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The XMM-Newton observatory, launched by the European Space Agency in 1999, is still one of the scientific community’s most important high-energy astrophysics missions. After almost 15 years in orbit its instruments continue to operate smoothly with a performance close to the immediate post-launch status. The competition for the observing time remains very high with ESA reporting a very healthy over-subscription factor. Due to the efficient use of spacecraft consumables XMM-Newton could potentially be operated into the next decade. However, since the mission was originally planned for 10 years, progressive ageing and/or failures of the on-board instrumentation can be expected. Dealing with them could require substantial changes of the on-board operating software, and of the command and telemetry database, which could potentially have unforeseen consequences for the on-board equipment. In order to avoid this risk, it is essential to test these changes on ground, before their upload. To this aim, two flight-spare cameras of the EPIC experiment (one MOS and one PN) are available on-ground. Originally they were operated through an Electrical Ground Support Equipment (EGSE) system which was developed over 15 years ago to support the test campaigns up to the launch. The EGSE used a specialized command language running on now obsolete workstations. ESA and the EPIC Consortium, therefore, decided to replace it with new equipment in order to fully reproduce on-ground the on-board configuration and to operate the cameras with SCOS2000, the same Mission Control System used by ESA to control the spacecraft. This was a demanding task, since it required both the recovery of the detailed knowledge of the original EGSE and the adjustment of SCOS for this special use. Recently this work has been completed by replacing the EGSE of one of the two cameras, which is now ready to be used by ESA. Here we describe the scope and purpose of this activity, the problems faced during its execution, the adopted solutions, and the tests performed to demonstrate the effectiveness of the new EGSE.

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 Imager proposed for the gamma-ray satellite project INTEGRAL is based on a multilayer two-dimensional array of CsI(TI) elements viewed by Si photodiodes. The total active area is ≈2500 cm2. The operative energy interval ranges from 0.05 to 10 MeV. A prototype version of this instrument, ready to be tested on a ballon-borne experiment, has been realized. In this article the expected performances of the instrument are presented, toghether with the first calibration results of the prototype.

The low energy balloon-borne gamma-ray telescope ZEBRA is capable of producing images of the sky with a resolution of 1° and a point source location accuracy of a few arcminutes. In order to fully exploit the sensitivity of this instrument, a platform stabilised in three axes to this precision has been developed, which however has an absolute pointing accuracy of 30′-1°. Therefore there is a need to have on board a system which will allow post facto reconstruction of the absolute pointing direction of the telescope as a function of time, for observations in both day- and night-time conditions. An independently steerable starsensor has been constructed, based on a CCD imaging system, for this purpose. The results obtained with this device during the first flight of the ZEBRA telescope in May 1989 from the NASA balloon base in Palestine, Texas are presented.

The New Hard X-ray Mission (NHXM) has been designed to provide a real breakthrough on a number of hot astrophysical issues that includes: black holes census, the physics of accretion, the particle acceleration mechanisms, the effects of radiative transfer in highly magnetized plasmas and strong gravitational fields. NHXM combines fine imaging capability up to 80 keV, today available only at E

The Energetic X-ray Imaging Survey Telescope (EXIST) will continuously survey the full sky in scanning mode for 2- years followed by a 3-years pointing phase. The mission includes three instruments: a High Energy coded mask Telescope; a 1.1m aperture optical-IR Telescope; and a Soft X-ray Imager (SXI), sensitive in the 0.1-10 keV band. SXI is proposed as a contribution of ASI-Italy, fully developed by Italian institutes. Here we will present the optical and mechanical design of the SXI mirror module, that includes also a pre-collimator and a magnetic diverter to ensure a low background on the detector. In particular we will describe the mirror module characteristics in term of effective area, imaging capability, thermal requirement and mechanical properties. The current optical design foresees 26 shells providing an effective area comparable to one XMM-Newton mirror module up to 3 keV. The realization of these shells is based on the well-proven Nickel replication-process technology.

