N. Omodei

IDENTIFICATION AND PROPERTIES OF THE PHOTOSPHERIC EMISSION IN GRB090902B

The Fermi Gamma-ray Space Telescope observed the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover th ...

DETECTION OF A THERMAL SPECTRAL COMPONENT IN THE PROMPT EMISSION OF GRB 100724B.

Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission component, but also includes a statistically highly significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.

Prospects for GRB Science with the Fermi Large Area Telescope

The Large Area Telescope (LAT) instrument on the Fermi mission will reveal the rich spectral and temporal gamma-ray burst (GRB) phenomena in the >100 MeV band. The synergy with Fermis Gamma-ray Burst Monitor detectors will link these observations to those in the well explored 10-1000 keV range; the addition of the >100 MeV band observations will resolve theoretical uncertainties about burst emission in both the prompt and afterglow phases. Trigger algorithms will be applied to the LAT data both onboard the spacecraft and on the ground. The sensitivity of these triggers will differ because of the available computing resources onboard and on the ground. Here we present the LATs burst detection methodologies and the instruments GRB capabilities.

Novel gaseous x-ray polarimeter: data analysis and simulation

We report on the development of a new higly efficient polarimeter, based on the photoelectric effect in gas, for the 2-10 keV energy range, a particularly interesting band for x-ray astronomy. We derive the polarization information by reconstructing the direction of photoelectron emission with a pixel gas detector. Attention is focused on the algorithms used in data analysis in order to maximize the sensitivity of the instrument. Monte Carlo simulation is also discussed in details.

A set of x-ray polarimeters for the New Hard X-ray Imaging and Polarimetric Mission

The New Hard X-Ray Imaging and Polarimetric Mission makes a synergic use of Hard X-Ray Imaging, Spectroscopy and Polarimetry, as independent diagnostic of the same physical systems. It exploits the technology of multi-layer optics that, with a focal length of 10 m, allow for spectroscopic and imaging, with a resolution from 15 to 20 arcseconds, on the band 0.2 - 80 keV. One of the four telescopes is devoted to polarimetry. Since the band of a photoelectric polarimeter is not that wide, we foresee two of them, one tuned on the lower energy band (2-10 keV) and another one tuned on higher energies (6 - 35 keV). The blurring due to the inclined penetration of photons in the gas , thanks to the long focal length is practically negligible. In practice the polarimeters fully exploit the resolution the telescope and NHXM can perform angular resolved simultaneous spectroscopy and polarimetry on the band 2 - 35 keV. We are also studying the possibility to extend the band up to 80 keV by means of a focal plane scattering polarimeter.

A photoelectric polarimeter for XEUS: a new window in x-ray sky

XEUS is a large area telescope aiming to rise X-ray Astronomy to the level of Optical Astronomy in terms of collecting areas. It will be based on two satellites, locked on a formation flight, one with the optics, one with the focal plane. The present design of the focal plane foresees, as an auxiliary instrument, the inclusion of a Polarimeter based on a Micropattern Chamber. We show how such a device is capable to solve open problems on many classes of High Energy Astrophysics objects and to use X-ray sources as a laboratory for a substantial progress on Fundamental Physics.

POLARIX: a small mission of x-ray polarimetry

X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber in the focus of a telescope. It requires large area optics for most important scientific targets. But since the technique is additive a dedicated mission with a cluster of small telescopes can perform many important measurements and bridge the 40 year gap between OSO-8 data and future big telescopes such as XEUS. POLARIX has been conceived as such a pathfinder. It is a Small Satellite based on the optics of JET-X. Two telescopes are available in flight configuration and three more can be easily produced starting from the available superpolished mandrels. We show the capabilities of such a cluster of telescopes each equipped with a focal plane photoelectric polarimeter and discuss a few alternative solutions.

The silicon-strip tracker of the Gamma ray Large Area Space Telescope

Abstract The Gamma ray Large Area Space Telescope (GLAST) is an astro-particle mission that will study the mostly unexplored, high energy ( 20 MeV – 1 TeV ) spectrum of photons coming from active sources in the universe. Construction of the GLAST silicon tracker, by far the largest ever built for a space mission, is now well on the way, as it is scheduled for launch by NASA in autumn 2006. We report on the basic technology adopted for the silicon detectors, particularly in connection to their use in space, on the first results of sensors testing and on the status of tracker assembly.

Micropattern gas detector for x-ray polarimetry

We report on a new instrument that brings high efficiency to x-ray polarimetry, which is the last unexplored field of x-ray astronomy. It derives the polarization information from the tracks of the photoelectrons imaged by a finely subdivided gas pixel detector. The device can also do simultaneously good imaging, moderate spectroscopy and fast, high rate timing down to 150 eV. Moreover, being truly 2D, it is non dispersive and does not require rotation. The great immprovement of sensitivity will allow direct exploration of the most dramatic objects of the x-ray sky; with integrations of the order of one day we could perform polarimetry of Active Galactic Nuclei at the percent level, a breakthrough in this fascinating window of high energy astrophysics.

An x-ray polarimeter for hard x-ray optics

Development of multi-layer optics makes feasible the use of X-ray telescope at energy up to 60-80 keV: in this paper we discuss the extension of photoelectric polarimeter based on Micro Pattern Gas Chamber to high energy X-rays. We calculated the sensitivity with Neon and Argon based mixtures at high pressure with thick absorption gap: placing the MPGC at focus of a next generation multi-layer optics, galatic and extragalactic X-ray polarimetry can be done up till 30 keV.