618 research outputs found
Spin frequency evolution and pulse profile variations of the recently re-activated radio magnetar XTE J1810-197
After spending almost a decade in a radio-quiet state, the Anomalous X-ray
Pulsar XTE J1810-197 turned back on in early December 2018. We have observed
this radio magnetar at 1.5 GHz with ~daily cadence since the first detection of
radio re-activation on 8 December 2018. In this paper, we report on the current
timing properties of XTE J1810-197 and find that the magnitude of the spin
frequency derivative has increased by a factor of 2.6 over our 48-day data set.
We compare our results with the spin-down evolution reported during its
previous active phase in the radio band. We also present total intensity pulse
profiles at five different observing frequencies between 1.5 and 8.4 GHz,
collected with the Lovell and the Effelsberg telescopes. The profile evolution
in our data set is less erratic than what was reported during the previous
active phase, and can be seen varying smoothly between observations. Profiles
observed immediately after the outburst show the presence of at least five
cycles of a very stable ~50-ms periodicity in the main pulse component that
lasts for at least tens of days. This remarkable structure is seen across the
full range of observing frequencies.Comment: 9 pages, 7 figures, updated with additional analysis of the 50-ms
oscillation, accepted for publication in MNRA
STEM analysis of deformation and B distribution in nanosecond laser ultra-doped Si B
We report on the structural properties of highly B-doped silicon (> 2 at. %)
realised by nanosecond laser doping. We investigate the crystalline quality,
deformation and B distribution profile of the doped layer by STEM analysis
followed by HAADF contrast studies and GPA, and compare the results to SIMS
analyses and Hall measurements. When increasing the active B concentration
above 4.3 at.%, the fully strained, perfectly crystalline, Si:B layer starts
showing dislocations and stacking faults. These only disappear around 8 at.%
when the Si:B layer is well accommodated to the substrate. When increasing B
incorporation, we increasingly observe small precipitates, filaments with
higher active B concentration and stacking faults. At the highest
concentrations studied, large precipitates form, related to the decrease of
active B concentration. The structural deformation, defect type and
concentration, and active B distribution are connected to the initial increase
and subsequent gradual loss of superconductivity
High-precision timing of 42 millisecond pulsars with the European Pulsar Timing Array
We report on the high-precision timing of 42 radio millisecond pulsars (MSPs) observed by the European Pulsar Timing Array (EPTA). This EPTA Data Release 1.0 extends up to mid-2014 and baselines range from 7–18 yr. It forms the basis for the stochastic gravitational-wave background, anisotropic background, and continuous-wave limits recently presented by the EPTA elsewhere. The Bayesian timing analysis performed with temponest yields the detection of several new parameters: seven parallaxes, nine proper motions and, in the case of six binary pulsars, an apparent change of the semimajor axis. We find the NE2001 Galactic electron density model to be a better match to our parallax distances (after correction from the Lutz–Kelker bias) than the M2 and M3 models by Schnitzeler. However, we measure an average uncertainty of 80 per cent (fractional) for NE2001, three times larger than what is typically assumed in the literature. We revisit the transverse velocity distribution for a set of 19 isolated and 57 binary MSPs and find no statistical difference between these two populations. We detect Shapiro delay in the timing residuals of PSRs J1600−3053 and J1918−0642, implying pulsar and companion masses m_p=1.22^(+0.5)_(−0.35) M_⊙, m_c=0.21^(+0.06)_(−0.04) M_⊙ and m_p=1.25^(+0.6)_(−0.4) M_⊙, m_c=0.23^(+0.07)_(−0.05) M_⊙, respectively. Finally, we use the measurement of the orbital period derivative to set a stringent constraint on the distance to PSRs J1012+5307 and J1909−3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600−3053 and J1909−3744
Precision timing of PSR J1012+5307 and strong-field GR tests
We report on the high precision timing analysis of the pulsar-white dwarf
binary PSR J1012+5307. Using 15 years of multi-telescope data from the European
Pulsar Timing Array (EPTA) network, a significant measurement of the variation
of the orbital period is obtained. Using this ideal strong-field gravity
laboratory we derive theory independent limits for both the dipole radiation
and the variation of the gravitational constant.Comment: 3 pages, Proceedings of the 12th Marcel Grossmann Meeting on General
Relativity (MG 12
Evidence for an intermediate-mass black hole in the globular cluster NGC 6624
PSR B182030A is located in the globular cluster NGC 6624 and is the
closest known pulsar to the centre of any globular cluster. We present more
than 25 years of high-precision timing observations of this millisecond pulsar
and obtain four rotational frequency time derivative measurements. Modelling
these higher-order derivatives as being due to orbital motion, we find
solutions which indicate that the pulsar is in either a low-eccentricity
() smaller orbit with a low mass companion (such as
a main sequence star, white dwarf, neutron star, or stellar mass black hole) or
a high-eccentricity () larger orbit with a massive companion. The
cluster mass properties and the observed properties of 4U 182030 and the
other pulsars in the cluster argue against the low-eccentricity possibility.
The high-eccentricity solution reveals that the pulsar is most likely orbiting
around an intermediate-mass black hole (IMBH) of mass ~M
located at the cluster centre. A gravitational model for the globular cluster,
which includes such a central black hole (BH), predicts an acceleration that is
commensurate with that measured for the pulsar. It further predicts that the
model-dependent minimum mass of the IMBH is ~M. Accounting
for the associated contribution to the observed period derivative indicates
that the -ray efficiency of the pulsar should be between 0.08 and 0.2.
Our results suggest that other globular clusters may also contain central black
holes and they may be revealed by the study of new pulsars found sufficiently
close to their centres.
Note that we found an erratum in Section 5 and thus, the
60,000~M mass mentioned above has to be replaced by the correct
model-dependent mass limit of 20,000~M. See the erratum appended.Comment: 15 pages, 10 figures, Accepted by MNRAS on 23 February 2017. Erratum
was accepted by MNRAS on 17 May 201
Amélioration de la productivité des brebis berrichonnes du cher par croisement. III. – Performances de reproduction des trois premières genérations de brebis croisées entre les races berrichonne du cher et romanov
International audienc
- …