4,471 research outputs found
Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305
We perform a timing analysis on RXTE data of the accreting millisecond pulsar
XTE J1751-305 observed during the April 2002 outburst. After having corrected
for Doppler effects on the pulse phases due to the orbital motion of the
source, we performed a timing analysis on the phase delays, which gives, for
the first time for this source, an estimate of the average spin frequency
derivative = (3.7 +/- 1.0)E-13 Hz/s. We discuss the torque resulting
from the spin-up of the neutron star deriving a dynamical estimate of the mass
accretion rate and comparing it with the one obtained from X-ray flux.
Constraints on the distance to the source are discussed, leading to a lower
limit of \sim 6.7 kpc.Comment: 7 pages, 3 figures, Accepted for publication by MNRA
The Status of a PA Endangered Bird- the Upland Sandpiper
The upland sandpiper (Bartramia Longuardia) has experienced a steep population decline in the northeastern U.S. since the mid-20th Century. In Pennsylvania it was found in less than 0.5% of atlas blocks during the Second Atlas of Breeding Birds in Pennsylvania project (2nd PBBA; 2004-09) and breeding was confirmed at only two locations. Due to continued declines and a small population size, the upland sandpiper was listed as PA endangered in 2012. During May 2012 the areas around 15 2nd PBBA upland sandpiper sightings were resurveyed by Gettysburg College students and volunteer birdwatchers. The aim was to establish whether the atlas records related to persisting populations. We used five-minute audio playback at up to 10 locations within 4km of the atlas sightings. A maximum of 19 pairs/calling male upland sandpipers were found across the state in 2012, most of them on or close to reclaimed surface mines. However, locating such a scarce species can be problematic, and it is still not known to what extent the species is under-reported. To help direct future surveys we analyzed data from the 2nd PBBA and the 2012 survey to produce a habitat suitability model for the upland sandpiper in Pennsylvania. We used a GIS framework to determine areas of suitable habitat and then stratified these by proximity to recent (2004-2012) upland sandpiper sightings. We recommend that our suitability model be used to establish a sampling protocol for more thorough statewide upland sandpiper survey every five years, in order that the species’ precarious status can be closely monitored
Searching for pulsed emission from XTE J0929-314 at high radio frequencies
The aim of this work is to search for radio signals in the quiescent phase of
accreting millisecond X-ray pulsars, in this way giving an ultimate proof of
the recycling model, thereby unambiguously establishing that accreting
millisecond X-ray pulsars are the progenitors of radio millisecond pulsars.
To overcome the possible free-free absorption caused by matter surrounding
accreting millisecond X-ray pulsars in their quiescence phase, we performed the
observations at high frequencies. Making use of particularly precise orbital
and spin parameters obtained from X-ray observations, we carried out a deep
search for radio-pulsed emission from the accreting millisecond X-ray pulsar
XTE J0929-314 in three steps, correcting for the effect of the dispersion due
to the interstellar medium, eliminating the orbital motions effects, and
finally folding the time series.
No radio pulsation is present in the analyzed data down to a limit of 68
microJy at 6.4 GHz and 26 microJy at 8.5 GHz.
