85 research outputs found
Progressive cavitating leukoencephalopathy: Case report of a rare childhood onset neurodegenerative disease
The leukoencephalopathies with cystic changes form a distinct subtype of childhood onset neurodegenerativedisorders. This group has heterogeneous etiological differentials that primarily include mitochondrial disorders, someleukodystrophies and central nervous system infections. We report this case of a 17-month old girl who presented withseizures, episodic encephalopathy, elevated blood lactate level and lactate peak on magnetic resonance spectroscopy,a typical imaging picture noted on cranial magnetic resonance imaging and absence of deletions or duplications ofmitochondrial deoxyribonucleic acid. Progressive cavitating leukoencephalopathy (PCL) is a recently described entitywith only a few cases reported so far. We report the first case of PCL from India. Accurate diagnosis can be made, notonly, by the presence of typical clinicoradiological findings of PCL, but also by the awareness of, and, ruling out of,the various other differential diagnoses that are discussed in detail below
Relativistic spin precession in the binary PSR J11416545
PSR J11416545 is a precessing binary pulsar that has the rare potential to
reveal the two-dimensional structure of a non-recycled pulsar emission cone. It
has undergone of relativistic spin precession in the
years since its discovery. In this paper, we present a detailed Bayesian
analysis of the precessional evolution of the width of the total intensity
profile, to understand the changes to the line-of-sight impact angle ()
of the pulsar using four different physically motivated prior distribution
models. Although we cannot statistically differentiate between the models with
confidence, the temporal evolution of the linear and circular polarisations
strongly argue that our line-of-sight crossed the magnetic pole around MJD
54000 and that only two models remain viable. For both these models, it appears
likely that the pulsar will precess out of our line-of-sight in the next
years, assuming a simple beam geometry. Marginalising over suggests
that the pulsar is a near-orthogonal rotator and provides the first
polarization-independent estimate of the scale factor () that
relates the pulsar beam opening angle () to its rotational period ()
as : we find it to be at 1.4
GHz with 99\% confidence. If all pulsars emit from opposite poles of a dipolar
magnetic field with comparable brightness, we might expect to see evidence of
an interpulse arising in PSR J11416545, unless the emission is patchy.Comment: Accepted for publication in Astrophysical Journal Letter
Modelling annual and orbital variations in the scintillation of the relativistic binary PSR J11416545
We have observed the relativistic binary pulsar PSR J11416545 over a
period of 6 years using the Parkes 64 m radio telescope, with a focus on
modelling the diffractive intensity scintillations to improve the accuracy of
the astrometric timing model. The long-term scintillation, which shows orbital
and annual variations, allows us to measure parameters that are difficult to
measure with pulsar timing alone. These include: the orbital inclination ;
the longitude of the ascending node ; and the pulsar system transverse
velocity. We use the annual variations to resolve the previous ambiguity in the
sense of the inclination angle. Using the correct sense, and a prior
probability distribution given by a constraint from pulsar timing
(), we find and we estimate the
pulsar distance to be kpc. This then gives us an estimate of
this pulsar's proper motion of mas
yr in right ascension and mas yr in
declination. Finally, we obtain measurements of the spatial structure of the
interstellar electron density fluctuations, including: the spatial scale and
anisotropy of the diffraction pattern; the distribution of scattering material
along the line of sight; and spatial variation in the strength of turbulence
from epoch to epoch. We find that the scattering is dominated by a thin screen
at a distance of , with an anisotropy axial ratio .Comment: 17 pages, 8 figures, 2 tables. Accepted for publication in MNRA
Lense-Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system
Radio pulsars in short-period eccentric binary orbits can be used to study
both gravitational dynamics and binary evolution. The binary system containing
PSR J11416545 includes a massive white dwarf (WD) companion that formed
before the gravitationally bound young radio pulsar. We observe a temporal
evolution of the orbital inclination of this pulsar that we infer is caused by
a combination of a Newtonian quadrupole moment and Lense-Thirring precession of
the orbit resulting from rapid rotation of the WD. Lense-Thirring precession,
an effect of relativistic frame-dragging, is a prediction of general
relativity. This detection is consistent with the evolutionary scenario in
which the WD accreted matter from the pulsar progenitor, spinning up the WD to
a period seconds.Comment: Accepted for publication in Scienc
The MeerTime Pulsar Timing Array -- A Census of Emission Properties and Timing Potential
MeerTime is a five-year Large Survey Project to time pulsars with MeerKAT,
the 64-dish South African precursor to the Square Kilometre Array. The science
goals for the programme include timing millisecond pulsars (MSPs) to high
precision (< 1 s) to study the Galactic MSP population and to contribute
to global efforts to detect nanohertz gravitational waves with the
