arXiv subjects

S. B. Kraemer

Publications and source records attributed to S. B. Kraemer.

At least 109 records · Page 6Linked to original sources

arXiv2002

The Kinematics and Physical Conditions of the Ionized Gas in Markarian 509. I. Chandra High-Energy Grating Spectroscopy

We observed the Seyfert 1 galaxy Mrk 509 simultaneously with Chandra/HETG, HST/STIS and RXTE. We measure strong absorption lines from He-like Ne and Mg, and from H-like N, O, and Ne. The lines are unresolved except for Ne Lya and Ne IX(r). The absorption-line profiles are blueshifted by ~200 km/s with respect to the systemic velocity of Mrk 509, and there is a hint of another component near systemic. The soft X-ray spectrum can be described in remarkable detail with a simple, single-zone photoionized absorber with a column density of 2.06 (+0.39,-0.45) x 10^21 cm^-2 and an ionization parameter of log{xi} = 1.76 (+0.13,-0.14) (or log{U}=0.27). The UV data, on the other hand, can easily detect eight kinematic components, covering roughly the same velocities as the X-ray absorption profiles. Even though the X-ray and UV absorbers share the same velocity space, the UV absorbers have a much smaller column density and ionization state. We show that models of the X-ray data do not predict significant UV absorption and are therefore consistent with the UV data. The UV absorbers could be embedded in the X-ray absorber, as a multiphase medium. Finally, we do not detect any soft X-ray emission lines.

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arXiv2002

The Kinematics and Physical Conditions pf the Ionized Gas in Markarian 509. II. STIS Echelle Observations

We present observations of the UV absorption lines in the luminous Seyfert 1 galaxy Mrk 509, obtained with the medium resolution (lambda/Delta-lambda ~ 40,000) echelle gratings of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The spectra reveal the presence of eight kinematic components of absorption in Ly-alpha, C IV, and N V, at radial velocities of -422, -328, -259, -62, -22, +34, +124, and +210 km s^-1 with respect to an emission-line redshift of z = 0.03440, seven of which were detected in an earlier Far Ultraviolet Spectrographic Explorer (FUSE) spectrum. The component at -22 km s^-1 also shows absorption by Si IV. The covering factor and velocity width of the Si IV lines were lower than those of the higher ionization lines for this component, which is evidence for two separate absorbers at this velocity. We have calculated photoionization models to match the UV column densities in each of these components. Using the predicted O VI column densities, we were able to match the O VI profiles observed in the FUSE spectrum. Based on our results, none of the UV absorbers can produce the X-ray absorption seen in simultaneous Chandra observations; therefore, there must be more highly ionized gas in the radial velocity ranges covered by the UV absorbers.

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arXiv2002

Balmer and He I absorption in the nuclear spectrum of NGC 4151

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.

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arXiv2002

Narrow Components within the Fe Kalpha Profile of NGC 3516: Evidence for the Importance of General Relativistic Effects?

We present results from a simultaneous Chandra HETG and XMM-Newton observation of NGC 3516. We find evidence for several narrow components of Fe Kalpha along with a broad line. We consider the possibility that the lines arise in an blob of material ejected from the nucleus with velocity ~0.25c. We also consider an origin in a neutral accretion disk, suffering enhanced illumination at 35 and 175 gravitational radii, perhaps due to magnetic reconnection. The presence of these narrow features indicates there is no Comptonizing region along the line-of-sight to the nucleus. This in turn is compelling support for the hypothesis that broad Fe Kalpha components are, in general, produced by strong gravity.