The Energetic X-ray Imaging Survey Telescope (EXIST) mission, submitted to the Decadal Survey, is a multiwavelength observatory mainly devoted to the study of Super Massive Black Holes, Gamma Ray Bursts and other transient sources. The set of instruments foreseen for EXIST includes a soft x-ray telescope (SXI), proposed as a contribution of the Italian Space Agency (ASI). We present the baseline design of the X-Ray camera for SXI telescope, that we have finalized under ASI contract. The camera is based on a focal plane detector consisting of a 450 μm thick silicon pixel sensor sensitive, with high QE, in the full SXI range (0.1-10 KeV), and capable of high energy resolution when operated in photon counting mode (E/dE ~ 47 at 6 keV), frame rate ~ 100-200 frames/s (enabling timing in the ms range), and spatial resolution matching the optical characteristics of the mirror module. We provide an overview of the mechanical, thermal and electrical concept of the camera.

NHXM, under study by ASI (Agenzia Spaziale Italiana), is an X-ray observatory in the energy band between 0.5 and 80 keV and will have 3 telescopes dedicated to X-ray imaging with a field of view diameter of 12 arcmin and a focal length of 10 m. We report on the development of high-speed and low-noise readout of a monolithic array of DEPFET detector. The DEPFET based detectors, thanks to an intrinsic low anode capacitance, are suitable as low-energy detectors (from 0.5 to 10 keV) of the new NHXM telescope. The challenging requirements of the NHXM cameras regard the necessity to obtain images and spectra with nearly Fano-limited energy resolution with an absolute time resolution of about 100 μs. In order to exploit the speed capability of the DEPFET array, it has been developed a readout architecture based on the VELA circuit: a drain current readout configuration to implement an extremely fast readout (2 μs/row) and preserve the excellent noise performance of the detector. In the paper the foreseen maximum achievable frame-rate and the best energy resolution will be presented in order to assert the VELA suitability for X-ray imaging and spectroscopy.

The SXI telescope is one of the three instruments on board EXIST, a multiwavelength observatory in charge of performing a global survey of the sky in hard X-rays searching for Supermassive Black Holes. One of the primary objectives of EXIST is also to study with unprecedented sensitivity the most unknown high energy sources in the Universe, like high redshift GRBs, which will be pointed promptly by the Spacecraft by autonomous trigger based on hard X-ray localization on board. The recent addition of a soft X-ray telescope to the EXIST payload complement, with an effective area of ~950 cm2 in the energy band 0.2-3 keV and extended response up to 10 keV will allow to make broadband studies from 0.1 to 600 keV. In particular, investigations of the spectra components and states of AGNs and monitoring of variability of sources, study of the prompt and afterglow emission of GRBs since the early phases, which will help to constrain the emission models and finally, help the identification of sources in the EXIST hard X-ray survey and the characterization of the transient events detected. SXI will also perform surveys: a scanning survey with sky coverage of about 2pi and limiting flux of 5x10^{-14}cgs plus other serendipitous. We give an overview of the SXI scientific performance and also describe the status of its design emphasizing how it has been derived by the scientific requirements., 9 pages, 6 figures, to be published in Proc. of SPIE, vol 7435-11, 2009

The Energetic X-ray Imaging Survey Telescope (EXIST) is a mission that has been studied for the NASA Physics of the Cosmos Program. EXIST will continuously survey the full sky by scanning for 2-years (with 2-3 interruptions per day for GRB follow-up) followed by a 3-years pointing phase. The mission includes three instruments: a High Energy coded mask Telescope; a 1.1m aperture optical-IR Telescope; and a Soft X-ray Imager (SXI), sensitive in the 0.1-10 keV band. SXI is proposed as a contribution of ASI-Italy, fully developed by Italian institutes. The current optical design foresees 26 shells providing an effective area comparable to one XMM-Newton mirror module up to 3 keV and somewhat lower from 3 to 10 keV. The realization of these shells is based on the well-proven Nichel replication-process technology. Here we will present the optical design of the SXI mirror module and describe its characteristics in term of effective area and imaging capability, summarizing also the characteristics of the full SXI telescope.