International Pulsar Timing Array (IPTA). In order to plan for the remainder of
the programme and to use the allocated time most efficiently, we have conducted
an initial census with the MeerKAT "L-band" receiver of 189 MSPs visible to
MeerKAT and here present their dispersion measures, polarization profiles,
polarization fractions, rotation measures, flux density measurements, spectral
indices, and timing potential. As all of these observations are taken with the
same instrument (which uses coherent dedispersion, interferometric polarization
calibration techniques, and a uniform flux scale), they present an excellent
resource for population studies. We used wideband pulse portraits as timing
standards for each MSP and demonstrated that the MeerTime Pulsar Timing Array
(MPTA) can already contribute significantly to the IPTA as it currently
achieves better than 1 s timing accuracy on 89 MSPs (observed with
fortnightly cadence). By the conclusion of the initial five-year MeerTime
programme in July 2024, the MPTA will be extremely significant in global
efforts to detect the gravitational wave background with a contribution to the
detection statistic comparable to other long-standing timing programmes.Comment: Accepted to PASA. 27 figures. Data to be made available under the DOI
10.5281/zenodo.5347875 at the time of publicatio
The SUrvey for Pulsars and Extragalactic Radio Bursts - III. Polarization properties of FRBs 160102 and 151230
We report on the polarization properties of two fast radio bursts (FRBs): 151230 and 160102 discovered in the SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) at the Parkes Radio Telescope. FRB 151230 is observed to be 6 ± 11 per cent circularly polarized and 35 ± 13 per cent linearly polarized with a rotation measure (RM) consistent with zero. Conversely, FRB160102 is observed to have a circular polarization fraction of 30±11 per cent, linear polarization fraction of 84 ± 15 per cent for RM = -221(6) radm-2, and the highest measured dispersion measure (2596.1±0.3 pc cm-3) for an FRB to date.We examine possible progenitor models for FRB 160102 in extragalactic, non-cosmological and cosmological scenarios. After accounting for the Galactic foreground contribution, we estimate the intrinsic RM to be -256(9) rad m-2in the low-redshift case and ~-2.4Ă102rad m-2in the highredshift case. We assess the relative likeliness of these scenarios and how each can be tested. We also place constraints on the scattering measure and study the impact of scattering on the signal's polarization position angle
The MeerKAT telescope as a pulsar facility: System verification and early science results from MeerTime
We describe system verification tests and early science results from the pulsar processor (PTUSE) developed for the newly commissioned 64-dish SARAO MeerKAT radio telescope in South Africa. MeerKAT is a high-gain ( ) low-system temperature ( ) radio array that currently operates at 580â1 670 MHz and can produce tied-array beams suitable for pulsar observations. This paper presents results from the MeerTime Large Survey Project and commissioning tests with PTUSE. Highlights include observations of the double pulsar , pulse profiles from 34 millisecond pulsars (MSPs) from a single 2.5-h observation of the Globular cluster Terzan 5, the rotation measure of Ter5O, a 420-sigma giant pulse from the Large Magellanic Cloud pulsar PSR , and nulling identified in the slow pulsar PSR J0633â2015. One of the key design specifications for MeerKAT was absolute timing errors of less than 5 ns using their novel precise time system. Our timing of two bright MSPs confirm that MeerKAT delivers exceptional timing. PSR exhibits a jitter limit of whilst timing of PSR over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. Our results confirm that the MeerKAT is an exceptional pulsar telescope. The array can be split into four separate sub-arrays to time over 1 000 pulsars per day and the future deployment of S-band (1 750â3 500 MHz) receivers will further enhance its capabilities
The SUrvey for Pulsars and Extragalactic Radio Bursts â II. New FRB discoveries and their follow-up
We report the discovery of four Fast Radio Bursts (FRBs) in the ongoing SUrvey for Pulsars and Extragalactic Radio Bursts at the Parkes Radio Telescope: FRBs 150610, 151206, 151230 and 160102. Our real-time discoveries have enabled us to conduct extensive, rapid multimessenger follow-up at 12 major facilities sensitive to radio, optical, X-ray, gamma-ray photons and neutrinos on time-scales ranging from an hour to a few months post-burst. No counterparts to the FRBs were found and we provide upper limits on afterglow luminosities. None of the FRBs were seen to repeat. Formal fits to all FRBs show hints of scattering while their intrinsic widths are unresolved in time. FRB 151206 is at low Galactic latitude, FRB 151230 shows a sharp spectral cut-off, and FRB 160102 has the highest dispersion measure (DM = 2596.1 ± 0.3âpcâcmâ3) detected to date. Three of the FRBs have high dispersion measures (DM > 1500âpcâcmâ3), favouring a scenario where the DM is dominated by contributions from the intergalactic medium. The slope of the Parkes FRB source counts distribution with fluences >2âJyâms is α=â2.2+0.6â1.2 and still consistent with a Euclidean distribution (α = â3/2). We also find that the all-sky rate is 1.7+1.5â0.9Ă103 FRBs/(4Ï sr)/day above âŒ2Jyms and there is currently no strong evidence for a latitude-dependent FRB sky rate
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