The measurement of a single-mode thermal field with a microwave cavity parametric amplifier

In this paper, we present the experimental study of a single-mode thermal field carried out using a microwave parametric amplifier tuned at 1.5 GHz and working at room temperature. The parametric amplifier is based on a variable capacitance diode placed inside a microwave resonant cavity. The measured distribution of the thermal photons inside the resonator follows the expected Bose–Einstein distribution probability

"Galileo Galilei" (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein

"Galileo Galilei" (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle-which is at the basis of the General Theory of Relativity-to 1 part in 1017. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009

The AGILE Mission

AGILE is an Italian Space Agency mission dedicated to observing the gamma-ray Universe. The AGILE's very innovative instrumentation for the first time combines a gamma-ray imager (sensitive in the energy range 30 MeV-50 GeV), a hard X-ray imager (sensitive in the range 18-60 keV), a calorimeter (sensitive in the range 350 keV-100 MeV), and an anticoincidence system. AGILE was successfully launched on 2007 April 23 from the Indian base of Sriharikota and was inserted in an equatorial orbit with very low particle background. Aims. AGILE provides crucial data for the study of active galactic nuclei, gamma-ray bursts, pulsars, unidentified gamma-ray sources, galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. Methods. An optimal sky angular positioning (reaching 0.1 degrees in gamma- rays and 1-2 arcmin in hard X-rays) and very large fields of view (2.5 sr and 1 sr, respectively) are obtained by the use of Silicon detectors integrated in a very compact instrument. Results. AGILE surveyed the gamma- ray sky and detected many Galactic and extragalactic sources during the first months of observations. Particular emphasis is given to multifrequency observation programs of extragalactic and galactic objects. Conclusions. AGILE is a successful high-energy gamma-ray mission that reached its nominal scientific performance. The AGILE Cycle-1 pointing program started on 2007 December 1, and is open to the international community through a Guest Observer Program

The 2009 december gamma-ray flare of 3C 454.3: The multifrequency campaign

During the month of 2009 December, the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F 2000 × 10 -8 photons cm-2 s-1 for E > 100 MeV. Starting in 2009 November intensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here, we report on the results of a two-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, and Rossi XTE for the high-energy observations and Swift/UVOT, KANATA, Goddard Robotic Telescope, and REM for the near-IR/optical/UV data. GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting 1 month at all wavelengths: in the gamma-ray band, peak emission was reached on 2009 December 2-3. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broadband spectral evolution severely constrain the theoretical modeling. We find that the pre- and post-flare broadband behavior can be explained by a one-zone model involving synchrotron self-Compton plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the 2009 December 2-3 super-flare and of the secondary peak emission on 2009 December 9 cannot be satisfactorily modeled by a simple one-zone model. An additional particle component is most likely active during these states. © 2010. The American Astronomical Society. All rights reserved

AGILE detection of intense gamma-ray activity from the blazar PKS 0537-441 in October 2008

We report the detection by the AGILE satellite of intense gamma-ray activity from the source 1AGL J0538-4424, associated with the low-energy-peaked BL Lac PKS 0537-441, during a target of opportunity (ToO) observation performed on 2008 October 10-17, triggered by a Fermi-LAT alert, together with REM and Swift observations. Aims. The quasi-simultaneous near-infrared, optical, UV, X-ray, and gamma-ray coverage allowed us to investigate the behaviour of the source in different energy bands and study the spectral energy distribution and a theoretical model that can describe the gamma-ray state observed in mid-October. Methods. AGILE observed the source with its two co-aligned imagers: the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (SuperAGILE), sensitive in the 30 MeV-30 GeV and 18-60 keV ranges, respectively. During the AGILE observation, the source was monitored simultaneously in the UV and X-ray bands by the Swift satellite through 6 ToO observations carried out between 2008 October 8 and 17. Moreover, the source was observed in the near-infrared and optical bands by the REM telescope on 2008 October 7, 8, and 9. Results. During 2008 October 10-17, AGILE-GRID detected gamma-ray emission from PKS 0537-441 at a significance level of 5.3-sigma with an average flux of (42 +/- 11) x 10(-8) photons cm(-2) s(-1) for energies higher than 100 MeV. A significant increase in the gamma-ray activity was detected between the first and the second halves of the observing period. REM and Swift/XRT detected the source in near-infrared/optical and X-rays during a relatively low and intermediate activity state, respectively, with no signs of evident variability in the different observations. However, Swift/UVOT detected an increase between the first and the second parts of the observing period, smaller than in the gamma-rays. Conclusions. The average gamma-ray flux of PKS 0537-441 detected by AGILE is close to the average flux observed for this source by the EGRET and Fermi-LAT instruments, with an increase of a factor 3 throughout the observation period up to a flux level slightly lower than the highest flux observed by Fermi-LAT during the first 11 months of operation. The spectral energy distribution of PKS 0537-441 in mid-October 2008 seems to require two synchrotron self-Compton components to be modelled, to account for both the near-infrared/optical bump and the X-ray data, together with the information on the gamma-ray flux level observed by AGILE. An alternative model based on the external Compton radiation, which requires an accretion disk with a relatively high luminosity, is also proposed

