313 research outputs found
Parameter-space metric of semicoherent searches for continuous gravitational waves
Continuous gravitational-wave (CW) signals such as emitted by spinning
neutron stars are an important target class for current detectors. However, the
enormous computational demand prohibits fully coherent broadband all-sky
searches for prior unknown CW sources over wide ranges of parameter space and
for yearlong observation times. More efficient hierarchical "semicoherent"
search strategies divide the data into segments much shorter than one year,
which are analyzed coherently; then detection statistics from different
segments are combined incoherently. To optimally perform the incoherent
combination, understanding of the underlying parameter-space structure is
requisite. This problem is addressed here by using new coordinates on the
parameter space, which yield the first analytical parameter-space metric for
the incoherent combination step. This semicoherent metric applies to broadband
all-sky surveys (also embedding directed searches at fixed sky position) for
isolated CW sources. Furthermore, the additional metric resolution attained
through the combination of segments is studied. From the search parameters (sky
position, frequency, and frequency derivatives), solely the metric resolution
in the frequency derivatives is found to significantly increase with the number
of segments.Comment: 14 pages, 5 figures (matching Phys.Rev.D version
Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853
The 1.69 ms spin period of PSR J1227-4853 was recently discovered in radio
observations of the low-mass X-ray binary XSS J12270-4859 following the
announcement of a possible transition to a rotation-powered millisecond pulsar
state, inferred from decreases in optical, X-ray, and gamma-ray flux from the
source. We report the detection of significant (5) gamma-ray pulsations
after the transition, at the known spin period, using ~1 year of data from the
Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The
gamma-ray light curve of PSR J1227-4853 can be fit by one broad peak, which
occurs at nearly the same phase as the main peak in the 1.4 GHz radio profile.
The partial alignment of light-curve peaks in different wavebands suggests that
at least some of the radio emission may originate at high altitude in the
pulsar magnetosphere, in extended regions co-located with the gamma-ray
emission site. We folded the LAT data at the orbital period, both pre- and
post-transition, but find no evidence for significant modulation of the
gamma-ray flux. Analysis of the gamma-ray flux over the mission suggests an
approximate transition time of 2012 November 30. Continued study of the pulsed
emission and monitoring of PSR J1227-4853, and other known redback systems, for
subsequent flux changes will increase our knowledge of the pulsar emission
mechanism and transitioning systems.Comment: 5 figures, 1 table, accepted for publication in ApJ, updated to
reflect accepted version and add additional coautho
Radio Detection of the Fermi LAT Blind Search Millisecond Pulsar J1311-3430
We report the detection of radio emission from PSR J1311-3430, the first
millisecond pulsar discovered in a blind search of Fermi Large Area Telescope
(LAT) gamma-ray data. We detected radio pulsations at 2 GHz, visible for <10%
of ~4.5-hrs of observations using the Green Bank Telescope (GBT). Observations
at 5 GHz with the GBT and at several lower frequencies with Parkes, Nancay, and
the Giant Metrewave Radio Telescope resulted in non-detections. We also report
the faint detection of a steep spectrum continuum radio source (0.1 mJy at 5
GHz) in interferometric imaging observations with the Jansky Very Large Array.
These detections demonstrate that PSR J1311-3430, is not radio quiet and
provides additional evidence that the radio beaming fraction of millisecond
pulsars is very large. The radio detection yields a distance estimate of 1.4
kpc for the system, yielding a gamma-ray efficiency of 30%, typical of
LAT-detected MSPs. We see apparent excess delay in the radio pulsar as the
pulsar appears from eclipse and we speculate on possible mechanisms for the
non-detections of the pulse at other orbital phases and observing frequencies.Comment: 6 pages, 4 figures. ApJ Letters, in pres
"My Children and I Will no Longer Suffer from Malaria": A Qualitative Study of the Acceptance and Rejection of Indoor Residual Spraying to Prevent Malaria in Tanzania.
