421 research outputs found
Insights into the development of Ixodes scapularis: a resource for research on a medically important tick species
Ticks (Acari: Ixodida) are arthropod ectoparasites dependent on a bloodmeal from a vertebrate host at each developmental stage for completion of their life cycle. This tick feeding cycle impacts animal health by causing damage to hides, secondary infections, immune reactions and diseases caused by transmission of pathogens. The genus Ixodes includes several medically important species that vector diseases, including granulocytic anaplasmosis and Lyme disease. I. scapularis, commonly called the black-legged or deer tick, is a medically-important tick species in North America and therefore was the first tick genome to be sequenced, thus serving as an important resource for tick research. This Primer focuses on the normal developmental cycle and laboratory rearing of I. scapularis. Definition of normal morphology, along with a consistent source of laboratory-reared I. scapularis, are fundamental for all aspects of future research, especially the effects of genetic manipulation and the evaluation of tick vaccine efficacy. Recent research important for the advancement of tick research, namely the development of tick cell culture systems for study of ticks and tick-borne pathogens, RNA interference for genetic manipulation of ticks and discovery of candidate antigens for development of tick vaccines, are briefly presented along with areas to target for future research.The preparation of this chapter was partially supported by the EU FP7 ANTIGONE project number 278976, and the Walter R. Sitlington Endowed Chair for Food Animal Research to K.M. Kocan.Peer Reviewe
Completing the puzzle of the 2004-2005 outburst in V0332+53: the brightening phase included
Analysis of the data obtained with the RXTE observatory during a powerful
outburst of the X-ray pulsar V0332+53 in 2004-2005 is presented. Observational
data covering the outburst brightening phase are analysed in detail for the
first time. A comparison of source parameters and their evolution during the
brightening and fading phases shows no evidence for any hysteresis behaviour.
It is found that the dependences of the energy of the cyclotron absorption line
on the luminosity during the brightening and fading phases are almost
identical. The complete data sequence including the outburst brightening and
fading phases makes it possible to impose the more stringent constraints on the
magnetic field in the source. The pulse profile and pulsed fraction are studied
as functions of the luminosity and photon energy.Comment: 9 pages, 10 figures, accepted for publication in MNRA
XMM-Newton observation of the persistent Be/NS X-ray binary pulsar RX J1037.5-5647 in a low luminosity state
The spectra of several X-ray binary pulsars display a clear soft excess,
which in most cases can be described with a blackbody model, above the main
power-law component. While in the high-luminosity sources it is usually
characterized by low temperature (kT
100 km), in the two persistent and low-luminosity pulsars 4U 0352+309 and RX
J0146.9+6121 this component has a high temperature (kT > 1 keV) and a smaller
radius (R < 0.5 km), consistent with the estimated size of the neutron-star
polar cap. Here we report on the timing and spectral analysis of RX
J1037.5-5647, another low-luminosity persistent Be binary pulsar, based on the
first XMM-Newton observation of this source. We have found a best-fit period P
= 853.4(+/-0.2) s, that implies an average pulsar spin-up dP/dt ~ -2E-8 s/s in
the latest decade. The estimated source luminosity is Lx ~ 10^34 erg/s, a value
comparable to that of the other persistent Be binary pulsars and about one
order of magnitude lower than in most of the previous measurements. The source
spectrum can be described with a power law plus blackbody model, with kTbb =
1.26(+0.16/-0.09) keV and Rbb = 128(+13/-21) m, suggesting a polar-cap origin
of this component. These results strengthen the hypothesis that, in addition to
low luminosities and long periods, this class of sources is characterized also
by common spectral propertiesComment: 9 pages, 8 figures, 2 tables. Accepted for publication by Astronomy
and Astrophysic
XMM-Newton observation of the persistent Be/neutron-star system X Persei at a high-luminosity level
We report on the XMM-Newton observation of the HMXRB X Persei, the prototype
