Calibration of the ART-XC mirror modules at MSFC

The Astronomical Röntgen Telescope X-ray Concentrator (ART-XC) is a hard X-ray telescope with energy response up to 30 keV, to be launched on board the Spectrum Röntgen Gamma (SRG) spacecraft in 2018. ART-XC consists of seven identical co-aligned mirror modules. Each mirror assembly is coupled with a CdTe double-sided strip (DSS) focal-plane detector. Eight X-ray mirror modules (seven flight and one spare units) for ART-XC were developed and fabricated at the Marshall Space Flight Center (MSFC), NASA, USA. We present results of testing procedures performed with an X-ray beam facility at MSFC to calibrate the point spread function (PSF) of the mirror modules. The shape of the PSF was measured with a high-resolution CCD camera installed in the focal plane with defocusing of 7 mm, as required by the ART-XC design. For each module, we performed a parametrization of the PSF at various angular distances Θ. We used a King function to approximate the radial profile of the near on-axis PSF (Θ < 9 arcmin) and an ellipse fitting procedure to describe the morphology of the far off-axis angular response (9 < Θ < 24 arcmin). We found a good agreement between the seven ART-XC flight mirror modules at the level of 10%. The on-axis angular resolution of the ART-XC optics varies between 27 and 33 arcsec (half-power diameter), except for the spare module.     

Experimental study of parameters of X-ray radiation from solar flares using the PENGUIN-M instrument aboard the CORONAS-PHOTON spacecraft

The main characteristics of the PENGUIN-M instrument are given. The instrument has been operating aboard the CORONAS-PHOTON spacecraft (SC) launched into orbit on January 30, 2009. The instrument includes the PENGUIN-MD detector unit (PMD) and the PENGUIN-ME electronic unit (PMD). The purpose of the experiment is to measure the degree of linear polarization of X-ray radiation from solar flares in the energy range of 20–150 keV and to obtain energy spectra of X-ray radiation from solar flares in the energy range of 2–500 keV. The paper describes the instrument, calibration procedure, and in-flight adjustment, and contains the first results of measurements.     

InFOCμS Hard X-ray Imaging Telescope

InFOCμS is a new generation balloon-borne hard X-ray telescope with focusing optics and spectroscopy. We had a successful 22.5-hour flight from Fort Sumner, NM on September 16,17, 2004. In this paper, we present the performance of the hard X-ray telescope, which consists of a depth-graded platinum/carbon multilayer mirror and a CdZnTe detector. The telescope has an effective area of 49 cm² at 30 keV, an angular resolution of 2.4 arcmin (HPD), and a field of view of 11 arcmin (FWHM) depending on energies. The CdZnTe detector is configured with a 12 × 12 segmented array of detector pixels. The pixels are 2 mm square, and are placed on 2.1 mm centers. An averaged energy resolution is 4.4 keV at 60 keV and its standard deviation is 0.36 keV over 128 pixels. The detector is surrounded by a 3-cm thick CsI anti coincidence shield to reduce background from particles and photons not incident along the mirror focal direction. The inflight background is 2.9 × 10⁻⁴ cts cm⁻² sec⁻¹ keV⁻¹ in the 20–50 keV band.     

A Deep Extragalactic Survey with the ART-XC Telescope of the Spectrum-RG Observatory: Simulations and Expected Results

To choose the best strategy for conducting a deep extragalactic survey with the ART-XC X-ray telescope onboard the Spectrum–Röntgen–Gamma (SRG) observatory and to estimate the expected results, we have simulated the observations of a 1.1° × 1.1° field in the 5–11 and 8–24 keV energy bands. For this purpose, we have constructed a model of the active galactic nuclei (AGN) population that reflects the properties of the X-ray emission from such objects. The photons that “arrived” from these sources were passed through a numerical model of the telescope, while the resulting data were processed with the standard ART-XC data processing pipeline. We show that several hundred AGNs at redshifts up to z ≈ 3 will be detected in such a survey over 1.2 Ms of observations with the expected charged particle background levels. Among them there will be heavily obscured AGNs, which will allow a more accurate estimate of the fraction of such objects in the total population to be made. Source confusion is expected at fluxes below 2 × 10^?14 erg s^?1 cm^?2 (5–11 keV). Since this value can exceed the source detection threshold in a deep survey at low particle background levels, it may turn out to be more interesting to conduct a survey of larger area (several square degrees) but smaller depth, obtaining a sample of approximately four hundred bright AGNs as a result.     

