706 research outputs found
Extensions of the space trajectories error analysis programs
A generalized covariance analysis technique which permits the study of the sensitivity of linear estimation algorithms to errors in a priori statistics has been developed and programed. Several sample cases are presented to illustrate the use of this technique. Modifications to the Simulated Trajectories Error Analysis Program (STEAP) to enable targeting a multiprobe mission of the Planetary Explorer type are discussed. The logic for the mini-probe targeting is presented. Finally, the initial phases of the conversion of the Viking mission Lander Trajectory Reconstruction (LTR) program for use on Venus missions is discussed. An integrator instability problem is discussed and a solution proposed
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 1908+075: An X-ray Binary with a 4.4 day Period
X 1908+075 is an optically unidentified and highly absorbed X-ray source that
appears in early surveys such as Uhuru, OSO-7, Ariel V, HEAO-1, and the EXOSAT
Galactic Plane Survey. These surveys measured a source intensity in the range
of 2-12 mCrab at 2-10 keV, and the position was localized to ~ 0.5 degrees. We
use the Rossi X-ray Timing Explorer (RXTE) All Sky Monitor (ASM) to confirm our
expectation that a particular Einstein IPC detection (1E 1908.4+0730) provides
the correct position for X 1908+075. The analysis of the coded mask shadows
from the ASM for the position of 1E 1908.4+0730 yields a persistent intensity ~
8 mCrab (1.5-12 keV) over a 3 year interval beginning in 1996 February.
Furthermore, we detect a period of 4.400 +- 0.001 days with a false alarm
probability < 1.0e-7 . The folded light curve is roughly sinusoidal, with an
amplitude that is 22 % of the mean flux. The X-ray period may be attributed to
the scattering and absorption of X-rays through a stellar wind combined with
the orbital motion in a binary system. We suggest that X 1908+075 is an X-ray
binary with a high mass companion star.Comment: 6 pages, two-column,"emulateapj" style, submitted to Ap
Highlights of RXTE Studies of Compact Objects after ~5 Years
Observations with the Rossi X-ray Timing Explorer (RXTE) have led to
fundamental progress in the study of compact objects, in particular neutron
stars and black holes. In this paper we present briefly some highlights from ~5
years of RXTE operations.Comment: Proceedings of the Ninth Marcel Grossman Meeting, July 2000, eds.,
Vahe Gurzadyan, Robert Jantzen and Remo Ruffini, World Scientific, Singapore
(in press). 15 pages, 12 figure
The Weak Blue Bump of H2106-099 and AGN De-Reddening
We present multi-frequency spectra of the Seyfert 1 galaxy H2106-099, from
radio to hard X-rays, spanning over a decade of observations. The hard X-ray
(2-20 keV) spectrum measured with Ginga had a Log slope of -0.80 +/- 0.02 on
1988 May 18 and -1.02 +/- 0.10 on 1988 May 22 / 23 UT, with no observed flux
changes. Other measurements showed variability and unusual spectral features:
The V band flux changed by a factor of 1.8 (> 10 sigma) in six weeks. Only
moderate optical Fe II emission is present, but strong [FeVII] and [Fe X] lines
are present in some epochs. The Balmer lines show > 25% variations in flux
relative to the mean, and He I changed by more than 100% relative to the mean
in <~ six years. The most surprising finds came from the composite UV through
near-IR spectrum: If the spectrum is de-reddened by the galactic extinction
value (from 21 cm observations), a residual 2175 Angstrom absorption feature is
present. Additional de-reddening to correct the feature yields E(B-V)=0.07 mag
due to material outside our galaxy, most probably associated with the AGN or
its host galaxy. No other clear indications of reddening are observed in this
object, suggesting that blue bump strength measurements in low and intermediate
red-shift AGN could be incorrect if derived without UV observations of the
region near 2175 Angstrom in the AGN frame. After all reddening corrections are
performed, the log slope of H2106-099 from the near IR (~12500 Angstrom) to the
UV (~1400 Angstrom), -0.94 +/- 0.05, is steep compared to other AGN, suggesting
that the blue bump in this object is intrinsically weak. Weak blue bumps are,
therefore, not always an artifact caused by reddening.Comment: Three parts: A. 33 pages text, B. one landscape table, C. 8 figure
RXTE confirmation of the intermediate polar status of IGR J15094-6649
Aims. To establish the X-ray properties of the intermediate polar candidate
IGR J15094-6649 and therefore confirm its inclusion into the class.
