pulsar system. Pulse profiles are becoming single-peaked in both
bright phases of the orbital modulation although there is no clear variation in
overall pulse width. The shape of the orbital modulation is also varying
systematically, with both bright phases shrinking in longitude by ~ 7 deg/yr.
However, the combined span of the two bright phases is relatively constant and
together they are shifting to higher longitudes at a rate of ~ 3 deg/yr. We
discuss the possible contributions of geodetic precession and periastron
advance to the observed variations.
Astrophys.J.621:L49-L52,2005 General relativity predicts that the spin axes of the pulsars in the
double-pulsar system (PSR J0737-3039A/B) will precess rapidly, in general
leading to a change in the ...observed pulse profiles. We have observed this
system over a one-year interval using the Parkes 64-m radio telescope at three
frequencies: 680, 1390 and 3030 MHz. These data, combined with the short survey
observation made two years earlier, show no evidence for significant changes in
the pulse profile of PSR J0737-3039A, the 22-ms pulsar. The limit on variations
of the profile 10% width is about 0.5 deg per year. These results imply an
angle delta between the pulsar spin axis and the orbit normal of <~ 60 deg,
consistent with recent evolutionary studies of the system. Although a wide
range of system parameters remain consistent with the data, the model proposed
by Jenet & Ransom (2004) can be ruled out. A non-zero ellipticity for the
radiation beam gives slightly but not significantly improved fits to the data,
so that a circular beam describes the data equally well within the
uncertainties.
Giant pulses (GPs), occasional individual pulses with an intensity 100 times the average intensity, have been detected in four pulsars todate. Their origin is not well understood, but studies suggest ...a connection between the strength of magnetic field at the light cylinder B_lc and the existence of GPs. Here, we report on detection of significant Large Amplitude Pulses (LAPs) in two more pulsars with high values of B_lc, PSRs J0218+4232 and B1957+20, observed using Giant Meterwave Radio Telescope (GMRT).
Astrophys.J. 618 (2004) L119-L122 We report the discovery during the Parkes Multibeam Pulsar Survey of PSR
J1756-2251, a 28.5 ms pulsar in a relativistic binary system. Subsequent timing
observations ...showed the pulsar to have an orbital period of 7.67 hrs and an
eccentricity of 0.18. They also revealed a significant advance of periastron,
2.585+/-0.002 deg./yr. Assuming this is entirely due to general relativity
implies a total system mass (pulsar plus companion) of 2.574+/-0.003 solar
mass. This mass and the significant orbital eccentricity suggest that this is a
double neutron star system. Measurement of the gravitational redshift, gamma,
and an evaluation of the Shapiro delay shape, s, indicate a low companion mass
of <1.25 solar mass. The expected coalescence time due to emission of
gravitational waves is only ~1.7 Gyr substantially less than a Hubble time. We
note an apparent correlation between spin period and eccentricity for normally
evolving double neutron star systems.
We have continued our long term study of the double-neutron-star binary pulsar PSR B1534+12, using new instrumentation to make very high precision measurements at the Arecibo Observatory. We have ...significantly improved our solution for the astrometric, spin, and orbital parameters of the system, as well as for the five "post-Keplerian" orbital parameters that can be used to test gravitation theory. The results are in good agreement with the predictions of general relativity. With the assumption that general relativity is the correct theory of gravity in the classical regime, our measurements allow us to determine the masses of the pulsar and its companion neutron star with high accuracy: 1.3332 \pm 0.0010 Msun and 1.3452 \pm 0.0010Msun, respectively. The small but significant mass difference is difficult to understand in most evolutionary models, as the pulsar is thought to have been born first from a more massive progenitor star and then undergone a period of mass accretion before the formation of the second neutron star. PSR B1534+12 has also become a valuable probe of the local interstellar medium. We have now measured the pulsar distance to be 1.02 \pm 0.05 kpc, giving a mean electron density along this line of sight of 0.011/cc. We continue to measure a gradient in the dispersion measure, though the rate of change is now slower than in the first years after the pulsar's discovery.
Astrophys.J.616:L131-L134,2004 We have investigated the eclipse of the 23-ms pulsar J0737-3039A by its 2.8-s
companion PSR J0737-3039B in the recently discovered double pulsar system using
data taken ...with the Green Bank Telescope at 820 MHz. We find that the pulsed
flux density at eclipse is strongly modulated with half the periodicity of the
2.8-s pulsar. The eclipse occurs earlier and is deeper at those rotational
phases of B when its magnetic axis is aligned with the line of sight than at
phases when its magnetic axis is at right angles to the line of sight. This is
consistent with the eclipse of A being due to synchrotron absorption by the
shock-heated plasma surrounding B, the asymmetry arising from the higher plasma
densities expected in the B magnetosphere's polar cusps.
