C. Reppin

The European Photon Imaging Camera on XMM-Newton: The pn-CCD camera

The European Photon Imaging Camera (EPIC) consortium has provided the focal plane instruments for the three X-ray mirror systems on XMM-Newton. Two cameras with a reflecting grating spectrometer in the optical path are equipped with MOS type CCDs as focal plane detectors (Turner 2001), the telescope with the full photon flux operates the novel pn-CCD as an imaging X-ray spectrometer. The pn-CCD camera system was developed under the leadership of the Max-Planck-Institut fur extraterrestrische Physik (MPE), Garching. The concept of the pn-CCD is described as well as the dierent operational modes of the camera system. The electrical, mechanical and thermal design of the focal plane and camera is briefly treated. The in-orbit performance is described in terms of energy resolution, quantum eciency, time resolution, long term stability and charged particle background. Special emphasis is given to the radiation hardening of the devices and the measured and expected degradation due to radiation damage of ionizing particles in the rst 9 months of in orbit operation.

The European Photon Imaging Camera on XMM-Newton: The MOS cameras

The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record the images and spectra of celestial X-ray sources focused by the three X-ray mirrors. There is one camera at the focus of each mirror; two of the cameras contain seven MOS CCDs, while the third uses twelve PN CCDs, dening a circular eld of view of 30 0 diameter in each case. The CCDs were specially developed for EPIC, and combine high quality imaging with spectral resolution close to the Fano limit. A lter wheel carrying three kinds of X-ray transparent light blocking lter, a fully closed, and a fully open position, is tted to each EPIC instrument. The CCDs are cooled passively and are under full closed loop thermal control. A radio-active source is tted for internal calibration. Data are processed on-board to save telemetry by removing cosmic ray tracks, and generating X-ray event les; a variety of dierent instrument modes are available to increase the dynamic range of the instrument and to enable fast timing. The instruments were calibrated using laboratory X-ray beams, and synchrotron generated monochromatic X-ray beams before launch; in-orbit calibration makes use of a variety of celestial X-ray targets. The current calibration is better than 10% over the entire energy range of 0.2 to 10 keV. All three instruments survived launch and are performing nominally in orbit. In particular full eld-of-view coverage is available, all electronic modes work, and the energy resolution is close to pre-launch values. Radiation damage is well within pre-launch predictions and does not yet impact on the energy resolution. The scientic results from EPIC amply full pre-launch expectations.

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.

A direct observation of solar neutrons following the 0118 UT flare on 1980 June 21

The Gamma Ray Spectrometer on the Solar Maximum Mission satellite has observed energetic solar neutrons (greater than 50 MeV) at the earth following a solar flare that occurred on the west limb on June 21, 1980 at 01:18:20 UT. Impulsive photon emission from 10 keV to greater than 65 MeV lasting over a period of about 66 s was followed by a transient flux of 50-600 MeV neutrons incident over a 17 minute period. The peak counting rate corresponds to an average flux at the earth of (3.8 + or - 0.6) x 10 to the -2nd neutrons/sq cm s at 130 MeV. These observations indicate the emission of 3 x 10 to the 28th neutrons/sr with energies greater than 50 MeV, requiring the rapid acceleration (much less than 60 s) of protons to GeV energies during the impulsive phase of the flare.

The pn-CCD on-chip electronics.

A new pn-CCD with an activa area of 3 × 1 cm2 was recently fabricated for ESAs X-ray Multi Mirror Mission (XMM). The front-end electronics has been integrated on the same chip as the detector, and its noise behaviour was investigated. X-rays from a 55Fe source have been used for the absolute calibration. The measured electronic Equivalent Noise Charge (ENC) of the on-chip amplifier was 8.8 e− at room temperature and 2.2 e− at the CCD operating temperature of 150 K. The improvements with respect to the last version with noise figures of 4.8 e− (at 150 K) are due to the reduction of the total input capacitance by a factor of 1.6, the improvement of the transistor transconductance by a factor of 2, and the reduction of 1ƒ noise because of the different p-well implant with a better thermal annealing.

