Simulations of the X-ray imaging capabilities of the Silicon Drift Detectors (SDD) for the LOFT Wide Field Monitor

The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionize the study of compact objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. The Large Area Detector (LAD), carrying an unprecedented effective area of 10 m^2, is complemented by a coded-mask Wide Field Monitor, in charge of monitoring a large fraction of the sky potentially accessible to the LAD, to provide the history and context for the sources observed by LAD and to trigger its observations on their most interesting and extreme states. In this paper we present detailed simulations of the imaging capabilities of the Silicon Drift Detectors developed for the LOFT Wide Field Monitor detection plane. The simulations explore a large parameter space for both the detector design and the environmental conditions, allowing us to optimize the detector characteristics and demonstrating the X-ray imaging performance of the large-area SDDs in the 2-50 keV energy band.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-210, 201

Techniques and detectors for polarimetry in X-ray astronomy

Polarimeters flown so far were based on the Thomson scattering and Bragg diffraction with intrinsically limited sensitivity. In the present paper, we review the experiments based on those techniques and discuss possible optimization and implementation for X-ray astronomy

A gas pixel detector for x-ray polarimetry

Even though lacking of solid experimental verifications, X-ray polarimetry is strongly established as a deep diagnostic tool for probing the emission mechanisms in astronomical sources of high energy radiation. The recent development of new, more efficient instrumentation, as well as the renewed interest of the theoreticians, has drawn a significant attention to the field. Particularly, the exploitation of the photoelectric effect for deriving polarization information seems to promise a great advance in sensitivity with respect to the conventional techniques. To this aim we have designed, produced and tested a CMOS VLSI array of 2101 pixels (with 80 μm pitch), to be directly used as the charge collecting anode of a Gas Electron Multiplier (GEM). Each pixel is fully covered by a hexagonal metal electrode and each of these electrodes is individually connected to a full electronics chain, built immediately below it; in this sense detector and read-out electronics become virtually the same thing. Even though we focus our attention on the polarimetric applications, our achievements are highly significant for the whole field of development of gas detectors, which for the first time reach the level of integration and resolution typical of solid state detectors

LOFT - a Large Observatory For x-ray Timing

The high time resolution observations of the X-ray sky hold the key to a number of diagnostics of fundamental physics, some of which are unaccessible to other types of investigations, such as those based on imaging and spectroscopy. Revealing strong gravitational field effects, measuring the mass and spin of black holes and the equation of state of ultradense matter are among the goals of such observations. At present prospects for future, non-focused X-ray timing experiments following the exciting age of RXTE/PCA are uncertain. Technological limitations are unavoidably faced in the conception and development of experiments with effective area of several square meters, as needed in order to meet the scientific requirements. We are developing large-area monolithic Silicon Drift Detectors offering high time and energy resolution at room temperature, which require modest resources and operation complexity (e.g., read-out) per unit area. Based on the properties of the detector and read-out electronics that we measured in the lab, we developed a realistic concept for a very large effective area mission devoted to X-ray timing in the 2-30 keV energy range. We show that effective areas in the range of 10-15 square meters are within reach, by using a conventional spacecraft platform and launcher of the small-medium class.Comment: 13 pages, 8 figures, 1 table, Proceedings of SPIE Vol. 7732, Paper No. 7732-66, 201

The characterization of the distant blazar GB6 J1239+0443 from flaring and low activity periods

In 2008 AGILE and Fermi detected gamma-ray flaring activity from the unidentified EGRET source 3EG J1236+0457, recently associated with a flat spectrum radio quasar GB6 J1239+0443 at z=1.762. The optical counterpart of the gamma-ray source underwent a flux enhancement of a factor 15-30 in 6 years, and of ~10 in six months. We interpret this flare-up in terms of a transition from an accretion-disk dominated emission to a synchrotron-jet dominated one. We analysed a Sloan Digital Sky Survey (SDSS) archival optical spectrum taken during a period of low radio and optical activity of the source. We estimated the mass of the central black hole using the width of the CIV emission line. In our work, we have also investigated SDSS archival optical photometric data and UV GALEX observations to estimate the thermal-disk emission contribution of GB6 J1239+0443. Our analysis of the gamma-ray data taken during the flaring episodes indicates a flat gamma-ray spectrum, with an extension of up to 15 GeV, with no statistically-relevant sign of absorption from the broad line region, suggesting that the blazar-zone is located beyond the broad line region. This result is confirmed by the modeling of the broad-band spectral energy distribution (well constrained by the available multiwavelength data) of the flaring activity periods and by the accretion disk luminosity and black hole mass estimated by us using archival data.Comment: 30 pages, 7 figures, 4 tables MNRAS Accepted on 2012 June 1

