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Register a new userDeep X-ray spectroscopy and imaging of the Seyfert 2 galaxy, ESO 138-G001
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We present a spectral and imaging analysis of the XMM-Newton and Chandra observations of the Seyfert 2 galaxy ESO138-G001, with the aim of characterizing the circumnuclear material responsible for the soft (0.3-2.0 keV) and hard (5-10 keV) X-ray emission. We confirm that the source is absorbed by Compton-thick gas. However, if a self-consistent model of reprocessing from cold toroidal material is used (MYTorus), a possible scenario requires the absorber to be inhomogenous, its column density along the line of sight being larger than the average column density integrated over all lines- of-sight through the torus. The iron emission line may be produced by moderately ionised iron (FeXII-FeXIII), as suggested by the shifted centroid energy and the low K{beta}/K{alpha} flux ratio. The soft X-ray emission is dominated by emission features, whose main excitation mechanism appears to be photoionisation, as confirmed by line diagnostics and the use of self-consistent models (CLOUDY).
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We report on our analysis of XMM-Newton observations of the Seyfert 2 galaxy ESO 138-G1 (z = 0.0091). These data reveal a complex spectrum in both its soft and hard portions. The 0.5-2 keV band is characterized by a strong soft-excess component with several emission lines, as commonly observed in other narrow-line AGN. Above 3 keV, a power-law fit yields a very flat slope (Gamma ~0.35), along with the presence of a prominent line-like emission feature around ~6.4 keV. This indicates heavy obscuration along the line of sight to the nucleus. We find an excellent fit to the 3-10 keV continuum with a pure reflection model, which provides strong evidence of a Compton-thick screen, preventing direct detection of the intrinsic nuclear X-ray emission. Although a model consisting of a power law transmitted through an absorber with Nh ~2.5 x 10^{23} cm^-2 also provides a reasonable fit to the hard X-ray data, the equivalent width value of ~800 eV measured for the Fe Kalpha emission line is inconsistent with a primary continuum obscured by a Compton-thin column density. Furthermore, the ratio of 2-10 keV to de-reddened [OIII] fluxes for ESO 138-G1 agrees with the typical values reported for well-studied Compton-thick Seyfert galaxies. Finally, we also note that the upper limits to the 15-150 keV flux provided by Swift/BAT and INTEGRAL/IBIS seem to rule out the presence of a transmitted component of the nuclear continuum even in this very hard X-ray band, hence imply that the column density of the absorber could be as high as 10^{25} cm^-2. This makes ESO 138-G1 a very interesting, heavy Compton-thick AGN candidate for the next X-ray missions with spectroscopic and imaging capabilities above 10 keV.
We present the first analysis of the X-ray warm absorber and nuclear obscuration in the Seyfert 1.8 galaxy ESO 113-G010. We used archival data from a 100 ks XMM-Newton observation made in 2005. From high resolution spectroscopy analysis of the RGS data, we detect absorption lines originating from a warm absorber consisting of two distinct phases of ionisation, with log xi ~ 3.2 and 2.3 respectively. The higher-ionised component has a larger column density and outflow velocity (N_H ~ 1.6 x 10^22 cm^-2, v ~ -1100 km/s) than the lower-ionised component (N_H ~ 0.5 x 10^22 cm^-2, v ~ -700 km/s). The shape of the optical-UV continuum and the large Balmer decrement (H_alpha/H_beta ~ 8) indicate significant amount of reddening is taking place in our line of sight in the host galaxy of the AGN; however, the X-ray spectrum is not absorbed by cold neutral gas intrinsic to the source. We discuss different explanations for this discrepancy between the reddening and the X-ray absorption, and suggest that the most likely solution is a dusty warm absorber. We show that dust can exist in the lower-ionised phase of the warm absorber, which causes the observed reddening of the optical-UV emission, whereas the X-rays remain unabsorbed due to lack of cold neutral gas in the ionised warm absorber. Furthermore, we have investigated the uncertainties in the construction of the Spectral Energy Distribution (SED) of this object due to obscuration of the nuclear source and the effects this has on the photoionisation modelling of the warm absorber. We show how the assumed SEDs influence the thermal stability of each phase and whether or not the two absorber phases in ESO 113-G010 can co-exist in pressure equilibrium.