The study of Gamma-ray bursts (GRBs) is a key field to expand our understanding of several astrophysical and cosmological phenomena. SVOM is a Chinese-French Mission which will permit to detect and rapidly locate GRBs, in particular those at high redshift, and to study their multiwavelength emission. The SVOM satellite, to be launched in 2013, will carry wide field instruments operating in the X/gamma-ray band and narrow field optical and soft X-ray telescopes. Here we describe a small soft X-ray telescope (XIAO) proposed as an Italian contribution to the SVOM mission. Thanks to a grazing incidence X-ray telescope with effective area of ~120 cm^2 and a short focal length, coupled to a very compact, low noise, fast read out CCD camera, XIAO can substantially contribute to the overall SVOM capabilities for both GRB and non-GRB science., 12 pages, 7 figures; Presented at ``SPIE Astronomical Telescopes and Instrumentation 2008'' - Marseille, June 23-28, 2008

The CNR (Consiglio Nazionale delle Ricerche) was founded in 1923. Its task was to organize and finance researches in various fields of science. During the years, few institutions, created within CNR to organize the activities in specific fields, became independent, like INFN, Istituto Nazionale di Fisica Nucleare, and ENEA (previously CNEN), Ente Nazionale per l’Energia Atomica (now Ente Nazionale Energie Alternative).

We are conducting a measurement program on back-up filters of the XMM-Newton EPIC camera aimed at monitoring possible aging effects during the mission lifetime. One thin and one medium EPIC back-up filters have been stored since 1997 in an environment similar to that one of the flight filters (dry nitrogen box before launch, high vacuum after launch). The transmission of the two filters has been measured periodically in the 1900-10000 angstrom wavelength range where effects of aging would be clearly evident. The preliminary results, after 5 years of monitoring, show that a slight aging effect has occurred on both filters which, however, has no significant impact onto the EPIC calibration for the correct analysis of the X-ray astrophysical observations.

EPIC, on the Newton Observatory, comprises three CCD cameras that provide spectroscopic imaging over the band 0.1-12 keV, with full coverage of the 30' diameter field of view of the three telescopes. The combination of bandwidth, throughput, and spectral resolution, has produced many interesting observations in more than two years of operation. These range from stars, normal, and neutron, SNR & Pulsars, via galaxies, to clusters of galaxies and the most distant quasars. Some of the latest results will be presented. A few days' operation on orbit provides more instrument performance data that can be gathered in the most thorough ground calibration, and many new facets of the instrument performance become evident in orbit. The high throughput of the Newton telescopes provides images and spectra of high statistical precision. This puts an additional burden on the calibration, and there has been much progress by the EPIC team in defining a precise and accurate calibration at the few percent level. The EPIC MOS CCDs perform well in orbit and show considerable radiation hardness against soft protons, due to their peculiar architecture. The degradation of spectral resolution, due to radiation damage, is dominated by hard solar flare protons. At present, this is within the predicted limits and the good spectral performance of EPIC is maintained.

A Mission into Hot Phenomena in the Universe is proposed by means of a small telescope of 50 cm aperture accommodated on the International Space Station. Two operating modes are envisaged: 3 angstrom dispersion imaging spectroscopy in the 90 - 320 nm range (1st priority) or wide field (1 degree) medium bandwidth imaging in the same range but Ly-(alpha) (2nd priority). It will use a pointing platform attached to an Express Pallet Adapter available to the Italian Space Agency (ASI) more than 4 - 6 months per year. During a life time of 6 yr focal plane instruments may be changed when on-ground refurbishment occurs. With reasonable exposure times hot thermal sources as faint as V equals 19 - 2 can be observed in the spectroscopy mode at 110 nm and active chromospheres on cool stars as faint as V equals 15 at 250 nm can be monitored. Assessment of FUV imaging is underway, possibly providing observations of hot sources as faint as V equals 21 - 22. Nominal uplift to ISS is set in Autumn 2005.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents the XMM-Newton first-light observations of the Hickson-16 compact group of galaxies. Groups are possibly the oldest large-scale structures in the Universe, pre-dating clusters of galaxies, and are highly evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is exceptional in the having the highest concentration of starburst or AGN activity in the nearby Universe. So it is a veritable laboratory for the study of the relationship between galaxy interactions and nuclear activity. Previous optical emission line studies indicated a strong ionising continuum in the galaxies, but its origin, whether from starbursts, or AGN, was unclear. Combined imaging and spectroscopy with the EPIC X-ray CCDs unequivocally reveals a heavily obscured AGN and a separately identified thermal (starburst) plasma, in NGC 835, NGC 833 and NGC 839. NGC 838 shows only starburst thermal emission. Starbursts and AGN can evidently coexist in members of this highly evolved system of merged and merging galaxies, implying a high probability for the formation of AGN as well as starbursts in post-merger galaxies., 6 pages, accepted for publication in A&A Special Letters Edition (First results from XMM-Newton)

On 10th December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-board pn-computer programs, we started the Calibration and Performance Verification Phase, which will last until the end of May 2000. In this paper we report on the results of the EPIC-pn Commissioning Phase with respect to the in-orbit performance of the camera. We also show some of the early results with the pn-camera, the first light image of a region in the Large Magellanic Cloud, and an observation of the Crab Nebular.

