11 research outputs found
The bright optical companion to the eclipsing millisecond pulsar in NGC 6397
We report the possible optical identification of the companion to the
eclipsing millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. A
bright variable star with an anomalous red colour and optical variability which
nicely correlates to the orbital period of the pulsar has been found close to
the pulsar position. If confirmed, the optical light curve, reminiscent of
tidal distorsions similar to those observed in detached and contact binaries,
support the idea that this is the first case of a Roche lobe filling companion
to a millisecond pulsar.Comment: 9 pages, 4 embedded figures, submitted to ApJ Letter
Recycling neutron stars to ultra short periods: a statistical analysis of their evolution in the mu-P plane
We investigate the statistical evolution of magnetic neutron stars, recycled
in binary systems, simulating synthetic populations. To bracket uncertainties,
we consider a soft (FP) and a stiff (PS) equation of state (EoS) for nuclear
matter and explore the hypothesis that the magnetic field is confined in the
stellar crust. We follow the magneto-rotational evolution within a simple
recycling scenario, including the possibility of magnetospheric propeller.
We find the presence of a tail in the period distribution of the synthetic
populations at periods shorter than 1.558 ms, the minimum detected so far. For
the soft EoS the recycling gives rise to a spin distribution which is
increasing monotonically toward short periods and a clear ``barrier'' forms at
the minimum period for the onset of mass shedding. For the stiff EoS the
distribution is flatter displaying a broad maximum about 2-4 ms.
The estimated fraction of neutron stars spinning close to their shedding
limit over the millisecond pulsar population is found to be significant.
Crustal magnetic field decay models predict the existence of massive (M>1.4
M_sun) rapidly spinning neutron stars with very low magnetic moment.Comment: 34 pages, 2 tables, 9 figures, Latex. Accepted (5 Jul 99) for
publication in the Astrophysical Journal Supplement
Neutron stars with submillisecond periods: a population of high mass objects?
Fast spinning neutron stars, recycled in low mass binaries, may have accreted
a substantial amount of mass. The available relativistic measurements of
neutron star masses, all clustering around 1.4 M_sun, however refer mostly to
slowly rotating neutron stars which accreted a tiny amount of mass during
evolution in a massive binary system. We develop a semi-analytical model for
studying the evolution of the spin period P of a magnetic neutron star as a
function of the baryonic mass load M_{ac}; evolution is followed down to
submillisecond periods and the magnetic field is allowed to decay significantly
before the end of recycling. We use different equations of state and include
rotational deformation effects, the presence of a strong gravitational field
and of a magnetosphere. For the non-magnetic case, comparison with numerical
relativistic codes shows the accuracy of our description. The minimum accreted
mass requested to spin-up a magnetized 1.35M_sun-neutron star at a few
millisecond is 0.05 M_sun, while this value doubles for an unmagnetized neutron
star. Below 1 millisecond the request is of at least 0.25 M_sun. There may
exist a yet undetected population of massive submillisecond neutron stars. The
discovery of a submillisecond neutron star would imply a lower limit for its
mass of about 1.7M_sun.Comment: To appear in the Astrophysical Journal, June 199
The Helium White Dwarf orbiting the Millisecond Pulsar in the halo of the Globular Cluster NGC 6752
We have used deep high-resolution multiband images taken at the ESO Very
Large Telescope to identify the optical binary companion to the millisecond
pulsar (PSR J1911-5958A) located in the halo of the Galactic Globular Cluster
NGC6752. The object turns out to be a blue star whose position in the Color
Magnitude Diagram is consistent with the cooling sequence of a low mass
(M~0.17-0.20Mo), low metallicity Helium white dwarf (He-WD) at the cluster
distance. This is the second He-WD which has been found to orbit a millisecond
pulsar in GGCs. Curiously both objects have been found to lie on the same mass
He-WD cooling sequence. The anomalous position of PSR J1911-5958A with respect
to the globular cluster center (~6') suggested that this system has recently
(<1 Gyr) been ejected from the cluster core as the result of a strong dynamical
interaction. The data presented here allows to constrain the cooling age of the
companion within a fairly narrow range (~1.2-2.8 Gyr), therefore suggesting
that such dynamical encounter must have acted on an already recycled
millisecond pulsar.Comment: 12 pages, 3 figures. ApJ Letters, (in press
Population synthesis of millisecond and submillisecond pulsars
Known millisecond pulsars have periods longer than 1.558 ms. Recycled in
binary systems, neutron stars can attain very short spin periods. In this paper
we investigate the expected properties of the millisecond pulsar distribution
by simulating synthetic populations under different assumptions for the neutron
star equation of state and decay of the magnetic field. We find evidence that a
tail in the distribution of millisecond pulsars may exist at periods shorter
than those observed.Comment: 16 pages, LaTex + 2 .eps figures To Appear in The Astrophysical
Journal Letter
Multi-wavelength observations of the radio magnetar PSR J1622-4950 and discovery of its possibly associated supernova remnant
We present multi-wavelength observations of the radio magnetar PSR J1622-4950 and its environment. Observations of PSR J1622-4950 with Chandra (in 2007 and 2009) and XMM (in 2011) show that the X-ray flux of PSR J1622-4950 has decreased by a factor of ~50 over 3.7 years, decaying exponentially with a characteristic time of Ï = 360 ± 11 days. This behavior identifies PSR J1622-4950 as a possible addition to the small class of transient magnetars. The X-ray decay likely indicates that PSR J1622-4950 is recovering from an X-ray outburst that occurred earlier in 2007, before the 2007 Chandra observations. Observations with the Australia Telescope Compact Array show strong radio variability, including a possible radio flaring event at least one and a half years after the 2007 X-ray outburst that may be a direct result of this X-ray event. Radio observations with the Molonglo Observatory Synthesis Telescope reveal that PSR J1622-4950 is 8' southeast of a diffuse radio arc, G333.9+0.0, which appears non-thermal in nature and which could possibly be a previously undiscovered supernova remnant (SNR). If G333.9+0.0 is an SNR then the estimates of its size and age, combined with the close proximity and reasonable implied velocity of PSR J1622-4950, suggest that these two objects could be physically associated
Secular and orbital changes in emission from J0737-3039 system
The double-pulsar J0737-3039 is not only the most promising system for testing general relativity, but appears a unique laboratory for investigating the so far unaccessible pulsar magnetosphere and the mechanism for radio emission. In fact, the very high orbital inclination gives the possibility of using the radio beams from pulsar A as a probe for investigating the region close to the surface of pulsar B, while relativistic effects modify the system geometry in a timescale suitable for comparing predictions of various models with observation. We present the status of the multi-wavelength observations performed in the 3 years since the discovery and discuss short and long term perspectives for the study of the magnetosphere of pulsar B