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arXiv2002

Variable UV Absorption in the Seyfert 1.5 Galaxy NGC 3516: The Case for Associated UV and X-ray Absorption

We present observations of the UV absorption lines in the Seyfert 1 galaxy NGC 3516, obtained at a resolution of $λ$/$Δλ$ $\approx$ 40,000 with the Space Telescope Imaging Spectrograph (STIS) on 2000 October 1. The UV continuum was $\sim$4 times lower than that observed during 1995 with the Goddard High Resolution Spectrograph (GHRS), and the X-ray flux from a contemporaneous {\it Chandra X-ray Observatory (CXO)} observation was a factor of $\sim$8 below that observed with {\it ASCA}. The STIS spectra show kinematic components of absorption in Ly$α$, C IV, and N V at radial velocities of -376, -183, and -36 km s$^{-1}$ (components 1, 2, and 3+4, respectively), which were detected in the earlier GHRS spectra; the last of these is a blend of two GHRS components that have increased greatly in column density. Four additional absorption components have appeared in the STIS spectra at radial velocities of -692, -837, -994, and -1372 km s$^{-1}$ (components 5 through 8); these may also have been present in earlier low-flux states observed by the {\it International Ultraviolet Explorer (IUE)}. Based on photoionization models, we suggest that the components are arranged in increasing radial distance in the order, 3+4, 2, 1, followed by components 5 -- 8. We have achieved an acceptable fit to the X-ray data using the combined X-ray opacity of the UV components 1, 2 and 3+4. By increasing the UV and X-ray fluxes of these models to match the previous high states, we are able to match the GHRS C IV column densities, absence of detectable C IV absorption in components 5 through 8, and the 1994 {\it ASCA} spectrum. We conclude that variability of the UV and X-ray absorption in NGC 3516 is primarily due to changes in the ionizing flux.

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arXiv2002

The Ionized Gas and Nuclear Environment in NGC 3783. I. Time-Averaged 900 ks Chandra Grating Spectroscopy

We present results from a 900 ks exposure of NGC 3783 with the High-Energy Transmission Grating Spectrometer on board the Chandra X-ray Observatory. The resulting X-ray spectrum has the best combination of signal-to-noise and resolution ever obtained for an AGN. This spectrum reveals absorption lines from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also possible absorption lines from H-like and He-like Ar and Ca. We also identify inner-shell absorption from lower-ionization ions such as Si_VII-Si_XII and S_XII-S_XIV. The iron absorption spectrum is very rich; L-shell lines of Fe_XVII-Fe_XXIV are detected, strong complex of M-shell lines, and probable resonance lines from Fe_XXV. The absorption lines are blueshifted relative to the systemic velocity by a mean velocity of -590+-150 km/s. We resolve many of the absorption lines, and their mean FWHM is 820+-280 km/s. We do not find correlations between the velocity shifts or the FWHMs with the ionization potentials of the ions. Most absorption lines show asymmetry, having more extended blue wings than red wings. In O_VII we have resolved this asymmetry to be from an additional absorption system at ~ -1300 km/s. The two X-ray absorption systems are consistent in velocity shift and FWHM with the ones identified in the UV lines of C IV, N V, and H I. Equivalent width measurements for all lines are given and column densities are calculated for several ions. We resolve the narrow Fe_Kαline at 6398.2+-3.3 eV to have a FWHM of 1720+-360 km/s, which suggests that this narrow line may be emitted from the outer part of the broad line region or the inner part of the torus. We also detect a `Compton shoulder' redward of the narrow Fe_Kαline which indicates that it arises in cold, Compton-thick gas.