The objective of this study was to identify attitudes and misconceptions related to acceptance or refusal of indoor residual spraying (IRS) in Tanzania for both the general population and among certain groups (e.g., farmers, fishermen, community leaders, and women). This study was a series of qualitative, semi-structured, in-depth interviews and focus group discussions conducted from October 2010 to March 2011 on Mainland Tanzania and Zanzibar. Three groups of participants were targeted: acceptors of IRS (those who have already had their homes sprayed), refusers (those whose communities have been sprayed, but refused to have their individual home sprayed), and those whose houses were about to be sprayed as part of IRS scale-up. Interviews were also conducted with farmers, fishermen, women, community leaders and members of non-government organizations responsible for community mobilization around IRS. Results showed refusers are a very small percentage of the population. They tend to be more knowledgeable people such as teachers, drivers, extension workers, and other civil servants who do not simply follow the orders of the local government or the sprayers, but are skeptical about the process until they see true results. Refusal took three forms: 1) refusing partially until thorough explanation is provided; 2) accepting spray to be done in a few rooms only; and 3) refusing outright. In most of the refusal interviews, refusers justified why their houses were not sprayed, often without admitting that they had refused. Reasons for refusal included initial ignorance about the reasons for IRS, uncertainty about its effectiveness, increased prevalence of other insects, potential physical side effects, odour, rumours about the chemical affecting fertility, embarrassment about moving poor quality possessions out of the house, and belief that the spray was politically motivated. To increase IRS acceptance, participants recommended more emphasis on providing thorough public education, ensuring the sprayers themselves are more knowledgeable about IRS, and asking that community leaders encourage participation by their constituents rather than threatening punishment for noncompliance. While there are several rumours and misconceptions concerning IRS in Tanzania, acceptance is very high and continues to increase as positive results become apparent
PSR J2030+3641: radio discovery and gamma-ray study of a middle-aged pulsar in the now identified Fermi-LAT source 1FGL J2030.0+3641
In a radio search with the Green Bank Telescope of three unidentified low
Galactic latitude Fermi-LAT sources, we have discovered the middle-aged pulsar
J2030+3641, associated with 1FGL J2030.0+3641 (2FGL J2030.0+3640). Following
the detection of gamma-ray pulsations using a radio ephemeris, we have obtained
a phase-coherent timing solution based on gamma-ray and radio pulse arrival
times that spans the entire Fermi mission. With a rotation period of 0.2 s,
spin-down luminosity of 3e34 erg/s, and characteristic age of 0.5 Myr, PSR
J2030+3641 is a middle-aged neutron star with spin parameters similar to those
of the exceedingly gamma-ray-bright and radio-undetected Geminga. Its gamma-ray
flux is 1% that of Geminga, primarily because of its much larger distance, as
suggested by the large integrated column density of free electrons, DM=246
pc/cc. We fit the gamma-ray light curve, along with limited radio polarimetric
constraints, to four geometrical models of magnetospheric emission, and while
none of the fits have high significance some are encouraging and suggest that
further refinements of these models may be worthwhile. We argue that not many
more non-millisecond radio pulsars may be detected along the Galactic plane
that are responsible for LAT sources, but that modified methods to search for
gamma-ray pulsations should be productive -- PSR J2030+3641 would have been
found blindly in gamma rays if only >0.8 GeV photons had been considered, owing
to its relatively flat spectrum and location in a region of high soft
background.Comment: Accepted for publication in ApJ, 9 pages, 6 figure
All-sky search of NAUTILUS data
A search for periodic gravitational-wave signals from isolated neutron stars
in the NAUTILUS detector data is presented. We have analyzed half a year of
data over the frequency band Hz/s and over the entire sky. We have divided the
data into 2 day stretches and we have analyzed each stretch coherently using
matched filtering. We have imposed a low threshold for the optimal detection
statistic to obtain a set of candidates that are further examined for
coincidences among various data stretches. For some candidates we have also
investigated the change of the signal-to-noise ratio when we increase the
observation time from two to four days. Our analysis has not revealed any
gravitational-wave signals. Therefore we have imposed upper limits on the
dimensionless gravitational-wave amplitude over the parameter space that we
have searched. Depending on frequency, our upper limit ranges from to . We have attempted a statistical
verification of the hypotheses leading to our conclusions. We estimate that our
upper limit is accurate to within 18%.Comment: LaTeX, 12 page
Gamma-Ray Emission from Two Blazars Behind the Galactic Plane: B2013+370 & B2023+336
B2013+370 and B2023+336 are two blazars at low-galactic latitude that were
previously proposed to be the counterparts for the EGRET unidentified sources,
3EG J2016+3657 and 3EG J2027+3429. Gamma-ray emission associated with the EGRET
sources has been detected by the Fermi Gamma-ray Space Telescope, and the two
