Coded aperture imaging in X- and gamma-ray astronomy

Caroli, E.; Stephen, J. B.; Cocco, G. Di; Natalucci, L.; Spizzichino, A.

doi:10.1007/bf00171998

Cited by 375 publications

(239 citation statements)

References 74 publications

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“…Since its launch on October 17, 2002, the soft γ-ray imager IBIS/ISGRI (15-1000 keV; Lebrun et al 2003, Ubertini et al 2003 on board INTEGRAL has detected more than 200 AGN, among which about 90 were detected for the first time in the hard X-rays. IBIS/ISGRI uses the coded-aperture technique (Caroli et al 1987) and has a large field of view of 29 • square with a spatial resolution of 12 arcmin.…”

Section: Introductionmentioning

confidence: 99%

Reflection in Seyfert galaxies and the unified model of AGN

Ricci

Walter

Courvoisier

et al. 2011

A&A

128

143

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We present a deep study of the average hard X-ray spectra of Seyfert galaxies. We aim to test the unified model of active galactic nuclei, and constrain differences and similarities between different classes of objects. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the 165 Seyfert galaxies detected at z < 0.2. Our final sample consists of 44 Seyfert 1s, 29 Seyfert 1.5s, 78 Seyfert 2s, and 14 narrow-line Seyfert 1s. For each subsample, we stacked all the images, and derived their average hard X-ray spectra in the 17-250 keV energy range. We performed a detailed spectral analysis using both a model-independent and a model-dependent approach. All classes of Seyfert galaxies show on average the same nuclear continuum, as foreseen by the zeroth order unified model, with a cutoff energy of E C 200 keV, and a photon index of Γ ≃ 1.8. The average optical depth of the Comptonizing medium is consistent for the different classes (τ ≃ 0.8). Compton-thin Seyfert 2s show a reflection component stronger than Seyfert 1s and Seyfert 1.5s. Most of this reflection is due to mildly obscured (10 23 cm −2 ≤ N H < 10 24 cm −2 ) Seyfert 2s, which have a significantly stronger reflection component (R = 2.2 +4.5 −1.1 ) than Seyfert 1s (R ≤ 0.4), Seyfert 1.5s (R ≤ 0.4) and lightly obscured (N H < 10 23 cm −2 ) Seyfert 2s (R ≤ 0.5). This cannot be explained easily by the unified model. The absorber/reflector in mildly obscured Seyfert 2s might cover a large fraction of the X-ray source, and contain clumps of Compton-thick material. The large reflection found in the spectrum of mildly obscured Seyfert 2s reduces the amount of Compton-thick objects needed to explain the peak of the cosmic X-ray background. Our results are consistent with the fraction of Compton-thick sources being ∼ 10%. The spectra of Seyfert 2s with and without polarized broad lines do not show significant differences, the only difference between the two samples being the higher hard X-ray and bolometric luminosity of Seyfert 2s with polarized broad lines. The average hard X-ray spectrum of narrow-line Seyfert 1s is steeper than those of Seyfert 1s and Seyfert 1.5s, probably due to a lower energy of the cutoff.

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Section: Introductionmentioning

confidence: 99%

Reflection in Seyfert galaxies and the unified model of AGN

Ricci

Walter

Courvoisier

et al. 2011

A&A

128

143

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“…In other words, the collimator blades will only start shadowing the detectors for incident directions outside this angular range, centered on the camera axis. The source location accuracy (see Caroli et al 1987) will depend on the incident angle and will be limited by the precision of the pointing system. In the best case, it will be around 10 for a 10σ source in the center of the FOV.…”

Section: The Coded Maskmentioning

confidence: 99%

The protoMIRAX hard X-ray imaging balloon experiment

Braga

D'Amico

Ávila

et al. 2015

A&A

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Context. The protoMIRAX hard X-ray imaging telescope is a balloon-borne experiment developed as a pathfinder for the MIRAX satellite mission. The experiment consists essentially in a coded-aperture hard X-ray (30-200 keV) imager with a square array (13 × 13) of 2 mm-thick planar CZT detectors with a total area of 169 cm 2 . The total, fully-coded field-of-view is 21 • × 21 • and the angular resolution is 1 • 43 . Aims. The main objective of protoMIRAX is to carry out imaging spectroscopy of selected bright sources to demonstrate the performance of a prototype of the MIRAX hard X-ray imager. In this paper we describe the protoMIRAX instrument and all the subsystems of its balloon gondola, and we show simulated results of the instrument performance. Methods. Detailed background and imaging simulations were performed for protoMIRAX balloon flights. The 3σ sensitivity for the 30-200 keV range is ∼1.9 × 10 −5 photons cm −2 s −1 for an integration time of 8 h at an atmospheric depth of 2.7 g cm −2 and an average zenith angle of 30 • . We developed an attitude-control system for the balloon gondola and new data handling and ground systems that also include prototypes for the MIRAX satellite.Results. We present the results of Monte Carlo simulations of the camera response at balloon altitudes, showing the expected background level and the detailed sensitivity of protoMIRAX. We also present the results of imaging simulations of the Crab region. Conclusions. The results show that protoMIRAX is capable of making spectral and imaging observations of bright hard X-ray source fields. Furthermore, the balloon observations will carry out very important tests and demonstrations of MIRAX hardware and software in a near space environment.

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“…The flutter shutter approach chooses a shutter timing pattern with the intent of optimally preserving image content at all spatial frequencies, and preserving those frequencies at a nearly uniform level of contrast. Because the effective PSF is zero-padded, the MURA pattern [12] is not necessarily optimal. Raskar's shutter timing pattern is found by dividing the acquisition time into several chops of uniform duration, and by assigning a label of open or closed shutter to each of the chops subject to a constraint on the total exposure.…”

Section: Related Workmentioning

confidence: 99%

Velocity-Dependent Shutter Sequences for Motion Deblurring

McCloskey

2010

Computer Vision – ECCV 2010

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Abstract. We address the problem of high-quality image capture of fast-moving objects in moderate light environments. In such cases, the use of a traditional shutter is known to yield non-invertible motion blur due to the loss of certain spatial frequencies. We extend the flutter shutter method of Raskar et al. to fast-moving objects by first demonstrating that no coded exposure sequence yields an invertible point spread function for all velocities. Based on this, we argue that the shutter sequence must be dependent on object velocity, and propose a method for computing such velocity-dependent sequences. We demonstrate improved image quality from velocity-dependent sequences on fast-moving objects, as compared to sequences found using the existing sampling method.

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Coded aperture imaging in X- and gamma-ray astronomy

Cited by 375 publications

References 74 publications

Reflection in Seyfert galaxies and the unified model of AGN

Reflection in Seyfert galaxies and the unified model of AGN

The protoMIRAX hard X-ray imaging balloon experiment

Velocity-Dependent Shutter Sequences for Motion Deblurring

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