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ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed it was highly variable on the timescale of $sim2times10^4$ s in the hard X-ray (2-10 keV) band, while the soft X-ray (0.5-2 keV) flux remained constant during the observations. The spectral analysis suggests that this object is seen through an obscuring torus with the thickness of N$_{rm H}sim1.0times 10^{23}rm cm^{-2}$. The hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus; the soft X-ray is dominated by the scattered central continuum from an extended spatial region. Thus we have an obscured/absorbed and a scattered view of this source as expected from the unification model for Seyfert galaxies. More interestingly, the inferred X-ray column was observed to increase by $sim4times10^{22} rm cm^{-2}$ from 1994 to 1996, suggesting a ``patchy torus structure, namely the torus might be composed of many individual clouds. The observed iron line feature near 6.4 keV with the equivalent width of 170 eV is also consistent with the picture of the transmission of nuclear X-ray continuum through a non-uniform torus.
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We report the transition towards a type 1 Seyfert experienced by the classical type 2 Seyfert nucleus in NGC 7582. The transition, found at most 20 days from its maximum peak, presents a unique opportunity to study these rare events in detail. At maximum the Ha line width is of about 12000 km/s. We examine three scenarios that could potentially explain the transition: capture of a star by a supermassive black hole, a reddening change in the surrounding torus, and the radiative onset of a type IIn supernova exploding in a compact nuclear/circumnuclear starburst.
The Seyfert 2 galaxy NGC 2110 has been observed with BeppoSAX between 0.5 and 150 keV. The high energy instrument onboard, PDS, has succeeded in measuring for the first time the spectrum of this source in the 13-150 keV range. The PDS spectrum, having a photon index Gamma~1.86 is fully compatible with that expected from a Seyfert 1 nucleus. In the framework of unified models, the harder (Gamma~1.67) 2-10 keV spectrum is well explained assuming the presence of a complex partial + total absorber (Nh~30x10^22 cm^-2 x25% + Nh~4x10^22 cm^-2 x100%). The high column density of this complex absorber is consistent both with the FeK_alpha line strength and with the detection of an absorption edge at E~7.1 keV in the power-law spectrum.
We present the result of the Chandra high-resolution observation of the Seyfert~2 galaxy NGC 7590. This object was reported to show no X-ray absorption in the low-spatial resolution ASCA data. The XMM observations show that the X-ray emission of NGC 7590 is dominated by an off-nuclear ultra-luminous X-ray source (ULX) and an extended emission from the host galaxy, and the nucleus is rather weak, likely hosting a Compton-thick AGN. Our recent Chandra observation of NGC 7590 enables to remove the X-ray contamination from the ULX and the extended component effectively. The nuclear source remains undetected at ~4x10^{-15} erg/s/cm^-2 flux level. Although not detected, Chandra data gives a 2--10 keV flux upper limit of ~6.1x10^{-15} erg/s/cm^-2 (at 3 sigma level), a factor of 3 less than the XMM value, strongly supporting the Compton-thick nature of the nucleus. In addition, we detected five off-nuclear X-ray point sources within the galaxy D25 ellipse, all with 2 -- 10 keV luminosity above 2x10^{38} erg/s (assuming the distance of NGC 7590). Particularly, the ULX previously identified by ROSAT data was resolved by Chandra into two distinct X-ray sources. Our analysis highlights the importance of high spatial resolution images in discovering and studying ULXs.
NGC 7582 is a well-studied X-ray bright Seyfert 2 with moderately heavy ($N_{text{H}}sim10^{23}-10^{24}$~cm$^{-2}$), highly variable absorption and strong reflection spectral features. The spectral shape changed around the year 2000, dropping in observed flux and becoming much more highly absorbed. Two scenarios have been put forth to explain this spectral change: 1) the central X-ray source partially ``shut off around this time, decreasing in intrinsic luminosity, with a delayed decrease in reflection features due to the light-crossing time of the Compton-thick material or 2) the source became more heavily obscured, with only a portion of the power law continuum leaking through. NuSTAR observed NGC~7582 twice in 2012, two weeks apart, in order to quantify the reflection using high-quality data above 10 keV. We find that the most plausible scenario is that NGC 7582 has recently become more heavily absorbed by a patchy torus with a covering fraction of $sim,80-90%$ and an equatorial column density of $sim 3 times10^{24}$ cm$^{-2}$. We find the need for an additional highly variable full-covering absorber with $N_{text{H}}= 4-6 times10^{23}$ cm$^{-2}$ in the line of sight, possibly associated with a hidden broad line region.
Context. The putative tori surrounding the accretion disks of active galactic nuclei (AGNs) play a fundamental role in the unification scheme of AGNs. Infrared long-baseline interferometry allows us to study the inner dust distribution in AGNs with unprecedented spatial resolution over a wide infrared wavelength range. Aims. Near- and mid-infrared interferometry is used to investigate the milli-arcsecond-scale dust distribution in the type 1.5 Seyfert nucleus of NGC 3783. Methods. We observed NGC 3783 with the VLTI/AMBER instrument in the K-band and compared our observations with models. Results. From the K-band observations, we derive a ring-fit torus radius of 0.74 +/- 0.23 mas or 0.16 +/- 0.05 pc. We compare this size with infrared interferometric observations of other AGNs and UV/optical-infrared reverberation measurements. For the interpretation of our observations, we simultaneously model our near- and mid-infrared visibilities and the SED with a temperature/density-gradient model including an additional inner hot 1400 K ring component.
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