760 research outputs found
On canonical quantization of the gauged WZW model with permutation branes
In this paper we perform canonical quantization of the product of the gauged
WZW models on a strip with boundary conditions specified by permutation branes.
We show that the phase space of the -fold product of the gauged WZW model
on a strip with boundary conditions given by permutation branes is
symplectomorphic to the phase space of the double Chern-Simons theory on a
sphere with holes times the time-line with and gauge fields both
coupled to two Wilson lines. For the special case of the topological coset
we arrive at the conclusion that the phase space of the -fold product
of the topological coset on a strip with boundary conditions given by
permutation branes is symplectomorphic to the phase space of Chern-Simons
theory on a Riemann surface of the genus times the time-line with four
Wilson lines.Comment: 18 page
One year of monitoring the Vela pulsar using a Phased Array Feed
We have observed the Vela pulsar for one year using a Phased Array Feed (PAF)
receiver on the 12-metre antenna of the Parkes Test-Bed Facility. These
observations have allowed us to investigate the stability of the PAF
beam-weights over time, to demonstrate that pulsars can be timed over long
periods using PAF technology and to detect and study the most recent glitch
event that occurred on 12 December 2016. The beam-weights are shown to be
stable to 1% on time scales on the order of three weeks. We discuss the
implications of this for monitoring pulsars using PAFs on single dish
telescopes.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PAS
Canonical quantization of the WZW model with defects and Chern-Simons theory
We perform canonical quantization of the WZW model with defects and
permutation branes. We establish symplectomorphism between phase space of WZW
model with defects on cylinder and phase space of Chern-Simons theory on
annulus times with Wilson lines, and between phase space of WZW model
with defects on strip and Chern-Simons theory on disc times with
Wilson lines. We obtained also symplectomorphism between phase space of the
-fold product of the WZW model with boundary conditions specified by
permutation branes, and phase space of Chern-Simons theory on sphere with
holes and two Wilson lines.Comment: 26 pages, minor corrections don
Empirical study of communication structures and barriers in geographically distributed teams
Conway's law asserts that communication structures of organisations constrain the design of the products they develop. This law is more explicitly observable in geographically distributed contexts because distributed teams are required to share information across different time zones and barriers. The diverse business processes and functions adopted by individual teams in geographically distributed settings create challenges for effective communication. Since the publication of Conway's law, a significant body of research has emerged in its relation to the communication structures. When it comes to software projects, the explicit observation about Conway's law has produced mixed results. The research reported in this study explores the communication structures and corresponding challenges faced by teams within a large geographically distributed software development organisation. The data was collected from relevant documents, a questionnaire and interviews with relevant stakeholders. The findings suggest that Conway's law is observable within the communication structures of globally distributed software development teams. The authors have identified the barriers and challenges of effective communications in this setting and have investigated the benefits of utilising an integrated system to overcome these challenges
Spin-down evolution and radio disappearance of the magnetar PSR J16224950
We report on 2.4 yr of radio timing measurements of the magnetar PSR
J16224950 using the Parkes telescope, between 2011 November and 2014 March.
During this period the torque on the neutron star (inferred from the rotational
frequency derivative) varied greatly, though much less erratically than in the
2 yr following its discovery in 2009. During the last year of our measurements
the frequency derivative decreased in magnitude monotonically by 20\%, to a
value of s, a factor of 8 smaller than when
discovered. The flux density continued to vary greatly during our monitoring
through 2014 March, reaching a relatively steady low level after late 2012. The
pulse profile varied secularly on a similar timescale as the flux density and
torque. A relatively rapid transition in all three properties is evident in
early 2013. After PSR J16224950 was detected in all of our 87 observations
up to 2014 March, we did not detect the magnetar in our resumed monitoring
starting in 2015 January and have not detected it in any of the 30 observations
done through 2016 September.Comment: 8 pages, 5 figures, submitted to Ap
Peculiar Spin Frequency and Radio Profile Evolution of PSR J11196127 Following Magnetar-like X-ray Bursts
We present the spin frequency and profile evolution of the radio pulsar
J11196127 following magnetar-like X-ray bursts from the system in 2016 July.
Using data from the Parkes radio telescope, we observe a smooth and fast
spin-down process subsequent to the X-ray bursts resulting in a net change in
the pulsar rotational frequency of \,Hz.
