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Register a new userHigh-Resolution X-ray Spectroscopy and Modeling of the Absorbing and Emitting Outflow in NGC 3783
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(abridged) The high-resolution X-ray spectrum of NGC 3783 shows several dozen absorption lines and a few emission lines from the H-like and He-like ions of O, Ne, Mg, Si, and S as well as from Fe XVII - Fe XXIII L-shell transitions. We have reanalyzed the Chandra HETGS spectrum using better flux and wavelength calibrations along with more robust methods. Combining several lines from each element, we clearly demonstrate the existence of the absorption lines and determine they are blueshifted relative to the systemic velocity by -610+/-130 km/s. We find the Ne absorption lines in the High Energy Grating spectrum to be resolved with FWHM=840{+490}{-360} km/s. We have used regions in the spectrum where no lines are expected to determine the X-ray continuum, and we model the absorption and emission lines using photoionized-plasma calculations. The model consists of two absorption components which have an order of magnitude difference in their ionization parameters. The two components are spherically outflowing from the AGN and thus contribute to both the absorption and the emission via P Cygni profiles. The model also clearly requires O VII and O VIII absorption edges. The low-ionization component of our model can plausibly produce UV absorption lines with equivalent widths consistent with those observed from NGC 3783. However, we note that this result is highly sensitive to the unobservable UV-to-X-ray continuum, and the available UV and X-ray observations cannot firmly establish the relationship between the UV and X-ray absorbers. We find good agreement between the Chandra spectrum and simultaneous ASCA and RXTE observations. We set an upper limit on the FWHM of the narrow Fe Kalpha emission line of 3250 km/s. This is consistent with this line originating outside the broad line region, possibly from a torus.
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Our Swift monitoring program triggered two joint XMM-Newton, NuSTAR and HST observations on 11 and 21 December 2016 targeting NGC 3783, as its soft X-ray continuum was heavily obscured. Consequently, emission features, including the O VII radiative recombination continuum, stand out above the diminished continuum. We focus on the photoionized emission features in the December 2016 RGS spectra and compare them to the time-averaged RGS spectrum obtained in 2000--2001 when the continuum was unobscured. A two-phase photoionized plasma is required to account for the narrow emission features. These narrow emission features are weakly varying between 2000--2001 and December 2016. We also find a statistically significant broad emission component in the time-averaged RGS spectrum in 2000--2001. This broad emission component is significantly weaker in December 2016, suggesting that the obscurer is farther away than the X-ray broad-line region. In addition, by analyzing the archival high-resolution X-ray spectra, we find that nine photoionized absorption components with different ionization parameters and kinematics are required for the warm absorber in X-rays.
Aims: Using XMM-Newton data, we have aimed to study the nuclear outflow of the nearby starburst galaxy NGC 253 in X-rays with respect to its morphology and to spectral variations along the outflow. Methods: We analysed XMM-Newton RGS spectra, RGS brightness profiles in cross-dispersion direction, narrow band RGS and EPIC images and EPIC PN brightness profiles of the nuclear region and of the outflow of NGC 253. Results: We detect a diversity of emission lines along the outflow of NGC 253. This includes the He-like ions of Si, Mg, Ne and O and their corresponding ions in the next higher ionisation state. Additionally transitions from Fe XVII and Fe XVIII are prominent. The derived temperatures from line ratios along the outflow range from 0.21+/-0.01 to 0.79+/-0.06 keV and the ratio of Fe XVII lines indicates a predominantly collisionally ionised plasma. Additionally we see indications of a recombining or underionized plasma in the Fe XVII line ratio. Derived electron densities are 0.106+/-0.018 cm^-3 for the nuclear region and 0.025+/-0.003 cm^-3 for the outflow region closest to the centre. The RGS image in the O VIII line energy clearly shows the morphology of an outflow extending out to ~750 pc along the south-east minor axis, while the north-west part of the outflow is not seen in O VIII due to the heavy absorption by the galactic disc. This is the first time that the hot wind fluid has been detected directly. The limb brightening seen in Chandra and XMM-Newton EPIC observations is only seen in the energy range containing the Fe XVII lines (550-750 eV). In all other energy ranges between 400 and 2000 eV no clear evidence of limb brightening could be detected.