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arXiv2001

The Density and Location of the X-ray Absorbing Gas in NGC 3516

A new Chandra observation and archival observations by ASCA are used to investigate spectral variations in the Sy1 galaxy NGC 3516 over a period of 7 years. A large change in flux (factor ~50 at 1keV) is observed between an ASCA observation in '94 and the Chandra observation in 2000, with the source close to the all-time maximum and minimum X-ray flux states, respectively. We find the variations in the observed flux and spectra at these epochs to be consistent with a constant column density of line-of-sight material reacting to changes in the ionizing continuum. The data from the two epochs are consistent with a simple decrease (by a factor 8-10) in the luminosity of a constant 0.5-50 keV slope source and a line-of-sight absorber with an equivalent hydrogen column density of 10^21.9 cm^-2. Intermediate luminosities, sampled during other ASCA observations, are all fitted by the same model with a very small change in spectral index (well below ΔΓ=0.2). In addition, analysis of the long (360 ks) ASCA observation in 1998 shows clear "color" variations that are entirely consistent with this model and are interpreted as due to changes in the opacity of the absorbing gas. The data allow us to put a conservative upper limit of 60 ks on the recombination time which translates to a lower limit of about 2.4 times 10^6 cm^-3 on the density of the recombining gas and an upper limit of about 6 times 10^17 h_{75}^-2 cm on its distance from the central source. These are the best limits obtained so far on the density and location of the X-ray absorbing gas in a type-1 AGN. They indicate that the absorbing gas is different, in terms of its density and location, from the ionized gas commonly observed in type-II AGN. [Abridged]

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arXiv2001

The Detection of Circumnuclear X-ray Emission from the Seyfert Galaxy NGC 3516

We present the first high-resolution, X-ray image of the circumnuclear regions of the Seyfert 1 galaxy NGC 3516, using the Chandra X-ray Observatory (CXO). All three of the CXO observations reported were performed with one of the two grating assemblies in place, and here we restrict our analysis to undispersed photons (i.e. those detected in the zeroth-order). A previously-unknown X-ray source is detected approx 6 arcsec (1.1 h_{75}^{-1} kpc) NNE of the nucleus (position angle approx 29 degrees) which we designate CXOU 110648.1+723412. Its spectrum can be characterized as a power law with a photon index Gamma ~ 1.8--2.6, or as thermal emission with a temperature kT~0.7--3 keV. Assuming a location within NGC 3516, isotropic emission implies a luminosity L ~ 2--8e39 h_{75}^{-2} erg s^{-1} in the 0.4--2 keV band. If due to a single point source, the object is super-Eddington for a 1.4 M_sun neutron star. However, multiple sources or a small, extended source cannot be excluded using the current data. Large-scale extended X-ray emission is also detected out to ~10 arcsec (~1.7 h_{75}^{-1} kpc) from the nucleus to the NE and SW, and is approximately aligned with the morphologies of the radio emission and extended narrow emission line region (ENLR). The mean luminosity of this emission is 1--5e37 h_{75}^{-2} erg s^{-1} arcsec^{-2}, in the 0.4--2 keV band. Unfortunately the current data cannot usefully constrain its spectrum. These results are consistent with earlier suggestions of circumnuclear X-ray emission in NGC 3516. If the extended emission is due to scattering of the nuclear X-ray continuum, then the pressure in the X-ray emitting gas is at least two orders of magnitude too small to provide the confining medium for the ENLR clouds.

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arXiv2001

The Spectral Energy Distribution of the Seyfert galaxy Ton S180

We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the source, combining simultaneous Chandra, ASCA and EUVE data with contemporaneous FUSE, HST, and ground-based optical and infra-red data. The resulting SED shows that most of the energy is emitted in the 10 -- 100 eV regime, which must be dominated by the primary energy source. No spectral turnover is evident in the UV regime. This, the strong soft X-ray emission, and the overall shape of the SED indicate that emission from the accretion disk peaks between 15 and 100 eV. High resolution FUSE spectra showing UV absorption due to O VI and the lack of detectable X-ray absorption in the Chandra spectrum demonstrate the presence of a low column density of highly ionized gas along our line-of-sight. The highly-ionized state of the circumnuclear gas is most likely linked to the high luminosity and steep spectrum of the active nucleus. Given the strong ionizing flux in Ton S180, it is possible that the clouds within a few tens of light days of the central source are too highly ionized to produce much line emission. Thus the narrow width of the emission lines in Ton S180 is due to the emission arising from large radii.