During the transition, a net spin-down rate increase of
\,Hz\,s is observed, followed by a
return of to its original value. In addition, the radio pulsations
disappeared after the X-ray bursts and reappeared about two weeks later with
the flux density at 1.4\,GHz increased by a factor of five. The flux density
then decreased and undershot the normal flux density followed by a slow
recovery back to normal. The pulsar's integrated profile underwent dramatic and
short-term changes in total intensity, polarization and position angle. Despite
the complex evolution, we observe correlations between the spin-down rate,
pulse profile shape and radio flux density. Strong single pulses have been
detected after the X-ray bursts with their energy distributions evolving with
time. The peculiar but smooth spin frequency evolution of PSR~J11196127
accompanied by systematic pulse profile and flux density changes are most
likely to be a result of either reconfiguration of the surface magnetic fields
or particle winds triggered by the X-ray bursts. The recovery of spin-down rate
and pulse profile to normal provides us the best case to study the connection
between high magnetic-field pulsars and magnetars.Comment: Accepted for publication in MNRAS on 2018 July 2
A Shapiro delay detection in the binary system hosting the millisecond pulsar PSR J1910-5959A
PSR J1910-5959A is a binary pulsar with a helium white dwarf companion
located about 6 arcmin from the center of the globular cluster NGC6752. Based
on 12 years of observations at the Parkes radio telescope, the relativistic
Shapiro delay has been detected in this system. We obtain a companion mass Mc =
0.180+/-0.018Msun (1sigma) implying that the pulsar mass lies in the range
1.1Msun <= Mp <= 1.5Msun. We compare our results with previous optical
determinations of the companion mass, and examine prospects for using this new
measurement for calibrating the mass-radius relation for helium white dwarfs
and for investigating their evolution in a pulsar binary system. Finally we
examine the set of binary systems hosting a millisecond pulsar and a low mass
helium white dwarf for which the mass of both stars has been measured. We
confirm that the correlation between the companion mass and the orbital period
predicted by Tauris & Savonije reproduces the observed values but find that the
predicted Mp - Pb correlation over-estimates the neutron star mass by about
0.5Msun in the orbital period range covered by the observations. Moreover, a
few systems do not obey the observed Mp - Pb correlation. We discuss these
results in the framework of the mechanisms that inhibit the accretion of matter
by a neutron star during its evolution in a low-mass X-ray binary.Comment: 4 figures, 2 tables, accepted for publication in the Astrophysical
Journa
Radio disappearance of the magnetar XTE J1810-197 and continued X-ray timing
We report on timing, flux density, and polarimetric observations of the
transient magnetar and 5.54 s radio pulsar XTE J1810-197 using the GBT, Nancay,
and Parkes radio telescopes beginning in early 2006, until its sudden
disappearance as a radio source in late 2008. Repeated observations through
2016 have not detected radio pulsations again. The torque on the neutron star,
as inferred from its rotation frequency derivative f-dot, decreased in an
unsteady manner by a factor of 3 in the first year of radio monitoring. In
contrast, during its final year as a detectable radio source, the torque
decreased steadily by only 9%. The period-averaged flux density, after
decreasing by a factor of 20 during the first 10 months of radio monitoring,
remained steady in the next 22 months, at an average of 0.7+/-0.3 mJy at 1.4
GHz, while still showing day-to-day fluctuations by factors of a few. There is
evidence that during this last phase of radio activity the magnetar had a steep
radio spectrum, in contrast to earlier behavior. There was no secular decrease
that presaged its radio demise. During this time the pulse profile continued to
display large variations, and polarimetry indicates that the magnetic geometry
remained consistent with that of earlier times. We supplement these results
with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the
first 4 years, XTE J1810-197 experienced non-monotonic excursions in f-dot by
at least a factor of 8. But since 2007, its f-dot has remained relatively
stable near its minimum observed value. The only apparent event in the X-ray
record that is possibly contemporaneous with the radio shut-down is a decrease
of ~20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However,
the permanence of the high-amplitude, thermal X-ray pulse, even after the radio
demise, implies continuing magnetar activity.Comment: ApJ, accepted, 12 pages, 9 figure
Long-term observations of the pulsars in 47 Tucanae. I. A study of four elusive binary systems
For the past couple of decades, the Parkes radio telescope has been regularly
observing the millisecond pulsars in 47 Tucanae (47 Tuc). This long-term timing
program was designed to address a wide range of scientific issues related to
these pulsars and the globular cluster where they are located. In this paper,
the first of a series, we address one of these objectives: the characterization
of four previously known binary pulsars for which no precise orbital parameters
were known, namely 47 Tuc P, V, W and X (pulsars 47 Tuc R and Y are discussed
elsewhere). We determined the previously unknown orbital parameters of 47 Tuc V
and X and greatly improved those of 47 Tuc P and W. For pulsars W and X we
obtained, for the first time, full coherent timing solutions across the whole
data span, which allowed a much more detailed characterization of these
systems. 47 Tuc W, a well-known tight eclipsing binary pulsar, exhibits a large
orbital period variability, as expected for a system of its class. 47 Tuc X
turns out to be in a wide, extremely circular, 10.9-day long binary orbit and
its position is ~3.8 arcmin away from the cluster center, more than three times
the distance of any other pulsar in 47 Tuc. These characteristics make 47 Tuc X
a very different object with respect to the other pulsars of the cluster.Comment: Accepted for publication by MNRAS, 18 pages, 11 figure
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