sources, 1FGL J2015.7+3708 and 1FGL J2027.6+3335, have been classified as
unidentified in the 1-year catalog. This analysis of the Fermi-LAT data
collected during 31 months reveals that the 1FGL sources are spatially
compatible with the blazars, and are significantly variable, supporting the
hypothesis of extragalactic origin for the gamma-ray emission. The gamma-ray
light curves are compared with 15 GHz radio light curves from the 40-m
telescope at the Owens Valley Radio Observatory (OVRO). Simultaneous
variability is seen in both bands for the two blazar candidates. The study is
completed with the X-ray analysis of 1FGL J2015.7+3708 using Swift observations
that were triggered in August 2010 by a Fermi-detected flare. The resulting
spectral energy distribution shows a two-component structure typical of
blazars. We also identify a second source in the field of view of 1FGL
J2027.6+3335 with similar characteristics to the known LAT pulsars. This study
gives solid evidence favoring blazar counterparts for these two unidentified
EGRET and Fermi sources, supporting the hypothesis that a number of
unidentified gamma-ray sources at low galactic latitudes are indeed of
extragalactic origin.Comment: 10 pages, 7 figures, 6 tables, accepted for publication in The
Astrophysical Journa
PSR J1838-0537: Discovery of a young, energetic gamma-ray pulsar
We report the discovery of PSR J1838-0537, a gamma-ray pulsar found through a
blind search of data from the Fermi Large Area Telescope (LAT). The pulsar has
a spin frequency of 6.9 Hz and a frequency derivative of -2.2e-11 Hz/s,
implying a young characteristic age of 4970 years and a large spin-down power
of 5.9e36 erg/s. Follow-up observations with radio telescopes detected no
pulsations, thus PSR J1838-0537 appears radio-quiet as viewed from Earth. In
September 2009 the pulsar suffered the largest glitch so far seen in any
gamma-ray-only pulsar, causing a relative increase in spin frequency of about
5.5e-6. After the glitch, during a putative recovery period, the timing
analysis is complicated by the sparsity of the LAT photon data, the weakness of
the pulsations, and the reduction in average exposure from a coincidental,
contemporaneous change in the LAT's sky-survey observing pattern. The pulsar's
sky position is coincident with the spatially extended TeV source HESS
J1841-055 detected by the High Energy Stereoscopic System (H.E.S.S.). The
inferred energetics suggest that HESS J1841-055 contains a pulsar wind nebula
powered by the pulsar.Comment: 6 pages, 3 figures. To appear in the Astrophysical Journal Letter
Einstein@Home discovery of four young gamma-ray pulsars in Fermi LAT data
We report the discovery of four gamma-ray pulsars, detected in computing-intensive blind searches of data from the Fermi Large Area Telescope (LAT). The pulsars were found using a novel search approach, combining volunteer distributed computing via Einstein@Home and methods originally developed in gravitational-wave astronomy. The pulsars PSRs J0554+3107, J1422-6138, J1522-5735, and J1932+1916 are young and energetic, with characteristic ages between 35 and 56 kyr and spin-down powers in the range - erg s. They are located in the Galactic plane and have rotation rates of less than 10 Hz, among which the 2.1 Hz spin frequency of PSR J0554+3107 is the slowest of any known gamma-ray pulsar. For two of the new pulsars, we find supernova remnants coincident on the sky and discuss the plausibility of such associations. Deep radio follow-up observations found no pulsations, suggesting that all four pulsars are radio-quiet as viewed from Earth. These discoveries, the first gamma-ray pulsars found by volunteer computing, motivate continued blind pulsar searches of the many other unidentified LAT gamma-ray sources
Batata con sanidad controlada. Modelo productivo para la provincia de Corrientes
Las regiones productoras de batata del país han sufrido disminución de la superficie plantada, con mermas de rendimientos de las principales variedades comerciales. Esto se atribuye a enfermedades causadas por la sinergia de al menos cinco virus de difícil detección, incluso a través de métodos serológicos/moleculares. La infección durante el ciclo de cultivo se produce a través de insectos vectores: pulgones y moscas blancas. Los efectos de estas enfermedades pueden mitigarse con el uso de material de propagación agámica de sanidad controlada, multiplicado a partir de semilla básica o fundación provista por el Instituto de Patología Vegetal (IPAVE), Córdoba, que se obtiene a su vez, mediante micropropagación in vitro de meristemas y termoterapia. La multiplicación masiva se realiza a través de viveros en las diferentes zonas productoras del país. En 2017 el Ministerio de Producción de Corrientes creó el programa Multiplicación de Batata con Sanidad Controlada, mediante el cual puso en funcionamiento el Vivero Hortícola del Centro Tecnológico de Producción, con diferentes cultivares (cvs). La macropropagación se realiza en invernadero cumpliendo con el protocolo sanitario establecido. La producción obtenida se destina principalmente a productores comerciales beneficiarios del Proyecto, que llevan adelante sus propios “núcleos semilleros”, donde se plantan los esquejes saneados y a partir de los cuales se obtiene material de propagación para lotes comerciales. Estos núcleos se encuentran protegidos con malla anti-insecto. Con lo que se pretende bajar la presión de inóculo, recuperar superficie y calidad de producción
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