Paolo Conconi

REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

Context. Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs. Aims. Currently, only lower limits were securely set to the initia l fireball Lorentz factor 0. We aim to provide a direct measure of 0. Methods. The early-time afterglow light curve carries information about 0, which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afte rglows of GRB 060418 and GRB 060607A with the REM robotic telescope. Results. For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of 0∼ 400, fully confirming the highly relativistic nature of GRB fi reballs. The deceleration radius was inferred to be Rdec≈ 10 17 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.E. Molinari, S.D. Vergani , D. Malesani , S. Covino, P. D’Avanzo, G. Chincarini , F.M. Zerbi, L.A. Antonelli, P. Conconi , V. Testa, G. Tosti , F. Vitali, F. D’Alessio, G. Malaspina, L. Nicastro, E. Palazzi , D. Guetta, S. Campana , P. Goldoni , N. Masetti , E.J.A. Meurs, A. Monfardini, L. Norci, E. Pian, S. Piranomonte , D. Rizzuto, M. Stefanon, L. Stella, G. Tagliaferri , P.A. Ward, G. Ihle, L. Gonzalez, A. Pizarro, P. Sinclair, J. Valenzuela 15

Hα Rotation Curves: The Soft Core Question

We present high-resolution Hα rotation curves of four late-type dwarf galaxies and two low surface brightness (LSB) galaxies, for which accurate H I rotation curves are available from the literature. Observations are carried out at Telescopio Nazionale Galileo. For LSB F583-1 an innovative dispersing element was used, the Volume Phase Holographic, with a dispersion of about 0.35 A pixel-1. We find good agreement between the Hα data and the H I observations and conclude that the H I data for these galaxies suffer very little from beam smearing. We show that the optical rotation curves of these dark matter-dominated galaxies are best fitted by the Burkert profile. In the centers of galaxies, where the N-body simulations predict cuspy cores and fast rising rotation curves, our data seem to be in better agreement with the presence of soft cores.

The REM telescope: detecting the near infra-red counterparts of Gamma-Ray Bursts and the prompt behavior of their optical continuum

Observations of the prompt afterglow of Gamma Ray Burst (GRB) events are unanimously considered of paramount importance for GRB science and related cosmology. Such observations at NIR wavelengths are even more promis- ing allowing one to monitor high-z Ly- absorbed bursts as well as events occurring in dusty star-forming regions. In these pages we present REM (Rapid Eye Mount), a fully robotized fast slewing telescope equipped with a high throughput NIR (Z, J, H, K) camera dedicated to detecting the prompt IR afterglow. REM can discover objects at extremely high redshift and trigger large telescopes to observe them. The REM telescope will simultaneously feed ROSS (REM Optical Slitless Spectrograph) via a dichroic. ROSS will intensively monitor the prompt optical continuum of GRB afterglows. The synergy between REM-IR cam and ROSS makes REM a powerful observing tool for any kind of fast transient phenomena.

A rapid and dramatic outburst in Blazar 3C 454.3 during May 2005 - Optical and infrared observations with REM and AIT

The flat-spectrum radio quasar 3C454.3 is well known to be a highly active and variable source with outbursts occurring across the whole electromagnetic spectrum over the last decades. In spring 2005, 3C454.3 has been reported to exhibit a strong optical outburst which subsequently triggered multi-frequency observations of the source covering the radio up to γ-ray bands. Here, we present first results of our near-IR/optical (V, R, I, H band) photometry performed between May 11 and August 5, 2005 with the Rapid Eye Mount (REM) at La Silla in Chile and the Automatic Imaging Telescope (AIT) of the Perugia University Observatory. 3C454.3 was observed during an exceptional and historical high state with a subsequent decrease in brightness over our 86 days observing period. The continuum spectral behaviour during the flaring and declining phase suggests a synchrotron peak below the near-IR band as well as a geometrical origin of the variations e.g. due to changes in the direction of forward beaming.

REM: a fully robotic telescope for GRB observations

The Rapid Eye Mount (REM) telescope is an ambitious project devoted to the prompt observations, in the optical and Near Infrared (NIR), of Gamma-Ray Bursts (GRBs) whose high energy emission is mainly detected by the Swift satellite. The system is able to immediately react to a GRB alert and perform observations, data reduction and analyses, distributing GRB counterparts in a timescale of tens of seconds. Apart from GRB observations, REM can also drive autonomous observations of a variety of targets as X-ray transients, flare stars, etc. We describe here how REM can manage all these tasks robotically, taking into account environmental and scientific parameters as seeing, visibility, target priority, etc.

