Giovanni Pareschi

Chasing the heaviest black holes of jetted active galactic nuclei

We investigate the physical properties of 10 blazars at redshift greater than 2 detected in the 3-yr all-sky survey performed by the Burst Alert Telescope (BAT) on board the Swift satellite. We find that the jets of these blazars are among the most powerful known. Furthermore, the mass of their central black hole, inferred from the optical–ultraviolet bump, exceeds a few billions of solar masses, with accretion luminosities being a large fraction of the Eddington one. We compare their properties with those of the brightest blazars of the 3-month survey performed by the Large Area Telescope (LAT) on board the Fermi satellite. We find that the BAT blazars have more powerful jets, more luminous accretion discs and larger black hole masses than LAT blazars. These findings can be simply understood on the basis of the blazar sequence, which suggests that the most powerful blazars have a spectral energy distribution with a high-energy peak at MeV (or even sub-MeV) energies. This implies that the most extreme blazars can be found more efficiently in hard X-rays, rather than in the high-energy γ -ray band. We then discuss the implications of our findings for future missions, such as the New Hard X-ray Mission (NHXM) and especially the Energetic X-ray Imaging Survey Telescope (EXIST) mission which, during its planned 2-yr all-sky survey, is expected to detect thousands of blazars, with a few of them at z 6.

XIPE: the X-ray imaging polarimetry explorer

Abstract X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017. The proposal was, unfortunately, not selected. To be compliant with this schedule, we designed the payload mostly with existing items. The XIPE proposal takes advantage of the completed phase A of POLARIX for an ASI small mission program that was cancelled, but is different in many aspects: the detectors, the presence of a solar flare polarimeter and photometer and the use of a light platform derived by a mass production for a cluster of satellites. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2–10 keV band in 105 s for pointed observations, and 0.6 % for an X10 class solar flare in the 15–35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin × 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 μs. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut für extraterrestrische Physik (MPE, Germany). XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil). The data policy is organized with a Core Program that comprises three months of Science Verification Phase and 25 % of net observing time in the following 2 years. A competitive Guest Observer program covers the remaining 75 % of the net observing time.

Simbol-X: mission overview

Simbol-X is a hard X-ray mission, operating in the ~ 0.5-80 keV range, proposed as a collaboration between the French and Italian space agencies with participation of German laboratories for a launch in 2013. Relying on two spacecraft in a formation flying configuration, Simbol-X uses for the first time a 20-30 m focal length X-ray mirror to focus X-rays with energy above 10 keV, resulting in over two orders of magnitude improvement in angular resolution and sensitivity in the hard X-ray range with respect to non-focusing techniques. The Simbol-X revolutionary instrumental capabilities will allow us to elucidate outstanding questions in high energy astrophysics such as those related to black-holes accretion physics and census, and to particle acceleration mechanisms, which are the prime science objectives of the mission. After having undergone a thorough assessment study performed by CNES in the context of a selection of a formation flight scientific mission, Simbol-X has been selected for a phase A study to be jointly conducted by CNES and ASI. The mission science objectives, the current status of the instrumentation and mission design are presented in this paper.

In focus measurements of IXO type optics using the new PANTER X-ray test facility extension

Future large X-ray observatories in space will require mirrors with large effective areas and long focal lengths to accomplish the proposed science. ESA programs for developing lightweight optics based on modules of silicon pore optics (SPO) and slumped glass optics (SGO) were put in place for the IXO mission (f=20m, r≈1m). To test such optics the MPE PANTER X-ray test facility has been upgraded / extended with support from ESA to accommodate in-focus measurements of such optics modules. We describe the extension to PANTER and the first results obtained from measuring such SPO and SGO modules during commissioning.

POLARIX: a pathfinder mission of X-ray polarimetry

Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 105 s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled.

Development of a Prototype Nickel Optic for the Constellation-X Hard-X-Ray Telescope

The Constellation-X mission planned for launch in 2015-2020 timeframe, will feature an array of Hard X-ray telescopes (HXT) with a total collecting area greater than 1500 cm at 40 keV. Two technologies are being investigated for the optics of these telescopes, one of which is multilayer-coated Electroformed-Nickel-Replicated (ENR) shells. The attraction of the ENR process is that the resulting full-shell optics are inherently stable and offer the prospect of better angular resolution which results in lower background and higher instrument sensitivity. We are building a prototype HXT mirror module using an ENR process to fabricate the individual shells.This prototype consists of 5 shells with diameters ranging from 15 cm to 28 cm with a length of 42.6 cm. The innermost of these will be coated with iridium, while the remainder will be coated with graded d-spaced W/Si multilayers. The assembly structure has been completed and last year we reported on full beam illumination results from the first test shell mounted in this structure. We have now fabricated and coated two (15 cm and 23 cm diameter) 100 micron thick shells which have been aligned and mounted. This paper presents the results of full beam illumination X-ray tests, taken at MPE-Panter. The HEW of the individual shells will be discussed, in addition to results from the full two shell optic test.