The MPI/AIT X-ray imager (MAXI) — High speed pn CCDs for X-ray detection

MAXI (MPI/AIT X-ray Imager) is part of a proposal submitted to the European Space Agency (ESA) as focal plane instrumentation of the X-ray Multi Mirror Mission (XMM). Within a collaboration of 13 European institutes we have proposed a fully depleted (sensitive) pn CCD of 280 μm thickness with a homogeneous sensitive area of 36 cm2 and a pixel size of 150×150 μm2 which is well matched with the telescopes angular resolution of 30 arcsec translating to a position resolution of approximately 1 mm in the focal plane. The X-ray sensitivity will be higher than 90% from 250 eV up to 10 keV, the readout time in the full frame mode of the complete focal plane will be 2 ms with a readout noise of better than 5 e− (rms). Prototypes of all individual components of the camera system have been fabricated and tested. The camera concept will be presented. The measured transfer properties of the CCD and the on-chip electronics will be treated. Taking into account the coupling of the on-chip amplifier to the following front-end electronics the expected performance will be derived.

Performance of the pn-CCD X-ray detector system designed for the XMM satellite mission

Abstract The pn-CCD detector system is designed as a focal plane instrument for the European Photon Imaging Camera (EPIC) on the X-ray Multi Mirror mission (XMM) of the European Space Agency. This satellite will be launched by the end of this century. The sensitive area of the detector consists of a 6 × 6 cm2 array of 12 pn-CCDs monolithically integrated on a single silicon wafer. The detector has been optimized for high-resolution X-ray spectroscopy between 100 eV and 15 keV with simultaneous good quantum efficiency for the investigation of faint objects. A fast readout achieves excellent time resolution for the observation of pulsed X-ray sources. The relevant performance parameters reflecting the state of the detector development are presented. Energy resolution reaches the theoretical limits given by the Fano noise. Due to a thin entrance window and full depletion of the device the quantum efficiency is better than 80% over a wide energy range. Evidence for radiation hardness and background rejection capability will also be provided.

EVIDENCE FOR STRONG CYCLOTRON EMISSION IN THE HARD X-RAY SPECTRUM OF HER X-1

It is well known from pulsar physics that neutron stars must possess surface magnetic fields of the order of loio to lo” gauss or possibly even higher. These figures are derived from considerations about ( I ) magnetic flux conservation during the gravitational collapse, (2) magnetic dipole braking of radio pulsars, and (3) accretion torques acting on binary neutron stars. Applying the latter argument to Hercules X-1, Elsner and Lamb6 estimated the stellar magnetic moment to be 1030cgs, which leads to a surface field of 10” gauss. An attempt to use spectral data in order to estimate the magnetic field strength in the polar cap of Her X-l has been made by Boldt et a f . 3 They explain the steep cutoff in the hard x-ray spectrum occurring a t 25 keV by a model that assumes that the plasma above the polar caps becomes optically thick at frequencies that approach the electron cyclotron frequency w H . These authors find that t i w H = 100 keV gives the best fi t to their data, which corresponds to a magnetic field strength of I O l 3 gauss. We note that this estimate is model dependent since it requires assumptions regarding the spatial energy release distribution of the accreted protons in the polar hot spot, as well as the radiative heat transfer characteristics of this region. Also, the predictions of this model on the energy dependence of the pulse profile are contradicted by our present data.” I n the following we report on the discovery of a strong line feature in the Her X-l spectrum at 53 keV, which we interpret as cyclotron emission. The corresponding magnetic field is 4.6 x 10I2 gauss.

First results with the pn-CCD detector system for the XMM satellite mission.

The pn-CCD is a novel CCD type which is developed for fast X-ray imaging and spectroscopy for the X-ray Multi Mirror (XMM) satellite mission. Each 200 × 64 pixel large pn-CCD unit with a sensitive area of 3 × 1 cm2 is a fully depleted detector. Full depletion allows for high photon detection efficiency (> 90% in the energy range of 500 eV-10 keV), for a small input capacitance necessary for low noise signal measurements and for backward illumination. For good time resolution and low noise performance each of the 64 CCD channels is terminated with an integrated input-JFET for signal amplification. With the use of the CMOS Amplifier and Multiplexing Chip (CAMEX64B) it is possible to read out the 64 CCD channels in parallel before they are multiplexed and sent to an ADC. For the first time the system of a 64 channel pn-CCD together with CAMEX64B readout, ADC conversion and data acquisition and storage has been brought into operation. First images of an 55Fe X-ray source are presented and discussed.

The first broad-band X-ray images and spectra of the 30 Doradus region in the LMC

We present the XMM-Newton first light image, taken in January 2000 with the EPIC pn camera during the instruments commissioning phase, when XMM-Newton was pointing towards the Large Magellanic Cloud (LMC). The field is rich in different kinds of X-ray sources: point sources, supernova remnants (SNRs) and diffuse X-ray emission from LMC interstellar gas. The observations are of unprecedented sensitivity, reaching a few 10