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Register a new userTracing a Disk Wind in NGC 3516
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X-ray spectra of AGN often contain signatures indicative of absorption in multiple layers of gas whose ionization-state and covering fraction may vary with time. It has been unclear to date how much of the observed X-ray spectral and timing behavior in AGN can be attributed to variations in absorption, versus variations in the strengths of emission or reflection components. Diagnostics of the inner regions of AGN cannot be reliably performed until the origin of observed effects is understood. We investigate the role of the X-ray absorbers in the Seyfert 1 galaxy NGC 3516. Time-averaged and flux-selected spectroscopy is used to examine the behavior of NGC 3516 observed in Chandra HETG and XMM data from Oct 2006. New H-like and He-like emission and absorption features discovered in the Fe K regime reveal a previously unknown zone of circumnuclear gas in NGC 3516 with log xi ~ 4.3 and column density 1E23 cm^-2. A lower-ionization layer with log xi ~2 and of similar column density is confirmed from previous observations, this layer has a covering fraction around 50%, and changes in covering provide a simple explanation of a deep dip in the light curve that we interpret as an eclipse of the continuum due to passage of a cloud across the sight line within half a day. These inner zones of absorbing gas are detected to have outflow velocities in the range 1000-2000 km/s, this, and constraints on radial location are consistent with an origin as part of a disk wind in NGC 3516.
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We present RGS data from an XMM-Newton observation of the Seyfert 1 galaxy NGC 3516, taken while the continuum source was in an extreme low state. The spectrum shows numerous emission lines including the H-like lines of C, N and O and the He-like lines of N, O and Ne. These data show that the N lines are far stronger than would be expected from gas of solar abundances. Based on our photoionization models, we find that N is overabundant compared to C, O and Ne by at least a factor of 2.5. We suggest this is the result of secondary production of N in intermediate mass stars, and indicative of the history of star formation in NGC 3516.
Spectroscopic data in wavelengths 900--3000A have been obtained in a low flux state of the nucleus of the Seyfert 1 galaxy NGC 3516. The line profiles show P Cygni characteristics, particularly in O VI 1032A, and are compared with data from an earlier higher state. The profiles are suggestive of, and consistent with, an accelerating wind driven by a disk continuum source, in which the ionisation radii have changed. This scenario may apply to the formation of other broad emission lines in AGN.
We test the reprocessing paradigm of the optical -- UV AGN variability by detailed modeling of the correlated X-ray -- optical (3590 and 5510 Angstrem) variability of the recent multiwavelength campaign of NGC 3516. We produce model optical light curves by convolving the observed X-ray flux with the response function of an infinite, thin accretion disk, illuminated by a point-like X-ray source at a given height above the compact object (the lamp-post model) and compare their properties to those observed. Special attention is given to the correct computation of the X-ray albedo of the disk. We further compute the X-ray reflection response at two energies (E = 1 and 20 keV) and argue for the possibility of hard lags in their cross spectra. We also compute the continuum Optical -- UV and the X-ray reflection spectra as well as the Fe K-alpha fluorescent line profiles which we also compare to observations. Despite the large (~50 percent) amplitude excursions of the X-ray flux, the model optical light curves exhibit variability amplitudes of 3 -- 4 percent, not unlike those observed. However, the model CCF between the X-ray and the model optical variations show clear lags of 0.1 and 0.25 days for black hole masses M = 10^7 and 10^8 Solar masses, respectively, not apparent in the data. The synchrony of X-ray - optical variations points toward the BH mass < 10^7 Solar masses, whereas the X-ray spectra prefer BH mass > 10^8. Our conclusion is that the combination of the observed optical/UV/X-ray spectral and timing observations are inconsistent with the lamp-post model geometry for NGC 3516.
We present the time-resolved spectral analysis of the XMM-Newton data of NGC 1365, collected during one XMM-Newton observation, which caught this changing-look AGN in a high flux state characterized also by a low column density ($N_{mathrm{H}}sim 10^{22}$ cm $^{-2}$) of the X-ray absorber. During this observation the low energy photoelectric cut-off is at about $sim 1$ keV and the primary continuum can be investigated with the XMM-Newton-RGS data, which show strong spectral variability that can be explained as a variable low $N_{mathrm{H}}$, which decreased from $N_{mathrm{H}} sim10^{23}$ cm $^{-2}$ to $10^{22}$ cm $^{-2}$ in a 100 ks time-scale. The spectral analysis of the last segment of the observation revealed the presence of several absorption features that can be associated with an ionized (log $xi sim 2$ erg cm s$^{-1}$) outflowing wind ($v_{mathrm{out}} sim 2000$ km s$^{-1}$). We detected for the first time a possible P-Cygni profile of the Mg,textsc{xii} Ly$alpha$ line associated with this mildly ionized absorber indicative of a wide angle outflowing wind. We suggest that this wind is a low ionization zone of the highly ionized wind present in NGC 1365, which is responsible for the iron K absorption lines and is located within the variable X-ray absorber. At the end of the observation, we detected a strong absorption line at $Esim 0.76$ keV most likely associated with a lower ionization zone of the absorber (log $xi sim 0.2$ erg cm s$^{-1}$, $N_{mathrm{H}} sim 10^{22}$ cm $^{-2}$), which suggests that the variable absorber in NGC 1365 could be a low ionization zone of the disk wind.
We obtained X-ray spectra of the Seyfert 1 galaxy NGC~3516 in March 1995 using ASCA. Simultaneous far-UV observations were obtained with HUT on the Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law of energy index 0.78. The low energy absorbing column is significantly less than previously seen. Prominent O~vii and O~viii absorption edges are visible, but, consistent with the much lower total absorbing column, no Fe K absorption edge is detectable. A weak, narrow Fe~K$alpha$ emission line from cold material is present as well as a broad Fe~K$alpha$ line. These features are similar to those reported in other Seyfert 1 galaxies. A single warm absorber model provides only an imperfect description of the low energy absorption. In addition to a highly ionized absorber with ionization parameter $U = 1.66$ and a total column density of $1.4 times 10^{22}~rm cm^{-2}$, adding a lower ionization absorber with $U = 0.32$ and a total column of $6.9 times 10^{21}~rm cm^{-2}$ significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to $< 160~rm km~s^{-1}$ at 90% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fit to the X-ray spectrum can match the observed equivalent widths of all the UV absorption lines. Accounting for the X-ray and UV absorption simultaneously requires an absorbing region with a broad range of ionization parameters and column densities.
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