Methods. 42 856 s of X-ray data from RXTE was analysed. Frequency analysis
was used to constrain temporal variations and spectral analysis used to
characterise the emission and absorption properties.
Results. A spin period of 809.7+-0.6 s is present, revealed as a complex
pulse profile whose modulation depth decreases with increasing X-ray energy.
The spectrum is well fitted by either a 19+-4 keV Bremsstrahlung or
Gamma=1.8+-0.1 power law, with an iron emission line feature and significant
absorption in each case.
Conclusions. IGR J15094-6649 is confirmed to be an intermediate polar.Comment: 3 pages, 5 figures. Submitted to A&
Cessation of X-ray Pulsation of GX 1+4
We report results from our weekly monitoring campaign on the X-ray pulsar GX
1+4 with the {\em Rossi X-ray Timing Explorer} satellite. The spin-down trend
of GX 1+4 was continuing, with the pulsar being at its longest period ever
measured (about 138.7 s). At the late stage of the campaign, the source entered
an extended faint state, when its X-ray (2-60 keV) flux decreased significantly
to an average level of . It was
highly variable in the faint state; the flux dropped to as low as . In several observations during this
period, the X-ray pulsation became undetectable. We can, therefore, conclude
conservatively that the pulsed fraction, which is normally 70%
(peak-to-peak), must have decreased drastically in those cases. This is very
similar to what was observed of GX 1+4 in 1996 when it became similarly faint
in X-ray. In fact, the flux at which the cessation of X-ray pulsation first
occurred is nearly the same as it was in 1996. We suggest that we have, once
again, observed the propeller effect in GX 1+4, a phenomenon that is predicted
by theoretical models of accreting X-ray pulsars.Comment: 13 pages, 9 figures (available at
http://www.physics.purdue.edu/~cui/ftp/cuifigs.tar.gz). To appear in Ap
Relativistic Iron Line Emission from the Neutron Star Low-mass X-ray Binary 4U 1636-536
We present an analysis of XMM-Newton and RXTE data from three observations of
the neutron star LMXB 4U 1636-536. The X-ray spectra show clear evidence of a
broad, asymmetric iron emission line extending over the energy range 4-9 keV.
The line profile is consistent with relativistically broadened Fe K-alpha
emission from the inner accretion disk. The Fe K-alpha line in 4U 1636-536 is
considerably broader than the asymmetric iron lines recently found in other
neutron star LMXBs, which indicates a high disk inclination. We find evidence
that the broad iron line feature is a combination of several K-alpha lines from
iron in different ionization states.Comment: 7 pages, 2 figures, Published in the Astrophysical Journa
On the Spin History of the X-ray Pulsar in Kes 73: Further Evidence For an Utramagnetized Neutron Star
In previous papers, we presented the discovery of a 12-s X-ray pulsar in the
supernova remnant Kes 73, providing the first direct evidence for an
ultramagnetized neutron star, a magnetar, with an equivalent dipole field of
nearly twenty times the quantum critical magnetic field. Our conclusions were
based on two epochs of measurement of the spin, along with an age estimate of
the host supernova remnant. Herein, we present a spin chronology of the pulsar
using additional GINGA, ASCA, XTE, & SAX datasets spanning over a decade.
Timing and spectral analysis confirms our initial results and severely limit an
accretion origin for the observed flux. Over the 10 year baseline, the pulsar
is found to undergo a rapid, constant spindown, while maintaining a steady flux
and an invariant pulse profile. Within the measurement uncertainties, no
systematic departures from a linear spin-down are found - departures as in the
case of glitches or simply stochastic fluctuations in the pulse
times-of-arrival (e.g. red timing noise). We suggest that this pulsar is akin
to the soft gamma-ray repeaters, however, it is remarkably stable and has yet
to display similar outbursts; future gamma-ray activity from this object is
likely.Comment: 6 pages with 3 embedded figures, LaTex, emulateapj.sty. Submitted to
the ApJ Letter
An X-Ray Dip in the X-Ray Transient 4U 1630-47
An x-ray dip was observed during a 1996 Rossi X-Ray Timing Explorer
observation of the recurrent x-ray transient 4U 1630-47. During the dip, the
2-60 keV x-ray flux drops by a factor of about three, and, at the lowest point
of the dip, the x-ray spectrum is considerably softer than at non-dip times. We
find that the 4U 1630-47 dip is best explained by absorption of the inner part
of an accretion disk, while the outer part of the disk is unaffected. The
spectral evolution during the dip is adequately described by the variation of a
single parameter, the column density obscuring the inner disk.Comment: 13 pages, 4 figures, Accepted for publication in Ap
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