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arXiv2001

On the Nature of Intrinsic Absorption in Reddened Seyfert 1 Galaxies

We discuss the origin of the ``dusty lukewarm absorber'', which we previously identified in the reddened Seyfert 1 galaxies NGC 3227 and Akn 564. This absorber is characterized by saturated UV absorption lines (C IV, N V) near the systemic velocity of the host galaxy, and is likely responsible for reddening both the continuum and the emission lines (including those from the narrow-line region) from these Seyferts. From a large sample of Seyfert 1 galaxies, we find that continuum reddening (as measured by UV color) tends to increase with inclination of the host galaxy. Furthermore, reddened, inclined Seyfert galaxies observed at moderate to high spectral resolution all show evidence for dusty lukewarm absorbers. We suggest that these absorbers lie in the plane of the host galaxy at distances > 100 pc from the nucleus, and are physically distinct from the majority of intrinsic absorbers that are outflowing from the nucleus.

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arXiv2001

Reddening, Emission-Line, and Intrinsic Absorption Properties in the Narrow-Line Seyfert 1 Galaxy Akn 564

We use Hubble Space Telescope UV and optical spectra of the narrow-line Seyfert 1 (NLS1) galaxy Akn 564 to investigate its internal reddening and properties of its emission-line and intrinsic UV absorption gas. We find that the extinction curve of Akn 564, derived from a comparison of its UV/optical continuum to that of an unreddened NLS1, lacks a 2200 A bump and turns up towards the UV at a longer wavelength (4000 A) than the standard Galactic, LMC, and SMC curves. However, it does not show the extremely steep rise to 1200 A that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The emission-lines and continuum experience the same amount of reddening, indicating the presence of a dust screen that is external to the narrow-line region (NLR). Echelle spectra from the Space Telescope Imaging Spectrograph show intrinsic UV absorption lines due to Ly-alpha, N V, C IV, Si IV, and Si III, centered at a radial velocity of -190 km/s (relative to the host galaxy). Photoionization models of the UV absorber indicate that it has a sufficient columnand is at a sufficient distance from the nucleus (D > 95 pc) to be the source of the dust screen. Thus, Akn 564 contains a dusty ``lukewarm absorber'' similar to that seen in NGC 3227.

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arXiv2001

Kinematics of the Narrow-Line Region in the Seyfert 2 Galaxy Mrk 3

We present measurements of radial velocities for the narrow-line region gas (NLR) in the Seyfert 2 galaxy Mrk 3 out to ~1 kpc from the nucleus. The observations consist of two datasets, both using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope: 1) An [O III] slitless spectrum with the G430M grating of the inner 3" around the nucleus, and 2) a long-slit observation centered on the nucleus (PA = 71 deg) using the G430L grating and the 52" x 0".1 aperture. Our results produce radial velocity maps of the emission-line gas. These maps indicate general trends in the gas motion, which include: blueshifts and redshifts on either side of the nucleus, steep velocity rises from systemic up to ~ +/-700 km/s taking place in the inner 0".3 (0.8 kpc) both east and west of the nucleus, gradual velocity descents back to near-systemic values from 0".3-1".0, slightly uneven velocity amplitudes on each side of the nucleus, and narrow velocity ranges over the entire observed region. When fitted to kinematic modeling programs for the NLR gas, the data clearly favor a model where the gas exists in a partially filled bicone, is accelerated radially away from the nucleus, and is followed by a constant deceleration. This geometry and general kinematic model is in agreement with previous work done on the NLR gas of NGC 1068 and NGC 4151. On scales of hundreds of parsecs, we conclude that radial outflow may be a common feature of Seyfert galaxies.