We discuss several mechanisms that could prevent the detection, concluding
that beaming factor and intrinsic low luminosity are the most likely
explanations.Comment: 7 pages, 4 figures. Accepted for publication in Astronomy &
Astrophysic
Timing of the Accreting Millisecond Pulsar XTE J1814-338
We present a precise timing analysis of the accreting millisecond pulsar XTE
J1814-338 during its 2003 outburst, observed by RXTE. A full orbital solution
is given for the first time; Doppler effects induced by the motion of the
source in the binary system were corrected, leading to a refined estimate of
the orbital period, P_orb=15388.7229(2)s, and of the projected semimajor axis,
a sini/c= 390.633(9) lt-ms. We could then investigate the spin behaviour of the
accreting compact object during the outburst. We report here a refined value of
the spin frequency (nu=314.35610879(1) Hz) and the first estimate of the spin
frequency derivative of this source while accreting (nu^dot=(-6.7 +/- 0.7)
10^(-14) Hz/s). This spin down behaviour arises when both the fundamental
frequency and the second harmonic are taken into consideration. We discuss this
in the context of the interaction between the disc and the quickly rotating
magnetosphere, at accretion rates sufficiently low to allow a threading of the
accretion disc in regions where the Keplerian velocity is slower than the
magnetosphere velocity. We also present indications of a jitter of the pulse
phases around the mean trend, which we argue results from movements of the
accreting hotspots in response to variations of the accretion rate.Comment: 7 pages, 4 figures, Accepted for publication by MNRA
Biomedical aspects of pyridoxal 5 -phosphate availability
The biologically active form of vitamin B6, pyridoxal 5'-phosphate (PLP), is a cofactor in over 160 enzyme activities involved in a number of metabolic pathways, including neurotransmitter synthesis and degradation. In humans, PLP is recycled from food and from degraded PLP-dependent enzymes in a salvage pathway requiring the action of pyridoxal kinase, pyridoxine 5'-phosphate oxidase and phosphatases. Once pyridoxal 5'-phosphate is made, it is targeted to the dozens different apoenzymes that need it as a cofactor. The regulation of the salvage pathway and the mechanism of addition of PLP to the apoenzymes are poorly understood and represent a very challenging research field. Severe neurological disorders, such as convulsions and epileptic encephalopathy, result from a reduced availability of pyridoxal 5'-phosphate in the cell, due to inborn errors in the enzymes of the salvage pathway or other metabolisms and to interactions of drugs with PLP or pyridoxal kinase. Multifactorial neurological pathologies, such as autism, schizophrenia, Alzheimer's disease, Parkinson's disease and epilepsy have also been correlated to inadequate intracellular levels of PLP
A broad iron line in the Chandra/HETG spectrum of 4U 1705-44
We present the results of a Chandra 30 ks observation of the low mass X-ray
binary and atoll source 4U 1705-44. Here we concentrate on the study of
discrete features in the energy spectrum at energies below 3 keV, as well as on
the iron Kalpha line, using the HETG spectrometer on board of the Chandra
satellite. Below 3 keV, three narrow emission lines are found at 1.47, 2.0, and
2.6 keV. The 1.47 and 2.6 keV are probably identified with Ly-alpha emission
from Mg XII and S XVI, respectively. The identification of the feature at 2.0
keV is uncertain due to the presence of an instrumental feature at the same
energy. The iron Kalpha line at ~6.5 keV is found to be intrinsically broad
(FWHM ~ 1.2 keV); its width can be explained by reflection from a cold
accretion disk extending down to 15 km from the neutron star center or by
Compton broadening in the external parts of a hot (~2 keV) Comptonizing corona.
We finally report here precise X-ray coordinates of the source.Comment: 8 pages including 2 figures. ApJ Letters, in pres
A re-analysis of the NuSTAR and XMM-Newton broad-band spectrum of Ser~X-1
Context: Ser X-1 is a well studied LMXB which clearly shows a broad iron
line. Recently, Miller et al. (2103) have presented broad-band, high quality
NuSTAR data of SerX-1.Using relativistically smeared self-consistent reflection
models, they find a value of R_in close to 1.0 R_ISCO (corresponding to 6 R_g),
and a low inclination angle, less than 10 deg. Aims: The aim of this paper is
to probe to what extent the choice of reflection and continuum models (and
uncertainties therein) can affect the conclusions about the disk parameters
inferred from the reflection component. To this aim we re-analyze all the
available public NuSTAR and XMM-Newton. Ser X-1 is a well studied source, its
spectrum has been observed by several instruments, and is therefore one of the
best sources for this study. Methods: We use slightly different continuum and
reflection models with respect to those adopted in literature for this source.
In particular we fit the iron line and other reflection features with
self-consistent reflection models as reflionx (with a power-law illuminating
continuum modified with a high energy cutoff to mimic the shape of the incident
Comptonization spectrum) and rfxconv. With these models we fit NuSTAR and
XMM-Newton spectra yielding consistent spectral results. Results: Our results
are in line with those already found by Miller et al. (2013) but less extreme.