Accurate integration of segmented x-ray optics using interfacing ribs

Abstract. Future lightweight and long-focal-length x-ray telescopes must guarantee a good angular resolution (e.g., 5 arc sec HEW) and reach an unprecedented large effective area. This goal can be reached with the slumping of borosilicate glass sheets that allow the fabrication of lightweight and low-cost x-ray optical units (XOU). These XOUs, based on mirror segments, have to be assembled together to form complete multishell Wolter-I optics. The technology for the fabrication and the integration of these XOUs is under development in Europe, funded by European Space Agency, and led by the Brera Observatory (INAF-OAB). While the achievement of the required surface accuracy on the glass segments by means of a hot slumping technique is a challenging aspect, adequate attention must be given to the correct integration and coalignment of the mirror segments into the XOUs. To this aim, an innovative assembly concept has been investigated, based on glass reinforcing ribs. The ribs connect pairs of consecutive foils, stacked into a XOU, with both structural and functional roles, providing robust monolithic stacks of mirror plates. Moreover, this integration concept allows the correction of residual low-frequency errors still present on the mirror foil profile after slumping. We present the integration concept, the related error budget, and the results achieved so far with a semi-robotic integration machine especially designed and realized to assemble slumped glass foils into XOUs.

SIMBOL-X: a formation flying mission for hard-x-ray astrophysics

SIMBOL-X is a hard X-ray mission, operating in the ~ 0.5-70 keV range, which is proposed by a consortium of European laboratories in response to the 2004 call for ideas of CNES for a scientific mission to be flown on a formation flying demonstrator. Relying on two spacecrafts in a formation flying configuration, SIMBOL-X uses for the first time a ~ 30 m focal length X-ray mirror to focus X-rays with energy above 10 keV, resulting in a two orders of magnitude improvement in angular resolution and sensitivity in the hard X-ray range with respect to non focusing techniques. The SIMBOL-X revolutionary instrumental capabilities will allow to elucidate outstanding questions in high energy astrophysics, related in particular to the physics of accretion onto compact objects, to the acceleration of particles to the highest energies, and to the nature of the Cosmic X-Ray background. The mission, which has gone through a thorough assessment study performed by CNES, is expected to start a competitive phase A in autumn 2005, leading to a flight decision at the end of 2006, for a launch in 2012. The mission science objectives, the current status of the instrumentation and mission design, as well as potential trade-offs are presented in this paper.

Glass mirrors by cold slumping to cover 100 m2 of the MAGIC II Cherenkov telescope reflecting surface

We report on the production and implementation of 100 square panels 1 m x 1 m, based on the innovative approach of cold slumping of thin glass sheets. The more than 100 segments will cover around one half of the 240 m-square reflecting surface of the MAGIC II, a clone of the atmospheric Cherenkov telescope MAGIC I (with a single-dish 17 m diameter mirror) which is already operating since late 2003 at La Palma. The MAGIC II telescope will be completed by the end of 2008 and will operate in stereoscopic mode with MAGIC I. While the central part of the of the reflector is composed of by diamond milled Aluminum of 1m2 area panels (following a design similar to that already used for MAGIC I), the outer coronas will be made of sandwiched glass segments. The glass panel production foresees the following steps: a) a thin glass sheet (1-2mm) is elastically deformed so as to retain the shape imparted by a master with convex profile - the radius of curvature is large, the sheet can be pressed against the master using vacuum suction -; b) on the deformed glass sheet a honeycomb structure that provides the needed rigidity is glued ; c) then a second glass sheet is glued on the top in order to obtain a sandwich; d) after on the concave side a reflecting coating (Aluminum) and a thin protective coating (Quartz) are deposited. The typical weight of each panel is about 12 kg and its resolution is better than 1 mrad at a level of diameter that contains the 90% of the energy reflected by the mirror; the areal cost of glass panels is ~2 k per 1m2. The technology based on cold slumping is a good candidate for the production of the primary mirrors of the telescopes forming the Cherenkov Telescope Array (CTA), the future large TeV observatory currently being studied in Europe. Details on the realization of MAGIC II new mirrors based on cold slumping glass will be presented.

Cold-shaping of thin glass foils as a method for mirror processing: from basic concepts to mass production of mirrors

Abstract. We present a method for the production of segmented optics. It is a process developed at INAF-Osservatorio Astronomico di Brera (INAF-OAB) employing commercial of-the-shelf materials. It is based on the shaping of thin glass foils by means of forced bending that occurs at room temperature [cold-shaping (CS)]. The glass is then assembled into a sandwich structure for retaining the imposed shape. The principal mechanical features of the mirrors are their low weight, rigidity and environmental robustness. The cost and production time also are competitive. We sum up the results achieved during research and development performed in the past years. We have investigated the theoretical limits of the structural components by means of parametric finite elements analyses; we also discuss the effects caused by the most common structural loads. Finally, the process implementation, the more significant validation tests and the mass production at the industry are described.