355 research outputs found
Lander Trajectory Reconstruction computer program
The Lander Trajectory Reconstruction (LTR) computer program is a tool for analysis of the planetary entry trajectory and atmosphere reconstruction process for a lander or probe. The program can be divided into two parts: (1) the data generator and (2) the reconstructor. The data generator provides the real environment in which the lander or probe is presumed to find itself. The reconstructor reconstructs the entry trajectory and atmosphere using sensor data generated by the data generator and a Kalman-Schmidt consider filter. A wide variety of vehicle and environmental parameters may be either solved-for or considered in the filter process
X-ray Shots of Cyg X-1
X-ray shots of Cyg X-1 in different energy bands and spectral states have
been studied with PCA/RXTE observations. The detailed shot structure is
obtained by superposing many shots with one millisecond time bin through
aligning their peaks with an improved algorithm. In general, the shots are
composed of a slow rise and fast decay. The shot structures in the different
states are different. The duration of shot in the high state is shorter than
that in the low and transition states. The shot profile in the high energy band
is more asymmetric and narrower than that in the low energy band. The average
hardness of shot is lower than that of steady emission in the transition and
low states but higher than that in the high state. The time lags between the
shots in higher and lower energy bands have been found in the different states.
In transition states, the time lag is the largest among the different states of
Cyg X-1, and it is the smallest in the low state. The implications of the
observed shot features for shot models are discussed.Comment: Latex, 20 pages, 12 figures(included), to be published in Ap
Future X-ray timing missions
Thanks to the Rossi X-ray Timing Explorer (RXTE), it is now widely recognized
that fast X-ray timing can be used to probe strong gravity fields around
collapsed objects and constrain the equation of state of dense matter in
neutron stars. We first discuss some of the outstanding issues which could be
solved with an X-ray timing mission building on the great successes of RXTE and
providing an order of magnitude better sensitivity. Then we briefly describe
the 'Experiment for X-ray timing and Relativistic Astrophysics' (EXTRA)
recently proposed to the European Space Agency as a follow-up to RXTE and the
related US mission 'Relativistic Astrophysics Explorer' (RAE).Comment: To be published in `Proceedings of the Third Microquasar Workshop:
Granada Workshop on galactic relativistic jet sources', Eds A. J.
Castro-Tirado, J. Greiner and J. M. Paredes, Astrophysics and Space Science,
in press. More about EXTRA can be found at:
http://www.cesr.fr/~barret/extra.htm
HE 0435-1223: a wide separation quadruple QSO and gravitational lens
We report the discovery of a new gravitationally lensed QSO, at a redshift z
= 1.689, with four QSO components in a cross-shaped arrangement around a bright
galaxy. The maximum separation between images is 2.6 arcsec, enabling a
reliable decomposition of the system. Three of the QSO components have g =
19.6, while component A is about 0.6 mag brighter. The four components have
nearly identical colours, suggesting little if any dust extinction in the
foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r
and not detected in g. Its spatial profile is that of an elliptical galaxy with
a scale length of 12 kpc. Combining the measured colours and a mass
model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4.
Predicted time delays between the components are \la 10 days. The QSO shows
evidence for variability, with total g band magnitudes of 17.89 and 17.71 for
two epochs separated by months. However, the relative fluxes of the
components did not change, indicating that the variations are intrinsic to the
QSO rather than induced by microlensing.Comment: 7 pages, submitted to Astronomy and Astrophysic
Guide to the twelve most-important Oklahoma mosquitoes of concern for pest control specialists
The Oklahoma Cooperative Extension Service periodically issues revisions to its publications. The most current edition is made available. For access to an earlier edition, if available for this title, please contact the Oklahoma State University Library Archives by email at [email protected] or by phone at 405-744-6311
A Systematic Search for Periodicities in RXTE/ASM Data
We present the results of a systematic search in 8.5 yr of Rossi X-Ray Timing Explorer All-Sky Monitor data for evidence of periodicities. The search was conducted by application of the Lomb-Scargle periodogram to the light curves of each of 458 actually or potentially detected sources in each of four energy bands (1.5–3, 3–5, 5–12, and 1.5–12 keV). A whitening technique was applied to the periodograms before evaluation of the statistical significance of the powers. We discuss individual detections with a focus on relatively new findings
A Giant Glitch in the Energetic 69 ms X-ray Pulsar AXS J161730-505505
We present new results on the recently discovered 69 ms X-ray pulsar AXS
J161730-505505, the sixth youngest sample of all known pulsars. We have
undertaken a comprehensive X-ray observing campaign of AXS J161730-505505 with
the ASCA, SAX, and XTE observatories and follow its long term spin-down history
between 1989 and 1999, using these, archival GINGA and ASCA data sets, and the
radio ephemeris. The spin-down is not simply described by a linear function as