The European photon imaging camera (EPIC) is one of the two main instruments onboard the ESA X-Ray Cornerstone Mission XMM. It is devoted to performing imaging and spectroscopy of the x-ray sky in the domain 0.1 10 keV with a peak sensitivity in 105 seconds of 2 multiplied by 10-15 erg/cm-2. The x-ray instrumentation is complemented by a radiation monitor which will measure the particle background. The spectral resolution is approximately 140 eV at 6.4 keV and 60 eV at 1 keV. The instrumentation consists of three separate focal plane cameras at the focus of the three XMM telescopes, containing CCDs passively cooled to typically minus 100 degrees via radiators pointing toward the anti-Sun direction. The two cameras with the field of view partially occulted by the RGS grating boxes will have MOS technology CCDs while the third camera, with full field of view, will be based on p-n technology. The CCDs in the focal plane of the cameras will cover the entire 30 foot by 30 foot field of view of the telescope while the pixel size (40 by 40 (mu) for the MOS camera and 150 multiplied by 150 (mu) for the p-n) will be adequate to sample the approximately 20' PSF of the mirrors. In order to cope with a wide range of sky background and source luminosity in the visible/UV band, a filter wheel with six positions has been implemented in each camera. The six positions correspond to: open position, closed position, one thin filter (1600 angstrom of plastic support and 400 angstrom of Al), one medium filter (1600 angstrom of plastic support and 800 angstrom of Al) and one thick filter (approximately 3000 angstrom of plastic support, approximately 1000 angstrom of Al and 300 Angstrom of Sn). The final position will be a redundant filter of type still to be decided. A set of radioactive sources in each camera will allow the calibration of the CCDs in any of the operating modes and with any filter wheel position. Vacuum doors and valves operated will allow the operation of other camera heads on the ground, in a vacuum chamber and/or in a controlled atmosphere, and will protect the CCDs from contamination until the spacecraft is safely in orbit. The MOS camera will have 7 CCDs, each of 600 by 600 pixels arranged in a hexagonal pattern with one central and six peripheral. The p-n camera head will have 12 CCDs, each with 200 multiplied by 64 pixels, in a rectangular arrangement, 4 quadrants of 3 CCDs each. The radiation monitor is based on two separate detectors to monitor the low (electrons greater than 30 keV) and the high (electrons greater than 200 keV and protons greater than 10 MeV) energy particles impinging on the telescope along its orbit.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a proposed joint ESA/NASA/Russia gamma-ray astronomy mission which will provide both imaging and spectroscopy. It is currently at the final stages of an ESA phase-A study which it is hoped will lead to it being adopted during 1993 as the second 'medium-class' mission within ESA's Horizon 2000 plan. Launched in less than 10 years time it will be the successor to the current generation of gamma-ray spacecraft, NASA's Compton Observatory (GRO) and the Soviet- French Granat/Sigma mission. The baseline is to have two main instruments covering the photon energy range 50 keV to 10 MeV, one concentrating on high-resolution spectroscopy, the other emphasizing imaging. In addition there will be two monitors--an X-ray monitor which will extend the photon energy range continuously covered down to a few keV, and an Optical Transient Camera which will search for optical emission from gamma-ray bursts.

