Joachim E. Truemper

Evidence for strong cyclotron line emission in the hard X-ray spectrum of Hercules X-1

We present further results of our Hercules X-1 balloon observation on 1976 May 3 which confirm the existence of a strong line feature at approx.58 keV in the pulsed (1.24s) X-ray spectrum we reported earlier. The spectral excess in the line region over the extrapolated continuum is 5-6 sigma. Our best estimates of the line flux and line width are 3 x 10/sup -3/ photons cm/sup -2/ s/sup -1/ and less than approx.12 keV, respectively. The most likely interpretation of this line is electron cyclotron emission at the basic frequency from the hot polar plasma of the rotating neutron star. The corresponding magnetic field strength is 5.3 x 10/sup 12/ gauss. We have searched for the second-harmonic cyclotron emission line in that part of our data showing the highest signal-to-noise ratio and find a 3.3 sigma spectral enhancement near the predicted energy (110 keV). We discuss implications of the line width and the line intensity ratio for the physical conditions of the emitting plasma and the beaming geometry.

The evolution of galactic X-ray binaries

The Role of Binaries in Globular Cluster Evolution.- Common Envelope Evolution.- Origin and Evolution of X-Ray Binaries in Globular Clusters.- A Note on the Nature of the Secondaries in Ultra-Compact Binaries.- Wind Fed X-Ray Binaries.- The Three Types of High Mass X-Ray Pulsator.- Orbital Period Changes in Massive X-Ray Binaries.- From Wide to Close Binaries?.- Evolution of Close Binaries and the Formation of Neutron Stars.- Quasi-Periodic Oscillations in GX 5-1 and SCO X-1.- Quasi-Periodic Oscillations in the X-Ray Flux of CYG X-2 and Their Relation to the Source Spectra.- Quasi-Periodic Oscillations as a Probe of Galactic-Bulge X-Ray Sources.- On the Nature of the Quasiperiodic Oscillations of Low Mass X-Ray Binaries.- The Duration of the Detached Phase in Low-Mass X-Ray Binaries in which the Neutron Star was Formed by Accretion-Induced Collapse of a White Dwarf.- Some Remarks on Classifications of Low-Mass X-Ray Binaries.- Two Spectral Components and Their Luminosity-Related Changes of Low-Mass Binary X-Ray Sources.- The Evolution of Low Mass Binary Systems.- Eclipse of a Bright Spot in the Disk of Her X-1.- The Orbital Periods of the Low Mass X-Ray Binaries.- Exosat Observations of the 35-Day Cycle of Her X-1 Evidence for Neutron Star Precession.- Timing Analysis of the Galactic Bulge X-Ray Source GX 17+2.- On the Evolution of Her X-1.- Do Neutron Star Magnetic Fields Decay?.- Secular Evolution of Cataclysmic Binaries.- The Evolution of Magnetic Cataclysmic Variables.- Variability of Apparent Radii in the Decay Part of Type I X-Ray Bursts.

Exosat observations of 4U 1705-44 - Type I bursts and persistent emission

During four Exosat observations, the bright galactic X-ray source 4U 1705-44 exhibited persistent emission variations from 1.3 to 10.7 x 10 to the -9th ergs/sq cm per sec in the 1-20 keV band. Type I X-ray bursts have been detected from this source whose properties correlate with source intensity. The burst shape changed with increasing intensity from a slow burst profile with a decay time of 100 sec to a feast profile with a decay time of 25 sec. The spectrum during maximum was best-fitted by a two-component model involving a blackbody together with a Boltzmann-Wien law, and an additional iron K emission line. 28 references.

Rosat observations of the LMC pulsar PSR 0540-69

The LMC pulsar PSR 0540-69, a young, rapidly rotating neutron star of dynamic age ∼1000 yr, was observed with the Position Sensitive Proportional Counter (PSPC) onboard ROSAT for ∼29,000 s in 1990 June, 1990 July, and 1991 February. The timing data are consistent with contemporaneous optical ephemerides suggesting that the optical and X-ray pulses are in phase. The characteristic broad sinusoidal pulse profile of PSR 0540-69 is observed at a pulsed fraction of ∼15% measured against the pulsar plus the unresolved nebula. The spectral distribution of the pulsar+nebula counts is well described by a simple power law with a photon index of α=(2.4-1.85) and a neutral hydrogen column density of N H =(3.6-4.6)×10 21 cm -2 at the 90% confidence level

