1,721,215 research outputs found
The properties of the absorbing and line emitting material in IGR J16318-4848
No full textWe analyzed the 2003 Target of Opportunity XMM-Newton observation of IGR J16318-4848, to derive the properties of the matter responsible for the obscuration and for the emission of Fe and Ni lines. The line of sight material has a column density of about 2 x 10(24) cm(-2) but, from the Fe K alpha line EW and Compton Shoulder, we argue that the average column density is a few x 10(23) cm(-2), while the covering factor is about 0.1-0.2. The iron K alpha line varies on time scales as short as 1000 s, implying a size of the emitting region less than 3 x 10(13) cm. An ongoing XMM-Newton/INTEGRAL monitoring campaign is confirming the non-transient nature of the source
The properties of the absorbing and line-emitting material in IGR J16318-4848
No full textWe have performed a detailed analysis of the XMM-Newton observation of IGR J16318-4848, to study the properties of the matter responsible for the obscuration and for the emission of Fe and Ni lines. Even if the line-of-sight material has a column density of about 2x10(24) m(-2), from the Fe Kalpha line EW and Compton Shoulder we argue that the matter should have an average column density of a few x10(23) cm(-2), along with a covering factor of about 0.1-0.2. The iron Kalpha line varies on time-scales as short as 1000 s, implying a size of the emitting region smaller than about 3x10(13) cm. The flux of the line roughly follows the variations of the continuum, but not exactly, suggesting a variation of the geometrical properties of the emitting region on similar time-scales
Changing look: from Compton-thick to Compton-thin, or the rebirth of fossil active galactic nuclei
No full textWe discuss the properties of a small sample of type 2 Seyfert galaxies whose X-ray spectra changed appearance on time-scales of years, becoming reflection-dominated from Compton-thin, or vice versa. A reflection-dominated spectrum is usually taken as evidence of Compton-thick absorption, but we instead argue that such a spectrum is due to a temporary switching-off of the nuclear radiation. The observations discussed here may help to explain mismatches between optical and X-ray classifications, and provide new strong and direct evidence for the presence of more than one cold circumnuclear region in type 2 Seyfert galaxies
X-ray obscuration and obscured AGN in the local universe
No full textWe discuss the X-ray properties of 49 local (z = sigma(t)(-1) similar or equal to 1.6 x 10(24) cm(-2)) is similar or equal to 50%, and reaches similar or equal to 80% for log (F2-10) 0.6 keV) are common in our sample ( 6 new detections at a confidence level >= 2 sigma). They are explained as due to reflection off the illuminated side of optically thick material. We confirm a correlation between the presence of a similar to 100-pc scale nuclear dust in the WFC2 images and Compton-thin obscuration. We interpret this correlation as due to the large covering fraction of gas associated with the dust lanes. The X-ray spectra of highly obscured AGN invariably present a prominent soft excess emission above the extrapolation of the hard X-ray component. This soft component can account for a very large fraction of the overall X-ray energy budget. As this component is generally unobscured - and therefore likely produced in extended gas structures - it may lead to a severe underestimation of the nuclear obscuration in z similar to 1 absorbed AGN, if standard X-ray colors are used to classify them. As a by-product of our study, we report the discovery of a soft X-ray, luminous (similar or equal to 7 x 10(40) erg s(-1)) halo embedding the interacting galaxy pair Mkn 266
On the hypothesis of an advection-dominated flow in the core of NGC 1052: new constraints from a BeppoSAX observation
No full textWe report the results of a broadband (0.1-100 keV) X-ray observation of the nearby elliptical galaxy NGC 1052, performed with the BeppoSAX observatory. We confirm the presence of a bright (2-10 keV luminosity similar to4 x 10(42) erg s(-1)) and strongly absorbed (N-H similar to 2 x 10(23) cm(-2)) X-ray source. The flatness of the X-ray spectrum (photon index, Gamma, similar or equal to1.4), the estimated low accretion rate ((m) over dot equivalent to (M) over dot/(M) over dot(Edd) similar to 10(-4)) and the radio-to-X-ray spectral energy distribution suggest that this observation may represent the first direct measurement above 10 keV of an accretion-dominated flow in an elliptical galaxy
Timescales trips to PG quasars: The Mkn 478 case
No full textThe X-ray bright PG quasar PG 1440+356 (Mkn 478) was observed four times across 13 months with the XMM-Newton observatory. Flux variations with a dynamical range of a factor about 6 were observed in both the soft (E 3 keV) X-ray band. However, large spectral variations are observed in the latter band only. We suggest that the X-ray emission in this object is due to Comptonization of kT similar or equal to 60 eV disk photons by a 20-50 keV plasma with a complex density structure. Analysis of the harmonic content of Mkn 478 light curves unveils a characteristic timescale similar to1 day, common to both energy bands. A longer (similar tomonths) timescale is detected in the soft X-ray band only
Harmonic coupling of the red noise in X-ray pulsars
No full textThe power spectra of X-ray pulsars often show the presence of a red-noise component. This noise is produced by aperiodic variability believed to be associated with instabilities that seem to occur in accretion hows onto compact objects. In this paper we discuss how, independently of the details of the physical processes that generate these instabilities, a careful analysis of the power spectra can furnish some constraints on the distance from the stellar surface at which the sudden energy release associated with the instabilities occurs. In particular, any aperiodic variability coming from the accretion flow funneled toward the magnetic poles should be modulated at the pulsar spin period (coupling). We show how, in the power spectra, this coupling results in a broadening at the base of the harmonics. To investigate this effect, we have adopted a mathematical description of the noise in order to produce simulated light curves and the resulting power spectra. A comparison of power spectra from simulations with real data allows the detection or exclusion of the broadening effect. As an application of this method we have compared simulated power spectra with one obtained from a Ginga observation of the X-ray pulsar SMC X-1. For this source the coupling effect is evident
XMM-Newton broad-band observations of NGC 7582: N{H} variations and fading out of the active nucleus
No full textThe early stage of a cosmic collision? XMM-Newton unveils two obscured AGN in the galaxy pair ESO509-IG066
No full textWe report the XMM-Newton discovery of a X-ray bright AGN pair in the interacting galaxy system ESO509-IG066. Both galaxies host an X-ray luminous ( L-X similar to 10(43) erg s(-1)) obscured nucleus with column densities N-H similar or equal to 7 x 10(22) cm(-2) and N-H similar or equal to 5 x 10(21) cm(-2). The optical morphology is only mildly disturbed, suggesting a merging system in the early stage of its evolution. Still, the pair is probably gravitationally bound, and might eventually evolve into a compact, fully gas embedded systems such as NGC 6240 ( Komossa et al. 2003)
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