The DEPMOSFET (Depleted p-channel MOSFET) is an Active Pixel Sensor (APS) for the XEUS Wide Field
Imager (WFI), which is developed and produced by the MPI semiconductor laboratory in Munich (HLL). The
current prototype detector consists of a hybrid where a 64 x 64 pixel matrix with 75 μm x 75 μm pixel size each
is mounted together with CMOS SWITCHER II ICs for row-selection and a CAMEX 64 ASIC for readout.
First measurements for this device have shown the high energy resolution and quantum efficiency as well as the
potential for fast readout. For fast timing studies on XEUS an instrument is needed which is able to deal with
count rates up to 106 photons s-1 with 10 μs time resolution. At the Institut fuer Astronomie und Astrophysik,
we have built a setup to investigate the timing performance of the current prototype detector and to study
the capability of the DEPMOSFET detector to handle high count rates. In this paper we present the Data
Acquisition System and the future plans for this setup.
With its large collecting area XEUS will be ideally suited to probe strong gravity fields around collapsed objects and to constrain the equation of state of dense matter in neutron stars. For these studies, detectors are needed which can measure 106 events/sec with high time resolution (10 μsec) and good energy resolution (ΔE = 200 - 300 eV FWHM) combined with an energy and flux independent dead time. The current baseline for a dedicated fast timing detector on XEUS is an array of 19 silicon drift detectors (SDD) operated as single photon detectors. Optionally we have studied an array of 40 x 20 SDD/DEPFET macro pixel detectors read out at a constant frame rate of 105/sec. Alternatively to these two dedicated detectors, a high time resolution mode of the Wide Field Imager (1024 x 1024 DEPFET array with 78μm x 78μm pixels) is considered here. We have simulated the expected timing performance of these detector options based on results from laboratory measurements. We have performed Monte Carlo simulations using the latest available XEUS mirror response files for Crab like sources and intensities ranging from 102 up to 4x106 events/sec. Our results are discussed in the light of the scientific requirements for fast timing as expressed in the ESA Cosmic Vision 2015-2025 plan.
X-ray timing with musec time resolution can be used to probe strong
gravity fields around collapsed objects and to constrain the equation
of state of dense matter in neutron stars. With its large collecting
area, XEUS will be ideally suited for very high signal to noise
studies of such objects. An instrument dedicated to X-ray timing of
bright Galactic sources has thus been foreseen as part of the XEUS
instrumentation. In this contribution we present numerical simulations
for silicon based detectors (silicon drift detectors and pixel based
sensors) for a variety of astrophysical sources such as neutron star
power spectra (including kHz quasi-periodic oscillations) and black
hole lightcurves to illustrate the expected scientific capabilities of
the fast timing mode instrument.
The large collecting area of XMM-Newton combined with the good energy resolution of the EPIC-pn CCDs allows the study, with unprecedented detail, of accretion processes onto neutron stars and black holes. The EPIC-pn CCD camera in Timing mode, in which data are read out continuously, is among the fastest X-ray CCD camera available; however, telemetry constraints do not allow full use of these capabilities for many sources because currently randomly distributed data gaps are introduced by the on-board data handling electronics. As an alternative, we have proposed to implement a modification of the Timing mode in which data from soft X-ray events are not transmitted to Earth. Here we discuss the properties of this modified Timing mode, which will first be used in simultaneous XMM-Newton, RXTE, and INTEGRAL observations of the Galactic black hole binary Cygnus X-1 in autumn 2004. We discuss the predicted performance of this new mode based upon laboratory measurements, Monte Carlo simulations, and data from existing Timing mode observations.