Development status of the LAUE project

We present the status of LAUE, a project supported by the Italian Space Agency (ASI), and devoted to develop Laue lenses with long focal length (up to 100 meters), for hard X--/soft gamma--ray astronomy (80-600 keV). Thanks to their focusing capability, the design goal is to improve the sensitivity of the current instrumention in the above energy band by 2 orders of magnitude, down to a few times $10^{-8}$ photons/(cm$^2$ s keV).Comment: 9 pages, 9 figures, presented at the Space Telescopes and Instrumentation Symposium in Amsterdam, 2012: Ultraviolet to Gamma Ray Conference. Published in the Proceedings of the SPIE, Volume 8443, id. 84430B-84430B-9 (2012

The LAUE project for broadband gamma-ray focusing lenses

We present the LAUE project devoted to develop an advanced technology for building a high focal length Laue lens for soft gamma--ray astronomy (80-600 keV). The final goal is to develop a focusing optics that can improve the current sensitivity in the above energy band by 2 orders of magnitude.Comment: 7 pages, 6 figures, presented at the SPIE conference on "Optics for EUV, X-ray, and Gamma-ray Astronomy". To be published in the Proceedings of SPIE, vol.8147, 201

Multiwavelength observations of 3C 454.3 II. The AGILE 2007 December campaign

We report on the second AGILE multiwavelength campaign of the blazar 3C 454.3 during the first half of December 2007. This campaign involved AGILE, Spitzer, Swift,Suzaku,the WEBT consortium,the REM and MITSuME telescopes,offering a broad band coverage that allowed for a simultaneous sampling of the synchrotron and inverse Compton (IC) emissions.The 2-week AGILE monitoring was accompanied by radio to optical monitoring by WEBT and REM and by sparse observations in mid-Infrared and soft/hard X-ray energy bands performed by means of Target of Opportunity observations by Spitzer, Swift and Suzaku, respectively.The source was detected with an average flux of~250x10^{-8}ph cm^-2s^-1 above 100 MeV,typical of its flaring states.The simultaneous optical and gamma-ray monitoring allowed us to study the time-lag associated with the variability in the two energy bands, resulting in a possible ~1-day delay of the gamma-ray emission with respect to the optical one. From the simultaneous optical and gamma-ray fast flare detected on December 12, we can constrain the delay between the gamma-ray and optical emissions within 12 hours. Moreover, we obtain three Spectral Energy Distributions (SEDs) with simultaneous data for 2007 December 5, 13, 15, characterized by the widest multifrequency coverage. We found that a model with an external Compton on seed photons by a standard disk and reprocessed by the Broad Line Regions does not describe in a satisfactory way the SEDs of 2007 December 5, 13 and 15. An additional contribution, possibly from the hot corona with T=10^6 K surrounding the jet, is required to account simultaneously for the softness of the synchrotron and the hardness of the inverse Compton emissions during those epochs.Comment: 13 pages, 8 figures, 2 tables, Accepted for publication in Ap

Scientific prospects in soft gamma-ray astronomy enabled by the LAUE project

This paper summarizes the development of a successful project, LAUE, supported by the Italian Space Agency (ASI) and devoted to the development of long focal length (up to 100 m) Laue lenses for hard X--/soft gamma--ray astronomy (80-600 keV). The apparatus is ready and the assembling of a prototype lens petal is ongoing. The great achievement of this project is the use of bent crystals. From measurements obtained on single crystals and from simulations, we have estimated the expected Point Spread Function and thus the sensitivity of a lens made of petals. The expected sensitivity is a few $\times10^{-8}$ photons cm$^{-2}$ s$^{-1}$ keV$^{-1}$. We discuss a number of open astrophysical questions that can settled with such an instrument aboard a free-flying satellite.Comment: 17 pages, 18 figures, published in Proceedings of the SPIE, Volume 8861, id. 886106 17 pp. (2013

Multiwavelength observations of 3C 454.3. I. The AGILE 2007 November campaign on the "Crazy Diamond"

