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

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

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 $\sim 3 \times 10^{-10} ergs cm^{-2} s^{-1}$. It was highly variable in the faint state; the flux dropped to as low as $\sim 3 \times 10^{-11} ergs cm^{-2} s^{-1}$. In several observations during this period, the X-ray pulsation became undetectable. We can, therefore, conclude conservatively that the pulsed fraction, which is normally $\gtrsim$ 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

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