of the persistent and low-luminosity Be/neutron star pulsars, which was
performed on February 2003. The source was detected at a luminosity level of ~
1.4x10^35 erg/s, which is the highest level of the latest three decades. The
pulsation period has increased up to 839.3 s, thus confirming the overall
spin-down of the NS detected in the previous observations. The folded
light-curve has a complex structure, with features not observed at lower
luminosities, and shows a significant energy dependence. The spectral analysis
reveals the presence of a significant excess at low energies over the main
power-law spectral component, which can be described by a black-body spectrum
of high temperature (kT_BB ~ 1.5 keV) and small emitting region (R_BB ~ 340 m);
its properties are consistent with a polar-cap origin. Phase-resolved
spectroscopy shows that the emission spectrum varies along the pulse period,
but it is not possible to prove whether the thermal component is pulsed or not.Comment: 8 pages, 8 figures, 4 tables. Accepted for publication by Astronomy &
Astrophysic
Suzaku X-ray Spectra and Pulse Profile Variations during the Superorbital Cycle of LMC X-4
We present results from spectral and temporal analyses of Suzaku and RXTE
observations of the high mass X-ray binary LMC X-4. Using the full 13 years of
available RXTE/ASM data, we apply the ANOVA and Lomb normalized Periodogram
methods to obtain an improved superorbital period measurement of 30.32 +/- 0.04
days. The phase-averaged X-ray spectra from Suzaku observations during the high
state of the superorbital period can be modeled in the 0.6--50 keV band as the
combination of a power-law with Gamma ~ 0.6 and a high-energy cutoff at ~ 25
keV, a blackbody with kT_BB ~ 0.18 keV, and emission lines from Fe K_alpha, O
VIII, and Ne IX (X Lyalpha). Assuming a distance of 50 kpc, The source has
luminosity L_X ~ 3 x 10^38 ergs s^-1 in the 2--50 keV band, and the luminosity
of the soft (blackbody) component is L_BB ~ 1.5 x 10^37 ergs s^-1. The energy
resolved pulse profiles show single-peaked soft (0.5-1 keV) and hard (6-10 keV)
pulses but a more complex pattern of medium (2-10 keV) pulses;
cross-correlation of the hard with the soft pulses shows a phase shift that
varies between observations. We interpret these results in terms of a picture
in which a precessing disk reprocesses the hard X-rays and produces the
observed soft spectral component, as has been suggested for the similar sources
Her X-1 and SMC X-1.Comment: 13 emulateapj pages, 11 figures, 4 tables; accepted for publication
in Ap
A model for cyclotron resonance scattering features
(abbreviated version of the abstract) We study the physics of cyclotron line
formation in the high-energy spectra of accreting X-ray pulsars using Monte
Carlo methods, assuming that the line-forming region is a low-density electron
plasma in a sub-critical magnetic field. We investigate the dependence of the
shape of the fundamental line on angle, geometry, optical depth and
temperature. We also discuss variations of the line ratios for non-uniform
magnetic fields. These numerical predictions for the line profiles are linked
to results from observational data analysis using an XSPEC model based on the
Monte Carlo simulations. We apply this model to observational data from RXTE
and INTEGRAL. The predicted strong emission wings of the fundamental cyclotron
feature are not found in observational data, hinting at a bottom illuminated
slab geometry for line formation.Comment: 16 pages, 15 figures, Astron. Astrophys. (in press
GX 301-2 as seen by Integral
We present observations of the High Mass X-ray Binary GX 301-2 taken during
the Galactic Plane Scan (GPS) with Integral following our RXTE observations
(Kreykenbohm et al. 2004). The optical companion of GX 301-2 is the B1Ia+
hypergiant Wray 977 with a luminosity of 1.3 x 10^6 Lsun and a mass of ~48 Msun
making the system one of the most massive X-ray binaries known. The system was
observed 24 times during the GPS thus covering many orbital phases including
the pre-periastron flare. The source is clearly detected in all Integral
instruments in most pointings. The derived X-ray light curves show strong
variability on all timescales. Depending on the orbital phase of the pointings,
the luminosity changes by factor of more than 10 during the pre-periastron
flare compared to other pointings. Furthermore, broad band spectra using all