A novel low energy astronomical gamma-ray detector is being developed for future satellite missions. Recent advances in the technology of photodiodes and small, low noise amplifier circuits have meant that more compact detectors can be assembled in a complex array in order to give a 3-D position reconstruction capability. In a mask-detector telescope this capability is potentially very useful since it allows the reconstruction of the path of the incident gamma rays making it valuable both for imaging and background rejection. A small prototype of a 3-D detector has been realized for test in a balloon mission. The detector is based on a 12 X 8 array of position sensitive CsI(T1) bars, typically 15 cm long with 1.3 X 1.3 cm cross section, viewed at each end by photodiodes. The detector includes four 1.3 X 1.3 X 2.5 cm CsI(T1) scintillators located above the main array in order to evaluate the low energy response of the imager. The detector constitutes an active block of 2400 cm3 of scintillator that can operate in the 0.2 - 10 MeV energy range. The energy resolution is 13% at 662 keV and the positional resolution is of the order of 1.5 cm in each dimension. An active shield of CSI(T1) and plastic scintillators surrounds the bar detector. The overall experiment is briefly described in general and preliminary results of laboratory tests are presented.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Analytical considerations and test results bearing on the performance of a CsI(Tl) scintillating crystal coupled with a photodiode when used as a gamma-ray spectrometer are addressed. Laboratory test results on a number of CsI(Tl) bars with different sizes, diffusive coatings, and preamplifier designs are presented. A suitable event selection electronic logic design is shown which reduces the effect of noise on the count rate while retaining the desired energy threshold.

The capabilities of the European Photon Imaging Camera (EPIC), the main instrument of ESA's 'Cornerstone' mission in X-ray astronomy with multiple mirrors (XMM), are discussed. The CCD characteristics, spatial resolution, energy bandpass and faint source sensitivity, spectral resolution and sensitivity, and timing capability are addressed, and the scientific rationale of the EPIC is summarized. The EPIC instrument system concept is briefly described.

A large area (6000 cm2) actively shielded low energy gamma-ray telescope is going to be built by an Anglo-Italian collaboration. The telescope, named ZEBRA, will be capable of producing images of the X and gamma ray sky in the energy range 0.015–20 MeV with an intrinsic angular resolution of a few tenths of a degree. A prototype detector has been built in order to experimentally study the main characteristics of the detection plane. The preliminary results obtained during a balloon flight from Trapani, Sicily in July 1981 are presented.

Recent developments in the field of position sensitive scintillation detectors have made possible the development of an astronomical gamma-ray telescope which is capable of generating images of the sky with a resolution of about 10 arc min. The position sensitive gamma-ray detector from which the focal plane of the telescope may be constructed is described in this paper. The instrument will operate in the photon energy range 100 keV to 10 MeV. The results of laboratory tests on the positional and energy resolution of incident gamma-rays is compared to the relevant theory and the expected performance evaluated via Monte Carlo simulation.

The MISO telescope, which has been described elsewhere, (Baker et al. 1979), has a sensitive area of 560 cm 2 and an aperture of 3° f.w.h.m. in both the azimuthal and zenithal planes. An alt—azimuth orientation system was used to point the telescope with a precision of ± 20'. A passively shielded hard X-ray detector (20—280 keV) having an effective area of 600 cm 2 was also mounted in parallel with the axis of the main telescope and had a field of view of 3° x 3° f.w.h.m. This instrument was used to study the region of the sky containing NGC 4151 on 30 September 1979 between 15h01 U.T. and 20h40 U.T. A series of five drift scans were performed to survey the region contained within the coordinate points 11h32 and 12h33 in right ascension. The declination was centred on + 39.8°. The Seyfert galaxy NGC 4151 was in the field of view of the telescope for a total period of 7.5 x 10 3 s. The total time spent on the background measurements associated with the data presented here, was 8.6 x 10 3 s. The mean float altitude during the observation was close to 4 mbar (400 Pa) and the telescope was set at a series of zenith angles between 9° and 30°.

Three active galaxies, generally classified as Seyferts, have been discovered recently to be powerful, low energy γ-ray sources. The similarity between their spectral characteristics and those of the cosmic background at γ-ray energies suggests that these objects could make a significant contribution to this diffuse flux. This contribution has been assessed using two different number densities of γ-ray-emitting Seyfert galaxies based on optical and X-ray data. The comparison of the estimated and measured diffuse γ-ray background intensities is used to gain a deeper understanding of the metabolism of Seyfert galaxies.

