A. Goldwurm

IBIS: The Imager on-board INTEGRAL

The IBIS telescope is the high angular resolution gamma-ray imager on-board the INTEGRAL Observatory, suc- cessfully launched from Baikonur (Kazakhstan) the 17th of October 2002. This medium size ESA project, planned for a 2 year mission with possible extension to 5, is devoted to the observation of the gamma-ray sky in the energy range from 3 keV to 10 MeV (Winkler 2001). The IBIS imaging system is based on two independent solid state detector arrays optimised for low (15 1000 keV) and high (0:175 10:0 MeV) energies surrounded by an active VETO System. This high eciency shield is essential to minimise the background induced by high energy particles in the highly excentric out of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and1 squared meter in dimension is the imaging device. The IBIS telescope will serve the scientific community at large providing a unique combination of unprecedented high energy wide field imaging capability coupled with broad band spectroscopy and high resolution timing over the energy range from X to gamma rays. To date the IBIS telescope is working nominally in orbit since more than 9 month.

XMM-Newton observation of the brightest X-ray flare detected so far from Sgr A

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from Sgr A* with a duration shorter than one hour (~2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of

A Multiwavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-Ray, Soft γ-Ray, and Submillimeter Emission

\Gamma =2.5 \pm0.3

The INTEGRAL IBIS/ISGRI System Point Spread Function and Source Location Accuracy ?

, and a peak 2–10 keV luminosity of 3.6

A new X-ray flare from the galactic nucleus detected with the XMM-Newton photon imaging cameras

^{+0.3}_{-0.4}\times 10 ^{35}

SIGMA: The hard X-ray and soft gamma-ray telescope on board the GRANAT space observatory

erg s -1 , i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of Sgr A* by bringing very strong constraints for the theoretical flare models.

SIMULTANEOUS MULTI-WAVELENGTH OBSERVATIONS OF Sgr A* DURING 2007 APRIL 1-11

Although Sgr A* is known to be variable in radio, millimeter, near-IR, and X-rays, the correlation of the variability across its spectrum has not been fully studied. Here we describe highlights of the results of two observing campaigns in 2004 to investigate the correlation of flare activity in different wavelength regimes, using a total of nine ground- and space-based telescopes. We report the detection of several new near-IR flares during the campaign based on HST observations. The level of near-IR flare activity can be as low as ~0.15 mJy at 1.6 μm and continuous up to ~40% of the total observing time, thus placing better limits than ground-based near-IR observations. Using HST NICMOS, XMM-Newton, and CSO, we also detect simultaneous bright X-ray and near-IR flare in which we observe for the first time correlated substructures as well as simultaneous submillimeter and near-IR flaring. X-ray emission is arising from the population of near-IR-synchrotron-emitting particles, which scatter submillimeter seed photons within the inner 10 Schwarzschild radii of Sgr A* up to X-ray energies. In addition, using the inverse Compton scattering picture, we explain the high-energy 20-120 keV emission from the direction toward Sgr A*, and the lack of one-to-one X-ray counterparts to near-IR flares, by the variation of the magnetic field and the spectral index distributions. In this picture, the evidence for the variability of submillimeter emission during a near-IR flare is produced by the low-energy component of the population of particles emitting synchrotron near-IR emission. Using the measurements of the duration of flares in near-IR and submillimeter wavelengths, we argue that the cooling could be due to adiabatic expansion with the implication that flare activity drives an outflow.

Three spectral states of 1E 1740.7-2942 : from standard Cygnus X-1 type spectrum to the evidence of electron-positron annihilation feature

The imager on board INTEGRAL (IBIS) presently provides the most detailed sky images ever obtained at energies above 30 keV. The telescope is based on a coded aperture imaging system which allows to obtain sky images in a large field of view (29 29) with an angular resolution of 12 0 . The System Point Spread Function of the telescope and its detailed charac- teristics are here described along with the specific analysis algorithms used to derive the accurate point-like source locations. The derived location accuracy is studied using the first in-flight calibration data on strong sources for the IBIS /ISGRI system. The dependence of the calibrated location accuracy with the signal to noise ratio of the sources is presented. These preliminary studies demonstrate that the IBIS/ISGRI telescope and the standard scientific analysis software allow source localizations with accuracy at 90% confidence level better than 1 0 for sources with signal to noise ratios >30 over the whole field of view, in agreement with the expected performances of the instrument.

The Two States of Sgr A* in the Near-infrared: Bright Episodic Flares on Top of Low-level Continuous Variability

Sgr A*, the compact radio source believed to be the counterpart of the massive black hole at the Galactic nucleus, was observed to undergo rapid and intense flaring activity in X-rays with Chandra in 2000 October. We report here the detection with XMM-Newton European Photon Imaging Cameras of the early phase of a similar X-ray flare from this source, which occurred on 2001 September 4. The source 2-10 keV luminosity increased by a factor of ≈20 to reach a level of 4 × 1034 ergs s-1 in a time interval of about 900 s, just before the end of the observation. The data indicate that the source spectrum was hard during the flare. This XMM-Newton observation confirms the results obtained by Chandra and suggests that in Sgr A* rapid and intense X-ray flaring is not a rare event. This can constrain the emission mechanism models proposed for this source and also implies that the crucial multiwavelength observation programs planned to explore the behavior of the radio/submillimeter and hard X-ray/gamma-ray emissions during the X-ray flares have a good chance of success.

Repeated X-ray Flaring Activity in Sagittarius A

Abstract The SIGMA telescope, the largest French scientific space-payload ever launched, is one of the main devices aboard the Soviet astronomy satellite GRANAT, successfully launched on December 1, 1989 from Baikonour, USSR. This high-energy space-telescope of unprecedented size, has been designed to produce high-resolution images of the hard X-ray and soft gamma-ray sky, in the energy range from 35 KeV to 1.3 MeV. After a comprehensive description of the instrument, a report is given on the most relevant characteristics of the telescope, including preliminary results from in-flight calibrations performed in the course of bright source observations.