instruments available on Integral are compared with data taken by the RXTE
instruments PCA and HEXTE (using the same data as in Kreykenbohm et al. 2004).Comment: accepted for publication in the proceedings of the 5th Integral
Workshop (The INTEGRAL Universe, Munich, 16-20 February 2004
Strong outburst activity of the X-ray pulsar X Persei during 2001-2011
We present results of a comprehensive analysis of the X-ray pulsar X Persei
over the period 1996 to 2011, encompassing the quite low state and subsequent
strong outburst activity. Using data from the RXTE and Swift observatories we
detected several consecutive outbursts, during which the source luminosity
increased by a factor of ~5 up to L_x~1.2x10^{35} erg/s. Previously the source
was observed in a high state only once. The source spectrum in a standard
energy band (4-25 keV) is independent of the flux change and can be described
by a model that includes both thermal and non-thermal components. With the help
of the INTEGRAL observatory data we registered the highly significant cyclotron
absorption line in the source spectrum and, for the first time, significantly
detected a hard X-ray emission from the pulsar up to ~160 keV. We also report
drastic changes of the pulse period during the outburst activity: a long
episode of spin-down was changed to spin-up with a rate of Pdot/P =
-(3-5)x10^{-4} yr^{-1}, that is several times higher than previous rates of
spin-up and spin-down. To search for a correlation between the X-ray and
optical lightcurves we took data from the AAVSO International Database. No
significant correlation between optical and X-ray fluxes at any time lag from
dozens of days to years was found.Comment: 8 pages, 6 figures, accepted for publication in MNRA
Is there a highly magnetized neutron star in GX 301-2?
We present the results of an in-depth study of the long-period X-ray pulsar
GX 301-2. Using archival data of INTEGRAL, RXTE ASM, and CGRO BATSE, we study
the spectral and timing properties of the source. Comparison of our timing
results with previously published work reveals a secular decay of the orbital
period at a rate of \simeq -3.25 \times 10^{-5} d yr^{-1}, which is an order of
magnitude faster than for other known systems. We argue that this is probably
result either of the apsidal motion or of gravitational coupling of the matter
lost by the optical companion with the neutron star, although current
observations do not allow us to distinguish between those possibilities. We
also propose a model to explain the observed long pulse period. We find that a
very strong magnetic field B \sim 10^{14} G can explain the observed pulse
period in the framework of existing models for torques affecting the neutron
star. We show that the apparent contradiction with the magnetic field strength
B_{CRSF} \sim 4 \times 10^{12} G derived from the observed cyclotron line
position may be resolved if the line formation region resides in a tall
accretion column of height \sim 2.5 - 3 R_{NS}. The color temperature measured
from the spectrum suggests that such a column may indeed be present, and our
estimates show that its height is sufficient to explain the observed cyclotron
line position.Comment: 10 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics. Referee comments are implemented
Broadband Observations of the Be/X-ray Binary Pulsar RX J0440.9+4431: Discovery of a Cyclotron Absorption Line
We report the results of an analysis of data obtained with the INTEGRAL,
Swift and RXTE observatories during the 2010 April and September outbursts of
the X-ray pulsar RX J0440.9+4431. The temporal and spectral properties of the
pulsar in a wide energy band (0.6-120 keV) were studied for the first time. We
discovered a ~32 keV cyclotron resonant scattering feature in the source
spectrum, that allowed us to estimate the magnetic field strength of the
neutron star as B~3.2 x 10^12 G. The estimate of the magnetic field strength
was confirmed by a comprehensive analysis of the noise power spectrum of the
source. Based on the recurrence time between Type I outbursts the orbital
period of the binary system can be estimated as ~155 days. We have shown that
the pulse profile has a sinusoidal-like single-peaked shape and has practically
no dependence on the source luminosity or energy band.Comment: 8 pages, 6 figures, accepted for publication in MNRA
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