originally thought, but instead we find evidence of a giant glitch (|Delta P/P|
> 10E-6) between 1993 August and 1997 September, perhaps the largest yet
observed from a young pulsar. The glitch is well described by steps in the
period and its first derivative accompanied by a persistent second derivative
similar to those in the Vela pulsar. The pulse profile of AXS J161730-505505
presents a single asymmetric peak which is maintained over all observation
epochs. The energy spectrum is also steady over time, characterized by a highly
absorbed power-law with a photon index 1.4 +/- 0.2, consistent with that found
for other young rotation powered pulsars.Comment: 6 pages with 2 figures, LaTex, emulateapj.sty. To appear in the
Astrophysical Journal Letter
X-Ray Light Curves of Gamma-ray Bursts Detected with the All-Sky Monitor on RXTE
We present X-ray light curves (1.5-12 keV) for fifteen gamma-ray bursts
(GRBs) detected by the All-Sky Monitor on the Rossi X-ray Timing Explorer. We
compare these soft X-ray light curves with count rate histories obtained by the
high-energy (>12 keV) experiments BATSE, Konus-Wind, the BeppoSAX Gamma-Ray
Burst Monitor, and the burst monitor on Ulysses. We discuss these light curves
within the context of a simple relativistic fireball and synchrotron shock
paradigm, and we address the possibility of having observed the transition
between a GRB and its afterglow. The light curves show diverse morphologies,
with striking differences between energy bands. In several bursts, intervals of
significant emission are evident in the ASM energy range with little or no
corresponding emission apparent in the high-energy light curves. For example,
the final peak of GRB 970815 as recorded by the ASM is only detected in the
softest BATSE energy bands. We also study the duration of bursts as a function
of energy. Simple, singly-peaked bursts seem consistent with the E^{-0.5} power
law expected from an origin in synchrotron radiation, but durations of bursts
that exhibit complex temporal structure are not consistent with this
prediction. Bursts such as GRB 970828 that show many short spikes of emission
at high energies last significantly longer at low energies than the synchrotron
cooling law would predict.Comment: 15 pages with 20 figures and 2 tables. In emulateapj format. Accepted
by ApJ
Mosquito-borne parasites in the Great Plains: Searching for vectors of nematodes and avian malaria parasites
Vector-borne diseases in the United States have recently increased as a result of the changing nature of vectors, hosts, reservoirs, parasite/pathogens, and the ecological and environmental conditions. While most focus has been on mosquito-borne pathogens affecting humans, little is known regarding parasites of companion animal, livestock and wildlife and their potential mosquito hosts in the United States. This study assessed the prevalence of mature infections of Dirofilaria immitis and avian malaria parasites (Haemosporida) within urban mosquito (Diptera, Culicidae) communities in Oklahoma. 2,620 pools consisting of 12,686 mosquitoes from 13 species collected over two summers were tested for the presence of filarioid and haemosporidian DNA. Dirofilaria immitis-infected mosquitoes were detected only in Aedes albopictus (MIR=0.18-0.22) and Culex pipiens complex (MIR=0.12) collected in cities in central and southern Oklahoma. Two other filarioid nematode species with 91-92% similarity with Onchocerca spp. and Mansonella spp. were also detected. Haemosporidian DNA was detected in 13 mosquito pools (0.9% of pools tested) from seven mosquito species out of 13 species tested. Plasmodium DNA in four species (Cx. coronator, Cx. pipiens complex, Cx. tarsalis, and Psorophora columbiae) had high homology with published sequences of avian Plasmodium species while DNA in four other species (Cx. nigripalpus, Ps. columbiae, Anopheles quadrimaculatus, and An. punctipennis) were closely related to Plasmodium species from deer. One pool of Cx. tarsalis was positive with a 100% sequence identity of Haemoproteus sacharovi. This study provides a baseline concerning the diversity of parasites in different mosquito species present in the southern Great Plains. These studies provide important information for understanding the factors of transmission involving the mosquito community, potential hosts, and different mosquito-borne parasites in this important region involved in livestock management and wildlife conservation.Peer reviewedEntomology and Plant Patholog
Evidence for a very slow X-ray pulsar in 2S0114+650 from RXTE All-Sky Monitor Observations
Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) observations of the
X-ray binary 2S0114+650 show modulations at periods close to both the optically
derived orbital period (11.591 days) and proposed pulse period (~ 2.7 hr). The
pulse period shows frequency and intensity variability during the more than 2
years of ASM observations analyzed. The pulse properties are consistent with
this arising from accretion onto a rotating neutron star and this would be the
slowest such period known. The shape of the orbital light curve shows
modulation over the course of the entire orbit and a comparison is made with
the orbital light curve of Vela X-1. However, the expected phase of eclipse,
based on an extrapolation of the optical ephemeris, does not correspond with
the observed orbital minimum. The orbital period derived from the ASM light
curve is also slightly longer than the optical period.Comment: To be published in the Astrophysical Journal, 1999, volume 511. 9
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