[Abridged] We report on a multiwavelength observation of the blazar 3C 454.3 (which we dubbed "crazy diamond") carried out on November 2007 by means of the astrophysical satellites AGILE, INTEGRAL, Swift, the WEBT Consortium, and the optical-NIR telescope REM. 3C 454.3 is detected at a $\sim 19-\sigma$ level during the 3-week observing period, with an average flux above 100 MeV of $F_{\rm E>100MeV} = (170 \pm 13) \times 10^{-8}$ \phcmsec. The gamma-ray spectrum can be fit with a single power-law with photon index $\Gamma_{\rm GRID} = 1.73 \pm 0.16$ between 100 MeV and 1 GeV. We detect significant day-by-day variability of the gamma-ray emission during our observations, and we can exclude that the fluxes are constant at the 99.6% ($\sim 2.9 \sigma$) level. The source was detected typically around 40 degrees off-axis, and it was substantially off--axis in the field of view of the AGILE hard X-ray imager. However, a 5-day long ToO observation by INTEGRAL detected 3C 454.3 at an average flux of about $F_{\rm 20-200 keV} = 1.49 \times 10^{-3}$ \phcmsec with an average photon index of $\Gamma_{\rm IBIS} = 1.75 \pm 0.24$ between 20--200 keV. Swift also detected 3C 454.3 with a flux in the 0.3--10 keV energy band in the range $(1.23-1.40) \times 10^{-2}$ \phcmsec{} and a photon index in the range $\Gamma_{\rm XRT} = 1.56-1.73$. In the optical band, both WEBT and REM show an extremely variable behavior in the $R$ band. A correlation analysis based on the entire data set is consistent with no time-lags between the gamma-ray and the optical flux variations. Our simultaneous multifrequency observations strongly indicate that the dominant emission mechanism between 30 MeV and 30 GeV is dominated by inverse Compton scattering of relativistic electrons in the jet on the external photons from the broad line region.Comment: Accepted for publication in ApJ. Abridged Abstract. 37 pages, 14 Figures, 3 Table

IXPE Mission System Concept and Development Status

The Goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mi SMEX), is to expand understanding of high-energy astrophysical processes and sources, in support of NASAs first science objective in Astrophysics: Discover how the universe works. IXPE, an international collaboration, will conduct X-ray imaging polarimetry for multiple categories of cosmic X-ray sources such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The Observatory uses a single science operational mode capturing the X-ray data from the targets. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three X-ray telescopes each consisting of a polarization-sensitive, gas pixel X-ray detector, paired with its corresponding grazing incidence mirror module assembly (MMA). A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These payload elements are supported by the IXPE spacecraft which is derived from the BCP-small spacecraft architecture. This paper summarizes the IXPE mission science objectives, updates the Observatory implementation concept including the payload and spacecraft ts and summarizes the mission status since last years conference

Flat-spectrum radio sources as likely counterparts of unidentified INTEGRAL sources (Research Note)

Many sources in the fourth INTEGRAL/IBIS catalogue are still unidentified, since they lack an optical counterpart. An important tool that can help in identifying/classifying these sources is the cross-correlation with radio catalogues, which are very sensitive and positionally accurate. Moreover, the radio properties of a source, such as the spectrum or morphology, could provide further insight into its nature. Flat-spectrum radio sources at high Galactic latitudes are likely to be AGN, possibly associated to a blazar or to the compact core of a radio galaxy. Here we present a small sample of 6 sources extracted from the fourth INTEGRAL/IBIS catalogue that are still unidentified/unclassified, but which are very likely associated with a bright, flat-spectrum radio object. To confirm the association and to study the source X-ray spectral parameters, we performed X-ray follow-up observations with Swift/XRT. We report the results obtained from this search and discuss the nature of each source. 5 of the 6 radio associations are also detected in X-rays; in 3 cases they are the only counterpart found. IGR J06073--0024 is a flat-spectrum radio quasar at z=1.08, IGR J14488--4008 is a newly discovered radio galaxy, while IGR J18129--0649 is an AGN of a still unknown type. The nature of IGR J07225--3810 and IGR J19386--4653 is less well defined, since in both cases we find another X-ray source in the INTEGRAL error circle; nevertheless, the flat-spectrum radio source, likely to be a radio loud AGN, remains a viable and more convincing association in both cases. Only for IGR J11544--7618 could we not find any convincing counterpart since the radio association is not an X-ray emitter.Comment: 7 pages, 7 figures, accepted for publication on Astronomy and Astrophysic

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. 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. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 arcmin $\times$ 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 10^5 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.Comment: 42 pages, 28 figure

Neutron Star Radius-to-mass Ratio from Partial Accretion Disc Occultation as Measured through Fe Kα\alpha Line Profiles

We present a new method to measure the radius-to-mass ratio (R/M) of weakly magnetic, disc-accreting neutron stars by exploiting the occultation of parts of the inner disc by the star itself. This occultation imprints characteristic features on the X-ray line profile that are unique and are expected to be present in low mass X-ray binary systems seen under inclinations higher than ~65 degrees. We analyse a NuSTAR observation of a good candidate system, 4U 1636-53, and find that X-ray spectra from current instrumentation are unlikely to single out the occultation features owing to insufficient signal-to-noise. Based on an extensive set of simulations we show that large-area X-ray detectors of the future generation could measure R/M to ~2{\div}3% precision over a range of inclinations. Such is the precision in radius determination required to derive tight constraints on the equation of state of ultradense matter and it represents the goal that other methods too aim to achieve in the future.Comment: 17 pages, 8 figures; this is a pre-print edition of an article that has been accepted for publication in the Astrophysical Journa