The performance of the position sensitive detector for the ZEBRA low energy gamma-ray imaging telescope is described. The detector consists of 9 position sensitive Nal(TI) elements each 5.8 × 5.0 × 56.0 cm viewed at either end of the long axis by 2 in. photomultiplier tubes. The total active area is 2470 cm2 with an average positional resolution of 2.1 cm and energy resolution of 15% FWHM at 661.6 keV. The method of flight calibration is described together with the provision within the on-board electronics to correct for sources of error in the calculation of event energy loss and position. The results presented are obtained from the calibration phase of the ZEBRA telescope project.

The background which arises from the presence of a coded aperture. The major contributions which have been considered here are the interactions with the mask of the isotropic gamma-ray background, a parallel gamma-ray beam, neutrons and the effect of the mask element profile. It is shown that none of these factors contribute to a significant excess or modulation in the background counting rate over the detection plane. In this way the use of a passive rather than an active coded apertuer mask is seen to be suitable for use in a low energy gamma-ray telescope.

Regions of the sky containing the high energy γ-ray sources CG135+1 and CG195+4 were searched for X-ray and γ-ray emission in the energy range from 20 keV to 25MeV from balloon altitudes on October 8, 1978. A 5σ excess was measured in the counting rate of the telescope above 120 keV from the region of the sky containing CG135+1 and the spectrum of the source evaluated. No X- and γ-rays were found from CG195+4.

During a balloon flight in September 1979 of the MISO low-energy γ-ray telescope, the BL Lac-object MkN 501 was studied in the hard X-ray range above 30 keV and in the low energy γ-ray range up to 19 MeV. No statistically significant X- and γ-ray fluxes were detected. The implications of the upper limits obtained are discussed in the light of the relativistic jet theories recently proposed.

The mechanical, elecrtical, and performance characteristics of one element of the ZEBRA telescope's position sensitive aetection plane are presented. One unit comprises a NaI(Tl) bar 55×5,8×5 cm thick and two photomultiplier tubes one mounted on each end. The surface of the bar has been treated to enhance the exponential attenuation of the scintillation light produced by an event. The signal from the two tubes are taken in coincidence and, by the application of two simple algoritms, the energy and position of the event along the bar can be calculated. The tubes are powered by two programmable low consumption high tension supplies. Their digital control makes automatic gain correction feasible during the flight.

A scientific forward step in the hard X-ray and soft gamma-ray astronomy will only be possible with the use of a new generation of space borne instruments. Their main characteristics have to the two-dimensional imaging capability over a large collecting area and the fine spectral resolution in order to discriminate between the weak signal coming from cosmic sources to be detected and the strong background induced by cosmic rays, in the space environment, on the detector. To reach this goal we have developed a new hard X-ray position sensitive proportional counter operating with the escape gate technique in the range 15–150 keV, to be used together with a pseudo-random coded mask in order to obtain sky images. The detector is a high pressure (5 bar) xenon-argon-isobutane filled chamber with a spatial resolution of 30 × 2 mm and a spectral resolution of 5% at 60 keV on the sensitive area of 3000 cm 2 .

An array of 1-dimensional position sensitive detectors designed to operate over the photon energy range 0.2–10.0 MeV, so as to form an efficient 2-dimensional position sensitive detection plane is described. A series of experimental tests has been carried out to evaluate and confirm the computed capabilities.

A series of approximately 100 laboratory images have been made with the ZEBRA astronomical telescope using a range of radioactive sources. These images were aimed at assessing the performance of the telescope and included combinations of point sources, extended sources, ring sources as well as vignetted sources. Besides linear reconstruction techniques a range of non linear image restoration processes are discussed.

This paper describes the balloon-flight version of a low energy (0.2–20 MeV) gamma-ray telescope developed in collaboration by the Milan and Southampton groups. The instrument embodies a Compton-coincidence system comprising an upper liquid scintillator and a large sodium iodide crystal (560 cm 2 ). This detector is mounted inside a semiactive shielding system which collimates the incident photons (1.5° fwhm). The telescope is mounted in an orientation system which has a pointing accuracy of better than 0.5°. The instrument has been extensively tested using beams of γ -rays, neutrons and high energy protons (2 GeV/ c ).