In particular, we find the inner disk radius at about 13 R_g and an inclination
angle with respect to the line of sight of about 27 deg. We conclude that,
while the choice of the reflection model has little impact on the disk
parameters, as soon as a self-consistent model is used, the choice of the
continuum model can be important in the precise determination of the disk
parameters from the reflection component. Hence broad-band X-ray spectra are
highly preferable to constrain the continuum and disk parameters.Comment: 13 pages including 8 figures. Accepted for publication in A&
Timing of the accreting millisecond pulsar IGR~J17511--3057
{Timing analysis of Accretion-powered Millisecond Pulsars (AMPs) is a
powerful tool to probe the physics of compact objects. The recently discovered
\newigrj is the 12 discovered out of the 13 AMPs known. The Rossi XTE satellite
provided an extensive coverage of the 25 days-long observation of the source
outburst.} {Our goal is to investigate the complex interaction between the
neutron star magnetic field and the accretion disk, determining the angular
momentum exchange between them. The presence of a millisecond coherent flux
modulation allows us to investigate such interaction from the study of pulse
arrival times. In order to separate the neutron star proper spin frequency
variations from other effects, a precise set of orbital ephemeris is
mandatory.} {Using timing techniques, we analysed the pulse phase delays
fitting differential corrections to the orbital parameters. To remove the
effects of pulse phase fluctuations we applied the timing technique already
successfully applied to the case of an another AMP, XTE J1807-294.} {We report
a precise set of orbital ephemeris. We demonstrate that the companion star is a
main sequence star. We find pulse phase delays fluctuations on the first
harmonic with a characteristic amplitude of about 0.05, similar to what also
observed in the case of the AMP XTE J1814-338. For the second time an AMP shows
a third harmonic detected during the entire outburst. The first harmonic phase
delays show a puzzling behaviour, while the second harmonic phase delays show a
clear spin-up. Also the third harmonic shows a spin-up, although not highly
significant (3 c.l.). The presence of a fourth harmonic is also
reported. In the hypothesis that the second harmonic is a good tracer of the
spin frequency of the neutron star, we find a mean spin frequency derivative
for this source of \np{1.65(18)}{-13} Hz s.} (continue ...)Comment: 9 pages, 12 figures, A&A accepted on 23/10/201
An Integrative, Multiparametric Approach for the Comprehensive Assessment of Microbial Quality and Pollution in Aquaculture Systems
As the aquaculture sector significantly expanded worldwide in the past decades, the concept of sustainable aquaculture has developed with the challenge of not only maximizing benefits but also minimizing the negative impacts on the environment assuring, at the same time, food security. In this framework, monitoring and improving the microbiological water quality and animal health are a central topic. In the present study, we evaluated the seawater microbiological quality in a mariculture system located in a Mediterranean coastal area (Northern Ionian Sea, Italy). We furnished, for the first time, a microbial inventory based on conventional culture-based methods, integrated with the 16S rRNA gene metabarcoding approach for vibrios identification and diversity analyses, and further implemented with microbial metabolic profiling data obtained from the Biolog EcoPlate system. Microbiological pollution indicators, vibrios diversity, and microbial metabolism were determined in two different times of the year (July and December). All microbial parameters measured in July were markedly increased compared to those measured in December. The presence of potentially pathogenic vibrios is discussed concerning the risk of fish disease and human infections. Thus, the microbial inventory here proposed might represent a new multiparametric approach for the suitable surveillance of the microbial quality in a mariculture system. Consequently, it could be useful for ensuring the safety of both the reared species and the consumers in the light of sustainable, eco-friendly aquaculture management
XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
We report on a 63-ks long XMM-Newton observation of the accreting millisecond
pulsar SAX J1808.4-3658 during the latest X-ray outburst which started on
September 21st 2008. The pn spectrum shows a highly significant emission line
in the energy band where the iron K-alpha line is expected, and which we
identify as emission from neutral (or mildly ionized) iron. The line profile
appears to be quite broad (more than 1 keV FWHM) and asymmetric; the most
probable explanation for this profile is Doppler and relativistic broadening
from the inner accretion disc. From a fit with a diskline profile we find an
inner radius of the disc of 8.7^(+3.7)_(-2.7) R_g, corresponding to
18.0^(+7.6)_(-5.6) km for a 1.4 Msun neutron star. The disc therefore appears
truncated inside the corotation radius (31 km for SAX J1808.4-3658) in
agreement with the fact that the source was still showing pulsations during the
XMM-Newton observation.Comment: 5 pages, 3 figures, accepted for publication in A&A Letters, typos
corrected, references adde
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