Characteristics of the flight model optics for the JET-X telescope onboard the Spectrum-X-Gamma satellite

The joint European x-ray telescope (JET-X) is one of the core scientific instruments of the RUssian SPECTRUM X-(gamma) astrophysics mission. JET-X is designed to study the emission from x-ray sources in the band of 0.3-10 keV; in particular to meet primary scientific goals in cosmology and extragalactic astronomy. JET-X consists of two identical, coaligned x-ray telescopes, each with a spatial resolution of better than 30 arcsec half energy width. Focal plane imaging is provided by cooled x-ray sensitive CCD detectors which combine high spatial resolution with good spectral resolution, including coverage of the iron line complex around 7 keV at a resolution of (Delta) E/E approximately 1.5 percent. Each telescope is composed of a nested array of 12 mirror shells with an aperture of 300 mm and focal length of 3500 mm; the total effective area is 330 cm2 at 1.5 keV and 145 cm2 at 8.1 keV. The mirror shells have a Wolter I geometry and are manufactured by an electroforming replica process. The paper presents the characteristic of the flight model x-ray optics.

Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes

Grazing incidence mirrors for X{ray astronomy are usually designed in the parabola-hyperbola (Wolter I) conguration. This design allows for optimal images on-axis, which however degrade rapidly with the o-axis angle. Mirror surfaces described by polynomia (with terms higher than order two), have been put forward to improve the performances over the eld of view. Here we present a rened procedure aimed at optimiz- ing wide-eld grazing incidence telescopes for X{ray astronomy. We improve the angular resolution over existing (wide-eld) designs by 20%. We further consider the corrections for the dierent plate scale and focal plane curvature of the mirror shells, which sharpen by another20% the image quality. This results in a factor of2 reduction in the observing time needed to achieve the same sensitivity over existing wide-eld designs and of5 over Wolter I telescopes. We demonstrate that such wide-eld X{ray telescopes are highly advantageous for deep surveys of the X{ray sky.

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.

The International Robotic Antarctic Infrared Telescope (IRAIT)

Thanks to exceptional coldness, low sky brightness and low content of water vapour of the above atmosphere Dome C, one of the three highest peaks of the large Antarctic plateau, is likely to be the best site on Earth for thermal infrared observations (2.3-300 μm) as well as for the far infrared range (30 μm-1mm). IRAIT (International Robotic Antarctic Infrared Telescope) will be the first European Infrared telescope operating at Dome C. It will be delivered to Antarctica at the end of 2006, will reach Dome C at the end of 2007 and the first winter-over operation will start in spring 2008. IRAIT will offer a unique opportunity for astronomers to test and verify the astronomical quality of the site and it will be a useful test-instrument for a new generation of Antarctic telescopes and focal plane instrumentations. We give here a general overview of the project and of the logistics and transportation options adopted to facilitate the installation of IRAIT at Dome C. We summarize the results of the electrical, electronics and networking tests and of the sky polarization measurements carried out at Dome C during the 2005-2006 summer-campaign. We also present the 25 cm optical telescope (small-IRAIT project) that will installed at Dome C during the Antarctic summer 2006-2007 and that will start observations during the 2007 Antarctic winter when a member of the IRAIT collaboration will join the Italian-French Dome C winter-over team.

The REM telescope: a robotic multiwavelength facility

The REM Observatory, recently installed and commissioned at la Silla Observatory Chile, is the first moderate aperture robotic telescope able to cover simultaneously the visible-NIR (0.45-2.3 microns) wavelength range. His very fast pointing and his full robotization makes it an ideal observing facility for fast transients. The high throughput Infrared Camera and the Visible imaging spectrograph simultaneously fed by a dichroic allows to collect high S/N data in an unprecedented large spectral range on a telescope of this size. The REM observatory is an example of a versatile and agile facility necessary complement to large telescopes in fileds in which rapid response and/or target pre-screening are necessary. We give in this paper an overview of the Observatory and its performances with emphasis to the innovative technical solution adopted to reach such performances.