Search

We present light curves and spectra of a ∼35ksec RXTE observation of Vela X-1 and a ∼300 ksec observation of Cen X-3. Both light curves show strong absorption which increases from no absorption at low orbital phases to large values at high orbital phases; in the case of Vela X-1 by a factor of almost 100. Superimposed are absorption dips which can be observed at any orbital phase, though mostly at high orbital phases. We study an unusually strong dip in Vela X-1 during which the flux is reduced by ∼90% and almost no pulses are detectable. The increase of N[sub H] and the scattered component show the in- and egress of material in the line of sight. A similar behaviour is observed in a pre-eclipse dip in Cen X-3. [ABSTRACT FROM AUTHOR]

We report phase resolved spectroscopy of the transient accreting pulsar, 4U 0115+63. For the first time, more than two cylotron resonance scattering features are detected in the spectrum of an X-ray pulsar. The shape of the fundamental line appears to be complex, and this is in agreement with predictions of Monte-Carlo models. As in other pulsars, the line energies and optical depths are strong functions of pulse phase. One possible model for this is an offset of the dipole of the neutron star magnetic field. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

© 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The black hole candidate LMC X-3 varies by a factor of four on a timescale of either 200 or 100 days (Cowley et al., 1991). We have monitored LMC X-3 with RXTE in three to four week intervals starting in December 1996, obtaining a large observational database that sheds light on the nature of the long term X-ray variability in this source. In this paper we present the results from this monitoring campaign, focusing on evidence of recurring hard states in this canonical soft state black hole candidate. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recently an Anomalous Low State in the 35d cycle of Her X-1, which is thought to be caused by the tilted accretion disk, was observed with the RXTE. This has been seen only twice before; in 1983 and again 1993. We present timing and spectral results of this latest anomalous low obtained 1999 April 26. Pulsations were observed in the 2–20 keV band but with a pulsed fraction down by a factor of 10 from the main-on. Spectral analysis indicates 70% absorbed flux (N[sub H]=7×10[sup 23]) with the remainder unabsorbed. This is consistent with continuous screening of the X-ray source by the accretion disk causing the anomalous low. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]