Christian Erd

Simultaneous absolute timing of the Crab pulsar at radio and optical wavelengths

Context. The Crab pulsar emits across a large part of the electromagnetic spectrum. Determining the time delay between the emission at different wavelengths will allow to better constrain the site and mechanism of the emission. We have simultaneously observed the Crab Pulsar in the optical with S-Cam, an instrument based on Superconducting Tunneling Junctions (STJs) with μs time resolution and at 2 GHz using the Nancay radio telescope with an instrument doing coherent dedispersion and able to record giant pulses data. Aims. We have studied the delay between the radio and optical pulse using simultaneously obtained data therefore reducing possible uncertainties present in previous observations. Methods. We determined the arrival times of the (mean) optical and radio pulse and compared them using the tempo2 software package. Results. We present the most accurate value for the optical-radio lag of 255±21 μs and suggest the likelihood of a spectral dependence to the excess optical emission asociated with giant radio pulses.

In-orbit calibration of the XMM-Newton telescopes

The High Throughput X-ray Spectroscopy Mission XMM-Newton of the European Space Agency (ESA) was launched on December 10, 1999 by an Ariane V rocket. The satellite observatory uses three grazing incidence telescopes coupled to reflection grating spectrometers and x-ray CCD cameras. Each x-ray telescope consists of 58 Wolter I mirrors which are nested in a coaxial and cofocal configuration. The XMM-Newton Science Operation Center has completed a coherent program for the in- orbit calibration and performance verification of the x-ray observatory. This paper presents first measurement results of the x-ray telescopes image quality and effective area obtained during this campaign.

ON THE DETECTION OF SINGLE OPTICAL PHOTONS WITH SUPERCONDUCTING TUNNEL JUNCTION

We report the detection of individual optical and ultraviolet photons using a different approach to photon detection based on a superconducting tunnel junction. A 20×20 μm2 junction, employing a 100 nm niobium film and operated at a temperature of ∼0.4 K, has been used to detect individual photons with inherently high quantum efficiency (>45%) over a broad wavelength range (between 200 and 500 nm), yielding high temporal (sub-ms) resolution, spatial resolution determined by the junction size, under conditions of minimal dark current, and in the absence of read noise. The quantum efficiency is limited by surface reflection, and could be improved by the deposition of antireflection coatings. The theoretical wavelength response range continues into the far UV and soft x-ray region, and is presently limited beyond 500 nm largely by the available signal processing electronics. The device intrinsically functions at very high incident photon rates—with count rates of order ∼10 kHz or higher being feasible and ag...

XMM flight mirror modules with reflection grating assembly and x-ray baffle testing

In the frame of the XMM project, several test campaigns are accomplished to qualify the optical elements of the mission. The test described in this paper are performed on a XMM flight model mirror module added with a reflection grating assembly (RGA). The mirror module contains 58 x-ray optical quality shells, an x-ray baffle (XRB) to reduce the straylight. This complete XMM flight model mirror assembly (MA) is tested in a vertical configuration at CSL, in a full aperture or partial EUV collimated beam illumination, and with an x-ray pencil beam. One of the advantages of the EUV collimated beam is to verify the correct position of the RGA when integrated in flight configuration on the mirror module structure. This is not possible in x-ray with a finite source distance. The partial EUV illumination is performed to verify the correct integration of the RGA grating stacks. The pencil beam allows to make an accurate metrology of the XRB position, and to verify the positions of the 0, 1 and 2 diffraction order foci. In this paper, the tested module is first exposed, and the approach to qualify the instrument is described. The analysis of the results achieved over the different test configurations is presented. The impact of the environmental test on the reflection grating box is also diagnosed.

Reflection grating arrays for the Reflection Grating Spectrometer on board XMM

The reflection grating spectrometer (RGS) on-board the x-ray multi-mirror (XMM) mission incorporates an array of reflection gratings oriented at grazing incidence in the x- ray optical path immediately behind a grazing incidence telescope. Dispersed light is imaged on a strip of CCD- detectors slightly offset from the telescope focal plane. The grating array picks off roughly half the light emanating from the telescope; the other half passes undeflected through the array where it is imaged by the European photon imaging camera (EPIC) experiment. XMM carries two such identical units, plus a third telescope with an EPIC detector, but no RGS. The basic elements of the RGA include: 202 identical reflection gratings, a set of precision rails with bosses that determine the position and alignment of each grating, a monolithic beryllium integrating structure on which the rails are mounted, and a set of three, kinematic support mounts which fix the array to the telescope. In this paper, we review our progress on the fabrication and testing of the RGA hardware, with particular attention to the components comprising the engineering qualification model, a flight-representative prototype which will be completely assembled in September of this year.