The MPE X-ray test facility PANTER: Calibration of hard X-ray (15–50 kev) optics

The Max-Planck-Institut für extraterrestrische Physik (MPE) in Garching, Germany, uses its large X-ray beam line facility PANTER for testing X-ray astronomical instrumentation. A number of telescopes, gratings, filters, and detectors, e.g. for astronomical satellite missions like Exosat, ROSAT, Chandra (LETG), BeppoSAX, SOHO (CDS), XMM-Newton, ABRIXAS, Swift (XRT), have been successfully calibrated in the soft X-ray energy range (< 15keV). Moreover, measurements with mirror test samples for new missions like ROSITA and XEUS have been carried out at PANTER. Here we report on an extension of the energy range, enabling calibrations of hard X-ray optics over the energy range 15–50 keV. Several future X-ray astronomy missions (e.g., Simbol-X, Constellation-X, XEUS) have been proposed, which make use of hard X-ray optics based on multilayer coatings. Such optics are currently being developed by the Osservatorio Astronomico di Brera (OAB), Milano, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA. These optics have been tested at the PANTER facility with a broad energy band beam (up to 50 keV) using the XMM-Newton EPIC-pn flight spare CCD camera with its good intrinsic energy resolution, and also with monochromatic X-rays between C-K (0.277 keV) and Cu-Kα (8.04 keV). PACS: 95.55.Ka, 95.55.Aq, 41 50.+h, 07.85.Fv     

Spectral calibration of scanning sky monitor on ASTROSAT

Scanning Sky Monitor (SSM) on-board ASTROSAT is an X-ray detector in the energy range 2–10 keV to monitor the sky for transient X-ray sources. The science objective of SSM is to detect and locate these transient X-ray sources. We discuss here in this paper, the spectral calibration of SSM along with on-board calibration plans using the X-ray flux from the Crab nebula. Spectral response for SSM is derived using a routine in ftools and the inputs for deriving the response are got from the results of the experiments done on the qualification model for SSM.     

Observation of soft X-ray emission from a region near Per X-1

Soft X-ray emission from the X-ray source Per X-1 was observed in the 0.4–2 keV energy interval from a rocket borne X-ray detector. Spectral analysis of the data indicates that in the 0.4–2 keV band the X-ray emission from Per X-1 can be fitted either with a power law of slope-(4.8±1.2) or a thermal bremsstrahlung spectrum with akT value of (0.26 _?0.08 ^+0.12 ) keV. Such a steep spectrum is inconsistent with the spectrum measured above 2 keV. The measured flux in 0.4–2 keV band corresponds to X-ray luminosity of 3×10⁴⁵ ergs s^?1 for Per X-1.     

IGR J16318-4848: An X-ray source in a dense envelope?

We analyze in detail the ASCA observations of the hard X-ray source IGR J16318-4848, which was recently discovered by the INTEGRAL observatory (Courvoisier et al. 2003). The source has an anomalously hard spectrum in the energy range 0.5–10 keV and is virtually undetectable below 4 keV because of strong photoabsorption (n _H L>4×10²³ cm^?2). The Kα line of neutral or weakly ionized iron with an equivalent width of ～2.5 keV dominates in the energy range 4–10 keV. There is also evidence for the presence of a second line at energy ～7 keV. Our analysis of archival observational data for the infrared counterpart of IGR J16318-4848 that was discovered by Foschini et al. (2003) revealed the source in the wavelength range 1–15 µm. Available data suggest that the object can be an X-ray binary system surrounded by a dense envelope. The source may be a high-mass X-ray binary similar to GX 301-2. We believe that IGR J16318-4848 can be the first representative of a hitherto unknown population of strongly absorbed Galactic X-ray sources that could not be detected by previous X-ray observatories.     

Broadband Spectrum of the X-ray Binary M33 X-6 from NuSTAR and Swift–XRT Data: An Extragalactic Z-Source?

