Preliminary results obtained from
BeppoSAX observation of the starburst galaxy NGC253 are presented. X-ray emission from the object is cleerly extended but most of the emission is concentrated on the ...optical nucleus. Preliminary analysis of the LECS and MECS data obtained using the central 4' region indicates that the continuum is well fitted by two thermal components at 0.9 keV and 7 keV. Fe K line at 6.7 keV is detected for the first time in this galaxy; the line has an equivalent width of ∼ 300 eV. The line enegy and the shape of the 2–10 keV continuum strongly support thermal origin of the hard X-ray emission of NGC253. From the measurement of the Fe K line the abundances can be unambiguously constrained to ∼ 0.25 the solar value. Other lines clearly detected are Si, S and Fe
XVIII
/Ne, in agreement with
ASCA results.
We report on the identification of a new soft gamma-ray source, IGR J12319-0749, detected with the IBIS imager on board the INTEGRAL satellite. The source, which has an observed 20−100 keV flux of ...approx 8.3 × 10(exp -12) erg/sq. cm/ s, is spatially coincident with an active galactic nucleus (AGN) at redshift z = 3.12. The broad-band continuum, obtained by combining XRT and IBIS data, is flat (Gamma = 1.3) with evidence for a spectral break around 25 keV (100 keV in the source restframe). X-ray observations indicate flux variability, which is also supported by a comparison with a previous ROSAT measurement. IGR J12319-0749 is also a radio-emitting object likely characterised by a flat spectrum and high radio loudness; optically it is a broad-line emitting object with a massive black hole (2.8 × 10(exp 9) solar masses) at its centre. The source spectral energy distribution is similar to another high-redshift blazar, 225155+2217 at z = 3.668: both objects are bright, with a high accretion disk luminosity and a Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319-0749 is likely the second-most distant blazar detected so far by INTEGRAL.
The similarity between the spectral characteristics of the three active galaxies NGC 4151, NGC 1275 and MCG 8-11-11, which are generally classified as Seyferts and are powerful, low-energy gamma-ray ...sources, with those of the cosmic background at gamma-ray energies suggests that these objects may significantly contribute to this diffuse flux. Two number densities of gamma-ray-emitting Seyfert galaxies based on both optical and X-ray data are employed in an assessment of this contribution, and a comparison of the estimated and measured diffuse gamma-ray background intensities is used to gain a deeper understanding of the metabolism of Seyfert galaxies.
Analysis of INTEGRAL Core Program and public Open Time observations has
recently provided a sample of 60 extragalactic sources selected in the 20-100
keV band above a flux of 1.5 10^-11 erg/cm2/s. As ...this band probes heavily
obscured regions/objects, i.e. those that could be missed in optical, UV, and
even X-ray surveys, our sample offers the opportunity to study the
extragalactic sky from a different point of view with respect to surveys at
lower energies. We present an update of our analysis, including the first
sample of AGNs detected above 100 keV. We also discuss the results of follow up
observations performed at optical and X-ray frequencies with the aim of
classifying our objects and studying the effects of intrinsic absorption in
gamma-ray selected AGNs. The average redshift of our sample is 0.134 while the
mean 20-100 keV luminosity in Log is 43.84; if blazars are excluded these
numbers become 0.022 and 43.48 respectively. Defining an absorbed object as one
with NH above 10^22 atoms/cm2, we find that absorption is present in 60% of the
objects with at most 14% of the total sample due to Compton thick active
galaxies. Almost all Seyfert 2s in our sample are absorbed as are 24% of
Seyfert 1s. We also present broad-band spectral information on a sub-sample of
the brightest objects: our observations indicate a mean photon index of 1.8
spanning from 30-50 keV to greater than 200 keV. Finally, we discuss the
LogN/LogS distribution in the 20-100 and 100-150 keV bands derived from our
sample. The present data highlight the capability of INTEGRAL to probe the
extragalactic gamma-ray sky, to discover new AGNs and to find absorbed objects.
In order to help in the identification of INTEGRAL/ISGRI sources, we have
developed a software package which allows a rapid and detailed
cross-correlation to be performed between various source ...catalogues. It allows
subsets of catalogues to be constructed at a selected level of probability of
association, which can then be used to construct multi-waveband correlations.
In this paper, we present the hard X-ray spectral analysis of a complete sample of AGN de- tected by INTEGRAL/IBIS. In conjunction with IBIS spectra, we make use of Swift/BAT data, with the aim of ...cross-calibrating the two instruments, studying source variability and con- straining some important spectral parameters. We find that flux variability is present in at least 14% of the sample, while spectral variability is found only in one object. There is general good agreement between BAT and IBIS spectra, despite a systematic mismatch of about 22% in normalisation. When fitted with a simple power-law model, type 1 and type 2 sources appear to have very similar average photon indices, suggesting that they are powered by the same mechanism. As expected, we also find that a simple power-law does not always describe the data sufficiently well, thus indicating a certain degree of spectral complexity, which can be ascribed to features like a high energy cut-off and/or a reflection component. Fixing the reflection to be 0, 1 or 2, we find that our sample covers quite a large range in photon indices as well as cut-off energies; however, the spread is due only to a small number of objects, while the majority of the AGN lie within well defined boundaries of photon index (1<{\Gamma}<2) and cut-off energy (30<Ecut<300 keV).
We report on
BeppoSAX AO1 Core Program observations of 3C 279, performed in January 1997. 3C 279 was found in a low state, with constant X-ray flux in the 5 observations. The spectra obtained with ...the LECS and MECS instruments combining the 5 observations are well fitted by a single power law with energy spectral index α = 0.64 ± 0.03 and Galactic absorption. The source is weakly detected by the PDS instrument. Comparison with simultaneous γ-ray data obtained by EGRET and with previous multifrequency measurements shows that the X-ray emission is well correlated with the γ-ray emission over long timescales.
We report on the identification of a new soft gamma-ray source, IGR J12319 C0749, detected with the IBIS imager on board the INTEGRAL satellite. The source, which has an observed 20 C100 keV flux of ...8.3 10.12 erg cm.2 s.1, is spatially coincident with an AGN at redshift z = 3.12. The broad-band continuum, obtained by combining XRT and IBIS data, is flat ( =1.3) with evidence for a spectral break around 25 keV (100 keV in the source rest frame). X-ray observations indicate flux variability which is further supported by a comparison with a previous ROSAT measurement. IGR J12319 C0749 is also a radio emitting object likely characterized by a flat spectrum and high radio loudness; optically it is a broad-line emitting object with a massive black hole (2.8 109 solar masses) at its center. The source Spectral Energy Distribution is similar to another high redshift blazar, 225155+2217 at z = 3.668: both objects are bright, with a large accretion disk luminosity and a Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319 C0749 is likely the second most distant blazar detected so far by INTEGRAL.
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