Monitoring the hard X-ray sky with SuperAGILE

SuperAGILE is the hard X-ray monitor of the AGILE gamma ray mission, in orbit since 23 April 2007. It is an imaging experiment based on a set of four independent silicon strip detectors, equipped with one-dimensional coded masks, operating in the nominal energy range 18-60 keV. Aims. The main goal of SuperAGILE is the observation of cosmic sources simultaneously with the main gamma-ray AGILE experiment, the Gamma Ray Imaging Detector (GRID). Given its similar to steradian-wide field of view and its similar to 15 mCrab day-sensitivity, SuperAGILE is also well suited to the long-term monitoring of Galactic compact objects and the detection of bright transients. Methods. The SuperAGILE detector properties and design allow for a 6 arcmin angular resolution in each of the two independent orthogonal projections of the celestial coordinates. Photon by photon data are continuously available by means of experiment telemetry, and are used to derive images and fluxes of individual sources, with integration times depending on the source intensity and position in the field of view. Results. We report on the main scientific results achieved by SuperAGILE over its first two years in orbit, until April 2009. The scientific observations started in mid-July 2007, with the science verification phase, continuing during the complete AGILE Cycle 1 and the first similar to half of Cycle 2. Despite the largely non-uniform sky coverage, due to the pointing strategy of the AGILE mission, a few tens of Galactic sources were monitored, sometimes for unprecedently long continuous periods, leading to the detection also of several bursts and outbursts. Approximately one gamma ray burst per month was detected and localized, allowing for prompt multi-wavelength observations. A few extragalactic sources in bright states were occasionally detected as well. The light curves of sources measured by SuperAGILE are made publicly available on the web in almost real-time. To enable a proper scientific use of these, we provide the reader with the relevant scientific and technical background

AGILE detection of a rapid gamma-ray flare from the blazar PKS 1510-089 during the GASP-WEBT monitoring

We report the detection by the AGILE satellite of a rapid gamma-ray flare from the source 1AGL J1511-0908, associated with the powerful gamma-ray quasar PKS 1510-089, during a pointing centered on the Galactic center region from 1 March to 30 March 2008. This source has been continuosly monitored in the radio-to-optical bands by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). Moreover, the gamma-ray flaring episode triggered three ToO observations by the Swift satellite in three consecutive days, starting from 20 March 2008. The quasi-simultaneous radio-to-optical, UV, X-ray and gamma-ray coverage allows us to make a detailed study of the multifrequency time evolution, the spectral energy distribution of this source, and its theoretical interpretation based on the synchrotron and inverse Compton (IC) emission mechanisms. Methods. During the radio-to-optical monitoring provided by the GASP-WEBT, AGILE observed the source with its two co-aligned imagers, the gamma-ray imaging detector (GRID) and the hard X-ray imager (SuperAGILE), which are sensitive in the 30 MeV-30 GeV and 18-60 keV energy bands, respectively. Results. In the period 1-16 March 2008, AGILE detected gamma-ray emission from PKS 1510-089 at a significance level of 6.2-sigma with an average flux over the entire period of (84 +/- 17) x 10(-8) photons cm(-2) s(-1) for photon energies above 100 MeV. After a predefined satellite re-pointing, between 17 and 21 March 2008, AGILE detected the source at a significance level of 7.3-sigma, with an average flux (E > 100 MeV) of (134 +/- 29) x 10(-8) photons cm-2 s-1 and a peak level of (281 +/- 68) x 10(-8) photons cm(-2) s(-1) with daily integration. During the observing period January-April 2008, the source also showed an intense and variable optical activity, with several flaring episodes and a significant increase in the flux was observed at millimetric frequencies. Moreover, in the X-ray band, the Swift/XRT observations seem to show a harder-when-brighter behavior of the source spectrum. Conclusions. The flat spectrum radio quasar PKS 1510-089 showed strong activity between January and April 2008, with episodes of rapid variability from radio to gamma-ray energy bands, in particular with a rapid gamma-ray flaring episode. The spectral energy distribution of mid-March 2008 is modeled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions from inverse Compton scattering of external photons from both the accretion disk and the broad line region. Indeed, some features in the optical-UV spectrum seem to indicate Seyfert-like components such as the little and the big blue bumps