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Register a new userIron Features in the XMM-Newton spectrum of NGC 4151
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Authors
N.J. Schurch
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We present a detailed analysis of the hard X-ray (>2.5 keV) EPIC spectra from the first observations of NGC 4151 made by XMM-Newton. We fit the spectra with a model consisting of a power-law continuum modified by line-of-sight absorption (arising in both partially photoionized and neutral gas) plus additional iron-K emission and absorption features. This model provides an excellent overall fit to the EPIC spectra. The iron K-alpha line is well modelled as a narrow Gaussian component. In contrast to several earlier studies based on data from ASCA, a relativistically broadened iron K-alpha emission feature is not required by the XMM-Newton data. The upper limit on the flux contained in any additional broad line is ~8% of that in the narrow line. The measured intrinsic line width (sigma =32+_7 eV) may be ascribed to (i) the doublet nature of the iron K-alpha line and (ii) emission from low ionization states of iron, ranging from neutral up to ~FeXVII. The additional iron absorption edge arises in cool material and implies factor ~2 overabundance of iron in this component.
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We study the X-ray spectral variability of the Narrow Line Seyfert 1 galaxy NGC 4051 as observed during two XMM-Newton observations. The data show evidence for a neutral and constant reflection component and for constant emission from photoionized gas, which are included in all spectral models. The nuclear emission can be modelled both in terms of a ``standard model (pivoting power law plus a black body component for the soft excess) and of a two--component one (power law plus ionized reflection from the accretion disc). The standard model results indicate that the soft excess does not follow the standard black body law. Moreover, although the spectral slope is correlated with flux, which is consistent with spectral pivoting, the hardest photon indexes are so flat as to require rather unusual scenarios. These problems can be solved in terms of the two-component model in which the soft excess is not thermal, but due to the ionized reflection component. The variability of the reflection component from the inner disc closely follows the predictions of the light bending model, suggesting that most of the primary nuclear emission is produced in the very innermost regions, only a few gravitational radii from the central black hole. (abridged)
We disentangle X-ray disk reflection from complex line-of-sight absorption in the nearby Seyfert NGC 4151, using a suite of Suzaku, NuSTAR, and XMM-Newton observations. Extending upon earlier published work, we pursue a physically motivated model using the latest angle-resolved version of the lamp-post geometry reflection model relxillCp_lp together with a Comptonization continuum. We use the long-look simultaneous Suzaku/NuSTAR observation to develop a baseline model wherein we model reflected emission as a combination of lamp-post components at the heights of 1.2 and 15.0 gravitational radii. We argue for a vertically extended corona as opposed to two compact and distinct primary sources. We find two neutral absorbers (one full-covering and one partial-covering), an ionized absorber ($log xi = 2.8$), and a highly-ionized ultra-fast outflow, which have all been reported previously. All analyzed spectra are well described by this baseline model. The bulk of the spectral variability between 1 keV and 6 keV can be accounted for by changes in the column density of both neutral absorbers, which appear to be degenerate and inversely correlated with the variable hard continuum component flux. We track variability in absorption on both short (2 d) and long ($sim$1 yr) timescales; the observed evolution is either consistent with changes in the absorber structure (clumpy absorber at distances ranging from the broad line region (BLR) to the inner torus or a dusty radiatively driven wind) or a geometrically stable neutral absorber that becomes increasingly ionized at a rising flux level. The soft X-rays below 1 keV are dominated by photoionized emission from extended gas that may act as a warm mirror for the nuclear radiation.
We report on the nuclear X-ray properties of the radio galaxy NGC 6251 observed with XMM-Newton. NGC 6251 is a well-known radio galaxy with intermediate FRI/II radio properties. It is optically classified as a Seyfert 2 and hosts a supermassive black hole with mass~6e8 solar masses. The 0.4-10 keV EPIC pn continuum is best fitted by two thermal components (kT~0.5 and 1.4 keV, respectively), plus a power law with photon index ~1.9 absorbed by a column density NH~5e20 cm-2. We confirm the previous ASCA detection of a strong iron line. The line, resolved in the EPIC pn spectrum, is adequately fitted with a broad (sigma~0.6 keV) Gaussian at rest-frame energy 6.4 keV with EW 220 eV. We also detect, for the first time, short-term, low-amplitude variability of the nuclear flux on a timescale of a few ks. The spectral properties argue in favor of the presence of a standard accretion disk, ruling out the base of the jet as the sole origin of the X-rays. The moderate X-ray luminosity and lack of strong intrinsic absorption suggest that NGC 6251 is a ``pure type 2 AGN which lacks a broad-line region.
Spectra taken with the Space Telescope Imaging Spectrograph (STIS) allow accurate location and extraction of the nuclear spectrum of NGC 4151, with minimal contamination by extended line emission and circumnuclear starlight. Spectra since 1997 show that the P Cygni Balmer and He I absorption seen previously in low nuclear states, is present in higher states, with outflow velocity that changes with the nuclear flux. The phenomenon is discussed in terms of some of the absorbers seen in the UV resonance lines, and outflows from the central source and surrounding torus.
We observe the magnetar CXOU J171405.7-381031 with XMM-Newton and obtain the most reliable X-ray spectral parameters for this magnetar. After removing the flux from the surrounding supernova remnant CTB~37B, the radiation of CXOU J171405.7-381031 is best described by a two-component model, consisting of a blackbody and power law. We obtain a blackbody temperature of 0.58^{+0.03}_{-0.03} keV, photon index of 2.15^{+0.62}_{-0.68}, and unabsorbed 2-10 keV flux of 2.33^{+0.02}_{-0.02} x 10^{-12} erg cm^{-2} s^{-1}. These new parameters enable us to compare CXOU 171405.7-381031 with other magnetars, and it is found that the luminosity, temperature and the photon index of CXOU J171405.7-381031 are aligned with the known trend among the magnetar population with a slightly higher temperature, which could be caused by its young age. All the magnetars with a spin-down age of less than 1~kyr show time variation or bursts except for CXOU J171405.7-381031. We explore the time variability for ten observations in between 2006 and 2015, but there is no variation larger than sim 10%.
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