We present results from the zeroth-order imaging of a Chandra HETGS observation of the nearby Seyfert 2 galaxy Circinus. Twelve X-ray sources were detected in the ACIS-S image of the galaxy, embedded in diffuse X-ray emission. The latter shows a prominent (~18arcsec) soft ``plume in the N-W direction, coincident with the [OIII] ionization cone. The radial profiles of the brightest X-ray source at various energies are consistent with an unresolved (FWHM ~0.8arcsec) component, which we identify as the active nucleus, plus two extended components with FWHMs ~ 2.3arcsec and 18arcsec, respectively. In a radius of 3arcsec, the nucleus contributes roughly the same flux as the extended components at the softest energies (< 2 keV). However, at harder energies (> 2 keV), the contribution of the nucleus is dominant. The zeroth-order ACIS spectrum of the nucleus exhibits emission lines at both soft and hard X-rays, including a prominent Fe Kalpha line at 6.4 keV, showing that most of the X-ray lines previously detected with ASCA originate in a compact region (<15 pc). Based on its X-ray spectrum, we argue that the 2.3arcsec extended component is scattered nuclear radiation from nearby ionized gas. The large-scale extended component includes the emission from the N-W plume and possibly from the outer starburst ring.
We report on the unveiling of the nature of the unidentified X-ray source 3XMM J005450.3-373849 as a Seyfert-2 galaxy located behind the spiral galaxy NGC 300 using Hubble Space Telescope data, new spectroscopic Gemini observations and available XMM-Newton and Chandra data. We show that the X-ray source is positionally coincident with an extended optical source, composed by a marginally resolved nucleus/bulge, surrounded by an elliptical disc-like feature and two symmetrical outer rings. The optical spectrum is typical of a Seyfert-2 galaxy redshifted to z=0.222 +/- 0.001, which confirms that the source is not physically related to NGC 300. At this redshift the source would be located at 909+/-4 Mpc (comoving distance in the standard model). The X-ray spectra of the source are well-fitted by an absorbed power-law model. By tying $N_mathrm{H}$ between the six available spectra, we found a variable index $Gamma$ running from ~2 in 2000-2001 years, to 1.4-1.6 in the 2005-2014 period. Alternatively, by tying $Gamma$, we found variable absorption columns of N_H ~ 0.34 x $10^{-22}$ cm$^{-2}$ in 2000-2001 years, and 0.54-0.75 x $10^{-22}$ cm$^{-2}$ in the 2005-2014 period. Although we cannot distinguish between an spectral or absorption origin, from the derived unabsorbed X-ray fluxes, we are able to assure the presence of long-term X-ray variability. Furthermore, the unabsorbed X-ray luminosities of 0.8-2 x 10$^{43}$ erg s$^{-1}$ derived in the X-ray band are in agreement with a weakly obscured Seyfert-2 AGN at $z approx 0.22$.
The bright and highly-variable Seyfert I Active Galactic Nucleus, IC4329A, was observed with Suzaku 5 times in 2007 August with intervals of ~ 5 days, and a net exposure of 24-31 ks each. Another longer observation was carried out in 2012 August with a net exposure of 118 ks. In the 6 observations, the source was detected in 2-45 keV with average 2-10 keV fluxes of $(0.67-1.2)times10^{-10}$ erg cm$^{-2}$ s$^{-1}$. The intensity changed by a factor of 2 among the 5 observations in 2007, and 1.5 within the 2012 observation. Difference spectra among these observations revealed that the variability of IC4329A was carried mainly by a power-law component with a photon index $Gammasim2.0$. However, in addition to this primary component and the associated reflection, the broad-band Suzaku data required another, harder, and less variable component with $Gammasim1.4$. The presence of this new continuum was also confirmed by analyzing the same 6 data sets through the spectral decomposition technique developed by Noda et al. 2013a. This $Gammasim1.4$ continuum is considered to be a new primary component that has not been recognized in the spectra of IC4329A so far, although it was recently identified in those of several other Seyfert I galaxies (Noda et al. 2013a, 2014).
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