EXOSAT observations of 4U/MXB 1636-53 - On the relation between the amount of accreted fuel and the strength of an X-ray burst

During Exosat observations of 4U/MXB 1636-53 in August 1985, three bursts were observed in 6 h and 24 bursts in 79 h of uninterrupted observation. The burst times, burst fluences, peak burst fluxes, burst rise times, decay times, burst intervals, mean persistent fluxes, and the product of the latter two are listed, analyzed, and discussed. The implications of the results for thermonuclear flash models are examined. A model which fits the data well involves bursts which suffer from nuclear energy losses due to stable hydrogen burning between bursts. Thus, the percentage of lost energy increases with increasing burst intervals. For individual bursts, however, there are significant deviations from the approximate linear relationship. 43 references.

Exosat Observations of the 35-Day Cycle of Her X-1; Evidence for Neutron Star Precession

We have observed Her X-1 with the EXOSAT satellite throughout a 35-day cycle at about four day sampling intervals. These measurements include for the first time, an accurate measurement of the 1.24 sec pulse profiles seen during the short-on state at the middle of the 35-day cycle. The data show a large change in the pulse profiles between the main and short-on states, suggesting a precession of the magnetic dipole axis of the rotating neutron star. We propose that the clock mechanism resides in the free precession of the neutron star and examine further consequences of this precession with respect to the inner structure of the accretion disk.

X-ray evolving universe spectroscopy mission (XEUS)

XEUS: The X-ray Evolving Universe Spectroscopy mission represents a potential follow-on mission to the ESA XMM cornerstone currently nearing completion. XEUS represents the next logical step forward in x-ray astrophysics after the current set of mission have been launched and completed their operational lives. The development and ultimate success relies heavily on the capability of the International Space Station (ISS). In this paper we describe the key characteristics of the mission including the requirements placed specifically on the ISS and discuss the significant advances in high energy astrophysics expected from such an observatory.

Experimental verification of a micrometeoroid damage in the pn-CCD camera system aboard XMM-Newton

The pn-CCD is the focal plane detector of one of the three X-ray telescopes aboard the XMM-Newton observatory. During revolution #156 more than 30 individual bright pixels lightened up out of approximately 150,000 pixels of the 6 cm × 6 cm large detector area. The amount of leakage current generated in the pixels cannot be explained by single heavy ions impact, however. We suggest that a micrometeoroid scattered off the mirror surface under grazing incidence reached the focal plane detector and produced the bright pixels. This proposal was studied by us experimentally at the Heidelberg dust accelerator. Micron-sized iron particles were accelerated to speeds of the order of 5 km/s impinging on the surface of an X-ray mirror under grazing incidence. Scatter products have been found with detectors placed behind the mirror. They have been analyzed by various methods to characterize their properties and the effects produced by them in the pn-CCD. Micrometeoroid damage to semiconductor detectors in the focus of grazing incidence optics might be of concern for future space projects with very large collecting area and are proposed to be studied in detail.

X-ray pn-CCDs on the XMM Newton Observatory

XMM-Newton, the most powerful X-ray telescope ever built was launched from the european space port Kourou on december 10 last year. Three large X-ray Wolter type mirror systems are focusing the incoming X-rays from 100 eV up to 15,000 eV onto the focal instruments: fully depleted backside illuminated pn-CCDs and frontside illuminated MOS-CCDs. The concept of the pn-CCD camera will be briefly described and its performance on ground and in orbit will be shown. Special emphasis will be given to the radiation hardening of the devices, to the instrument background and to the experience of charged particle background in space. A comparison of the performance on ground and after 5 months in space will be shown.

36-cm2 large monolythic pn-CCD detector for EPIC on XMM

Monolithic arrays of 12 CCDs, 3 by 1 cm2 each, have been developed and produced for the focal plane instrumentation of the European photon imaging camera (EPIC) on XMM and the German ABRIXAS x-ray satellite mission. The design parameters have been optimized to match the properties of the x-ray imaging optics as well as the x-ray intensity, energy bandwidth and characteristic time constants of the objects to observe. The pixel size is 150 by 150 micrometer2; readout is performed in parallel; low noise, spectroscopic performance is realized by on-chip integrated JFET electronics; highohmic, ultrapure bulk material allows full depletion and enhances the efficiency for higher energy x-ray detection. The fabrication process, the layout topology and the operating conditions guarantee for a ten year operation in space without performance degradation.