Soft X-ray Spectrum Of NGC Research Articles

The complex soft X-ray spectrum of NGC 4151

We present a detailed analysis of the complex soft X-ray spectrum of NGC 4151 measured by the RGS instruments aboard XMM-Newton. The XMM-Newton RGS spectra demonstrate that the soft X-ray emission is extremely rich in X-ray emission lines and radiative recombination continua (RRC), with no clear evidence for any underlying continuum emission. Line emission, and the associated RRC, are clearly detected from hydrogen-like and helium-like ionization states of neon, oxygen, nitrogen and carbon. The measured lines are blueshifted with a velocity of between ~100-1000 km/s, with respect to the systemic velocity of NGC 4151, approximately consistent with the outflow velocities of the absorption lines observed in the UV, suggestive of an origin for the UV and soft X-ray emission in the same material. Plasma diagnostics imply a range of electron temperatures of ~1-5x10^4 K and electron densities of between 10^8-10^10 cm^-3. The soft X-ray spectrum of NGC 4151 is extremely similar to that of NGC 1068, suggesting that the soft X-ray excesses observed in many Seyfert galaxies may be composed of similar emission features. Modelling the RGS spectra in terms of emission from photoionized and photoexcited gas in an ionization cone reproduces all of the hydrogen-like and helium-like emission features observed in the soft X-ray spectrum of NGC 4151 in detail and confirms the correspondence between the soft X-ray emission in NGC 4151 and NGC 1068.

Relativistic OviiiEmission and Ionized Outflow in NGC 4051 Measured withXMM‐Newton

We present XMM-Newton RGS observations of the soft X-ray spectrum of NGC 4051, and explore their implications for the inner accretion disk and ionized outflow in the active galactic nucleus. We fit the soft X-ray excess with a relativistically broadened O VIII recombination spectrum, including the entire line series and recombination continuum. This plus an underlying power law continuum provides a much better fit to the soft X-ray spectrum than a single temperature or disk blackbody plus power law. The emission line profiles, computed for a Kerr metric around a maximally rotating black hole, reveal a sharply peaked disk emissivity law and inner radius smaller than 1.7 R_G. The spectrum also includes narrow absorption and emission lines from C, N, O, Ne, and Fe in an ionized outflow. Outflow column densities are relatively low and do not create significant edges in the spectrum. The small amount of absorption bolsters confidence in the detection of relativistic emission line features. The narrow-line emitter has a large (76%) global covering fraction, leading to strong forbidden lines and filling in of the resonance absorption lines. We also find broad C VI Ly-alpha and very broad O VII emission from the broad-line region. The narrow and broad-line regions span large ranges in ionization parameter, and may arise in a disk outflow. The ionized absorber has a large ionization range which is inconsistent with pressure equilibrium in a multiphase medium. The mass outflow rate exceeds the accretion rate by a factor of one thousand.

The Kinematics and Physical Conditions of the Ionized Gas in NGC 4593 fromChandraHigh‐Energy Grating Spectroscopy

We observed the Seyfert 1 galaxy NGC 4593 with the Chandra high energy transmission gratings and present a detailed analysis of the soft X-ray spectrum. We measure strong absorption lines from He-like O, Ne, Mg, Si, H-like N, O, Ne, Mg, Si and highly ionized Fe XIX-XXV. Only the NLya, OLya and MgLya lines appear to be marginally resolved. We identify a spectral feature at $\sim 0.707$ keV with a neutral Fe L edge, which might suggest that there is dust along the line-of-sight to \ngc. Neutral Si absorption, which might also be expected from absorption due to dust is present (though not significantly) in the form of a weak neutral Si edge. We also detect, at marginal signficance, NLya and O VII (r) 1s-2p ($\lambda 21.602 $) absorption at $z \sim 0$, due to a hot medium in our Local Group. The soft X-ray spectrum of NGC 4593 is adequately described by a simple, single-zone photoionized absorber with an equivalent Hydrogen column density of $5.37^{+1.45}_{-0.79} \times 10^{21} \rm{cm}^{-2}$ and an ionization parameter of $\log \xi= 2.52^{+0.06}_{-0.04}$ ergs cm $\rm{s}^{-1}$ although there remain some features which are not identified. Although the photoionized gas almost certainly is comprised of matter in more than one ionization state and may consist of several kinematic components, data with better signal-to-noise ratio and better spectral resolution are required to justify a more complex model.

The soft X-ray spectrum of NGC 4151

NGC 4151 is one of the brightest and best studied AGN in the sky. This is certainly true in the soft/medium X-ray regime where there is now an extensive set of data encompassing a fifteen year time-frame. Most problematic is the spectral form observed below 4 keV where we see a unique combination of complex absorption and a soft excess component. Here we discuss some recent results from ROSAT and Ginga which provide new insight into the X-ray properties of NGC 4151. The bulk of the soft X-ray flux probably arises from electron scattering of the underlying continuum and/or extended thermal emission. There is no direct evidence for an absorbing molecular torus in this galaxy.

The soft X-ray spectrum of NGC 4151 revisited

The soft X-ray spectrum of NGC 4151 revisited

The complex variable soft X-ray spectrum of NGC 5548

We present ROSAT 0.2 – 2 keV monitoring data on NGC 5548 taken over the period 1992 December – 1993 January, when the source was at its historical maximum in X-ray flux. The data show a soft excess and partially ionized absorber modifying the high-energy power-law (α ~ 0.9) spectrum. The major variability during the campaign is a strong flare event over 8 d, in which the soft excess brightens without a corresponding change in the power-law intensity. This is incompatible with the simple reprocessing models which are currently popular, where the soft excess is produced from thermalized hard X-ray emission illuminating an accretion disc. Given the high source luminosity, ≥ 0.1 LEdd, it seems likely that the soft excess is dominated by intrinsic emission from the accreting material. While the data do not allow the ionization of the absorbing material to be constrained in each single spectrum, a comparison of the brightest spectrum with that from a long exposure taken 2 d later and which is a factor of 2 fainter shows a significant decrease in the ionization. This implies a density of ≥ 5 × 105 cm–3 for the warm material, and hence a distance of less than ~ 1018 cm from the central source.

The soft X-ray spectrum of NGC 4151

Les observations de NGC 4151 faites de juillet 1983 a avril 1984 par EXOSAT ont revele un flux decroissant dans la bande 2-10 keV. D'autres observations ont montre que cela a coincide avec une chute pour l'ensemble du continuum, de l'IR a l'UV et un affaiblissement marque des raies d'emission larges

The soft X-ray spectrum of NGC 4151

EXOSAT observations of the Seyfert galaxy NGC 4151 over the period July 1983 to April 1984 have revealed a decreasing flux in the 2 –10 keV band. In accord with previous measurements a power law spectrum attenuated with a simple column of cold gas does not provide a satisfactory spectral fit below ∼3 keV, where a lower relative opacity is required. Inclusion of additional low energy data from the EXOSAT telescopes allows the modelling of the absorbing column to be improved and reveals a second, separate, soft X-ray spectral component.