N. J. Westergaard

JEM-X: The X-ray monitor aboard INTEGRAL ?

The JEM-X monitor provides X-ray spectra and imaging with arcminute angular resolution in the 3 to 35 keV band. The good angular resolution and the low energy response of JEM-X plays an important role in the identification of gamma ray sources and in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture instrument consisting of two identical, coaligned telescopes. Each of the detectors has a sensitive area of 500 cm 2 , and views the sky through its own coded aperture mask. The two coded masks are inverted with respect to each other and provides an angular resolution of 3 0 across an eective field of view of about 10 diameter.

Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations

We report on the analysis of 100 ks INTEGRAL observations of the Galactic microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the source was found to exhibit a new type of variability as preliminarily reported in Hannikainen (2003, A&A, 411, L415). The variability pattern, which we name ξ, is characterized by a pulsing behaviour, consisting of a main pulse and a shorter, softer, and smaller amplitude precursor pulse, on a timescale of 5 min in the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a study of the individual RXTE/PCA pulse profiles we find that the rising phase is shorter and harder than the declining phase, which is opposite to what has been observed in other otherwise similar variability classes in this source. The position in the colour-colour diagram throughout the revolution corresponds to Stale A (Belloni et al. 2000, A&A, 355, 271) but not to any previously known variability class. We separated the INTEGRAL data into two subsets covering the maxima and minima of the pulses and fitted the resulting two broadband spectra with a hybrid thermal-non-thermal Comptonization model. The fits show the source to be in a soft state characterized by a strong disc component below ∼6 keV and Comptonization by both thermal and non-thermal electrons at higher energies.

JEM-X science analysis software

The science analysis of the data from JEM-X on INTEGRAL is performed through a number of levels including corrections, good time selection, imaging and source finding, spectrum and light-curve extraction. These levels consist of individual executables and the running of the complete analysis is controlled by a script where parameters for detailed settings are introduced. The end products are FITS files with a format compatible with standard analysis packages such as XSPEC.

First results from the INTEGRAL galactic plane scans

Scans of the Galactic plane performed at regular intervals constitute a key element of the guaranteed time obser- vations of the INTEGRAL observing programme. These scans are done for two reasons: frequent monitoring of the Galactic plane in order to detect transient sources, and time resolved mapping of the Galactic plane in continuum and diuse line emission. This paper describes first results obtained from the Galactic plane scans executed so far during the early phase (Dec. 2002-May 2003) of the nominal mission.

High-energy observations of the state transition of the X-ray nova and black hole candidate XTE J1720-318

We report the results of extensive high-energy observations of the X-ray transient and black hole candidate XTE J1720-318 performed with INTEGRAL, XMM-Newton and RXTE. The source, which underwent an X-ray outburst in 2003 January, was observed in February in a spectral state dominated by a soft component with a weak high-energy tail. The XMM-Newton data provided a high column density Nh of 1.2*e22 cm^{-2} which suggests that the source lies at the Galactic Centre distance. The simultaneous RXTE and INTEGRAL Target of Opportunity observations allowed us to measure the weak and steep tail, typical of a black-hole binary in the so-called High/Soft State. We then followed the evolution of the source outburst over several months using the INTEGRAL Galactic Centre survey observations. The source became active again at the end of March: it showed a clear transition towards a much harder state, and then decayed to a quiescent state after April. In the hard state, the source was detected up to 200 keV with a power law index of 1.9 and a peak luminosity of 7*e36 erg s^{-1} in the 20-200 keV band, for an assumed distance of 8 kpc. We conclude that XTE J1720-318 is indeed a new member of the black hole X-ray novae class which populate our galactic bulge and we discuss its properties in the frame of the spectral models used for transient black hole binaries.

The potential of INTEGRAL for the detection of high redshift GRBs

We discuss INTEGRALs ability to detect a high redshift population of Gamma-Ray Bursts (GRBs) in comparison to other high-energy missions. Emphasis is placed on the study of the relative capabilities of IBIS on board INTEGRAL with respect to SWIFT and HETE 2 in detecting a high redshift population of GRBs. We conclude that, if the GRB rate is proportional to the star formation rate, INTEGRALs ability to study GRBs are complementary to the ones of missions like SWIFT and HETE 2, devoted to prompt localisations of GRBs. Whereas SWIFT and HETE 2 would detect a higher number of GRBs than INTEGRAL, IBIS might be able to detect high redshift (z > 7) GRBs, unreachable by SWIFT and HETE 2. We discuss the relevance of performing near-infrared (NIR) observations of the INTEGRAL GRBs and the strategy that large-class telescopes might follow.

JEM-X inflight performance

We summarize the inflight performance of JEM-X, the X-ray monitor on the INTEGRAL mission during the initial ten months of operations. The JEM-X instruments have now been tuned to stable operational conditions. The performance is found to be close to the pre-launch expectations. The ground calibrations and the inflight calibration data permit to determine the instruments characteristics to fully support the scientific data analysis.

First INTEGRAL observations of GRS 1915+105

We present data from the first of six monitoring Open Time observations of GRS 1915+105 undertaken with the orbiting INTEGRAL satellite. The source was clearly detected with all three X-ray and gamma-ray instruments on board. GRS 1915+105 was in a highly variable state, as demonstrated by the JEM X-2 and ISGRI lightcurves. These and simultaneous RXTE/PCA lightcurves point to a novel type of variability pattern in the source. In addition, we fit the combined JEM X-2 and ISGRI spectrum between 3-300 keV with a disk blackbody + powerlaw model leading to typical parameter values found earlier at similar luminosity levels. A new transient, IGR J19140+098, was discovered during the present observation.

X-ray facility for the ground calibration of the X-ray monitor JEM-X on board INTEGRAL

We describe the X-ray facility developed for the calibration of the X-ray monitor JEM-X on board the INTEGRAL satellite. The apparatus allowed the scanning of the detector geometric area with a pencil beam of desired energy over the major part of the passband of the instrument. The monochromatic radiation is obtained with the use of a double crystal monochromator at fixed exit. We discuss the facility performance.

X-ray observations of the Crab Pulsar and Nebula with JEM-X on INTEGRAL ?

The Crab pulsar is the best studied rotation powered pulsar. We report the results obtained in the 3-35 keV energy band with the X-ray monitor, JEM-X, on ESAs recently launched-ray mission, INTEGRAL.