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arXiv2001

STIS Echelle Observations of the Intrinsic UV Absorption in the Seyfert 1 Galaxy NGC 3783

We present observations of the UV absorption lines in the Seyfert 1 galaxy NGC 3783, obtained with the medium resolution echelle gratings of the Space Telescope Imaging Spectrograph(STIS) on the Hubble Space Telescope (HST). The spectra reveal the presence of three kinematic components of absorption in Ly-alpha, C IV, and N V, at radial velocities of -1365, -548, and -724 km/s with respect to the systemic velocity of the host galaxy (Components 1, 2 and 3, respectively); Component 1 also shows absorption by Si IV. Component 3 was not detected in any of the earlier Goddard High Resolution Spectrograph (GHRS) spectra, and the C IV absorption in the other components has changed since the most recent GHRS observation obtained 5 yr earlier. Somewhat unexpectedly, each component has a covering factor (of the continuum source + broad emission line region) of about 0.6. We have calculated photoionization models to match the UV column densities in each of the three components. Based on the model results, there should be strong absorption in the bandpass of the Far Ultraviolet Spectroscopic Explorer (FUSE), 912 - 1200 A, including saturated O VI lines at each component velocity. The models also predict large O VII and O VIII column densities but suggest that the UV absorbers cannot account for all of the X-ray absorption detected in recent Chandra spectra. Finally, there is no evidence for a correlation between the characteristics of the UV absorbers and the UV continuum flux, which suggests that the variations observed in the GHRS and STIS spectra are due in large part to changes in the column densities of the absorbers as the result of transverse motion.

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arXiv2001

Absorption and Reddening in the Seyfert Galaxy NGC 3227

We have obtained low-dispersion spectra of NGC 3227 with the Space Telescope Imaging Spectrograph (STIS) to study the intrinsic UV absorption and the reddening of the nucleus in this Seyfert 1 galaxy. The UV spectra show a wealth of absorption lines at the systemic redshift that span a wide range in ionization state (Mg I to N V). The equivalent widths of the lines are consistent with our earlier prediction that a ``lukewarm absorber'' (T= 18,000 K at the ionized face) with a substantial column of gas [N(H) = 2 x 10^21 cm^-2] is present and likely responsible for the reddening of the nucleus. The lukewarm absorber is also responsible for most of the absorption in the X-rays at energies less than 1 keV, although a more highly ionized ``warm absorber'' is needed to account for the O VII and O VIII ionization edges. In addition, we require a small column [N(H) = 5 x 10^19 cm^-2] of cold gas to match the strengths of the neutral and singly-ionized lines in the UV spectra. NGC 3227 is the first Seyfert galaxy in which a strong link between the reddening and intrinsic UV absorption has been found. By comparing our STIS UV and optical spectra with those of the unreddened Seyfert NGC 4151, we have determined a reddening curve for the nuclear continuum source in NGC 3227 over the 1150 - 10,200 A range. The reddening curve does not show a 2200 AA bump, and is steeper in the UV than reddening curves derived for the Galaxy, LMC, and SMC, suggesting a preponderence of small dust grains near the nucleus.

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arXiv2001

STIS Echelle Observations of the Seyfert Galaxy NGC 4151: Physical Conditions in the Ultraviolet Absorbers

We have examined the physical conditions in intrinsic UV-absorbing gas in the Seyfert galaxy NGC 4151, using echelle spectra obtained with the Space Telescope Imaging Spectrograph (STIS). We confirm the presence of the kinematic components detected in earlier GHRS observations as well as a new broad absorption feature at a radial velocity of -1680 km/s. The UV continuum of NGC 4151 decreased by a factor of 4 over the previous two years, and we argue the changes in the column density of the low ionization absorption lines associated with the broad component at -490 km/s reflect the decrease in the ionizing flux. Most of the strong absorption lines (e.g., N V, C IV, Si IV) from this component are saturated, but show substantial residual flux in their cores, indicating that the absorber does not fully cover the source of emission. Our interpretation is that the unocculted light is due to scattering by free electrons from an extended region, which reflects continuum, emission lines, and absorption lines. We have been able to constrain the densities for the kinematic components based on absorption lines from metastable states of C III and Fe II, and/or the ratios of ground and fine structure lines of O I,C II, and Si II. We have generated a set of photoionization models which match the ionic column densities for each component during the present low flux state and those seen in previous high flux states with the GHRS and STIS, confirming that the absorbers are photoionized and respond to the changes in the continuum flux. We have been able to map the relative radial positions of the absorbers, and find that the gas decreases in density with distance. None of the UV absorbers is of sufficiently large column density or high enough ionization state to account for the X-ray absorption.