We present the results of our study of the X-ray spectrum for the source X-6 in the nearby galaxy M33 obtained for the first time at energies above 10 keV from the data of the NuSTAR orbital telescope. The archival Swift–XRT data for energy coverage below 3 keV have been used, which has allowed the spectrum of M33 X-6 to be constructed in the wide energy range 0.3–20 keV. The spectrum of the source is well described by the model of an optically and geometrically thick accretion disk with a maximum temperature of ~2 keV and an inner radius of ~5 cos^?1/2θ km (where >θ is the unknown disk inclination angle with respect to the observer). There is also evidence for the presence of an additional hard component in the spectrum. The X-ray luminosity ofM33 X-6 measured for the first time in the wide energy range 0.3–20 keV is ~2 × 10³⁸ erg s^?1, with the luminosity in the hard 10–20 keV X-ray band being ~10% of the source’s total luminosity. The results obtained suggest that X-6 may be a Z-source, i.e., an X-ray binary with subcritical accretion onto a weakly magnetized neutron star.     

Calibration measurements on the DEPFET Detectors for the MIXS instrument on BepiColombo

The Mercury Imaging X-ray Spectrometer (MIXS) will be launched on board of the 5th ESA cornerstone mission BepiColombo. The two channel instrument MIXS is dedicated to the exploration of the elemental composition of the mercurian surface by imaging x-ray spectroscopy of the elemental fluorescence lines. One of the main scientific goals of MIXS is to provide spatially resolved elemental abundance maps of key rock-forming elements. MIXS will be the successor of the XRS instrument, which is currently orbiting Mercury on board of NASAs satellite MESSENGER. MIXS will provide unprecedented spectral and spatial resolution due to its innovative detector and optics concepts. The MIXS target energy band ranges from 0.5 to 7 keV and allows to directly access the Fe-L line at 0.7 keV, which was not accessible to previous missions. In addition, the high spectroscopic resolution of FWHM ≤ 200 eV at the reference energy of 1 keV after one year in Mercury orbit, allows to separate the x-ray fluorescence emission lines of important elements like Mg (1.25 keV) and Al (1.49 keV) without the need for any filter. The detectors for the energy and spatially resolved detection of x-rays for both channels are identical DEPFET (DEpleted P-channel FET) active pixel detectors. We report on the calibration of the MIXS flight and flight spare detector modules at the PTB (Physikalisch-Technische Bundesanstalt) beamlines at the BESSY II synchrotron radiation facility. Each detector was calibrated at least at 10 discrete energies in the energy range from 0.5 to 10 keV. The excellent spectroscopic performance of all three detector modules was verified.     

Peculiarities of Super-Eddington Flares from the X-ray Pulsar LMC X-4 Based on NuSTAR Data

We present the results of our analysis of super-Eddington flares recorded fromthe X-ray pulsar LMCX-4 by theNuSTAR observatory in the energy range 3–79 keV. The pulsar spectrumis well described by the thermal Comptonization model (COMPTT) both in quiescence and during flares, when the peak luminosity reaches L_x ~ (2?4) × 10³⁹ erg s^?1. An important feature that has been investigated for the first time in this paper is that an increase in luminosity during flares by more than an order of magnitude is observed at energies below 25–30 keV, while at higher energies (30–70 keV) the spectrum shape and the source flux remain virtually unchanged. The increase in luminosity is accompanied by changes in the source pulse profile—in the energy range 3–40 keV it becomes approximately triangular and the pulsed fraction increaseswith rising energy, reaching 60–70%in the energy range 25–40 keV.We discuss possible changes in the geometry of the accretion column consistent with similar changes in the spectra and pulse profiles.     

Prospects of hard X-ray polarimetry with Astrosat-CZTI

Astrosat is the first Indian satellite mission dedicated for astronomical studies. It is planned for launch during 2014 and will have five instruments for multi-wavelength observations from optical to hard X-rays. Cadmium Zing Telluride Imager (CZTI) is one of the five instruments aiming for simultaneous X-ray spectroscopy and imaging in the energy range of 10 keV to 100 keV (along with all sky photometric capability unto 250 keV). It is based on pixilated CZT detector array with total geometric area of 1024 cm². It will have two-dimensional coded mask for medium resolution X-ray imaging. The CZT detector plane will be realized using CZT detector modules having integrated readout electronics. Each CZT detector module consists of 4 cm × 4 cm CZT with thickness of 5 mm which is further pixilated into 16 × 16 array of pixels. Thus each pixel has size of 2.5 mm × 2.5 mm and thickness of 5 mm. Such pixilated detector plane can in principle be used for hard X-ray polarization measurements based on the principle of Compton scattering by measuring azimuthal distribution of simultaneous events in two adjacent pixels. We have carried out detailed Geant4 simulations for estimating polarimetric capabilities of CZTI detector plane. The results indicate that events in the energy range of 100 keV to 250 keV, where the 5 mm thick CZT detector has significant detection efficiency, can be used for polarimetric studies. Our simulation results indicate the minimum detectable polarization (MDP) at the level of ～ 10% can be achieved for bright Crab like X-ray sources with exposure time of ～500 ks. We also carried out preliminary experiments to verify the results from our simulations. Here we present detailed method and results of our simulations as well as preliminary results from the experimental verification of polarimetric capabilities of CZT detector modules used in Astrosat CZTI.     