IPN localizations of Konus short gamma-ray bursts

Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration gamma-ray bursts (including 23 bursts which can be classified as short bursts with extended emission). During this period, the IPN consisted of up to eleven spacecraft, and using triangulation, the localizations of 271 bursts were obtained. We present the most comprehensive IPN localization data on these events. The short burst detection rate, $\sim$18 per year, exceeds that of many individual experiments.Comment: Published versio

AGILE detection of a strong gamma-ray flare from the blazar 3C 454.3

We report the first blazar detection by the AGILE satellite. AGILE detected 3C 454.3 during a period of strongly enhanced optical emission in July 2007. AGILE observed the source with a dedicated repointing during the period 2007 July 24-30 with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV-50 GeV and 18-60 keV, respectively. Over the entire period, AGILE detected gamma-ray emission from 3C 454.3 at a significance level of 13.8-$\sigma$ with an average flux (E$>$100 MeV) of $(280 \pm 40) \times 10^{-8}$ photons cm$^{-2}$ s$^{-1}$. The gamma-ray flux appears to be variable towards the end of the observation. No emission was detected by Super-AGILE in the energy range 20-60 keV, with a 3-$\sigma$ upper limit of $2.3 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$. The gamma-ray flux level of 3C 454.3 detected by AGILE is the highest ever detected for this quasar and among the most intense gamma-ray fluxes ever detected from Flat Spectrum Radio Quasars.Comment: Accepted by Astrophysical Journal Letters; 14 pages, 3 EPS Figures, 1 Tabl

Detection of Gamma-ray Emission from the Eta-Carinae Region

We present the results of extensive observations by the gamma-ray AGILE satellite of the Galactic region hosting the Carina nebula and the remarkable colliding wind binary Eta Carinae (Eta Car) during the period 2007 July to 2009 January. We detect a gamma-ray source (1AGL J1043-5931) consistent with the position of Eta Car. If 1AGL J1043-5931 is associated with the Eta Car system our data provide the long sought first detection above 100 MeV of a colliding wind binary. The average gamma-ray flux above 100 MeV and integrated over the pre-periastron period 2007 July to 2008 October is F = (37 +/- 5) x 10-8 ph cm-2 s-1 corresponding to an average gamma-ray luminosity of L = 3.4 x 10^34 erg s-1 for a distance of 2.3 kpc. We also report a 2-day gamma-ray flaring episode of 1AGL J1043-5931 on 2008 Oct. 11-13 possibly related to a transient acceleration and radiation episode of the strongly variable shock in the system.Comment: 5 pages, 4 figure, accepted for publication in ApJ Letter

The brightest gamma-ray flaring blazar in the sky: AGILE and multi-wavelength observations of 3C 454.3 during November 2010

Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one gamma-ray flare per year, becoming the most active gamma-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, SWIFT, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary gamma-ray flare of 3C 454.3 which occurred in November 2010. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E>100 MeV) of F_gamma(p) = (6.8+-1.0)E-5 ph/cm2/s on a time scale of about 12 hours, more than a factor of 6 higher than the flux of the brightest steady gamma-ray source, the Vela pulsar, and more than a factor of 3 brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make a thorough study of the present event possible: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the gamma-ray flare, we find that the radio, optical and X-ray emission varies within a factor 2-3, whereas the gamma-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.Comment: Accepted for publication in ApJ Letters. 18 Pages, 4 Figures, 1 Tabl