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arXiv2000

STIS Echelle Observations of NGC 4151: Variable Ionization of the Intrinsic UV Absorbers

We present echelle observations of the intrinsic UV absorption lines in the Seyfert galaxy NGC 4151, which were obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope on 1999 July 19. The UV continuum flux at 1450 Angstroms decreased by factor of about four over the previous two years and there was a corresponding dramatic increase in the column densities of the low-ionization absorption lines (e.g., Si II, Fe II, and Al II), presumably as a result of a decrease in the ionizing continuum. In addition to the absorption lines seen in previous low states, we identify a large number of Fe II absorption lines that arise from metastable levels as high as 4.1 eV above the ground state, indicating high densities (> 10^6 cm^-3). We find that the transient absorption feature in the blue wing of the broad C IV emission, seen in a Goddard High Resolution Spectrograph spectrum and thought to be a high-velocity C~IV component, is actually a Si II fine-structure absorption line at a radial velocity of -560 km/s (relative to systemic). We also demonstrate that the ``satellite'' emission lines of C~IV found in International Ultraviolet Explorer spectra are actually regions of unabsorbed continuum plus broad emission that become prominent when the UV continuum of NGC 4151 is in a low state.

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arXiv2000

A Kinematic Model for the Narrow-Line Region in NGC 4151

We present a simple kinematic model for the narrow-line region (NLR) of the Seyfert 1 galaxy NGC 4151, based on our previous observations of extended [O III] emission with the Space Telescope Imaging Spectrograph (STIS). The model is similar to a biconical radial outflow model developed for the Seyfert 2 galaxy NGC 1068, except that the bicone axis is tilted much more into our line of sight (40 degrees out of the plane of the sky instead of 5 degrees), and the maximum space velocities are lower (750 km/s instead of 1300 km/s. We find evidence for radial acceleration of the emission-line knots to a distance of 160 pc, followed by deceleration that approaches the systemic velocity at a distance of 290 pc (for a distance to NGC 4151 of 13.3 Mpc). Other similarities to the kinematics of NGC 1068 are: 1) there are a number of high-velocity clouds that are not decelerated, suggesting that the medium responsible for the deceleration is patchy, and 2) the bicone in NGC 4151 is at least partially evacuated along its axis. Together, these two Seyfert galaxies provide strong evidence for radial outflow (e.g., due to radiation and/or wind pressure) and against gravitational motion or expansion away from the radio jets as the principal kinematic component in the NLR.

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arXiv2000

On The Reddening in X-ray Absorbed Seyfert 1 Galaxies

There are several Seyfert galaxies for which there is a discrepancy between the small column of neutral hydrogen deduced from X-ray observations and the much greater column derived from the reddening of the optical/UV emission lines and continuum. The standard paradigm has the dust within the highly ionized gas which produces O~VII and O~VIII absorption edges (i.e., a ``dusty warm absorber''). We present an alternative model in which the dust exists in a component of gas in which hydrogen has been stripped, but which is at too low an ionization state to possess significant columns of O~VII and O~VIII (i.e, a ``lukewarm absorber''). The lukewarm absorber is at sufficient radial distance to encompass much of the narrow emission-line region, and thus accounts for the narrow-line reddening, unlike the dusty warm absorber. We test the model by using a combination of photoionization models and absorption edge fits to analyze the combined ROSAT/ASCA dataset for the Seyfert 1.5 galaxy, NGC 3227. We show that the data are well fit by a combination of the lukewarm absorber and a more highly ionized component similar to that suggested in earlier studies. We predict that the lukewarm absorber will produce strong UV absorption lines of N V, C IV, Si IV and Mg II. Finally, these results illustrate that singly ionized helium is an important, and often overlooked, source of opacity in the soft X-ray band (100 - 500 eV).

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