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We compiled X-ray and Optical observations of the accreting X-ray binary sytem A0535+26 since its discovery in 1975, that will allow us to shed light on the unpredictible behavior of this binary system. We present the data in terms of the Be-disc interaction with the neutron star companion. In addition, we show recent results from the continous monitoring of this source by the Gamma-ray Burst Monitor (GBM), on board the Fermi observatory, since its launch in 2008 June 11. [ABSTRACT FROM AUTHOR]

The Galactic Bulge region is a rich host of variable high-energy point sources. These sources include bright and relatively faint X-ray transients, X-ray bursters, persistent neutron star and black-hole candidate binaries, X-ray pulsars, etc.. We have a program to monitor the Galactic Bulge region regularly and frequently with the γ-ray observatory INTEGRAL. As a service to the scientific community the high-energy light curves of all the active sources as well as images of the region are made available through the WWW. We show the first results of this exciting new program. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present results from simultaneous observations of Cyg X-1 with INTEGRAL and RXTE in 2002 November and December, employing the new RXTE calibration from HEASOFT 5.3. The broad-band X-ray/γ-ray spectrum is well described by Comptonization spectra with an additional reflection component. The temperature of the Comptonizing plasma is kTe ∼ 60–80 keV and its optical depth is τ ∼ 0.8–1.2. The covering factor of the reflector is Ω/2π ∼ 0.1. There is a possible soft excess below 10 keV, interpreted as emission from the accretion disk. The spectral parameters are slightly different from those obtained by us earlier due to the different RXTE-PCA calibration. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A great deal of emphasis on timing in the RXTE era has been on pushing toward higher and higher frequency phenomena, particularly kHz QPOs. However, the large areas of the RXTE pointed instruments provide another capability which is key for the understanding of accreting X-ray pulsars — the ability to accumulate high quality spectra in a limited observing time. For the accreting X-ray pulsars, with their relatively modest spin frequencies, this translates into an ability to study broad band spectra as a function of pulse phase. This is a critical tool, as pulsar spectra are strong functions of the geometry of the “accretion mound” and the observers’ viewing angle to the ∼1012 G magnetic field. In particular, the appearance of “cyclotron lines” is sensitively dependent on the viewing geometry, which must change with the rotation of the star. These spectral features, seen in only a handful of objects, are quite important, as they give us our only direct measure of neutron star magnetic fields. Furthermore, they carry a great deal of information as to the geometry and physical conditions in the accretion mound. In this paper, we review the status of cyclotron line studies with the RXTE. We present an overview of phase-averaged results and give examples of observations which illustrate the power of phase-resolved spectroscopy. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present the spectral analysis of our 35 ksec continuous RXTE observation of the High Mass X-ray Binary Vela X-1. The spectral models used normally to describe pulsar spectra like a power law with an exponential cutoff or the NPEX model (Negative Positive EXponential), do not work for our data. Our successful model consists of two NPEX components: one is heavily absorbed, while the other is due to reflection. But we still find large deviations around ∼21 keV and ∼50 keV. We interpret the feature at ∼55 keV as a cyclotron absorption line while the lower deviation might be due to instrument calibration problems around 25 keV in the PCA. [ABSTRACT FROM AUTHOR]

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 present results from a 20 h RXTE observation of Vela X-1, including a peculiar low state of a few hours duration, during which the pulsation of the X-ray emission ceased, while significant non-pulsed emission remained. This “quiescent state” was preceded by a “normal state” without any unusual signs and followed by a “high state” of several hours of increased activity with strong, flaring pulsations. While there is clear spectral evolution from the normal state to the low state, the spectra of the following high state are surprisingly similar to those of the low state. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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

The INTEGRAL Science Data Center (ISDC) is designed as an interface between the INTEGRAL data and the user community. Its main task is to receive and process all the INTEGRAL data in order to (1) detect GRBs and other bright transient sources, for alerting the astronomical community and for initiating possible INTEGRAL Target Of Opportunity (TOO) observation, and (2) produce and archive a set of standard data products, and to distribute them to the observers. It is also foreseen to provide help and support to the observers in analyzing INTEGRAL data. The ISDC is funded by a consortium of European and US institutes. It is located in Versoix near Geneva. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]