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Register a new userThe INTEGRAL View of the Galactic Nucleus
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We present the preliminary results of the observational campaign performed in 2003 to study the Galactic Nucleus with INTEGRAL. The mosaicked images obtained with the IBIS/ISGRI coded aperture instrument in the energy range above 20 keV, give a yet unseen view of the high-energy sources of this region in hard X and gamma-rays, with an angular resolution of 12. We report on the discovery of a source, IGR J17456-2901, compatible with the instruments point spread function and coincident with the Galactic Nucleus Sgr A* to within 0.9. The source is visible up to 60-80 keV with a 20-100 keV luminosity at 8 kpc of 3 x 10E35 erg/s. Although we cannot unequivocally associate the new INTEGRAL source to the Galactic Nucleus, this is the first report of significant hard X-ray emission from within the inner 10 of the Galaxy and a contribution from the galactic center supermassive black hole itself cannot be excluded. Here we discuss the results obtained and the perspectives for future observations of the Galactic Nucleus with INTEGRAL and other observatories
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We present preliminary results of INTEGRAL/IBIS observations on Cas A, Tycho and Vela Junior Supernova remnants in the line emission of 44Ti. This radioactive nucleus is thought to be exclusively produced in supernovae during the first stages of the explosion. It has a lifetime of about 87 y and is then the best indicator of young SNRs, as exemplified by the detection of 44Ti in the youngest known Galactic SNR Cas A with GRO/COMPTEL and latter with BeppoSAX. In this paper, we will focus on this SNR for which we confirm the detection of 44Ti and point out the importance to know the nature of the hard X-ray continuum, the Tycho SNR, for which no indication of 44Ti was ever reported, and Vela Junior, for which the claimed detection of 44Ti with COMPTEL is still controversial. The INTEGRAL/IBIS observations bring new constraints on the nature of these SNRs and on the nucleosynthesis which took place during the explosions.
AGN are among the most energetic phenomena in the Universe and in the last two decades INTEGRALs contribution in their study has had a significant impact. Thanks to the INTEGRAL extragalactic sky surveys, all classes of soft X-ray detected (in the 2-10 keV band) AGN have been observed at higher energies as well. Up to now, around 450 AGN have been catalogued and a conspicuous part of them are either objects observed at high-energies for the first time or newly discovered AGN. The high-energy domain (20-200 keV) represents an important window for spectral studies of AGN and it is also the most appropriate for AGN population studies, since it is almost unbiased against obscuration and therefore free of the limitations which affect surveys at other frequencies. Over the years, INTEGRAL data have allowed to characterise AGN spectra at high energies, to investigate their absorption properties, to test the AGN unification scheme and to perform population studies. In this review the main results are reported and INTEGRALs contribution to AGN science is highlighted for each class of AGN. Finally, new perspectives are provided, connecting INTEGRALs science with that at other wavelengths and in particular to the GeV/TeV regime which is still poorly explored.
We present the first results from an XMM-Newton observation of the FRI galaxy NGC 4261, which harbors a supermassive black hole and a low-ionization nuclear emission-line region (LINER). Here we focus on the X-ray properties of the nucleus, using the EPIC pn data. The 0.6-10 keV continuum in best fitted by a thermal component with kT ~0.7 keV, plus a power law with photon index ~1.4, absorbed by a column density NH~4e22 cm-2. An unresolved Fe K emission line with EW 280 eV is detected at 7 keV. We also detect, for the first time, short-term flux variability from the nucleus, on a timescale of 3-5 ks. The short-term variations rule out an ADAF as the only production mechanism of the X-ray continuum. Instead, we argue that the inner jet contributes to the emission in the X-ray band.
BeppoSAX observed NGC4258 on December 1998, when its 2-10 keV luminosity was ~1E41 erg/s. 100% variability is observed in the 3-10 keV band on timescales of a half a day while 20% variability is observed on timescales of one hour. The nuclear component is visible above 2 keV only, being obscured by a column density of (9.5+/-1.2)E22 cm-2; this component is detected up to 70 keV with S/N>=3 and with the steep power law energy index of 1.11+/-0.14. Bremsstrahlung emission for the 2-70 keV X-ray luminosity, as expected in ADAF models with strong winds, is ruled out by the data. The ratio between the nuclear radio and the X-ray luminosities is <=1E-5, similar to that of radio quiet AGN. X-ray variability and spectral shape, radio to X-ray and NIR to X-ray luminosity ratios suggest that the nucleus of NGC4258 could be a scaled-down version of a Seyfert nucleus. The soft (E<=2keV) X-ray emission is complex. There are at least two thermal-like components, with T1=0.6+/-0.1 keV and T2>=1.3 keV. The cooler (L(0.1-2.4keV)=1E40 erg/s) component is probably associated with the jet, resolved in X-rays by the ROSAT HRI. The second component, which can be modeled equally well by an unobscured power law model, has L(0.1-2.4keV)~7E39 erg/s, consistent with that expected from discrete X-ray sources in the host galaxy. NGC4258 and other maser AGNs show strong nuclear X-ray absorption. We propose that this large column of gas might be responsible for shielding the regions of maser emission from X-ray illumination. So a large column density gas may be a necessary property of masing AGNs.
The Galactic Bulge region is a rich host of variable high-energy point sources. These sources include bright and relatively faint X-ray transients, X-ray bursters, persistent neutron star and black-hole candidate binaries, X-ray pulsars, etc.. We have a program to monitor the Galactic Bulge region regularly and frequently with the gamma-ray observatory INTEGRAL. As a service to the scientific community the high-energy light curves of all the active sources as well as images of the region are made available through the WWW. We show the first results of this exciting new program.
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