We report on the results of detailed X-ray spectroscopy of the Fe K region in the Seyfert 1 galaxy NGC 3783 from five ~170 ks observations with the Chandra high energy gratings. Monitoring was conducted over an interval of ~125 days in 2001. The combined data constitute the highest signal-to-noise Fe K spectrum having the best velocity resolution in the Fe K band to date (FWHM ~1860 km/s). The data show a resolved Fe K line core with a center energy of 6.397 +/- 0.003 keV, consistent with an origin in neutral or lowly ionized Fe, located between the BLR and NLR, as found by Kaspi et al. (2002). We also find that excess flux around the base of the Fe K line core can be modeled with either a Compton scattering ``shoulder or an emission line from a relativistic accretion disk, having an inclination angle of 11 degrees or less. This disk line model is as good as a Compton-shoulder model for the base of the Fe K line core. In the latter model, the column density is 7.5 [+2.7,-0.6] x 10^{23} cm^{-2}, which corresponds to a Thomson optical depth of ~0.60. An intrinsic width of 1500 [+460,-340] km/s FWHM is still required in this model. Moreover, more complicated scenarios involving both a Compton-shoulder and a disk line cannot be ruled out. We confirm an absorption feature due to He-like Fe (FWHM = 6405 [+5020,-2670] km/s), found in previous studies.
We present a detailed analysis of the XMM-Newton RGS high resolution X-ray spectra of the Seyfert 2 galaxy, Mrk573. This analysis is complemented by the study of the Chandra image, and its comparison to optical (HST) and radio (VLA) data. The soft X-ray emission is mainly due to gas photoionised by the central AGN, as indicated by the detection of radiative recombination continua from OVII and OVIII, as well as by the prominence of the OVII forbidden line. This result is confirmed by the best fit obtained with a self-consistent CLOUDY photoionisation model. However, a collisionally excited component is also required, in order to reproduce the FeXVII lines, accounting for about 1/3 of the total luminosity in the 15-26 A band. Once adopted the same model in the Chandra ACIS data, another photoionised component, with higher ionisation parameter, is needed to take into account emission from higher Z metals. The broadband ACIS spectrum also confirms the Compton-thick nature of the source. The imaging analysis shows the close morphological correspondence between the soft X-ray and the [OIII] emission. The radio emission appears much more compact, although clearly aligned with the narrow line region. The collisional phase of the soft X-ray emission may be due to starburst, requiring a star formation rate of $simeq5-9$ M$_odot$ yr$^{-1}$, but there is no clear evidence of this kind of activity from other wavelengths. On the other hand, it may be related to the radio ejecta, responsible for the heating of the plasma interacting with the outflow, but the estimated pressure of the hot gas is much larger than the pressure of the radio jets, assuming equipartition and under reasonable physical parameters.
We utilize the complimentary capabilities of XMM-Newton and Chandra, to conduct a detailed imaging and spectral study of the nearby galaxy NGC 4945 focussing on its nucleus and immediate surroundings (within ~1 kpc of the nucleus). A complex morphology is revealed including a predominantly hard, but partially resolved, nuclear source plus a spectrally soft, conically shaped X-ray plume, which extends 30 (500 pc) to the northwest. In NGC 4945 our direct view of the active galactic nucleus (AGN) is blocked below ~10 keV by extremely heavy line-of-sight absorption and the observed X-ray spectrum is dominated by multi-temperature thermal emission associated with the nuclear starburst and the X-ray plume. Nevertheless the signature of the AGN is present in the form of a neutral Compton reflection component and a 6.4 keV fluorescent iron Ka line. We conjecture that the site of the continuum reprocessing is the far wall of a highly inclined molecular torus, a geometry which is consistent with the presence of H2O megamaser emission in this source. The soft spectrum (~0.6 keV) and limb-brightened appearance of the X-ray plume suggest an interpretation in terms of a mass-loaded superwind emanating from the nuclear starburst.
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