Development of compound semiconductor arrays for x- and gamma-ray spectroscopy

We present preliminary results of X-ray measurements on three small format compound semiconductor arrays. The devices, a 4x4 pixel GaAs array fabricated on 325 micrometers epitaxial material, a 4x4 pixel CdZnTe array fabricated on a 4X4X1 mm3 mono crystal and a 3x3 TlBr array fabricated on a 2.7 x 2.7 x 1.0 mm3 mono crystal. The pixel size for all arrays is 350x350micrometers 2. Results are presented of 55Fe and 241Am measurements at 5.9 keV and 59.54 keV. For detector temperatures <+5 degree(s)C typical FWHM energy resolutions of 410 eV, and 600 eV at 5.9 keV and 640 eV and 1.4 keV at 59.54 keV were recorded for the GaAs, and CdZnTe arrays, respectively. Unlike the GaAs and CdZnTe arrays, the TlBr array showed a much wider variation in pixel performance and was difficult to operate with all pixels at a common bias. For example, biasing the detector so that all pixels worked within the operating envelope of the preamplifiers resulted in average energy resolutions of 20 keV at 59.54 keV. However, optimizing the operating conditions of individual pixels resulted in a marked improvement to ~2keV.

Performance characterization of the reflection grating arrays (RGA) for the RGS experiment aboard XMM

The Reflection Grating Spectrometer (RGS) aboard XMM is a large collecting area, dispersive soft x-ray spectrometer providing high resolution and a bandpass of 5-35 angstrom. We have built and characterized the two, nearly identical, flight model reflection grating arrays for the RGS instrument. Precision alignment and assembly of 182 grating elements into each array was performed at Columbia Astrophysics/Nevis Laboratory, and end-to-end X-ray calibration and testing were performed at the MPE-Panter facility. Preliminary results from the calibration are summarized, and reconciliation of those results with baseline optical design, simulations and error budgets are discussed.

X‐ray detection by superconducting tunnel junctions via phonon propagation in the substrate

The x‐ray performance of Nb‐Al‐AlOx‐Al‐Nb superconducting tunnel junctions deposited on sapphire has been studied for phonon mediated detection of x rays absorbed in the substrate in the energy range 750 to 6000 eV. Two separate channels of phonon propagation can be identified. One produces a discrete signal peak, due to high frequency phonons originating from the x‐ray absorption sites in a shallow layer below the junction. The other contributes to a monotonic signal tail, due to low frequency phonons, reaching the junction after diffusive or multiple scattering at surfaces.

Demonstration of highly integrated payload architectures and instrumentation for future planetary missions

Future planetary missions will require advanced, smart, low resource payloads (P/Ls) and satellites1,2 to enable the exploration of the solar system in a more frequent, timely and multi-mission manner with reasonable cost. The concept of highly integrated payload architectures was introduced during the re-assessment of the payload of the BepiColombo Mercury Planetary Orbiter3. Considerable mass and power savings were achieved throughout the instrumentation by better definition of the instruments design, higher integration and identification of resource drivers4. Higher integration and associated synergy effects permit optimisation of the payload performance at minimum resource requirements while meeting demanding science requirements. This promising concept has been applied to a set of hypothetical Planetary Technical Reference Studies11 (PTRS) on missions to Venus5, Jupiter/Europa6, Deimos7, Mars8 and the investigation of the Interstellar Heliopause9. The needs on future instrumentation were investigated for these mission concepts and potential instruments were proposed10. A demonstration programme is now proposed in form of an elegant breadboard that consists of a photon counting laser altimeter, a stereoscopic high resolution camera, and a broadband radiometric mapping spectrometer. The aim of the activity is to demonstrate to feasibility of such a miniaturised, low resource and highly integrated payload based on innovative instrument designs. The activity shall thereby provide a clear detailed definition of the technical and managerial aspects for implementation into potential future planetary space science missions.

Reflection Grating Spectrometer on board XMM

The x-ray multi-mirror (XMM) mission is the second of four cornerstone projects of the ESA long-term program for space science, Horizon 2000. The payload comprises three co- aligned high-throughput, imaging telescopes with a FOV of 30 arcmin and spatial resolution less than 20 arcsec. Imaging CCD-detectors (EPIC) are placed in the focus of each telescope. Behind two of the three telescopes, about half the x-ray light is utilized by the reflection grating spectrometer (RGS). The x-ray instruments are co-aligned and measure simultaneously with an optical monitor (OM). The RGS instruments achieve high spectral resolution and high efficiency in the combined first and second order of diffraction in the wavelength range between 5 and 35 angstrom. The design incorporates an array of reflection gratings placed in the converging beam at the exit from the x-ray telescope. The grating stack diffracts the x-rays to an array of dedicated charge-coupled device (CCD) detectors offset from the telescope focal plane. The cooling of the CCDs is provided through a passive radiator. The design and performance of the instrument are described below.