The MISO telescope is a gamma-ray detector operating in the (0.1÷20) MeV energy range. This instrument was flown success-fully from Palestine, Texas (U.S.A.) in May 1977, October 1978, September 1979 and May 1980. During the four flights, the telescope observed a number of galactic and extragalactic sources. The Crab Nebula was detected in 1980 and its spectrum was measured up to 2 MeV. Cygnus X-1 was observed in 1979 and 1980 and was found to be in different hard X-ray states on each occasion: in a superlow state in 1979 and in a low state in 1980. The COS-B high-energy (E>50 MeV) gamma-ray sources CG 135+1 (1978) and CG 195+4 (1978) were also observed by the same instrument. From the region containing CG 135+1 a 5σ excess was measured in the counting rate of the telescope above 120 keV. No statistically significant low-energy gamma-ray flux was detected from CG 195+4. The Seyfert galaxies NCG 4151 (1977, 1979, 1980), and MCG 8-11-11 (1979), the BL LAC object MK 501 (1979) and the «peculiar» galaxy NGC 1275 (1979) were also searched for gamma-ray emission. The data on NGC 4151 and MCG 8-11-11 are consistent with power law spectra having photon indices α∼1 in the (0.1÷3) MeV energy range. Above this energy, the MISO and SAS-2/COS-B measurements require spectral breaks to α≥3. Upper limits were obtained on the emission from both MK 501 and NGC 1275.

Following the first detection of X-ray emission from the Seyfert galaxy NGC41511, later observations2–4 have demonstrated that the X-ray spectrum up to 100 keV may be described by a power law having a differential spectral index 1

In order to improve the low energy capability (15 ÷ 150 KeV) of the balloon borne “ZEBRA” low energy gamma imaging telescope (150 KeV-20 MeV), a large area, high spectral resolution (5% at 60 KeV), low background detector has been designed and is now under development. It consists of two MultiWire Spectroscopic Proportional Counter (SPC), escape gated, that have a sensitive area of 6000 cm2, and are placed above the large area array of sodiumiodide position sensitive elements.

During a balloon flight of the MISO telescope on 1980 May 17, the Crab Nebula and the Seyfert galaxy NGC 4151 were studied over the photon energy range 0.03 –16 MeV. The photon spectrum of the Crab Nebula was measured up to ∼ 2 MeV. No gamma-ray emission from NGC 4151 was detected on this occasion.

The galaxy MCG8 –11 –11 inside the 0.093 square degrees error-box of the X-ray source 2A0551 + 466 (ref. 1), was recently found to be a Type 1 Seyfert galaxy2. A 40-arcs error-box from the A3 experiment on HEAO1 has confined the X-ray emission to the nucleus or bar of this 14-mv galaxy3. The redshift is z = 0.0205 (ref. 2), corresponding to a distance of 123 Mpc (H0 = 50 km s−1 Mpc−1). The 2–10 keV luminosity ranges from 5 × 1043erg s−1 to 1.2 × 1044erg s−1 (refs 1,3). Hard X-ray emission above 20 keV from the region of MCG8 –11 ‐11 has been recently reported4, and the A2 experiment on HEAO 1 has provided for the first time the emission spectrum of this object up to 30 keV (ref. 5). During a balloon flight on 30 September 1979 from Palestine, Texas of the Milan/Southampton (MISO) low-energy γ-ray telescope, an excess at the 3.9σ level in the flux above 90 keV was detected from a region of the sky containing MCG8 –11 –11. The emission spectrum, evaluated in the energy range 0.02–19 MeV, has similar spectral characteristics to those observed with the same telescope and associated with the Seyfert galaxy NGC4151 (ref. 6). Both spectra show evidence for a high-energy cutoff close to 3 MeV and this feature could be interpreted on the basis of the ‘Penrose–Compton scattering’ process7. A large amount of the observed low-energy γ-ray diffuse background8 could be produced by a few per cent of the X-ray emitting Seyfert galaxies having a γ-ray luminosity comparable with that observed from the region of NGC4151 or MCG8 –11 –11.

During a balloon flight of the MISO telescope on the 30th September 1979 the Seyfert galaxies NGC 4151 and MGC 8-11-11 were studied in the hard X-ray range (Ex > 20 keV) and low-energy γ-ray range up to 19 MeV. An emission at the 4.5 a level above 20 keV (4 σ above 260 keV) was detected in the direction of NGC 4151. γ-ray emission at the 3.9 σ level above 90 keV was also observed from the direction of MCG 8-11-11. The emission photon spectrum shows a high-energy cutoff at about 3 MeV. A large amount of the observed low-energy γ-ray diffuse background could be produced by a few percent of the X-ray emitting Seyfert galaxies having a γ-ray luminosity comparable to that observed from the regions of NGC 4151 or MCG 8-11-11.