A focal plane detector design for a wide-band Laue-lens telescope

The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1mm, an energy resolution of a few keV at 500keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy. Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies.     

PheniX: a new vision for the hard X-ray sky

We are proposing a mission devoted to high energy X-ray astronomy that is based on a focusing telescope operating in the 1?C200?keV energy range but optimized for the hard X-ray range. The main scientific topics concern: Physics of compact objects: The proximity of compact objects provides a unique laboratory to study matter and radiation in extreme conditions of temperature and density in strong gravitational environment. The emission of high energy photons from these objects is far from being understood. The unprecedented sensitivity in the high energy domain will allow a precise determination of the non-thermal processes at work in the vicinity of compact objects. The full 1?C200?keV energy coverage will be ideal to disentangle the emission processes produced in the spacetime regions most affected by strong-gravity, as well as the physical links: disk?Cthermal emission?Ciron line?Ccomptonisation?Creflection?Cnon-thermal emission?Cjets. Neutron stars?Cmagnetic field?Ccyclotron lines: Time resolved spectroscopy (and polarimetry) at ultra-high sensitivity of AXP, milliseconds pulsars and magnetars will give new tools to study the role of the synchrotron processes at work in these objects. Cyclotron lines?Cdirect measurement of magnetic filed?Cequation of state constraints?Cshort bursts?Cgiant flares could all be studied with great details. AGN: The large sensitivity improvement will provide detailed spectral properties of the high energy emission of AGN??s. This will give a fresh look to the connection between accretion and jet emission and will provide a new understanding of the physical processes at work. Detection of high-redshift active nuclei in this energy range will allow to introduce an evolutionary aspect to high-energy studies of AGN, probing directly the origin of the Cosmic X-ray Background also in the non-thermal range (> 20?keV). Element formation?CSupernovae: The energy resolution achievable for this mission (<0.5?keV) and a large high energy effective area are ideally suited for the 44Ti line study (68 and 78?keV). This radioactive nuclei emission will give an estimate of their quantities and speed in their environment. In addition the study of the spatial structure and spectral emission of SNR will advance our knowledge of the dynamics of supernovae explosions, of particles acceleration mechanisms and how the elements are released in the interstellar medium. Instrumental design: The progress of X-ray focusing optics techniques allows a major step in the instrumental design: the collecting area becomes independent of the detection area. This drastically reduces the instrumental background and will open a new era. The optics will be based on depth-graded multi-layer mirrors in a Wolter I configuration. To obtain a significant effective area in the hundred of keV range a focal length in the 40?C50 meters range (attainable with a deployable mast) is needed. In addition such a mission could benefit from recent progress made on mirror coating. We propose to cover the 1?C200?keV energy range with a single detector, a double-sided Germanium strip detector operating at 80?K. The main features will be: (a) good energy resolution (.150?keV at 5?keV and <.5?keV at 100?keV), (b) 3 dimensional event localization with a low number of electronic chains, (c) background rejection by the 3D localization, (d) polarisation capabilities in the Compton regime.     

天宫2号POLAR探测器的低能X射线在轨定标

伽马暴偏振探测仪(POLAR)是天宫2号实验室上搭载的一个γ射线偏振仪,于2016年9月15日搭载在天宫2号进入低轨运行,主要用于探测在50-500 keV能区的硬X射线辐射的线偏振.POLAR由25个模块组成,每个模块有64个塑料闪烁体棒,总计有1600个塑料闪烁体棒,具有较大的有效探测面积和视场.在轨运行期间探测到多个小耀斑,它们的硬X射线光子能量通常小于50 keV,无法直接使用在轨和地面的高能定标结果来进行能谱分析.结合拉马第太阳高能光谱成像探测器(RHESSI)对耀斑SOL2016112907能谱的观测和蒙特卡洛模拟,对耀斑期间被激活的闪烁体棒进行能量低于50 keV的低能相对定标.虽然定标得到的能量阈值(～10 keV)和转换因子相对稳定,但是和高能定标给出的结果相比有显著差异,并且不同闪烁体棒显示出的差异没有明显的规律性.     