The Soft X-ray Imager (SXI) is one of the three instruments on board EXIST, a multi-wavelength observatory in charge of performing a global survey of the sky in hard X-rays searching for Super-massive Black Holes (Grindlay & Natalucci, these Proceedings). One of the primary objectives of EXIST is also to study with unprecedented sensitivity the most unknown high energy sources in the Universe, like high redshift GRBs, which will be pointed promptly by the Spacecraft by autonomous trigger based on hard X-ray localization on board. The presence of a soft X-ray telescope with an effective area of about 950cm2 in the energy band 0.2-3 keV and extended response up to 10 keV will allow to make broadband studies from 0.1 to 600 keV. In particular, investigations of the spectra components and states of AGNs and monitoring of variability of sources, study of the prompt and afterglow emission of GRBs since the early phases, which will help to constrain the emission models and finally, help the identification of sources in the EXIST hard X-ray survey and the characterization of the transient events detected. SXI will also perform surveys: a scanning survey with sky coverage 2pi and a limiting flux of 5x10^(-14) cgs plus other serendipitous., 6 pages, 4 figures. Accepted for publication on PoS (contribution PoS(extremesky2009)088), proceedings of "The Extreme sky: Sampling the Universe above 10 keV", held in Otranto (Italy), 13-17 October 2009

The ZEBRA telescope is a balloon borne low energy gamma ray instrument, sensitive in the photon energy range 0.2-10MeV. The main characteristics and components of the telescope are described, and its performance during laboratory calibration is discussed, after its integration with the flight electronics.

The results of hard x-ray, soft gamma-ray observations of the galactic black hole candidate, Cyg X-1, taken with the MISO telescope in October 1979 and May 1980 are presented, confirming the superlow state measured during September-October 1979 by the HEAO 3 satellite. The 1980 observation coincides with a low- to high-state transition and is consistent with HEAO 3 observations taken at the same epoch. No gamma-ray counting-rate excess above 200 keV was recorded in either observation. Apart from these two measurements, the observation of the Crab Nebula as an a posteriori calibration source is also described. 15 references.

The COS-B source CG135+1 (ref. 1) is an extremely interesting object because of its possible identification with the QSO 0241+622. Radio observations have identified a strong point source within 2 arc s (ref. 2) of QSO 0241+622. X-ray emissions have also been observed from this region of the sky by the Uhuru (ref. 3), SAS-3 (ref. 2) and HEAO-A (ref. 4) telescopes. The HEAO-A (A1) data indicate that there are two soft X-ray sources in this region of the sky, H0241+62 which contains the QSO, and H0235+60 which includes the radio source GT0236+61 (ref. 5). The OSO-7 data in the energy range 1–40 keV (ref. 6) and measurements using the high-energy X-ray experiment on Ariel-V between 0.26 and 1.2 MeV (ref. 7) have indicated that the photon emission from this region of the sky is of an extremely hard nature, with a power law spectral index of γ≈1.0. However, the poor angular resolution of these telescopes make it uncertain whether the high-energy X-ray fluxes are due to the same celestial object. We now report the results of a balloon flight carried out on 8 October 1978 from Palestine, Texas, in which the region of the sky including the COS-B source CG135+1 was scanned by the Milan/Southampton telescope (MISO telescope). A 5σ excess in the counting rate of the telescope in the energy range 0.15–20 MeV was observed. The origin of this low-energy γ-ray emission is compatible with the measured position of CG135+1.

The Seyfert galaxy NGC 4151 was observed on May 18, 1980 at hard X-ray/low gamma ray energies with the MISO telescope. The only excess detected was at the 3.5 sigma level in the X-ray energy range 35-105 keV. Concurrent UV, IR, optical and soft X-ray observations performed from January-May 1980 are used in conjunction with the MISO data to estimate the radiation characteristics of NGC 4151 and to define limits to models for the central powerhouse of the object, one of the most luminous in the sky. 39 references.