Observations of cosmic gamma-ray bursts with the main detector of the SIGMA telescope onboard the Granat Observatory

We present the observations of cosmic gamma-ray bursts (GRBs) with the main detector of the SIGMA telescope onboard the Granat Observatory from January 1990 through September 1994. The observations were carried out in the energy range 35–1300 keV. We detected 36 GRBs and 31 high-energy solar flares during this period. No GRB fell within the main field of view; they were all recorded by the “secondary optics” of the telescope. The SIGMA telescope recorded relatively bright bursts with peak fluxes of 10^?6–10^?4 erg s^?1 cm^?2 in the 100–500-keV energy band. Stable detector background allows the long-term variability of GRB sources on a time scale of ～1000 s to be studied. The results of our search for early afterglows of GRBs are presented. The flux averaged over all bursts in the interval 100–800 s after the main event is 0.36±0.14 counts s^?(35–300 keV), suggesting that there is soft gamma-ray emission on this time scale after a considerable number of GRBs.     

X-ray emission from solar flares

Solar X-ray Spectrometer (SOXS), the first space-borne solar astronomy experiment of India was designed to improve our current understanding of X-ray emission from the Sun in general and solar flares in particular. SOXS mission is composed of two solid state detectors, viz., Si and CZT semiconductors capable of observing the full disk Sun in X-ray energy range of 4–56 keV. The X-ray spectra of solar flares obtained by the Si detector in the 4–25 keV range show evidence of Fe and Fe/Ni line emission and multi-thermal plasma. The evolution of the break energy point that separates the thermal and non-thermal processes reveals increase with increasing flare plasma temperature. Small scale flare activities observed by both the detectors are found to be suitable to heat the active region corona; however their location appears to be in the transition region.     

Soft X-ray sources at the centers of the elliptical galaxies NGC 4472 and NGC 4649

Analysis of recent observations of the elliptical galaxies NGC 4472 and NGC 4649 with the Chandra X-ray space telescope has revealed faint soft X-ray sources at their centers. The sources are located at the galactic centers, to within 1″, and are most likely associated with the radiation from the supermassive black holes that are assumed to be at the optical centers of these galaxies. Interest in these and several other similar objects stems from the unusually low luminosity of the supermassive black hole embedded in a dense interstellar medium. The sources have soft energy spectra in the Chandra energy range 0.2–10 keV. The source is detected at a 3σ confidence level only in the range 0.2–0.6 keV with a luminosity of ～6×10³⁷ erg s^?1 in NGC 4649 and in the range 0.2–2.5 keV with a luminosity of ～ 1.7×10³⁸ erg ^?1 in NGC 4472.     

An Improved Method to Derive the Lower Energy Cutoff of non-Thermal Electrons From Hard x-Rays of Solar Flares

By changing a dimensionless calculation to a dimensional one, introducing a more accurate bremsstrahlung cross section, and using a more reasonable fitting energy range, we have recalculated the hard X-ray bremsstrahlung produced by a beam of power-law electrons with a lower energy cutoff (E _c). The method to deduce E _c from the hard X-ray spectral observations has therefore been refined in comparison with our previous one. The universality of this method has been clarified and discussed. We have applied this improved method to the 54 BATSE/Compton Gamma Ray Observatory (CGRO) hard X-ray events. It was found that about 44% of sample hard X-ray spectra can be directly explained by a beam of power-law electrons with a lower energy cutoff. The value of E _c, varying from 45 keV to 97 keV, is on average 60 keV. Another 44% of sample hard X-ray spectra might be explained by a beam of power-law electrons with the energy cutoff lower than 45 keV, which is however beyond the availability of BATSE/CGRO. Still another 11% sample hard X-ray spectra cannot be explained by a beam of power-law electrons with a lower energy cutoff. These results, based on the lower energy resolution data, however, should be compared in the future with that based on a higher energy resolution data, like the data from HESSI.